微量乐果农药残留比色光谱快速检测方法

为快速、安全地检测常用有机磷农药乐果的残留，根据乐果含有硫基，和氯化钯反应生成黄色络合物硫化钯的原理，使用乙酸代替常用的浓盐酸溶解氯化钯，配置成氯化钯乙酸溶液作为比色剂，与不同浓度的乐果乳油分别发生显色反应。采集显色反应后溶液的吸光度谱图表明：用乙酸代替浓盐酸作为氯化钯溶剂效果更理想，在300～900 nm波段的吸收光谱可以区分0.5 mg·kg-1的农药浓度，满足国标GB2763—2012规定的部分水果及蔬菜中农残的检测要求。随机配置40个0.5～88 mg·kg-1样本浓度，对比SG等预处理效果，分别用PCA和PLS方法建立预测模型，30个作为建模集，10个作为验证集。在350～900 nm波段建立的模型相关系数r较低。根据吸光度谱图计算出乐果的相关系数在458 nm处达到最大值0.957 2，由此分别选取特征区间453～463和400～600 nm。经过比较得出以下结论：经过SG等预处理后，在400～600 nm波段，使用PLS方法建立的模型在主成分为4时最优，其训练集r=0.994 1，RMSEP=2.770，验证集r=0.9933，RMSEP=2.214。该方法操作安全，显色反应时间为2 min，为进一步研究快速、安全的有机磷农药实用检测仪器提供了理论与技术支撑。

Rapid Detection of Trace Dimethoate Pesticide Residues Based on Colorimetric Spectroscopy

In order to detect dimethoate pesticide residues rapidly and safely, a feasible method based on colorimetric spectroscopy was developed. Because dimethoate is one of organophosphorus pesticides containing sulfur, its sulfenyl can react with Pd2+ to produce a yellow complex named palladium sulfide. PdCl₂ was used as the color agent, which was dissolved in acetic acid instead of the common concentrated hydrochloric acid. The dimethoate solution was prepared by dissolving the commercial pesticides into distilled water at different concentrations. The pesticide samples were reacted with the same amount of PdCl₂ solution respectively. The absorbance spectra of the samples after coloring reaction were measured in the region of 300～900 nm by a spectrophotometer. The result showed that the effect of using acetic acid instead of concentrated hydrochloric acid was not only safe but also preferable, and 0.5 mg·kg-1 was the minimum concentration of the pesticide that could be distinguished in the spectra. The result met the pesticide residue detecting requirements of part fruits and vegetables in the national standard GB2763—2012 regulations. Further studies on random 40 dimethoate samples from 0.5 to 88 mg·kg-1 were carried out. Thirty samples were randomly selected to establish the training model and remaining 10 samples were used to test the model. The preprocessing methods were carried on the spectrum data such as normalization and smoothing to get a better effect through comparison their prediction results with the correlation coefficient (r) and the root mean square error of cross-validation (RMSEP). The principal component analysis (PCA) method and partial least squares(PLS)method were used to establish prediction models respectively in the different wave ranges. By calculating the correlation coefficient of dimethoate samples in 350～900 nm the maximum of 0.957 2 was obtained at wavelength 458 nm, so 453～463 and 400～600 nm were selected as feather regions. Experiments showed that the effect of SG preprocessing on the absorbance spectra in the region of 350～900 and 400～600 nm was obvious, and PLS method were better than PCA method. The optimum model was obtained in the region of 400～600 nm, when principal component number was 4, the training set r=0.994 1, RMSEP=2.770 3 and the validation set r=0.993 3, RMSEP=2.214 8. This method was safe in operation and the colorimetric reaction time was 2 min, which provided theoretical and technical support for further studying on development of rapid, safe organophosphorus pesticide detection instrument.