Abstract:

Chlorpropham is a plant growth regulator and a herbicide. It is commonly used in the post-harvest treatment of potato to inhibit germination. It can also be used for flower thinning and fruit thinning of fruit trees, and for controlling annual gramineous weeds and a few broad-leaved weeds. Improper or excessive use of chlorpropham in crop cultivation will affect the safety of animal-derived food and impair human health through the food chain and water cycle. Therefore, accurate quantification of chlorpropham is imperative for risk assessment and mitigating risks to food safety.

A method based on solid phase extraction and ultra-high performance liquid chromatography-tandem mass spectrometry (SPE-UHPLC-MS/MS) was established for the determination of chlorpropham in animal-derived food. First, the pretreatment conditions were optimized. To purify the samples and remove impurities, SPE column cartridges with different packing materials such as PXC, PXA, Florisil, and PLS were investigated. Based on the retention of chlorpropham, the ProElut PLS SPE column was selected as the pretreatment purification column. The washing solution and eluents were then optimized. When water was used as the washing solution, chlorpropham remained adsorbed on the SPE column and was not eluted along with other water-soluble substances. When the proportion of acetonitrile exceeded 40%, chlorpropham adsorbed on the filler of the SPE column could be gradually washed down. Acetonitrile-water solution(30∶70, v/v) was used for washing the SPE column. The elution ability of seven eluents for chlorpropham on the SPE column was then investigated. Among them, pure methanol, pure acetonitrile, and 1% (v/v) formic acid-methanol showed better elution effect. Considering that acetonitrile was used in the sample extraction, it was chosen as the mobile phase eluent. Subsequently, the chromatographic conditions and MS parameters were optimized. By examining the ionization cracking of chlorpropham, the quasimolecular ions and corresponding fragmentations in the chlorpropham primary MS were determined. The separation effect of three C18 columns was investigated. Based on the retention ability and peak effect of chlorpropham on the column, the Agilent ZORBAX SB-C18 (150 mm×2.1 mm, 5 μm) column was used for chlorpropham separation. The response of chlorpropham in the positive and negative ionization modes was investigated and optimized. The results showed that the response was better in the positive ion mode than that in the negative ion mode. After optimizing the chromatographic conditions and MS parameters, the sensitivity of the method was improved. Finally, the analytes were separated on the Agilent ZORBAX SB-C18 (150 mm×2.1 mm, 5 μm) under a gradient elution program using acetonitrile and 0.2% (v/v) formic acid aqueous solution as the mobile phases. The analytes were detected in the multiple reaction monitoring (MRM) mode under positive electrospray ionization (ESI⁺) conditions.

The standard curve solutions were prepared using the matrix solution and quantified by the external standard method. The results showed a good linear relationship in the range of 0.5-100.0 μg/L, with correlation coefficients (r²) greater than 0.9929. The limit of quantification (LOQ) of this method was 3 μg/kg (S/N ≥ 10). At three spiked levels (0.003, 0.006, and 0.060 mg/kg) in 13 animal-derived foods (pork, milk, beef, chicken, duck, egg, chicken gizzard, duck egg, pork kidney, pork liver, beef liver, mutton, duck gizzard), the average recoveries were in the range of 74.9% to 97.6%, and the RSDs were in the range of 2.9% to 9.5% (n=6). Sixty batches of animal-derived food available on the market were analyzed by the developed method, and chlorpropham was not detected in any of these foods. The developed method is rapid, sensitive, and accurate, and it is suitable for the qualitative and quantitative detection of chlorpropham in a variety of animal-derived foods.

Key words: ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS), solid phase extraction (SPE), chlorpropham, animal derived foods, residues