A high-throughput gas chromatography-mass spectrometry method was established for the analysis of 54 pesticide residues in milk. Samples were extracted with acetonitrile while shaking, and the extract was concentrated and purified using solid-phase extraction (SPE) on a C18 column using acetonitrile as the eluent. The external standard method was used for quantification. The results showed that good linearity was observed over the concentration range from 0 to 1.00 μg/mL, with correlation coefficient (R2) greater than 0.990. Recoveries were between 43.33% and 113.87% with a relative standard deviation (RSD) of 1.8%–19.8% (n = 6). This method is accurate, simple and suitable for large numbers of milk samples.

A gas chromatographic method for determining the iodine content in milk powder was established, and the homogeneity and stability of iodine reference material were evaluated. Butanone derivative with iodine produced under acidic conditions was detected by gas chromatography (GC) with an electron capture detector and quantified by an external standard method. The proposed method showed a good linear relationship (R2 = 0.999 6), the recoveries from spiled samples were between 95.3% and 101.3%, and the relative standard deviation (RSD) was 2.3% (n = 6). This method had high accuracy and could be used for the determination of the iodine content in milk powder.

In this paper, a high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) method was proposed to simultaneously detect multiple pesticide residues in milk. The sample was extracted with acetonitrile, and partitioned by adding sodium chloride and magnesium sulfate. The extraction was carried out twice, and then the extract was purified with a C18 solid phase extraction column. Finally, the eluate was collected and evaporated to dryness after rotary evaporation, and the resulting residue was redissolved prior to instrumental analysis. The chromatographic separation was performed on a C18 column using gradient elution with a mobile phase consisting of 5 mmol/L ammonium acetate (containing 0.1% formic acid) and methanol. The detection was conducted using an electrospray ionization source under the multireaction monitoring (MRM) mode. The results showed that the calibration curves for acetamiprid, aldicarb, clothianidin, methamidophos, novaluron, fenbutatin-oxide, spirodiclofen, difenoconazole, cycloxydim, metaflumizone and 2-methyl- 4-chloro-phenoxyacetic acid (MCPA) had a good linearity in the concentration range of 0–100 ng/mL with correlation coefficients (R2) all greater than 0.995 0. The average recoveries for blank milk samples at three spiked concentration levels (1, 2 and 4 μg/L) were 40.2%–99.2%, with relative standard deviation (RSD) less than 18.9%, and the detection limit of the method was 1.00 μg/L. This method could allow quick and sensitive analysis of the contents of 11 pesticide residues in milk.