METHOD FOR QUANTITATIVE EXTRACTION-COLORIMETRIC DETERMINATION OF CALCIUM Russian patent published in 2024 - IPC G01N21/25 

FIELD: analytical chemistry.

SUBSTANCE: invention relates to analytical chemistry, specifically for quality control of milk and infant formula. Method for quantitative extraction and colorimetric determination of calcium in whole and dry milk, milk infant formulas includes precipitation of proteins, conversion of calcium into solution in form of ions, formation of coloured complex between chromogenic reagent and calcium ions, microextraction of the obtained complex in the primary amine phase and determination of its colour intensity using a smartphone. Precipitation of proteins of whole milk sample, dry milk, milk infant formula and calcium release is carried out by way of addition of aqueous solution of trichloroacetic acid, stirring, and also centrifugation till phase separation. Obtained transparent supernatant is diluted so that concentration of trichloroacetic acid in sample is not more than 2 %, and bringing the acidity of the sample using a strong base to a neutral reaction of the medium. Then, a coloured form of the analyte is obtained and extracted into a primary amine phase while mixing the neutralized supernatant with the primary amine, a solution of a chromogenic reagent and an electrolyte solution. Centrifugation is performed to phase separation. Container with separated liquid phases, which are an aqueous phase and a primary amine phase, is transferred into a chamber intended for obtaining images and protected from external light, light source is switched on, and the camera is tightly closed, then an image of the container is obtained using a smartphone by attaching it to the hole in the box. Based on the portion of the image relating to the coloured phase of the primary amine, values of colour coordinates are obtained, then calculating the value of the analytical signal A, which correlates with the colour intensity of the primary amine phase, by formula: where G and B are the colour coordinates values for the green and blue channels for the analysed sample, respectively, a G₀ and B₀ are the same characteristics for the blank sample, and the calcium concentration in whole milk, dry milk, infant formula C is calculated according to the formula obtained by the absolute calibration method: where p, k and t are numerical coefficients.

EFFECT: simplification of sample preparation, increase of rapidness, availability and accuracy of analysis.

3 cl, 3 tbl