Patent GB-1369981-A (GB)
Title: Analysis of complex organic substances
IPC: G01N21/25
Filed: 1971-11-17
Abstract: 1369981 Photo-electric absorption analysis; determination of oestriol P W PERRYMAN and D H RICHARDS 17 Nov 1971 [20 Aug 1970] 40129/70 Headings G1A and G1B [Also in Divisions G2 and H2] The determination of a complex organic substance in a sample solution is carried out by mixing a predetermined amount of said sample solution with a material capable of forming a colour complex with said substance (i.e. a simple solution of the substance in a solvent which solution is coloured), dissolving the colour complex in a solvent, and measuring the colour by absorption measurement in three or more different optical wavebands, one of which contains the absorption maximum of the colour complex and two of the others being on either side of said maximum, the latter wavebands giving a measure of the concentrations of substances other than that to be determined. Determination of oestriol in urine. This represents an example of the type of analysis of a complex organic substance which may be carried out. The urine is held in container 2, while those 1 and 3 contain respectively a 20% (U/V) solution of trichloracetic acid in chloroform and Kober reagent; (a solution of 2 gms hydroquinone in 100 ml of concentrated sulphuric acid). By means of a peristaltic pump 8, whose fingers act on silicone rubber tubes 4, 5, 6, 7 of varying diameters, liquid from 2 and 3 plus air in line 7 produce a segmented stream of liquid passing to vessel 9. Here the residence time is about 10 minutes and electric heating to 130‹C is carried out, to develop the colour complex. Extraction of the latter is carried out by mixing with the solvent from reservoir 1, in spiral tube 10. Phase separation takes place at 11. The lighter aqueous phase separates off at 13 and the heavier phase containing the colour complex is led via 13a and in aliquot proportions to photo-meter cells 14, 15, 16. Photo-metric analysis. Each flow cell is associated with a respective reference cell and the differential output of pairs of photo-cells 31 (e.g. cadmium sulpho-selenide cells) used. Illumination of all cells is from a common halogen lamp source 28 via fibre optic guide 29. Filters 30 are provided so as to restrict radiation to the above -specified wavebands. Supply circuits for the photo-cells and the electric heater are detailed, Fig. 3 and Fig. 5 (not shown). The photo-cell circuit includes four Zener diodes and balance control R 5 . An analog arithmetic circuit is provided for the photo-metric output signals. This enables the absorption signals due to unwanted (background) substances to be subtracted from the absorption at the absorption maximum of the colour complex. The circuit is given in Fig. 4 (not shown). A further additional feature is to monitor fluorescence in the colour complex due to excitation at the three wavebands. Square crosssection flow cells are used. When sequential analysis of a plurality of samples is to be carried out, a turn-table carrying these may be used instead of vessel 2. A graphical recorder may be used to indicate both the concentration of the substance to be determined and the proportion of background substances.