WO2009147504A1

WO2009147504A1 - Composition for the colorimetric detection and/or determination of metal cations in solution, reaction column, flow cell and method for the colorimetric detection and/or determination of metal cations in solution

Info

Publication number: WO2009147504A1
Application number: PCT/IB2009/005824
Authority: WO
Inventors: Jorge Luis Grinstein; Fernando Alberto Inon; Diego Alejandro Grassi; Sebastian Javier Salvo; Enrique Salvo
Original assignee: Jenck S.A.
Priority date: 2008-06-03
Filing date: 2009-06-02
Publication date: 2009-12-10
Also published as: AR066836A1

Abstract

Reaction column for the colorimetric detection and/or determination of metal cations in solution, by formation of complexes with a reagent selected from diphenylcarbazide and diphenylthiocarbazone. The column comprises at least a circulation zone of the solution to be analyzed, containing said reagent immobilized in an inert support comprising a polymeric resin. Flow cells for a spectrophotometric device comprising said reaction column in a physically integrated form. Method for the detection and/or determination of metal cations in solution using said reaction column or said flow cell.

Description

COMPOSITION FOR THE COLORIMETRIC DETECTION AND/OR

DETERMINATION OF METAL CATIONS IN SOLUTION, REACTION COLUMN,

FLOW CELL AND METHOD FOR THE COLORIMETRIC DETECTION AND/OR

DETERMINATION OF METAL CATIONS IN SOLUTION

Field of the invention

The present invention is related to analytical chemistry, more precisely to the colorirαetric detection and/or determination of metal cations in solution, preferably by spectrophotometry analysis.

Background of the invention

The speciation analysis of metals in solution is crucial in various toxicological and environmental applications, due to the fact that their effect depends on the chemical species of the metal. For example in the case of chromium, Cr(VI) is carcinogen and mutagenic, while Cr(III) is an essential element for the ' human being. In these cases the concentration of each species in water is internationally regulated and in certain European countries and in the United States, its concentration in effluents is also regulated.

Since 2005 regulations known as European Restriction of Hazardous Substances require that this analysis be made in all automobile components and electronic devices to be commercialized in the European Union and similar regulations are being adopted in the United States and Japan.

These requirements have caused a sustained demand from manufacturers and retailers of these products for new and improved technologies for the rapid and reliable determination of said chemical species, especially Cr(VI) . In scientific literature, in commercial reagents specifications, and in official analysis methods (such as US- EPA, AOAC, ASTM, Standard Methods), the derivatization reaction of said metals for the formation of a specific product (which have at least one physicochemical property allowing its determination, for example, a specific color) is performed by mixing sample and reagents solutions. There is the possibility of adding the reagents in solid and pure state, but always trying to achieve the complete dissolution of the added matter before the detection step.

The detection of colored species and compounds is performed by means of its interaction with electromagnetic radiation. The term "colored" indicates that the substance has the property of absorbing electromagnetic radiation within the visible spectrum, i.e. radiation characterized by a wavelength between 380 and 700 nm. Within a certain concentration range, there is proportionality between the concentration of the absorbent species and the absorbed radiation intensity or power. In order to quantify said magnitude, an optical assembly having at least three components: light source, sample and detector, is required. The location of these three components varies depending on the way the desired measurement is made, either by transmission or by reflection.

In the measurements by transmission, the radiation emitted by the light source, either collimated or not collimated, perpendicularly crosses a region where the sample is placed in and reaches the detector. On the contrary, in the measurements by reflection, the radiation emitted by the source incides on the sample forming a certain angle, and the detector is placed within the spatial region formed by the reflected radiation. In each of said basic detection methods, any optical elements, such as integrating spheres, plane and curve mirrors, lenses, etc., may be used, with a view to improving the efficiency of radiation transmission and collection processes. In both cases, the source and the detector must comply with a basic requisite: emission and detection, respectively, of radiation at a wavelength absorbed by the species to be detected. The range of emitted and detected wavelengths is very important because it influences the selectivity of the method.

There are commercially available instruments that allow one performing this type of measurement, the most common being the spectrophotometers, where the measurement mode is by transmission. Among the spectrophotometer manufacturers, Shimadzu, Varian and Perkin Elmer, may be mentioned, among others, providing various models with different performance characteristics (noise, drift, effective nominal band width, etc) .

In order to gain versatility, spectrophotometers have one or more continuous radiation lamps, typically deuterium discharge lamps for the ultraviolet region, and incandescent lamps for the visible region, and the selection of the preferred wavelength is performed by means of optical elements such as monochromators or filters. Another common inclusion in these instruments is a second detector, which is capable of monitoring the radiation emitted by the lamp, before or after the optical element that carries out the wavelength selection, commonly being after it, but without being influenced by its interaction with the sample. This optical array is known as "dual beam" system and its main advantage is its ability for compensating any variation of the radiation emitted by the lamp during the sample analysis. In order to carry out the measurements, in both for transmission or reflection mode, two opposite conditions, which are, in a way, arbitrary, should be standardized. In the following, the transmission mode will be described, but the reflection mode is analog thereto. The first condition is defining when what is being interposed in the described optical path is not capable of absorbing the chosen electromagnetic radiation at all, in other words, that it transmits 100% of said radiation (total transmission) . The second condition is defining when what is interposed in the described optical path is capable of absorbing the chosen electromagnetic radiation completely, in other words, it transmits 0% of input radiation (total absorption) .

The transmission percentage for a given material is calculated mathematically from the quotient between the power of the radiation detected by the detector (s) when the absorbent material i's in place and the power of the radiation detected by the detector (s) in the conditions selected or_. established as producing total transmission (i.e., nothing interposed) . This quotient is known as transmittance (T) and percent transmittance (T%) when the quotient is multiplied by 100. Also, the value of 100% T% may be set in the case of interposing a cell in the optical path, defining a cell as a body with at least 2 faces ideally parallel to each other, that absorb a minimum of the chosen electromagnetic radiation and are separated at a given distance, having the cell an empty gap or volume comprised therein and suitable to be filled with liquid samples. Also, this volume may be filled with a solvent, wherein the species to be detected will be ideally dissolved, and under this condition -cell + solvent, T% may be defined as 100%. The measurement of a sample or standard material will involve displacing the solvent in a mechanical way and occupying said volume with the sample or standard material.

Finally, the empiric Lambert and Beer Law is used for quantification of the analyzed species, this law lineally correlates the concentration of the absorbent species (c) , the length of the optical path (b) (sample distance covered by the electromagnetic radiation beam) and the intrinsic properties of the absorbent species for absorbing electromagnetic radiation of the selected wavelength (ε_\) (known as the molar absorption coefficient) to the minus logarithm of T (known as absorbance, A) . This law determines that under certain boundary conditions the following equation is valid: Aχ= ε_λ*b*c.

Regarding the presentation form of the analytical reagents, there are, in turn, and only in scientific literature (for example The Analyst, Vol. 121, 613-616 (1996), Journal of Flow Injection Analysis, 17(2), 174-179 (2000)), descriptions of techniques based on the addition of the reagent in solid form, being dispersed in an inert matrix (sand, silicon oxide base) disposed within a column for allowing the sample flow therethrough. In this' particular case, in the presence of the chemical species of the metal to be determined, for example Cr(VI), a reaction product is generated while passing through the column and it is quantified at the exit of the column by means of a spectrophotometer.

The disadvantage of this method is that the pressure drop occurring in the flow analysis system (and the stability thereof throughout continuous use) due to column packing, as well as the generation of the packing itself, limits the commercial application of this approach. In fact, there are no records of its use in this sense. Also, if it is desired to use this approach for the in situ detection of the formed products, the only optical alternative is the reflectance measurement, which is intrinsically less sensitive than the transmission measurements. Because of this, the application of these columns to low concentration levels is only viable through its use coupled serially to a transmission cell.

On the other hand, this latter approach is valid, provided the reagent solubility itself is low in the sample dissolution medium and in the carrier solution of the flow system. Otherwise, the dissolution of the reagent will prevent the use of the column for more than one sample.

There is another approach in case of reagents having higher solubility, wherein the dissolution control is performed by means of fusion and re-solidification of the reagent so as to form a channel in the center for circulating the sample (The Analyst (London), 127(7), 990-994 (2002)) . This approach is very dependent upon the thermal behavior of the reagent and the change in solubility obtained after the applied thermal process. Because of this, no commercial exploitation has been found regarding this approach. The column lifetime in said case is limited by the reagent solubility and the physicochemical conditions of the sample; the higher the decrease in solubility due to thermal treatment, the longer the column lifetime.

As a consequence, there is still a need for means that allow the determination of metals from the Groups IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table in a simple way, improving the handling of reagents, which may be directly applied in photometric analysis. Brief Description of the Invention

The present invention is directed to the detection and determination of metal cations of the groups- IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table.

More specifically, the present invention is directed to the specific colorimetric detection and determination of said metal cations, by formation of colored complexes with a reagent selected from diphenylcarbazide (DPC) and diphenylthiocarbazone (dithizone) , in a simple way, with a high reagent economy and capable of being directly applied in spectrophotometric determination methods .

More particularly, the present invention is directed to the colorimetric detection and determination of metal cations of the groups IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table by a solid-liquid heterogeneous phase reaction with a reagent selected from diphenylcarbazide and diphenylthiocarbazone, which is immobilized into or onto a polymeric support.

As a consequence, it is an object of the present invention to provide a composition for the detection and/or determination of metal cations of the groups IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table, in solution, comprising a reagent selected from diphenylcarbazide and diphenylthiocarbazone in an immobilized form into or onto an inert support of polymeric resin.

Also, other objects of the present invention are a reaction column containing said composition, a flow cell for a spectrophotometric device incorporating said reaction column and a method for the detection of said metal cations which uses said composition, reaction column or flow cell. For the purposes of the present invention, the expressions "metals" and "metal cations" and their equivalents are used interchangeably, for higher simplicity, with the meaning of chemical species of metal cations of the groups IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table, unless otherwise indicated. Similarly, the names of the reagents are used intercangeably with respect to their abbreviated forms: DPC for diphenylcarbazide and dithizone for diphenylthiocarbazone .

Also, the expressions "metal solution", "solution to be analyzed", "sample" and equivalents thereof refer to the solution of metal cations of the groups IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table that is the object of analysis for the detection and/or determination of the content of metal cations of interest.

Brief Description of the Drawings

Figure 1 shows a side view of a reaction column according to an embodiment of the present invention.

Figure 2 shows a side view of a reaction column according to another embodiment of the present invention.

Figure 3 shows a perspective view of a reaction column integrated with a flow cell according to an embodiment of the present invention.

Figure 4 shows a perspective and exploded view of the reaction column integrated with a flow cell of Figure 3, according to an embodiment of the present invention.

Figure 5 shows a perspective view of a reaction column integrated with .a flow cell according to another embodiment of the present invention. Figure β shows a perspective and exploded view of the reaction column integrated with a flow cell of Figure 5.

Figure 7 shows a top view of a reaction column integrated with a flow cell according to yet another embodiment of the present invention.

Figure 8 shows a perspective and exploded view of the reaction column integrated with a flow cell of Figure 7.

Figure 9 shows a perspective • and exploded view of the reaction column integrated with a flow cell as alternative embodiment to that of Figure 7.

Figure 10 shows a perspective view of a reaction column integrated with a flow cell according to yet another embodiment of the present invention.

Figure 11 shows a perspective and exploded view of the cell of Figure 10.

Figure 12 shows a perspective view of a detail of the reaction column integrated with a flow cell of Figure 10.

Detailed description of the invention

The drawbacks mentioned in the prior art description may be overcome and the desired improvement goals may be achieved in the processes for the determination of metals of the groups IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table based on a colorimetric analysis by means of performing the present invention, which relates to a composition for the colorimetric detection and/or determination of said metals by formation of complexes with a reagent selected from DPC and dithizone, through heterogeneous phase reaction, where the reagent is immobilized in a polymeric support. As a result of scientific research, it has been surprisingly- found that, contrary to other diverse tested materials, such as sand, sintered glass (fritted glass) , mesoporous glass or silica gel, the use of a polymeric resin as the inert support for the immobilization of the reagents such as diphenylcarbazide o dithizone, allows for the preparation of compositions for reaction columns or flow cells for the photometric analysis, with excellent properties. The term "inert" is intended to mean that the support does not participate in the chemical reaction

The compositions of the present invention, used in colorimetric analysis applications, for example in the reaction columns and flow cells of the present invention, do not show a disadvantageous pressure drop, have very good sensitivity and allow for obtaining a spectroscopic signal selective of the chemical species of interest, such us for example Cr(VI), with stable baselines in time and with relatively low noise.

Therefore, it is an object of the present invention to provide a composition for the detection and/or determination in solution of metal¹ cations of the groups IB, IIB, IIIA,

IVA, VA, VIB, VIIB and VIIIB of the Periodic Table, comprising a reagent selected from diphenylcarbazide and diphenylthiocarbazone that is immobilized in a polymeric resin inert support.

In a preferred embodiment of the invention, the polymeric resin supporting the diphenylcarbazide or the diphenylthiocarbazone is in a granulated or powder form.

In yet another preferred embodiment of the invention, the polymeric resin supporting the diphenylcarbazide or the diphenylthiocarbazone constitutes the walls of a circulation zone of a solution containing said metal cations to be analyzed.

In a preferred embodiment of the present invention, said polymeric resin is acrylic resin.

An additional object of the present invention is a reaction column for the colorimetric detection and/or determination in solution of metal cations of the groups IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table, by formation of complexes with a reagent selected from diphenylcarbazide and diphenylthiocarbazone, comprising at least a circulation zone of the solution to be analyzed, containing a composition of said reagent immobilized in an inert support comprising a polymeric resin.

For the purposes of the present invention, the expression "reaction column" means a device containing a substantially elongated reaction chamber, which allows the flow income, circulation and exit, of at least one of the reagents or reaction products, and that may be located in any spatial position, i.e., vertical, horizontal or bent, and show straight, curved or mixed forms.

In an embodiment of the invention, the reaction column is placed physically separated apart from a flow cell of a spectrophotometric or colorimetric device, being them in fluid connection by appropriate means for the circulation of the sample solution to be analyzed and of the liquid carrier that may be necessary for causing the circulation of the sample to be analyzed.

In another embodiment of the invention, the reaction column is physically integrated with a flow cell of a spectrophotometric device, constituting a single means or device wherein the formation of the colored complex of the chemical specie of the metal to be determined and diphenylcarbazide or diphenylthiocarbazone take place, and afterwards or simultaneously, the photometric measurements are made.

Therefore, it is another object of the present invention, to provide a flow cell for a photometric device, comprising, in physically integrated form, a reaction column for the detection and/or determination in solution of metals from the groups IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table, comprising at least a circulation zone for the solution to be analyzed, containing a composition comprising said reagent selected from DPC and dithizone immobilized in a polymeric resin inert support.

In a more preferred embodiment, the reaction column integrated with the flow cell is comprised within a polymeric resin block, showing (a) circulation conducts carved or drilled in the block, for the solution sample to be analyzed where the circulation zone contains the composition comprising the reagent selected from DPC and dithizone immobilized in the resin constituting the column block, and (b) the cavity corresponding to the flow cell, particularly the optical path for the electromagnetic radiation.

In a yet more preferred embodiment of the invention, the polymeric resin block containing the reaction column integrated with the flow cell is an acrylic resin block.

In a preferred embodiment of the invention, in the reaction column integrated with a flow cell, the composition comprising the reagent selected from DPC and dithizone immobilized in the resin, is located upstream of the optical path of the cell. In yet another preferred embodiment of the invention, in the reaction column integrated with a flow cell, the composition comprising the reagent selected from DPC ^' and dithizone immobilized in the resin is located within the optical path of the cell, without obstructing the light path, for example on the walls of the optical path, whereby the circulation zone containing the composition comprising the reagent and the optical path are coincident.

In a preferred embodiment of the present invention, a radiation light source is used, as well as one or more detectors for performing the spectrophotometric measurements. The light source may be for example LEDs (light-emitting diode) , with an emission wavelength at which the chemical species of interest absorbs, directly coupled to the cavity generated by hollowing out the resin composition containing the immobilized reagent, for example DPC or dithizone, the cavity being located within the flow cell.

This embodiment comprises a set of three aligned blocks, wherein one of the end blocks contains the source and optionally a detector and the other end block contains a detector. The central block contains the hollowed resin constituting the integrated reaction and detection cells, i.e., the circulation zone in contact with the reagent, and the optical path are coincident. The axial dimension of this block determines the length of the optical path of the system.

In a preferred embodiment of the present invention, the optical path may be varied as a function of the desired sensitivity and detection limit, being it for example, 3 mm or more.

It is yet another object of the present invention to provide a method for the detection and/or determination in solution of metal cations of the groups IB, HB, 11IA₁. IVA, VA, VIB, VIIB and VIIIB of the Periodic Table by formation of complexes with a reagent selected from diphenylcarbazide and diphenylthiocarbazone, comprising: reacting a sample solution containing said metal cations with a composition of a reagent selected from diphenylcarbazide and diphenylthiocarbazone, the reagent composition being immobilized in a polymeric resin, the resin being contained within a circulation zone of the solution in a reaction column or flow cell, and analyzing the colored complex solution obtained by spectrophotometry or other colorimetric methods for detecting/determining the metal content in said sample solution.

The compositions and reaction columns of the present invention are suitable for use in conventional photometry processes, being particularly adaptable to devices such as Shimadzu UV-1800, UVMINI-1204, and any spectrophotometer, of any brand or model, equipped with a standard support for cells and allowing transmission measurements in the spectral range required, both in manual and automatic liquid propulsion modes.

Examples

The invention will be now described in more detail based on specific embodiment examples intended to illustrate the invention and in no way limit the scope thereof.

The spectrophotometric tests performed with the compositions, reaction columns and flow cells of the present invention that are illustrated in the examples below were performed on the basis of the detection and/or determination of Cr(VI) at pH < 2 using DPC, because of the industrial importance of the contamination with this cation.

Operating in a similar way and regulating the pH at the suitable known values for its reaction with DPC, the colored complexes with Mn(II), Cd(II) and Ni(II) at pH 7.4-7.5; Pb(II) at pH 6.5; Zn(II) and Fe(II) at about pH 6.0; Co(II) at about pH 5.3; Cu(II) at about pH 4.0; Cu(I) at about pH 3.75; Hg(I), Hg(II) and Sn(II) at about pH 3.0; and Fe(III) and Hg2(II) at pH 1.9-2, are obtained.

The reaction columns of the present invention containing dithizone may be operated at the known basic pHs (7.5-9) for the detection of Cd, Pb, Cu, Zn, Hg(II), Co, Bi, In, Au, Pd, Pt and Ag.

Example 1

Preparation of resin composition with immobilized reagent

A self-priming acrylic resin composition (commercially available as Vaicel Auto®, Vaicel) was prepared with 15% (w/w) DPC, by grinding and homogenizing an acrylic and DPC mixture in an agatha mortar and transferring it into a beaker. The monomer provided by said manufacturer was added to the blend obtained, mixed gently and left for setting at room temperature overnight.

Once the required hardening was achieved, the resin obtained was subjected to grinding. The heterogeneous reaction kinetics was measured with the smallest fractions, the kinetics being exactly the same as pure DPC, without reduction in the analytical performance of the DPC after being mixed with acrylic, and making possible the construction of diverse reaction columns. Example 2

Preparation of a resin composition with immobilized reagent

Analogously to Example 1, a self-setting acrylic resin composition containing 15% (w/w) dithizone was prepared. The corresponding monomer provided by the manufacturer was added to the obtained mixture of Vaicel Auto® and dithizone by grinding and homogenization, the blend was mixed gently and left for setting at room temperature overnight. The resin was then grinded and used for the construction of reaction columns .

Example 3

Preparation of a resin composition with immobilized reagent

A resin composition was preparing by dissolving in chloroform a commercial acrylic bar consisting of methyl polymethacrylate, cut in small pieces, incorporating the solid DPC to the solution and letting it evaporate.

The resin obtained shows a DPC distribution which is less homogenous than the resin of Example 1, but its obtaining process is a much simpler and faster.

Examples 4-7

Preparation of resin compositions with immobilized reagent

In a similar way to Example 1 other three resin compositions using thermo-setting acrylic resin (commercially available as Vaicel Termo®, Vaicel) (set at 70-90⁰C for 20 minutes) were prepared.

Each resin composition obtained is separated by sieving according to the particle size ranges, which data is depicted in Table 1 below: Table 1

* The resin of Example 6, being grinded, formed a powder too fine together with flat form particles, not so suitable for use as packing material for columns.

With this type of packing material, sensitive absorbance peaks were obtained, having stable baselines in time and relatively low noise .

With the purpose of characterizing the resin compositions of Examples 4 to 6, they were used for packing the columns shown in Figures 1 and 2. Standard solutions of chromium (VI) having different concentration were analyzed. At least three replicates analysis was carried out for each standard solution. A commercial quartz cell for flow measurements (Helima 178.712-QS) was used. A Shimadzu UVMINI-12401 spectrophotometer was used for the spectrophotometry measurements .

The data obtained are depicted in the following Table 2.

Table 2

Notes :

Δtb = peak width at the base

RSD% = relative standard deviation (percent) ppb = parts per billion (μg/1) ppm = parts per million (nig/1)

It could be concluded by said performed studies that the peak width is an inverse function of the particle size, i.e., the smaller the particle, the wider the peak. Also, it was observed that the variation coefficient is much higher for those particles tested having bigger size. The sensitivity (measured as peak height) does not vary too much with DPC content and particle size; however, the optimum/ideal variation coefficient found corresponds to the resin of Example 6 having 22.5% DPC and a particle size of 0.4-0.75 mm.

In order to compare the aging of the resin compositions, 200 sample injections were performed in each reaction column. Each reaction column had previously been used for about 50 further injections and in particular, the column containing the ^■ resin of Example 6 [0.4-0.75 mm] had undergone the passage of 100 ml liquid carrier for a study of DPC dissolution.

It was observed from this aging study, that the lifetime of the columns is in general acceptable, with a slight linear drop in sensitivity, which is solved by calibration each time the samples are analyzed. The resin of Example 6 having 22.5% DPC and a particle size of 0.4-0.75 mm, resulted particularly durable, with no loss of sensitivity during 200 injections of the most concentrated standard solution. Example 8

Preparation of a resin composition with immobilized reagent

Analogously to Example 2, but using a Vaicel Termo® thermosetting resin, mixed with dithizone and subsequent setting at 70-90°C for 20-30 minutes, a suitable resin composition is obtained, after its grinding, for use in the manufacture of a reaction column of the present invention.

Example 9 Reaction Column

Referring to Figure 1, a reaction column 10 was manufactured based on the body of a 1 ml syringe (approximately 0.5 cm internal diameter by 4.5 cm length) . A DPC composition supported on thermo-setting acrylic resin in granulated state was used as filler 11. The filler was confined using a pair of pieces of fritted glass 12 (sintered glass) . Silicone tubes 13 were used for connection with the rest of the tubes in the system, either directly coupled to, or fixed by means of an epoxy adhesive.

The composition forming the filler material was prepared as illustrated in Examples 4-7, by intimately mixing (in an agatha mortar) 0.85 g acrylic polymer and 0.15 g DPC, transferring the mixture to a beaker and adding the liquid monomer. Polymerization is effected by heating and then it is grinded in a coffee grinding machine.

Example 10 Reaction Column

Referring now to Figure 2, a reaction column 20 having a different size than that of Example 9, was prepared using a PTFE tube of 2 mm internal diameter. The filler 21, prepared in a .similar way to Example 1, was placed between two pieces of fritted glass 22 and two pieces of silicone tube were fixed by epoxy adhesive 23 for making the couplings.

Reaction columns having 8.5 cm length and 2 mm internal diameter, packed with the resin composition of Example 6 (0.4-0.75 mm), were also prepared and evaluated using Shimadzu spectrophotometry devices UV-1700 and UV-1203 and a Hellma flow cell having 1 cm optical path and 1.5 mm opening. The results are depicted in the following Table 3:

Table 3

Notes :

Δtb = peak width at the base

LOD = limit of detection defined according to the standard deviation of the regression, which is considered less optimistic than the present IUPAC definition

RSD% = relative standard deviation percent ppb = parts per billion (μg/1) ppm = parts per million (mg/1) Example 11

Reaction Column integrated with Flow Cell

Referring now to Figures 3 and 4, they illustrate an embodiment of the present invention corresponding to a reaction column integrated with a flow cell. In Figure 4 the same cell of Figure 3 is shown, with its fittings/accessories in an exploded view. The set was prepared by using a transparent 12 mm wide acrylic bar 30. Inlet orifice and an conduct 31, 2 mm in diameter and 5 cm long, and outlet orifice and conduct 32, are drilled in the bar 30 as well as an optical path 33 in fluid communication with conducts 31 and 32, so as to delimit the circulation of the solution to be analyzed.

Once the body of the cell is finished, it is painted with synthetic black enamel for preventing part of the light beam from passing through the cell without passing through the sample zone at the time of use. Separately, acrylic windows 42 having 5 mm diameter and 1 mm width are prepared and placed by means of adhesive. The cell also carries HPLC-type connectors 41 for the connection to tubing and pumps (not shown), holders 43 for holding both LEDs and detectors 44.

The resin composition containing the reagent, prepared according to Example 6 (0.4-0.75 mm) is placed in the inlet conduct 31, held by a sintered glass of the same diameter as that of the conduct.

Table 4 below depicts the characteristic data of the reaction column integrated with a flow cell of the present example, operated in a signal electronic amplification and processing device, being the acquired data processed in a ^'personal computer. Table 4

Notes :

Δtb = peak width at the base

RSD% = relative standard deviation percent ppb = parts per billion (μg/1) ppm = parts per million (mg/1)

Example 12

Reaction Column integrated with Flow Cell with a composition of DPC or dithizone immobilized in acrylic resin in the optical path

Referring now to Figures 5 and 6, they show a reaction column integrated with a flow cell, where Figure 6 corresponds to an exploded view of the embodiment of Figure 5. The reaction column integrated with a flow cell of said embodiment of the invention comprises an acrylic body 51, a circulation circuit for the sample formed by two vertical conducts 52 with two connectors 53 for tubing and pumps (not shown) and two transparent acrylic (or glass) windows 54 at the ends of the optical path conduct 55. The DPC or dithizone reagent composition is forming part of the walls of the optical path 55.

Between conducts 52 and the optical path conduct 55 there is a fluid channel, delimiting the circulation of the solution to be analyzed.

The analytical signal in this type of cell is directly obtained as an absorbance, which is the result of the degree of reaction achieved at measuring time. The sample is transported to the cell where the flow is stopped. DPC or dithizone is immobilized forming part of the walls of the cell. When the sample enters the cell, the heterogeneous phase reaction begins and absorbance starts to increase, until it is stabilized after all the metal diffuses and reacts on the cell wall. The analytical signal may be (a) the absorbance measured after a given time prefixed since sample injection, (b) the absorbance average after the signal is stabilized in a prefixed time window.

Liquid propulsion may, in principle, be carried out by an automatic or manual method (using syringes) .

The inclusion of the DPC or dithizone composition in the walls of the optical path of the cell of Figures 5 and 6 begins by making on the acrylic body an orifice 4.5 mm in diameter, concentric with the optical path. Afterwards, a mixture is prepared of thermo-setting resin, as the one used above, and DPC or dithizone in a preferable 50:50 (w/w) ratio, homogenized by pressing the mixture with the curved part of a spatula for 30 minutes. Then, the monomer is added (as before) and the orifice made in the cell is filled. It is left to dry at room temperature, preferably overnight, and then set in a stove, preferably at 90°C, preferably for 1 hour and 30 minutes. Afterwards, the optical path conducts and the inlets thereof are made by using a Dremell mini drill.

The alternative embodiment which uses isolated, only packed DPC or dithizone as a filler, forming the central orifice by means of a cast that gives the form to the optical path orifice does not provide satisfactory results, because of the fact that when attempting to cast the inlet conducts to the optical path, the packed reagent disaggregates, thus, taking an irregular form.

Moreover, it was found to be indispensable that the mixture between resin and DPC or dithizone be intimate, given that otherwise, when the thermo-setting is performed, reagent lumps with no resin are produced that disaggregate easily.

The cell obtained has an optical path 9 mm long and an opening of 1.5 mm. A cell with a small opening results in less time for the analyzed metal in the sample, to diffuse to the wall where it should react, and on the other hand, a cell with a big opening provides less noise due to the fact that it allows a wider solid angle of light beam to pass.

Tests carried out in three cells with this configuration and DPC as the reagent provided the following results, grouped in Tables 5, 6 and 7 below, wherein the Cr(VI) concentrations are expressed as chromate. For data acquisition, the Shimadzu UV-1700 or UV 1240 mini software was used.

Table 5

Table 6

Table 7

Notes:

All concentrations are expressed as chromate (CrO₄ ^")

Δtb = peak width at the base

This cell shows several advantages: sensitivity, low limit of detection, reproducibility and suitable lifetime. On the other hand, it needs a slightly higher time for sample analysis, due to the fact that a portion of the sample needs to be stopped in the cell in order for the cations to diffuse to the wall thereof and react with the reagent.

Example 13

Reaction Column integrated with a Plow Cell with a composition of DPC or dithizone immobilized in acrylic resin in the optical path

Referring now to Figure 7 and 8, they show a reaction column integrated with a flow cell, where Figure 8 corresponds . to the exploded view of the embodiment of Figure 7. The reaction column integrated with a flow cell of the this embodiment of the invention comprises an acrylic body 71, two connectors 72 for tubing and pumps (not shown) in the inlet and outlet orifices of the circulation circuit 73 for the samples and liquid carrier. The cell .also comprises holders 74 for holding two LEDs and detectors 75 facing the acrylic windows 76 which delimit the optical path 77 of the cell.

Conducts 73 and optical path conduct 77 are in fluid communication, delimiting the circulation of the solution to be analyzed.

Similarly to Example 12, the reaction column with an optical path of the flow cell were made by preparing a mixture of thermo-setting acrylic resin, like the one used above, and DPC or dithizone in a preferable ratio of 50:50 (w/w) , homogenizing by pressing the mixture with the curved part of a spatula for 30 minutes, adding the monomer and filling an orifice made in the acrylic body of the cell. It is left to dry at room temperature, preferably overnight, and then thermo-set in stove, preferably at 90°C, preferably over 1 hour and 30 minutes.

Afterwards, the optical path conducts and the inlets thereof are made by using a Dremell mini drill.

The cell obtained has an optical path 2.9 cm long and an opening of 1.5 mm.

The arbitrary constructions of cells of a given optical path allow for the control of analytical performance in terms of sensitivity, limit of detection, etc, and also for the ability to choose the same according to the required performance of the analytical problem at issue (water, effluents analysis, etc)

Table 8 below depicts characteristic data of the cell of the present example, using DPC as reagent for the detection of Cr(VI) . Table 8

Notes : •

LOD = limit of detection defined according to the standard deviation of the regression, which is considered less optimistic than the present IU¹PAC definition

RSD% = relative standard deviation percent

Example 14

Reaction Column integrated with a Flow Cell with a composition of DPC or dithizone immobilized in acrylic resin in the optical path

Referring now to Figure 9, this shows a reaction column integrated with a flow cell, which comprises an acrylic body 81, inlet and outlet orifices 82 for the connection of the circulation circuit 83 for the samples and liquid carrier, to tubing and pumps (not shown) . The cell also comprises holder 84 for holding two LEDs and detectors and acrylic (or glass) windows 85 which close the circulation circuit for the sample and the optical path 86. Between circuit 83 and the optical path conduct 86 there is a fluid channel that delimits the circulation of the solution to be analyzed. Similarly to Example 13, the integrated cell was made by preparing a ^"reagent composition by mixing thermo-setting acrylic resin, like the one used above, and DPC. or dithizone in a preferable ratio of 50:50 (w/w) , homogenizing by pressing the mixture with the curved part of a spatula for 30 minutes, adding the monomer and filling the orifice performed on the cell. It is left to dry at room temperature, preferably overnight, and then thermo-set in a stove, preferably at 90⁰C for preferably 1 hour 30 minutes.

Afterwards, the optical path conducts and the inlets therein are made by using a Dremell mini drill.

Example 15

Reaction Column integrated with a Flow Cell with a composition of DPC or dithizone immobilized in acrylic resin

Referring now to Figures 10 to 12, they show a reaction column integrated with a flow cell, where Figure 11 corresponds to the exploded view of the column of Figure 10 and Figure 12 showing a partial enlarged view of Figure 11. The reaction column integrated with a flow cell of this embodiment of the invention comprises an acrylic body 91 which carries a threaded cylindrical piece 92 comprising the optical path 96. Said piece 92 comprises corresponding inlet and outlet orifices and conducts 93 for the circulation circuit of the solution to be analyzed. The cell also comprises threaded holders 94 for holding acrylic windows 95 which close the circulation conduct for the sample and the optical path 96, by means of sealing joints 97 and optionally for holding two LEDs and detectors. Between conducts 93 and the optical path conduct 96 there is fluid communication, delimiting the circulation of the solution to be analyzed. Similarly to Examples 13 and 14, the integrated cell was made by preparing a reagent composition by mixing thermo-setting acrylic resin, like the one used above, and DPC or dithizqne in a preferable ratio of 50:50 (w/w) , homogenizing by pressing the mixture with the curved part of a spatula for 30 minutes, adding the monomer and filling the central conduct 96 of the threaded piece 92. It is left to dry at room temperature, preferably overnight, and then thermo-set in a stove, preferably at 90°C for preferably 1 hour 30 minutes.

Afterwards, the optical path conduct 96 is made by using a Dremell mini drill, through the thermo-set resin mass.

Having thus described and illustrated the present invention, different modifications and variations based on the present specification and the ordinary knowledge in the art, will become evident for those skilled in the art. All such modifications and variations will be comprised within the scope and spirit of the present invention.

Claims

1. Composition for the colorimetric detection and/or determination in solution of metal cations of the groups IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table, by formation of colored complexes of said metal cations, characterized in that the composition comprises a reagent selected from diphenylcarbazide and diphenylthiocarbazone immobilized in an inert support comprising a polymeric resin.

2. Composition according to claim 1, characterized in that the polymeric resin is acrylic resin.

3. Reaction column for the colorimetric detection and/or determination in solution of metal cations of the groups IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table, by formation of complexes with a reagent selected from diphenylcarbazide and diphenylthiocarbazone, characterized in that said column comprises at least a circulation zone for the solution to be analyzed, the circulation zone containing a composition of said reagent selected from diphenylcarbazide and diphenylthiocarbazone immobilized in an inert support comprising a polymeric resin, according to claims 1 or 2.

4. Reaction column according to claim 3, characterized in that the polymeric resin supporting said reagent selected from diphenylcarbazide and diphenylthiocarbazone is acrylic resin.

5. Reaction column as claimed in claims 3 or 4, characterized in that the polymeric resin supporting said reagent selected from diphenylcarbazide and diphenylthiocarbazone is in granulated or powdered form.

6. Reaction column according to claim 5, characterized in that the polymeric resin supporting said reagent selected from diphenylcarbazide and diphenylthiocarbazone, in granulated or powdered form, is comprised within a tube, preferably cylindrical.

7. Reaction column according to claims 3 or 5, characterized in that the polymeric resin supporting said reagent selected from diphenylcarbazide and diphenylthiocarbazone constitutes the walls of said circulation zone.

8. Flow cell for a spectrophotometry device which comprises means for the circulation of the solution to be analyzed and an optical path for the electromagnetic radiation, characterized in that said circulation means comprise the reaction column according to anyone of claims 3 to 7 , in a physically integrated form to said flow cell, comprising said reaction column at least a circulation zone for the solution to be analyzed, where the circulation zone contains a reagent selected from diphenylcarbazide and diphenylthiocarbazone immobilized in an inert support comprising^' a polymeric resin.

9. Flow cell as claimed in claim 8, characterized in that the polymeric resin supporting the reagent selected from diphenylcarbazide and diphenylthiocarbazone is placed within said circulation zone for the solution to be analyzed, in granulated or powdered form, being said circulation zone upstream of the optical path of the cell.

10. Flow cell as claimed in claim 8, characterized in that the polymeric resin supporting the reagent selected from diphenylcarbazide and diphenylthiocarbazone constitutes the walls of the circulation zone for the solution to be analyzed, said circulation zone being upstream of the optical path of the cell.

11. Flow cell as claimed in claim 8, characterized in that the polymeric resin supporting the reagent selected from diphenylcarbazide and diphenylthiocarbazone constitutes the walls of the circulation zone for the solution to be analyzed, said circulation zone being coincident at least partially with the optical path of the cell.

12. Flow cell according to claims 10 or 11, characterized in that the polymeric resin supporting the reagent selected from diphenylcarbazide and diphenylthiocarbazone constitutes a solid block in which the circulation zone for the solution to be analyzed and the optical path of said flow cell have been carved or drilled.

13. Flow cell according to claim 12, characterized in that said solid block has at least a substantially prismatic portion, being the circulation zone for the solution to be analyzed constituted by vertical conducts extending from the upper side of the prism up to connecting by means of a curved portion, to the optical path of the cell in the lower part of the prism, and being said optical path constituted by a horizontal pass-through conduct drilled between the back side and the front side of the prism.

14. Flow cell according to claim 12, characterized in that said solid block has at least a substantially prismatic portion, being said optical path constituted by a horizontal pass-through conduct drilled between the back side and the front side of the prism; being the circulation zone for the solution to be analyzed ^' constituted by two horizontal conducts which extend diagonally from the lateral sides of the prism, one of them to the back side of the prism and the other to the front side of the prism, wherein said back and front sides are connected to the corresponding conduct to the optical path of the cell.

15. A method for the colorimetric detection and/or determination in solution of metal cations of the groups IB, HB, IHA, IVA, VA, VIB, VIIB and VIIIB of the Periodic Table, by formation of colored complexes with a reagent selected from diphenylcarbazide and diphenylthiocarbazone, characterized by comprising: reacting a sample solution to be analyzed, containing said metal cations with a reagent selected from diphenylcarbazide and diphenylthiocarbazone, the reagent being in immobilized form in a polymeric resin, contained within a circulation zone for the solution to be analyzed in a reaction column or flow cell according to anyone of claims 3 to 14, and analyzing the colored complex solution obtained by spectrophotometry or other colorimetric methods for detecting and/or determining the contents of said metals in said sample solution.