AU2017331805A1

AU2017331805A1 - A method and system for quantifying a concentration of anionic surfactants in a sample

Info

Publication number: AU2017331805A1
Application number: AU2017331805A
Authority: AU
Inventors: Morrow Dong; Cheng Fang; Yanju LIU; Megh Mallavarapu; Ravi Naidu
Original assignee: CRC Care Pty Ltd
Current assignee: CRC Care Pty Ltd
Priority date: 2016-09-21
Filing date: 2017-09-18
Publication date: 2019-04-18
Also published as: WO2018053580A1

Abstract

A system and method of quantifying a concentration of anionic surfactants in a sample, the method including: contacting a cationic dye with the sample and a solvent, such that an anionic surfactant in the sample complexes with the cationic dye to form a detectable dye-surfactant complex that is preferentially soluble in the solvent; obtaining image data of the dye-surfactant complex in the solvent; for a plurality of pixels in the image data, generating RGB colour space values by applying one or more filters to the image data; analysing the RGB colour space values to derive a concentration of the anionic surfactant in the sample; and outputting an indication of the concentration of the anionic surfactant in the sample.

Description

[0001] The present invention relates to a method and system for quantifying a concentration of anionic surfactants in a sample by obtaining image data of a dyesurfactant complex formed by contacting a cationic dye with the sample, and analysing the image data to derive the concentration of the anionic surfactant in the sample. Particularly, but not exclusively, the present invention relates to contacting the sample with ethyl violet and the anionic surfactant is a fluorinated anionic surfactant or an aqueous film forming foam.

Background of Invention [0002] Surfactants are a group of organic compounds that are of increasing concern. They are a group of chemicals that are in widespread use around the world with global production exceeding 9.86 x 10⁹ kg per year. Surfactants are used in large amounts daily in households around the world in cleaning products and detergents, in industrial applications including the manufacturing of pesticides, plasticizers in the cement and concrete industries, mining, pharmaceuticals and many other products.

[0003] Anionic surfactants are the major class of surfactants that are used in detergents. Linear alkylbenzene sulfonate (LAS) is published to be the most widely used anionic surfactant. Wastewater treatment facilities receive anionic surfactants in significant amounts due to the enormous use of detergents for washing purposes and from other sources. While most of the surfactants are able to be eliminated through conventional wastewater treatment, some surfactants have low biodegradability and, in others, undesired biodegradation products are formed and discharged with effluents into surface waters. Another route for introducing these chemicals into the environment includes the use of sewage sludge as fertilizer in agriculture. The surfactants can leach into the surrounding soils and be further transported to groundwater and surface waters.

WO 2018/053580

PCT/AU2017/051013 [0004] One particular class of specialty surfactants, fluorinated surfactants, have properties that make them particularly well suited to fire-fighting applications. PFOS (perfluorooctane sulfonate C8F17SO3-) and PFOA (perfluorooctanoic acid C7F15CO2H) are two commonly used fluorinated surfactants. These surfactants have been detected in human blood, water, soils, sediments, air, and biota samples. The compounds have been found to be globally distributed, persistent and bioaccumulative. Another class of surfactants is linear alkylbenzene sulfonate (LAS), which includes sodium dodecylbenzenesulfonate (SDBS), which is also commonly used in detergents.

[0005] In order to be able to detect anionic surfactant contamination in the environment, various assays for the detection of anionic surfactants have been developed.

[0006] One existing assay for detecting anionic surfactants in a sample is described in the Applicant’s Australian patent 2008310306, the contents of which are enclosed herein by way of reference. The method of detection described in this patent included the steps of: providing an assay in the form of a cationic dye (e.g. ethyl violet) capable of complexing with an anionic surfactant from a sample to form a detectable dye-surfactant complex that is preferentially soluble in a solvent (e.g. organic solvent, such as ethyl acetate), which is substantially immiscible with an aqueous sample; contacting the cationic dye with either the sample and the solvent such that an anionic surfactant in the sample complexes with the cationic dye to form a detectable dye-surfactant complex that is preferentially soluble in the organic solvent; and detecting the dye-surfactant complex in the organic solvent to indicate the presence of an anionic surfactant in the aqueous sample.

[0007] This method was described as being used for detecting any suitable anionic surfactant, but particularly an anionic surfactant constituent of an aqueous film forming foam and/or a fluorinated anionic surfactant. In addition, this existing method was described as being used in relation to a kit for detecting the anionic surfactant in the sample. The exemplary kit included a cationic dye, such as ethyl violet, capable of complexing with an anionic surfactant from the sample to form a detectable dye

WO 2018/053580

PCT/AU2017/051013 surfactant complex that is preferentially soluble in a solvent (e.g. organic solvent); and instructions for performing the method.

[0008] While this existing method and kit can be used to readily detect the presence of anionic surfactants in a sample. The ability to quantify a concentration of anionic surfactant in a sample is difficult. Quantifying of the concentration is based on a user making a colorimetric comparison of the dye-surfactant complex in the solvent with visual reference colours. That is, the colour change in the solvent phase of the assay is quantified by visually comparing the colour of the solvent with a physical visual reference colour chart. The visual reference colours on the chart are predetermined colours comprising the colour of the solvent phase when the assay is used with known concentrations of a known anionic surfactant in a sample. Quantification of the anionic surfactant in an unknown sample is then performed by the user visually matching the colour of the solvent phase from the assay of the unknown sample with the closest reference colour and then reading the known concentration associated with the closest reference colour. This method of quantification is therefore subjective and subject to inconsistent interpretation by users and is subject to illumination interference, such as different ambient light conditions.

[0009] Thus, a need exists for an improved quantification method and system that can provide a more accurate quantification of concentrations of anionic surfactants in a sample.

[0010] Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.

Summary of Invention [0011] Accordingly, in one aspect, the present invention provides a method of quantifying a concentration of anionic surfactants in a sample, the method including: contacting a cationic dye with the sample and a solvent, such that an anionic surfactant in the sample complexes with the cationic dye to form a detectable dyesurfactant complex that is preferentially soluble in the solvent; obtaining image data of

WO 2018/053580

PCT/AU2017/051013 the dye-surfactant complex in the solvent; for a plurality of pixels in the image data, generating RGB colour space values by applying one or more filters to the image data; analysing the RGB colour space values to derive a concentration of the anionic surfactant in the sample; and outputting an indication of the concentration of the anionic surfactant in the sample.

[0012] In an embodiment, the method further includes generating a ratio of RGB colour space values of the dye-surfactant complex formed by the anionic surfactants in the sample. Preferably, the ratio of RGB colour space values is: Blue colour space value/(2* Blue colour space value - Green colour space value - Red colour space value).

[0013] In the embodiment, the method further includes deriving the concentration of the anionic surfactant in the sample using the ratio of said RGB colour space values on a calibration curve for known concentrations of known anionic surfactants. Preferably, the calibration curve is defined as:

C = A1 *((A2-A3)/(x-A3)-1 )^A4 where:

c is concentration (in ppb);

A1-A4 are constants associated with the known anionic surfactant; and x is the ratio of said RGB colour space values.

[0014] For example, for SDBS, A1 is 199.9; A2 is 1.012; A3 is 0.594; and A4 is 0.60. It will be appreciated by those persons skilled in the art that the values for A1 A4 are constants which vary according to the surfactant. In another example, for PFOA, A1 is 205; A2 is 1.036; A3 is 0.551; and A4 is 0.676.

[0015] In an embodiment, the method further includes generating the calibration curve for known concentrations of known anionic surfactants by generating ratios of RGB colour space values of the dye-surfactant complex formed by at least one of the known anionic surfactants at the known concentrations and plotting the ratios of RGB colour space values in relation to the known concentrations.

[0016] In an embodiment, the method further includes selecting a particular calibration curve of a particular known anionic surfactant for deriving the

WO 2018/053580

PCT/AU2017/051013 concentration of the particular known anionic surfactant in the sample based on the ratio of said RGB colour space values fitting the particular calibration curve.

[0017] In another aspect, the present invention provides an system for quantifying a concentration of anionic surfactants in a sample, the system including: an imaging chamber configured to receive a reaction vessel therein, whereby a cationic dye is contacted with the sample and a solvent in the reaction vessel such that an anionic surfactant in the sample complexes with the cationic dye to form a detectable dyesurfactant complex that is preferentially soluble in the solvent; and an image capture device for obtaining image data of the dye-surfactant complex in the solvent in the reaction vessel in the imaging chamber, wherein the imaging chamber has a frame for positioning the image capture device and the reaction vessel relative to each other, and wherein a processor of the image capture device is configured to: generate RGB colour space values by applying one or more filters to the image data for a plurality of pixels in the image data; analyse the RGB colour space values to derive a concentration of the anionic surfactant in the sample; and output an indication of the concentration of the anionic surfactant in the sample.

[0018] In yet another aspect, the present invention provides an apparatus for quantifying a concentration of anionic surfactants in a sample, the system including: an imaging chamber configured to receive a reaction vessel therein, whereby a cationic dye is contacted with the sample and a solvent in the reaction vessel such that an anionic surfactant in the sample complexes with the cationic dye to form a detectable dye-surfactant complex that is preferentially soluble in the solvent, wherein the imaging chamber has a frame for positioning an image capture device, for obtaining image data of the dye-surfactant complex in the solvent in the reaction vessel in the imaging chamber, and the reaction vessel relative to each other, and wherein in use a processor of the image capture device is configured to: generate RGB colour space values by applying one or more filters to the image data for a plurality of pixels in the image data; analyse the RGB colour space values to derive a concentration of the anionic surfactant in the sample; and output an indication of the concentration of the anionic surfactant in the sample.

WO 2018/053580

PCT/AU2017/051013 [0019] In an embodiment, the processor of the image capture device is further configured to generate a ratio of RGB colour space values of the dye-surfactant complex formed by the anionic surfactants in the sample. And, preferably, the ratio of said RGB colour space values is: Blue colour space value/(2* Blue colour space value - Green colour space value - Red colour space value).

[0020] The processor is also further configured to derive the concentration of the anionic surfactant in the sample using the ratio of said RGB colour space values on a calibration curve for known concentrations of known anionic surfactants. And the calibration curve is defined as above.

[0021] In an embodiment, the image capture device is a mobile computing device with a camera including a colour sensor module for generating the RGB colour space values. For example, the mobile computing device is a smartphone and the processor generates RGB colour space values by applying filters (e.g. Red, Green and Blue filters) to the image data obtained by the camera of the smartphone and then generating a ratio of these RGB colour space values.

[0022] It will be appreciated by those persons skilled in the art that an RGB colour space is a colour space based on the RGB colour model, i.e. Red (R), Green (G), and Blue (B) primary colours. Different combinations of values (chromaticity) of these Red, Green and Blue additive primary colours can produce any chromaticity. For example, Royal Blue is: Red - 65; Green - 105; and Blue - 255.

[0023] In an embodiment, the frame includes an aperture for the camera of the mobile computing device to obtain the image data.

[0024] In an embodiment, the frame includes a mobile computing device holder configured to hold the mobile computing device with the camera of the mobile computing device aligned with the aperture of the frame.

[0025] In an embodiment, the system further includes a lighting source within the imaging chamber for illuminating the dye-surfactant complex in the reaction vessel when in the imaging chamber. For example, the lighting source is an LED light (e.g. white LED) with known light spectrum properties.

WO 2018/053580

PCT/AU2017/051013 [0026] In an embodiment, the mobile computing device includes a location module configured to determine a location of the mobile computing device, and the processor is configured to output a location of the mobile computing device and the sample with the indication of the concentration of the anionic surfactant in the sample. For example, the location module is a GPS module configured to determine GPS coordinates indicating the location of the mobile computing device.

[0027] The method and system disclosed herein may be used for detecting any suitable anionic surfactant. However, in some specific embodiments, the method and system are suitable for detecting an anionic surfactant constituent of an aqueous film forming foam and/or a fluorinated anionic surfactant.

[0028] Furthermore, at least some embodiments of the disclosed method are particularly suitable for a field-based assay for anionic surfactants.

[0029] TABLE 1: Summary of abbreviations used in the specification

Abbreviation	Meaning
AFFF	aqueous film forming foam
EVEA-AS	ethyl violet ethyl acetate active substances
LAS	linear alkylbenzene sulfonate
MBAS	methylene blue active substances
PFOA	perfluorooctanoic acid
PFOS	perfluorooctane sulfonate
SDS	sodium dodecyl sulfate
SPE	solid phase extraction
SDBS	sodium dodecylbenzenesulfonate

[0030] As set out above, the method and system disclosed herein is for the detection and quantification of concentration of an anionic surfactant in a sample. As would be readily understood by a person skilled in the art, a “surfactant” is an amphipathic molecule comprising both a hydrophobic portion and hydrophilic portion. In the case of an “anionic surfactant”, the hydrophilic portion of the molecule generally carries a negative charge at least at a pH of 7 or greater. As such, the term “anionic surfactant” may include molecules such as carboxylic acids which may form an anion

WO 2018/053580

PCT/AU2017/051013 (i.e. a conjugate base) at a pH of 7 or greater, but which may not necessarily be in an anionic form at a pH lower than 7. For example a carboxylic acid surfactant in an environmental sample may be regarded as an anionic surfactant even if the carboxylic acid surfactant is not necessarily in an anionic form until it is in the presence of a base such as a basic cationic dye.

[0031 ] A range of anionic surfactants that may be detected and quantified using the disclosed method would be readily ascertained by a person skilled in the art. Exemplary anionic surfactants include, for example, linear alkylbenzene sulfonate (LAS), sodium dodecyl sulfate (SDS), fluorinated surfactants such as perfluorooctane sulfonate (PFOS) or perfluorooctanioic acid (PFOA), sodium dodecylbenzenesulfonate (SDBS), and the like.

[0032] The method and system also has particular application for the detection and/or quantification of anionic surfactants which are constituents of aqueous film forming foams (AFFF), such as the fluorinated surfactants mentioned above.

[0033] In one embodiment, the sample may be an aqueous or water-based sample. In some embodiments, the aqueous sample may be an environmentally derived sample such as a water sample, a soil dilution or the like. The sample may be derived from, for example, industrial sites, sites suspected of surfactant contamination, such as sites where AFFFs have been used, industrial or domestic effluents, treated water samples, stormwater samples, lake or river water or sediment samples, marine water or sediment samples, among many others.

[0034] As would be appreciated, aqueous samples may also be derived from solids. For example, soils may be diluted in water or another aqueous solvent to produce a sample. Furthermore, other solids such as plant material, building material or the like may be crushed or macerated before being diluted into water or another aqueous solvent to produce a sample.

[0035] In further embodiments, samples may be extracted into an organic solvent used in the assay. In these embodiments, the solvent may be added to the sample which may be solid, semi-solid or liquid. Examples of such samples may include soils, plant material, building material or the like.

WO 2018/053580

PCT/AU2017/051013 [0036] In one embodiment, the solvent and dye may both be added to the sample and any anionic surfactant in the sample complexes with the cationic dye to form a detectable dye-surfactant complex that is preferentially soluble in the solvent. In a further embodiment, where the anionic surfactant and dye are soluble in the solvent used, the anionic surfactant and dye may dissolve into the solvent and the complex between the anionic surfactant and dye may form within the solvent phase. In a further embodiment, the solvent may be added to the sample to form an extract of the sample in the solvent for use in the assay. In some embodiments, the sample may be separated from the extract, or it may be used as a mixture. In any event, the cationic dye may be added to such extracts in order to allow the formation of a dye-surfactant complex which may then be detected in the solvent.

[0037] As set out above, the disclosed method contemplates the use of a cationic dye which is capable of complexing with an anionic surfactant from the sample to form a detectable dye-surfactant complex that is preferentially soluble in a solvent which is substantially immiscible with the sample. The cationic dyes useful in accordance with the disclosed method may include any positively charged (cationic) dyes which are able to complex with an anionic surfactant to produce a detectable dye-surfactant complex that is preferentially soluble in a solvent which is substantially immiscible with the sample. In further embodiments, the cationic dye is also a base such that upon addition to a sample (at approximately neutral pH) the dye causes an organic acid surfactant in the sample to form its anionic conjugate base, and thus become suitable for detection using the methods of the present invention. A range of suitable dyes may be used for the detection of anionic surfactants including, for example, ethyl violet, methylene blue, acridine orange, brilliant green and malachite green, amongst others. However, it has been determined that cationic dyes of the triarylmethane class are particularly suitable for use in accordance with the disclosed method.

[0038] In some embodiments of the present invention, the cationic dye of the triarylmethane class comprises the structure (I):

WO 2018/053580

PCT/AU2017/051013

wherein each of R¹, R² and R³ is independently selected from the group consisting of optionally substituted C1-C6 alkyl; and m is selected from the group consisting of 0 and 1.

[0039] In one particular embodiment, m is 1 and each of R¹, R² and R³ are ethyl groups. A dye having this structure is referred to herein as ethyl violet.

[0040] In specific embodiments of disclosed method, the cationic dye used is “ethyl violet or a derivative thereof”. “Derivatives” of ethyl violet, as referred to herein, include other cationic dyes comprising the structure (I) and/or other cationic dyes of the triarylmethane class.

[0041] In another embodiment, the method also contemplates the use of a solvent which is substantially immiscible with the sample into which the dye-surfactant complex is preferentially soluble.

[0042] As referred to herein the term “preferentially soluble” should be understood to refer to an increased level or rate of solubility of the dye-surfactant complex in the solvent than in the sample. Preferential solubility also encompasses the partitioning of the dye-surfactant complex into the solvent from the sample.

[0043] Without limiting the present disclosure to any particular mode of action, in the disclosed method, the hydrophilic (anionic) head of the anionic surfactant in a sample complexes with the cationic dye to form a dye-surfactant complex. This complex then preferentially dissolves or partitions into the solvent phase, wherein it can be detected using one of several detection methods (described later).

WO 2018/053580

PCT/AU2017/051013 [0044] Solvents which are substantially immiscible with the sample generally include organic solvents such as ethyl acetate, chloroform, toluene, dichloromethane and the like.

[0045] In some embodiments of the disclosed method, the cationic dye comprises ethyl violet or a derivative thereof and the solvent comprises ethyl acetate. Methods which utilise the combination of ethyl violet or a derivative thereof as a dye and ethyl acetate as a solvent are referred to herein as Ethyl Violet Ethyl Acetate Active Substances (EVEA-AS) methods or assays. One specific embodiment of an EVEAAS assay is set out in the examples.

[0046] As referred to herein, the improved sensitivity of the EVEA-AS assay should be understood to include reference to the lower detection limit of the EVEA-AS assay. In addition to improved sensitivity relative to a MBAS assay, the EVEA-AS assay also exhibits improved resolution. As referred to herein, the term “resolution” should be understood as the ratio of the amount of detectable dye-surfactant complex generated in the assay relative to the amount of anionic surfactant in the sample. For example, high resolution should be understood to refer to a relatively large amount of detectable dye-surfactant complex generated for a given amount of anionic surfactant in the sample. Conversely, low resolution should be understood as a relatively small amount of detectable dye-surfactant complex generated for the same amount of anionic surfactant in the sample.

[0047] In light of the foregoing, it will be appreciated that the resolution of an assay may be represented by the slope of a graphical calibration curve for the assay which relates the amount of detectable dye-surfactant complex in the solvent phase (on the y-axis) with increasing known amounts of anionic surfactant in a sample (on the x-axis). In this case, increased resolution of an assay is represented by an increased slope of the calibration curve.

[0048] Due to the increased response of a high resolution assay to an anionic surfactant in a sample, it would also be appreciated that increased resolution of an assay would also allow discrimination between smaller anionic surfactant concentration differences between different samples.

WO 2018/053580

PCT/AU2017/051013 [0049] In further embodiments, the disclosed method provides a method for quantification of concentrations of an anionic surfactant in a sample, wherein the method comprises a relative resolution, as measured by the slope of a calibration curve for an LAS standard, at a concentration between 0.5 mg/L and 5 mg/L, of at least 0.32, at least 0.35, at least 0.40, at least 0.45 or at least 0.5.

[0050] In yet further embodiments, the disclosed method provides a method for the quantification of the concentration of an anionic surfactant in a sample, wherein the method comprises a relative resolution, as measured by the slope of a calibration curve for an SDS standard, at a concentration between 0.5 mg/L and 5 mg/L, of at least 0.35, at least 0.40, at least 0.45 or at least 0.50.

[0051 ] In yet further embodiments, the disclosed method provides a method for the quantification of the concentration of an anionic surfactant in a sample, wherein the method comprises a relative resolution, as measured by the slope of a calibration curve for a PFOS standard, at a concentration between 0.25 mg/L and 1 mg/L, of at least 1.8, at least 2.0, at least 2.2 or at least 2.4.

[0052] That is, the resultant colour of the solvent phase when the assay is performed on a sample having a known concentration of an anionic surfactant is analysed for generating the calibration curve for the anionic surfactant. A range of colours corresponding to a range of known anionic surfactant concentrations in a sample are analysed to generate the calibration curve. In this way, when the assay is performed on a sample having an unknown concentration of anionic surfactant, the colour of the solvent phase after the assay is performed may be compared with one or more of the colours on the calibration curve to provide an estimation of the concentration of the anionic surfactant in the sample having the unknown concentration.

[0053] In an embodiment, the detection limit using the method is: 1 ppm - 10 ppb, and the detection limit can be enhanced by pre-concentrated the sample and then taking this into consideration when using the method described above to derive the concentration of the anionic surfactant in the sample.

WO 2018/053580

PCT/AU2017/051013 [0054] The EVEA-AS assay is also particularly suitable for a field-based assay for anionic surfactants. This is in part due to the use of the relatively safe solvent ethyl acetate, which enables the performance of the assay outside of controlled laboratory conditions and also potentially by relatively unskilled personnel. Furthermore, the increased sensitivity and resolution of the assay is also particularly well suited to visual assessment of the results of the assay, and thus is well suited for quantification of the concentration of anionic surfactants in the field without the use of bulky equipment such as a spectrophotometer.

[0055] In the disclosed method, an anionic surfactant in the sample complexes with the cationic dye to form a “detectable dye-surfactant complex” that is preferentially soluble in the solvent which is substantially immiscible with the sample. As used herein, the term “detectable dye-surfactant complex” refers to any complex formed between the cationic dye and anionic surfactant that is subsequently detectable in the solvent phase of the assay.

[0056] It will be appreciated by those persons skilled in the art that the dyesurfactant complex formed by the anionic surfactant and the cationic dye is coloured. The dye-surfactant complex is detected in the solvent phase by detection of a colour change in the solvent phase of the assay. The coloured dye-surfactant complex is then imaged and its RGB colour space values are analysed to quantify the concentration of the anionic surfactant in the sample.

[0057] In some embodiments, the method further comprises a concentration step to increase the concentration of one or more anionic surfactants in the sample prior to contacting the sample with the cationic dye and/or solvent. The concentration step may include any concentration step that increases the concentration of an anionic surfactant in a sample. Exemplary concentration steps include for example, solid phase extractions (SPE), solvent evaporation, solvent sublimation (e.g. freezedrying), preparative chromatography (e.g. preparative TLC, preparative HPLC or preparative GC) and the like.

[0058] The concentration step may be used, for example, to increase the concentration of an anionic surfactant in an environmental sample to within the detection range of an assay. As will be appreciated, if a concentration step is used in

WO 2018/053580

PCT/AU2017/051013 a quantitative assay, the concentration result obtained from the assay must take into account the concentration factor of the concentration step.

[0059] In some embodiments, the concentration step may comprise a solid phase extraction (SPE). A range of suitable SPE methods for the concentration of anionic surfactants from a sample would be readily ascertained by a person skilled in the art. As would be appreciated, however, for samples having high surfactant concentrations, a dilution step may also be used to bring the concentration of the assayed sample into the detection range of the method.

[0060] In yet another aspect, the present invention provides a kit when used for quantifying a concentration of anionic surfactants in a sample according to a method of the first aspect of the invention, the kit comprising: a cationic dye, wherein the cationic dye is capable of complexing with an anionic surfactant from the sample to form a detectable dye-surfactant complex that is preferentially soluble in a solvent (e.g. the cationic dye comprising ethyl violet or a derivative thereof, and the solvent comprising ethyl acetate); instructions for performing the method according to a first aspect of the invention; a reaction vessel whereby the cationic dye is contacted with the sample and the solvent in the reaction vessel; and an apparatus including: an imaging chamber configured to receive the reaction vessel therein, wherein the imaging chamber has a frame for positioning an image capture device for obtaining image data of the dye-surfactant complex in the solvent in the reaction vessel in the imaging chamber and the reaction vessel relative to each other. As discussed above, the processor of the image capture device is configured to: generate RGB colour space values by applying one or more filters to the image data for a plurality of pixels in the image data; analyse the RGB colour space values to derive a concentration of the anionic surfactant in the sample; and output an indication of the concentration of the anionic surfactant in the sample.

[0061] The reaction vessel included in the kit may be any suitable vessel for the assay such as a test tube, screw cap tube or vessel, flask or the like.

[0062] Embodiments of the present invention are further described by the following non-limiting examples and with reference to the following drawings.

WO 2018/053580

PCT/AU2017/051013

Brief Description of Drawings [0063] Figure 1 shows a flow chart of a method of quantifying a concentration of anionic surfactants in a sample according to an embodiment of the present invention.

[0064] Figure 2 shows RGB colour space values and different ratios of the RGB colour space values generated from image data of the dye-surfactant complex for different concentrations according to an embodiment of the present invention.

[0065] Figure 3 shows calibration curves ratios generated by plotting ratios of RGB colour space values in relation to known concentrations of known anionic surfactants according to an embodiment of the present invention.

[0066] Figure 4 shows test results for a PFOA anionic surfactant in a sample quantified according to an embodiment of the present invention.

[0067] Figure 5 shows a further flow chart of a method of quantifying a concentration of anionic surfactants in a sample according to an embodiment of the present invention.

[0068] Figure 6 shows an apparatus for quantifying a concentration of anionic surfactants in a sample according to an embodiment of the present invention.

[0069] Figure 7 shows the apparatus of Figure 6 and an image capture device.

Detailed Description [0070] An embodiment of a method 10 of quantifying a concentration of anionic surfactants in a sample is summarised in Figure 1. The method includes the steps of contacting 12 a cationic dye with the sample and a solvent, such that an anionic surfactant in the sample complexes with the cationic dye to form a detectable dyesurfactant complex that is preferentially soluble in the solvent; obtaining 14 image data of the dye-surfactant complex in the solvent; generating 16 RGB colour space values for a plurality of pixels in the image data by applying one or more filters to the image data; analysing 18 the RGB colour space values to derive a concentration of the anionic surfactant in the sample; and outputting 20 an indication of the concentration of the anionic surfactant in the sample.

WO 2018/053580

PCT/AU2017/051013 [0071] This method can be implemented using an apparatus 22 for quantifying the concentration of anionic surfactants in a sample, which is shown in Figures 6 and 7. The apparatus 22 including: an imaging chamber 24 configured to receive a reaction vessel 26 therein, whereby the cationic dye is contacted with the sample and solvent in the reaction vessel such that an anionic surfactant in the sample complexes with the cationic dye to form a detectable dye-surfactant complex that is preferentially soluble in the solvent.

[0072] The apparatus 22 shown in Figure 7 has an image capture device 28 attached thereto for obtaining image data of the dye-surfactant complex in the solvent in the reaction vessel 26 in the imaging chamber 24. The imaging chamber 24 has a frame 27 for positioning the image capture device 28 and the reaction vessel 26 relative to each other. The frame 27 in the embodiment has a cylindrical shape so that in use the reaction vessel 26 is inserted into the cylindrical frame 27 of the imaging chamber 24 into the desired position for imaging by the image capture device

28. It will be appreciated by those persons skilled in the art that other shapes of frame could be used, such as a square cross-section frame.

[0073] A processor (not shown) of the image capture device 28 is configured to: generate the RGB colour space values as described above by applying one or more filters to the image data for a plurality of pixels in the image data; analyse the RGB colour space values to derive a concentration of the anionic surfactant in the sample; and output an indication of the concentration of the anionic surfactant in the sample on a display of the image capture device 28.

[0074] As described, the image capture device 28 in the embodiment is a mobile computing device in the form of a smartphone with a camera including a colour sensor module for generating the RGB colour space values. Hereinafter, the image capture device 28 will be referred to as a smartphone 28. The smartphone 28 uses a CMOS sensor array to read the RGB colour space values when taking an image with its camera. For example, the filter is a RGB filter which creates three feature images for red, green and blue channels from the CMOS sensor array data. These feature images are then analysed to obtain RGB colour space values (e.g. blue: 0, 0, 255).

WO 2018/053580

PCT/AU2017/051013

Also, RGB colour space values are generated from multiple pixels in the image data and averaged.

[0075] The frame 27 includes an aperture (not shown) for the camera of the smartphone 28 to obtain an image of the dye-surfactant complex in the reaction vessel 26. The frame 27 also includes a phone holder 30 configured to hold the smartphone 28 with its camera aligned with the aperture of the frame 27. It will be appreciated by those persons skilled in the art that the phone holder 30 is adjustable and can hold various sizes of smartphones.

[0076] It will also be appreciated that the smartphone 28 has a display for outputting the indication of the concentration of the anionic surfactant in the sample. Thus, in use, the apparatus 22 can be taken into the field to detect and determine the concentration of anionic surfactants in a sample using the smartphone 28 with software instructions installed thereon for performing the method. These software instructions can be saved locally on the smartphone 28 or remotely on a server or a combination of both. In the latter case, the image data is transmitted over a network to be analysed by a server and the indication of the concentration is derived and transmitted back to the smartphone 28 for display. In addition, the smartphone 28 includes a location module configured to determine a location of the smartphone 28, such as GPS module, and the processor of the smartphone 28 is configured to output the GPS location of the smartphone 28 and thus of the sample being analysed with the indication of the concentration of the anionic surfactant in the sample. The concentration of the anionic surfactant in the sample and the location of the sample can be saved in a memory locally or remotely for later use.

[0077] Further, the reaction vessel 26 is mounted to a base 32 of the apparatus

22. The reaction vessel 26 and the base 32 are configured to be inserted into an opening 34 of the cylindrical frame 27 of the imaging chamber 24 so that the frame 27 positions the smartphone 28 and the reaction vessel 26 relative to each other for obtaining image data of the dye-surfactant complex in the reaction vessel 26. Further, the base 32 and the frame 27 have complementary features to ensure that the frame 27 positions the reaction vessel 26 in the desired positon for obtaining image data.

WO 2018/053580

PCT/AU2017/051013 [0078] In the embodiment shown in Figure 6, the apparatus 22 further includes a lighting source 36, powered by a battery (not shown), that provides light within the imaging chamber 24 for illuminating the dye-surfactant complex in the reaction vessel 24 when in the imaging chamber 26 for imaging. The lighting source 36 is typically an LED light source that emits a white light to ensure that the image of the dye-surfactant complex in the reaction vessel is obtained with a consistent colour spectrum backlight. Accordingly, the imaging chamber 24 ensures that the dye-surfactant complex in the reaction vessel 24 being imaged and analysed is done so with controlled lighting conditions.

[0079] To derive the concentration of the anionic surfactant in the sample for display, the processor of the smartphone 26 generates a ratio of RGB colour space values of the dye-surfactant complex formed by the anionic surfactants in the sample as follows: Blue colour space value/(2* Blue colour space value - Green colour space value - Red colour space value). The processor then derives the concentration of the anionic surfactant in the sample using the generated ratio of RGB colour space values on a calibration curve for known concentrations of known anionic surfactants as described above. The calibration curve is defined as:

C = A1 *((A2-A3)/(x-A3)-1 )^A4 where:

c is concentration (in ppb);

[0080] The generation of the calibration curve is described in further detail below with respect to example, whereby the calibration curve was determined for known concentrations of known anionic surfactants by generating ratios of RGB colour space values of the dye-surfactant complex formed by at least one of the known anionic surfactants at the known concentrations and plotting these ratios of RGB colour space values in relation to the known concentrations.

[0081] EXAMPLES: Ethyl Violet Ethyl Acetate Active Substances (EVEA-AS) Assay in DI water

WO 2018/053580

PCT/AU2017/051013 [0082] The above method 10 of quantifying a concentration of anionic surfactants in a sample is exemplified by the following examples using the above apparatus 22 and smartphone 28. In this example, the method uses the combination of the dye ethyl violet with ethyl acetate as a solvent, and thus is an embodiment of an EVEA-AS method as previously described.

[0083] All chemicals in this example including PFOA, PFOS, SDBS, styrenedivinylbenzene polymer resin (SDVB), fluoro-gel, acetone, methanol, ethyl acetate and ammonium acetate (NH4Ac) were purchased from Sigma-Aldrich (Australia). Only polypropylene containers/pipette tips were used throughout. Deionized water (DI water) was used (> 18 M0«cm) in the present study.

[0084] All samples were diluted in DI water in centrifuge tubes (polypropylene) without any pre-treatment. The tubes were kept at room temperature (~24^SC) without being shielded from the laboratory fluorescent lamp for domestic lighting. All the experiments were carried out at room temperature.

[0085] For the examples, PFOA/PFOS was spiked in tap water for some tests. In this case, tap water was collected in Callaghan campus, University of Newcastle, NSW, Australia. For better performance, tap water including spiked PFOA/PFOS was boiled for ~1 min and then cooled down to room temperature for further tests.

[0086] SPE concentration was carried out using 0.1 g SDVB as the absorbing matrix with the help of vacuum. Basically, 10-1000 ml_ aqueous sample flew through the cartridge containing the SDVB powder resin. The resin was then washed with 5 ml_ DI water 5 times to remove the potential interfering moieties. After washing, the absorbed AS was eluted with 1 ml_ methanol. The methanol extract was then concentrated to dryness with nitrogen in a heated water bath. It was then dissolved to a 10 ml_ DI water for app/visual test, or to 1 ml_ DI water for the subsequent fluoroSPE. Alternatively, EVEA-AS reagent can also be used for the elution. In this case, the extract will be balanced with 10 ml_ DI water as the aqueous phase to establish the distribution equilibrium between the aqueous phase and the organic phase.

[0087] Fluoro-SPE was conducted using 2 g F-gel as a filter to remove non fluorocarbon skeletons. The F-gel was pre-conditioned with 1 ml_ 80% methanol solution

WO 2018/053580

PCT/AU2017/051013 (20% water, v/v). After that, SPE extract using SDVB was loaded to F-gel with vacuum. The cartridge was washed off with 1 mL 80% methanol again to remove other AS whilst remain PFOA/PFOS. In the end, the PFOA/PFOS was eluted with 30 mL methanol. Similarly, the methanol extract was concentrated to dryness and then dissolved to a 10 mL DI water for the test.

[0088] Samples were analysed using the apparatus 22 and HPLC-MS (Agilent 1260 + Quadrupole 6130) for validation. In general, the apparatus 22 needs 10 mL aqueous sample to be mixed with a 7 mL dye in a container of 25 mL. After shaking for around 10 second and keeping it static for 1-2 min, the top layer of organic phase extracted the ion-pair of cationic dye and anionic surfactant. The colour is capable of being related to the anionic surfactant’s concentration level in the aqueous solution as described above. EVEA-AS provided an increased brightness of the organic phase corresponding to the ion-pair concentration and thus provides a better visible test of anionic surfactant concentration with a limit of detection around 10 ppb.

[0089] For the test, the apparatus 22 shown in Figures 6 and 7 was used. The reaction vessel 26 is of the same diameter of a common 50 mL centrifuge tube but is shorter. This diameter means a longer absorption length and a higher sensitivity. All surfaces inside the imaging chamber 24 are white or colourless in order to diminish the instance of interference when imaging.

[0090] For HPLC-MS analysis, a 10 pL sample solution was injected into Agilent 1260 high-performance liquid chromatography fitted with an Eclipse plus-C18 column kept at 40^sC with dimensions of: 4.6 mm internal diameter, 100 mm length and 3.5 pm particle size. The flow rate was 0.5 mL/min for gradient mobile phase of methanol: 5 mM aqueous NH4Ac for separation. Quadrupole 6130 detector was maintained under negative mode for scanning. Extraction of the molecular ions was conducted at m/z 413 for PFOA, 499 for PFOS, respectively.

[0091] Quantification was carried out by generating a calibration curve above using standard solutions of PFOA, PFOS (only linear isomers) with correlation coefficients higher than 0.99 and limit of detection ~0.2 ppb (signal to noise > 3). Blank samples of HPLC-grade Milli Q water and methanol were run prior to each set of test to minimize the background contamination that might originate from the Teflon

WO 2018/053580

PCT/AU2017/051013 components of HPLC instrument itself. The nebulizer gas (nitrogen) pressure was set at 35 psi, drying gas flow rate was 10 L/min and temperature 350 ^SC, the capillary voltage was + 3500 V.

[0092] For colouration justification, consistency of background illumination was critical. The intensity of the background illuminations can vary and depends on, for instance, the weather conditions (sunny or cloudy), test position (indoor or outdoor, under sunshine or in shadow), test background (white wall or colourful paper) etc. The apparatus 22 thus includes a light source 36 in the form of a white LED for illumination.

[0093] The holder 30 for the smartphone 28 shown in Figure 7 varies depending on the model of the phone - in the example the phone used was a Samsung S5. Figure 7 shows an image of the reaction vessel 26 taken with the Samsung S5 28 on its display. A top layer that is formed when the cationic dye is contacted with the sample and a solvent is the detectable dye-surfactant complex (e.g. extracted layer of organic phase) and the central part of this layer will be the reading area for colour analysis. The RGB colour space values were generated and an average of 7 pixels were analysed from this reading area.

[0094] The smartphone’s camera (e.g. 16 megapixel camera) has a CMOS sensor array to read RGB colour space values. In the example, the RGB colour space values are generated for analysis without any pre-treatment, which is particularly important for anionic surfactants with low concentration (< 100 ppb). For this reason, the frame 27 can fix the camera positon and distance and the LED light 36 can stabilise the illumination intensity of the background light to minimise variation for the generated RGB colour space values.

[0095] According to Beer-Lambert law, the absorbance of the ethyl violet (EV) anionic surfactant (AS) ion-pairs (EV-AS) at 595 nm is expected to be proportional with the concentration of the anionic surfactant (e.g. PFOA/PFOS). The concentration of the EV-AS ion-pair exhibits a relationship with the absorbance as follows:

A = -log(lt/IO) = SiC/

WO 2018/053580

PCT/AU2017/051013

Where:

A is the absorbance;

It the intensity of the transmission;

the intensity of excitation;

ε/the molar absorbance coefficient of the ion-pair;

c is the ion-pair concentration; and /is the path length of the illumination through the sample solution.

[0096] Thus, as indicated by Lambert-Beer law, the maximum absorbance wavelength is most important to deriving the concentration. The method uses RGB colour space values to simulate the light intensity at 595 nm. So, for example, light on the “Blue” range (-445 nm) which is far away from 595 nm can be used as the control or reference colour for background correction and more emphasis can be placed on the red and green light components. “Green” (-535 nm) and “Red” (-650 nm) are thus important to simulating the transmission intensity at 595 nm, which contains the information required for the quantitative analysis and concentration estimate.

[0097] Figure 2 shows different approaches to decoding and analysing the RGB colour space values generated from the image data. In Figure 2(a), the RGB values are plotted against concentration of SDBS in the sample. In Figure 2 (b), the ratio of these RGB colour space values is determined as (Blue/(Red + Green)), which was selected to mimic the absorption, is plotted against concentration of the SDBS in the sample. In Figure 2 (c), the curve formed with the ratio of (Blue/(2*(Blue - Green Red)) is a better fit than the curve in Figure 2(b); suggesting a better decoding algorithm. This was confirmed in Figure 2(d) where different samples with SDBS were measured. The data variation in the inset is big when the (Blue/(Red + Green)) ratio is selected, particularly at the high concentration range. However, the variation is significantly smaller when the ratio of (Blue/(2*(Blue - Green - Red))) is used. Accordingly, the ratio of Blue/(2*(Blue - Green - Red))) was selected for the following tests and for generation of the calibration curve.

[0098] It will be appreciated that, in the test to achieve a stable and repeatable RGB reading, all the auto functions of the camera of the smartphone 28 have been shut down, including, face-detection, HDR, ISO, auto-effect, etc. The centre-weighted

WO 2018/053580

PCT/AU2017/051013 function is used to emphasis the sample’s colour and the flash can be used as the illumination resource but the calibration curve will be shifted and requires compensation. Furthermore, to minimise reflection from the reaction vessel 26 and the interior surface of the imaging chamber 24 the LED 36 was used as the illumination source.

[0099] Calibration curves using Logistic equation are shown in Figure 3. Figure 3(c) is a zoomed image of Figure 3(b). Here, there is shown a good fit of ratio values with a coefficient of determination of R2 > 0.99. The variation of determined concentrations using the method is <5%, suggesting a success. Figure 3 (d) shows the data and calibration curves for SDBS and PFOA, respectively. The fitting equation for the calibration curve was kept the same when the AS was changed from SDBS to PFOA. This is because the molecular weights of PFOA and SDBS are different (414.1 vs. 348.5), which brings the different mol concentration (such as μΜ) that is directly linked with absorption.

[0100] The fitting equation for the calibration curve is shown in Figure 3 as a Logistic equation with co-efficient of determination > 0.99. It will be appreciated by those persons skilled in the art that other fitting equations could be used to derive the concentration curve, such as Boltzmann and Hill equations.

[0101 ] It will be appreciated that images of different concentrations of PFOA in DI water were taken by the smartphone 28 camera to generate the calibration curves shown in Figures 2 and 3.

[0102] EXAMPLE: Ethyl Violet Ethyl Acetate Active Substances (EVEA-AS) Assay in tap water [0103] The above tests with results shown in Figure 2 and 3 were carried out in DI water. Figure 4 shows the test results when tap water was used. It will be appreciated that inorganic ions in the water may interfere with test as the concentrations of inorganic ions might be much higher than those of contaminates. Therefore, the tap water was treated prior to this test. Treated tap water spiked with PFOA was tested and the results are shown in Figure 4. It can be seen that the ratio of RGB values is in alignment with the calibration curve.

WO 2018/053580

PCT/AU2017/051013 [0104] Accordingly, the calibration curve was determined by the plots of the ratio of RGB colour space values and known concentration of known anionic surfactants to be defined as:

C = A1 *((A2-A3)/(x-A3)-1 )^A4 where:

c is concentration (in ppb);

[0105] An example of the apparatus 22 in use is shown with respect to the flow chart of Figure 5. Here, a user wishing to quantify a concentration of anionic surfactants in a sample first opens a reagent container having the cationic dye, and pours the reagent into the sample into the reaction vessel 24 so that the cationic dye contacts the sample and the solvent. The resultant mixture is shaken in the reaction vessel 24 and then allowed to sit for layer-separation and imaging.

[0106] The anionic surfactant in the sample complexes with the cationic dye in the reaction vessel 24 as described above to form a detectable dye-surfactant complex. The reaction vessel 24 is then placed in the imaging chamber 24 for obtaining image data of the dye-surfactant complex in the solvent by the user’s smartphone 28. As described, the user’s smartphone 28 will have an application residing thereon that is implemented by the processor of the smartphone 28 to derive and display the concentration of the anionic surfactants in the sample. The processor does so by colour reading the top layer of the mixture in the reaction vessel 26, which involves generating RGB colour space values by applying one or more filters to the image data obtained by the camera of the smartphone 28 and then generating a ratio of these RGB colour space values. As described, the preferable ratio in the embodiments is: Blue colour space value/(2* Blue colour space value - Green colour space value Red colour space value). This ratio (x) is then inputted into the calibration curve defined as: c (concentration) = A1*((A2-A3)/(x-A3)-1)^A4 and the concentration thus derived.

WO 2018/053580

PCT/AU2017/051013 [0107] It will be appreciated that there may be other variations and modifications to the configurations described herein that are also within the scope of the present invention.

WO 2018/053580

PCT/AU2017/051013

Claims

The claims:

1. A method of quantifying a concentration of anionic surfactants in a sample, the method including:

contacting a cationic dye with the sample and a solvent, such that an anionic surfactant in the sample complexes with the cationic dye to form a detectable dyesurfactant complex that is preferentially soluble in the solvent;

obtaining image data of the dye-surfactant complex in the solvent;

for a plurality of pixels in the image data, generating RGB colour space values by applying one or more filters to the image data;

analysing the RGB colour space values to derive a concentration of the anionic surfactant in the sample; and outputting an indication of the concentration of the anionic surfactant in the sample.
2. A method according to claim 1, further including generating a ratio of RGB colour space values of the dye-surfactant complex formed by the anionic surfactants in the sample.
3. A method according to claim 2, wherein the ratio of said RGB colour space values is: Blue colour space value/(2* Blue colour space value - Green colour space value - Red colour space value).
4. A method according to claim 3, further including deriving the concentration of the anionic surfactant in the sample using the ratio of said RGB colour space values on a calibration curve for known concentrations of known anionic surfactants.
5. A method according to claim 4, wherein the calibration curve is defined as:

c = A1 *((A2-A3)/(x-A3)-1 )^A4 where:

c is concentration (in ppb);

A1-A4 are constants associated with the known anionic surfactant; and x is the ratio of said RGB colour space values.

WO 2018/053580

PCT/AU2017/051013
6. A method according to claim 5, wherein the anionic surfactant in the sample is sodium dodecylbenzenesulfonate (SDBS) and A1 is 199.9; A2 is 1.012; A3 is 0.594; and A4 is 0.60.
7. A method according to claim 5, further including generating the calibration curve for known concentrations of known anionic surfactants by generating ratios of RGB colour space values of the dye-surfactant complex formed by at least one of the known anionic surfactants at the known concentrations and plotting the ratios of RGB colour space values in relation to the known concentrations.
8. A method according to claim 7, further including selecting a particular calibration curve of a particular known anionic surfactant for deriving the concentration of the particular known anionic surfactant in the sample based on the ratio of said RGB colour space values fitting the particular calibration curve.
9. A method according to any one of claims 3 to 8, further including generating the ratio of said RGB colour space values generated by applying said one or more filters to different groups of pixels in the image data, and averaging the ratio of said RGB colour space values for the different groups of pixels.
10. A method according to any one of claims 1 to 9, wherein the cationic dye includes ethyl violet or a derivative thereof, and the solvent includes ethyl acetate.
11. A method according to any one of claims 1 to 10, wherein the anionic surfactant includes a fluorinated anionic surfactant or an aqueous film forming foam.
12. A method according to any one of claims 1 to 11, further including determining a location of the sample and outputting the location of the sample with the indication of the concentration of the anionic surfactant in the sample.
13. A system for quantifying a concentration of anionic surfactants in a sample, the system including:

WO 2018/053580

PCT/AU2017/051013 an imaging chamber configured to receive a reaction vessel therein, whereby a cationic dye is contacted with the sample and a solvent in the reaction vessel such that an anionic surfactant in the sample complexes with the cationic dye to form a detectable dye-surfactant complex that is preferentially soluble in the solvent; and an image capture device for obtaining image data of the dye-surfactant complex in the solvent in the reaction vessel in the imaging chamber, wherein the imaging chamber has a frame for positioning the image capture device and the reaction vessel relative to each other, and wherein a processor of the image capture device is configured to: generate RGB colour space values by applying one or more filters to the image data for a plurality of pixels in the image data;

analyse the RGB colour space values to derive a concentration of the anionic surfactant in the sample; and output an indication of the concentration of the anionic surfactant in the sample.
14. A system according to claim 13, wherein the processor of the image capture device is further configured to generate a ratio of RGB colour space values of the dye-surfactant complex formed by the anionic surfactants in the sample.
15. A system according to claim 14, wherein the ratio of said RGB colour space values is: Blue colour space value/(2* Blue colour space value - Green colour space value - Red colour space value).
16. A system according to claim 15, wherein the processor is further configured to derive the concentration of the anionic surfactant in the sample using the ratio of said RGB colour space values on a calibration curve for known concentrations of known anionic surfactants.
17. A system according to claim 16, wherein the calibration curve is defined as:

c = A1 *((A2-A3)/(x-A3)-1 )^A4 where:

c is concentration (in ppb);

WO 2018/053580

PCT/AU2017/051013

A1-A4 are constants associated with the known anionic surfactant; and x is the ratio of said RGB colour space values.
18. A method according to claim 17, wherein the calibration curve is generated for known concentrations of known anionic surfactants by generating ratios of RGB colour space values of the dye-surfactant complex formed by at least one of the known anionic surfactants at the known concentrations and plotting the ratios of RGB colour space values in relation to the known concentrations.
19. A system according to claim 18, wherein a particular calibration curve of a particular known anionic surfactant for deriving the concentration of the particular known anionic surfactant in the sample is selected based on the ratio of said RGB colour space values fitting the particular calibration curve.
20. A system according to any one of claims 13 to 19, wherein the image capture device is a mobile computing device with a camera including a colour sensor module for generating the RGB colour space values.
21. A system according to claim 20, wherein the frame includes an aperture for the camera of the mobile computing device to obtain the image data.
22. A system according to claim 21, wherein the frame includes a mobile computing device holder configured to hold the mobile computing device with the camera of the mobile computing device aligned with the aperture of the frame.
23. A system according to any one of claims 13 to 22, wherein the system further includes a lighting source within the imaging chamber for illuminating the dyesurfactant complex in the reaction vessel when in the imaging chamber.
24. A system according to any one of claims 13 to 23, wherein the mobile computing device includes a location module configured to determine a location of the mobile computing device, and the processor is configured to output a location of the

WO 2018/053580

PCT/AU2017/051013 mobile computing device and the sample with the indication of the concentration of the anionic surfactant in the sample.
25. An apparatus for quantifying a concentration of anionic surfactants in a sample, the system including:

an imaging chamber configured to receive a reaction vessel therein, whereby a cationic dye is contacted with the sample and a solvent in the reaction vessel such that an anionic surfactant in the sample complexes with the cationic dye to form a detectable dye-surfactant complex that is preferentially soluble in the solvent, wherein the imaging chamber has a frame for positioning an image capture device, for obtaining image data of the dye-surfactant complex in the solvent in the reaction vessel in the imaging chamber, and the reaction vessel relative to each other, and wherein in use a processor of the image capture device is configured to:

generate RGB colour space values by applying one or more filters to the image data for a plurality of pixels in the image data;

analyse the RGB colour space values to derive a concentration of the anionic surfactant in the sample; and output an indication of the concentration of the anionic surfactant in the sample.

WO 2018/053580

PCT/AU2017/051013