Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
  • G01J3/46—Measurement of colour; Colour measuring devices, e.g. colorimeters
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
  • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
  • G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
  • G01N21/79—Photometric titration

Definitions

• the invention relates to a method of identifying colour changes, prefer ⁇ ably during a titration, by means of a colour resolution unit decomposing the light of a sample from a number, preferably at least three colour components, and a device for measuring the signals emitted by each selected spectral interval, as well as by means of a device for evaluating the signals transmitted by the measuring device.
• GB Patent Application No. 2, 183,824 discloses a colour measuring system for identifying colour changes.
• the system includes three detectors covering their respective identifying area.
• the signals trans ⁇ mitted by the detectors are added, said detector signals being con ⁇ sidered scalars.
• DE Offenlegungsschrift No. 3, 134,273 discloses an appar ⁇ atus for comparing the colour of an article with selected colours.
• the apparatus comprises a colour TV camera adapted to detect three colour components.
• the signals matching the colours are compared with speci ⁇ fic reference values. When one of the colour signals deviates sufficiently from the reference value in question, the article is rejected.
• This appar ⁇ atus is, however, unable to provide a quantitative measurement of the total colour difference.
• WO 88/01 380 describes a microprocessor controlled titrator.
• a photo ⁇ electric measuring probe measures a possible colour change.
• the re- suiting colour measurement provides a quantitative measurement of the colour change, but all the information contained in the measuring signal is not utilized.
• the object of the invention is to provide a method, whereby it is poss ⁇ ible to indicate a quantitative measurement of the total colour change, such as in connection with a titration, in order to automatically identify a colour change spot during an influence.
• a method of the above type is according to the invention characterised by performing a vectorial addition of the signals identifying each selected spectral interval, whereby the vectors matching the signals of the selected spectral intervals are substantially perpendicular to one another and thereby mutually independent, and by the colour change being measured by a measuring of the vectorial change of the colour vector signal.
• the signals emitted by the selected spectral intervals are thereby correctly weighted relative to one another, and a measuring of the vectorial change of the colour vector signal results in a quantitative mea ⁇ surement of the total colour change.
• a method according to the invention may furthermore be characterised by the sum of the vectorially added signals being standardized, and by the colour change being measured by a measuring of the vectorial change of the standardized colour vector signal. As a result the light intensity changes caused by irrelevant conditions cannot influence the measuring result.
• numeric value of the vectorial change of the colour vector signal may be detected versus a titration, and a colour change corresponding to a percentage of the maximum value of the vectorial change of the colour detector signal may be used for an indication of a colour change.
• an empiric determination may be performed of the percentage of the maximum value of the vectorial change of the colour vector signal, said vectorial change indicating a colour change.
• the method may be used for deter ⁇ mining the alkalinity of a fluid on the basis of the amount of acid which must be added during a titration in order to cause a colour change of approximately 95%.
• the invention relates furthermore to an apparatus for carrying out the method according to the invention and for measuring colour changes, said apparatus comprising a colour resolution unit decomposing the light of a samr from a number, preferably at least three colour components, a device .or measuring the signals emitted by each spectral interval selected by the colour resolution unit, as well as by means of a device for evaluating the signals transmitted by the measuring device.
• This apparatus is characterised by the evaluating device being adapted partly to perform a vectorial addition of the signals emitted by the selected spectral intervals, whereby the vectors matching the signals of the selected spectral intervals are substantially perpendicularto one another, and partly to determine the vectorial change of the colour vector signal.
• the resulting apparatus is capable of providing a quantitative measur ⁇ ement of the total colour change.
• the evaluation device may be adapted to standardize the sum of the vectorially added signals and to indicate the colour change as the vectorial change of the standardized colour vector signal.
• the conditions influencing the light intensity cannot influence the measuring result, and accordingly a very accurate identification of the total colour change is obtained.
• a memory may be provided which records the change of the colour vector signal versus a titration, where ⁇ by a colour change corresponding to a specific percentage of the maxi ⁇ mum value of the colour change can be used as an indication of a colour change.
• Fig. 1 illustrates an apparatus according to the invention for measuring colour changes in a sample by means of an electronic colour resolution unit decomposing the light from the sample into three colour compo ⁇ nents,
• Fig. 2 illustrate the signals matching the individual colour components versus the added amount of acid
• Fig. 3 illustrates how a vector formed by the colour components is changed when acid is added
• Fig. 4 illustrates the numeric value of the vectorial colour change versus the added amount of acid
• Fig. 5 illustrates the difference function of the end portion of the curve of Fig. 4, which serves to indicate whether said portion will change further due to addition of more acid,
• Fig. 6 illustrates the end portion of the curve of Fig. 4 for determining the spot identifying a colour change of 95%
• Figs. 7 to 9 illustrate how the method according to the invention can be used for determining COD in waste water.
• the apparatus of Fig. 1 comprises a container 2 for a fluid, the alkalinity of which is to be measured by way of a titration. Fluid samples are removed from the container 2 by means of a measuring head. The fluid samples are transferred to a vessel 4 with a magnetic stirrer 6. A colour resolution unit 8 of the type Coloursensor CS50 (Yamatake-Honeywell) is arranged approximately 5 cm above the surface of the fluid. The colour resolution ur 8 decomposes the light received into three compo ⁇ nents, viz. a red, a green, and a blue component. The three components are indicated in . . T ⁇ of a decimal number between 0 and 1 50.
• a halogen lamp 10 is arranged above the vessel 4, said lamp illuminating the sur ⁇ face of the fluid.
• the acid is dosed by means of a so-called "autobu- rette" 1 2 of the type Dosimat sold by Metrohm.
• the colour resolution unit 8 and the autoburette 1 2 communicate through standard buses with an evaluation device in form of a personal computer 14 collecting data concerning colour changes versus the added amount of acid.
• a titration has been performed by the following method.
• a sample of 10 ml lemon juice of an alkalinity of about 0.5 has been admixed 30 ml of water, three drops of phenolphthalein indicator, and two drops of antifoaming film. Then the sample was titrated at the same time as a collection and recording was performed of cognate values of colour components and dosed amount of acid.
• Fig. 2 The result of such a titration appears from Fig. 2.
• the colour data concerning a titration can also be illustrated as a vectorial addition of the signals emitted by the selected spectral intervals.
• the vectors identifying the selected spectral intervals are preferably orthogonal, i.e.
• the signals emitted by the selected spectral intervals are mutually independent.
• the initial colour vector signal l 0 and a later colour vector signal I appear, which means that the colour has changed.
• the colour vector signals are preferably standardized.
• the difference between the colour vector signals represents then the vectorial colour change l d .
• An illustra ⁇ tion of the numeric value of the vectorial colour change l d appears from Fig. 4. Based on this illustration it is possible to deduct the same result as from the curves in Fig. 2.
• the amount of data has, however, been reduced from three colour components to one colour component without the information being discarded. Based on the resulting data the algorithm is created.
• the initial colour level is determined by means of the average value of 30 measurements.
• a measurement of the noise is simultaneously determined and corresponds to the maxi- mum distance between a single colour vector and the average colour vector.
• the average distance is con ⁇ tinuously observed from measuring to measuring.
• the titration and the collection of data are stopped when the above distance is less than 0.2 times the noise, the latter being considered an indication of the fact that the colour does not change any more, cf . Fig. 5. In other words the titration is stopped at about 5.25 ml of dosed acid.
• the final colour vector is determined as the average value of 30 measurements corresponding to a) .
• the colour change expressed in per ⁇ centages is determined as the distance between the immediate col ⁇ our vector and the initial colour vector relative to the distance between the initial colour vector and the final colour vector.
• the alkalinity is determined on the basis of the filtrated data represent- ing the average value of 5 measurements before and 5 measure ⁇ ments after the measuring procedure as well as on the basis of the amount of acid to be added in order to obtain a colour change of 95 %. In other words an excessive titration is performed until it is certain that the colour does not change any more.
• the col ⁇ lected data registered in a memory are reprocessed to provide the amount of acid corresponding to a colour change of 95%. This amount of acid represents then the alkalinity of the sample.
• Tests have been performed in order to evaluate the efficiency of the detection algorithm. These tests include a large number of titrations performed on a reservoir juice, where the possible operating limits of the alkalinity measuring device should be determined. The results appear from Table 1 .
• the developed detection algorithm is very reliable as it has not been possible to trick it even by way of a very rough treatment, such as by addition of a blue colour before the titration or by performing the titration under varying light conditions. Based on the variation coefficient the accuracy is calculated to be about 1.5%, which is considered a satisfying accuracy.
• the algorithm can be used in connection with other colorimetric titrations.
• Figs. 7 to 9 illustrate how the method according to the invention can be used for determining COD in waste water.
• the analysis is terminated by a titration of a sample con ⁇ taining an unknown amount of potassium dichromat.
• An iron(ll) solution is used as titrant.
• a ferroindicator is used as indicator.
• Fig. 7 The titration process is illustrated in Fig. 7 showing that the colour expressed by the three colour components red, green, and blue changes continuously during the titration and very quickly at the change spot.
• Fig. 8 shows the length of the vector l d and the derived function of first order concerning dosed amount of titrant versus the dosed amount of titrant.
• the colour change of the shown titration has been manually determined to 9.5 ml, which in Fig. 8 corresponds to the derived func ⁇ tion of first order having reached its maximum value when said colour change occurs.

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• Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• General Physics & Mathematics (AREA)
• Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)

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• 1992
  • 1992-12-08 DK DK147092A patent/DK147092A/da not_active Application Discontinuation
• 1993
  • 1993-12-07 EP EP94901780A patent/EP0667955A1/en not_active Withdrawn
  • 1993-12-07 AU AU56234/94A patent/AU5623494A/en not_active Abandoned
  • 1993-12-07 WO PCT/DK1993/000408 patent/WO1994014052A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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