Ultrasound assisted-cloud point extraction coupled with spectrophotometry for determination of low levels of formaldehyde from milk-based products

Abstract

In this study, a preconcentration method is proposed for the separation, extraction and spectrophotometric determination of free formaldehyde (FA) from milk-based products. The method is based on ion-pair formation between phenoxazine 3-one, resazurin, and hydroxymethanesulfonate (HMS), which is selectively formed by the reaction of FA with sulfite at pH 5.0, followed by its extraction into the micellar phase of Triton X-114. Resazurin was adopted as ion-pairing reagent for detection of low levels of FA at 610nm. The variables affecting the extraction efficiency were evaluated and optimized. A linear relationship was obtained in the range of 2–120μgL-1 with a detection limit of 0.501μgL-1. Under optimum conditions such as pH 5.0, 8 µmol L-1 Resazurin, 0.4mgL-1 sulfide, 0.03% (v/v) of Triton X-114, after applying ultrasonic assisted-cloud point extraction (UA-CPE), spectrophotometric determination was made at 610nm to measure the concentration of FA found in trace amounts in milk-based products such as liquid, semi-solid and solid-milk products including whole milk, semi-skimmed milk, cacao milk, banana flavored milk, strawberry flavored milk, goat milk, yogurt, fruit flavored yogurt, white cheese. The precision was in the range 2.5-4.8% (n: 5, for 5, 25 and 100μgL-1). After preconcentration of a 15mL sample, a sensitivity enhancement factor of 55.6 was obtained. To represent the sample matrix, the validation was checked by intra-day/inter-day accuracy and precision analysis of a spiked quality control sample and its recoveries at three concentration levels. Finally, the method was successfully applied to the determination of free FA in samples, and recoveries in the range 90.8-97.4% with RSD lower than 5.7% after spiking were obtained.