Rapid In Situ Esterification Method for the Determination of Benzoic Acid in Dairy Milk by GC-FID

An efficient and simple in situ ultrasonic assisted esterification method has been developed for gas chromatographic determination of benzoic acid (BA) in raw and processed milk samples. For optimization of variables, chemometric approach was employed using Plackett–Burman design (PBD) and face-centered central composite design (FCCCD). Firstly, major factors affecting benzoic acid methyl ester (BAME) yield, i.e., BA concentration, volume of methanol, sonication time, amount of milk, and sulfuric acid, were studied with PBD. After screening significant factors, further optimization was carried out with FCCCD. Analysis of variance (ANOVA) of the quadratic model demonstrated that BA concentration, interaction factors of BA with sulfuric acid, and methanol volume significantly (p < 0.05) affect the BAME %yield. The proposed in situ method has better BAME limit of detection (0.02 mg/L) and quantification (0.07 mg/L) for the rapid determination of BA in milk samples avoiding the use of sample pretreatment and solvent extraction step.