Separate determination of the content of added phosphates by ion chromatography

Abstract

Annotation. An interstate standard (GOST 34967-2023) has been developed for the separate determination of the content of added phosphates in food products in the measurement range from 0.02 to 20.00 g/kg (g/dm³) [1]. The standard applies to food products – milk (including powdered and concentrated milk), cream, young cheeses, meat of all types of animals and poultry, meat products and meat sausages, fish, aquatic invertebrates and products produced from them, with the exception of canned food and preserves, and establishes a method of ion chromatography with a conductive-classical detection of determination of the content of added phosphates in the form of phosphate anions: orthophosphate – (PO₄^3-), pyrophosphate- (P₂O₇^4-), trimethaphosphate- (P₃O₉^3-), tripolyphosphate- (P₃O₁₀^5-). A 2% solution of trifluoroacetic acid was used to extract the added phosphates from the analyzed sample, and the extracts were purified on solid-phase extraction cartridges filled with reverse-phase sorbent (C18). Phosphates were separated on an ion-exchange chromatographic column Dionex™ lonPac™ AS16 (250 x 4 mm) with a protective column lonPac™ AG16 (50 x 4 mm) in the gradient elution mode. A solution of potassium hydroxide with a concentration of 100 mmol/dm³ was used as mobile phase A, and deionized water was used as mobile phase B. The quantitative determination was carried out using an ion chromatograph, which included a gradient pump, a device for automatic sample entry, an eluent generator with a disposable cartridge containing potassium hydroxide, a background conductivity suppressor, a inductometric detector, and a chromatographic column thermostat providing a heating temperature of up to (40±1)°C. The use of a background electrical conductivity suppressor made it possible to increase the sensitivity of the detector by reducing background noise at high concentrations of potassium hydroxide necessary for the separation of polyphosphates. The calibration graph is linear for the orthophosphate anion in the range from 1 to 200 mg/dm3 and from 1 to 100 mg/dm³ for pyrophosphate, trimethaphosphate, and tripolyphosphate anions. The correlation coefficient for each anion is more than 99.5%. The detection limit for phosphate anions is 0.01 g/kg, the detection limit is 0.02 g/kg.