气相色谱-质谱法测定土壤中14种苯胺类和联苯胺类化合物

Determination of 14 aniline and benzidine compounds in soil by gas chromatography-mass spectrometry

针对土壤基质复杂及部分苯胺类化合物提取效率低的特点,基于气相色谱-质谱建立了土壤中14种苯胺类和联苯胺类化合物的分析方法。在采集后的土壤样品中加入5%亚硫酸钠水溶液进行密封,以防止目标物氧化变质,并于4℃以下冷藏保存,保存期限可达7天。实验比较了加速溶剂提取和振荡分散提取两种方式的提取效率,最终采用提取时加入碱性水溶液和乙酸乙酯-二氯甲烷(1∶4,v/v)的方法,在土壤-水相-有机相共存的条件下进行振荡分散萃取。萃取完成后经离心弃去土壤固相,将水相和有机相转移至分液漏斗中,并分离出有机相,再经弗罗里硅土固相净化柱净化、浓缩后,采用气相色谱-质谱联用仪测定,并以苯胺-d_(5)和苊-d_(10)为内标进行定量分析。实验考察了抗氧化剂和萃取溶剂种类、有机相与水相比例、盐析等对目标物萃取效率的影响,并在优化的实验条件下考察了方法的回收率及精密度。结果表明,14种目标化合物在0.5~100 mg/L范围内有良好的线性关系,相关系数(R)>0.999,方法检出限和定量限分别为0.02~0.07 mg/kg和0.08~0.28 mg/kg,在实际样品中的加标回收率为62.9%~101.0%,6次精密度试验的相对标准偏差为3.8%~10.3%。利用所建立方法对江苏某工业企业疑似苯胺污染地块的土壤进行了检测,共检出两种苯胺类化合物。本方法简便、稳定、回收率高,特别是能够有效抑制苯胺类和联苯胺类化合物的氧化,可用于土壤中苯胺类和联苯胺类化合物的检测。

The complex matrix of soil samples and low extraction efficiency of aniline compounds limit many methods developed for detecting aniline and benzidine compounds in soil.In this study,a rapid and sensitive method based on gas chromatography-mass spectrometry was developed for the simultaneous determination of 14 aniline and benzidine compounds in soil.The collected soil samples were sealed with 5%sodium sulfite solution and refrigerated to inhibit the oxidation of the target compounds for up to 7 d.The extraction efficiencies of accelerated solvent extraction and oscillating dispersion extraction were compared,and the recovery of accelerated solvent extraction was found to be unsuitable.Hence,three-phase oscillating dispersion extraction was adopted.A certain amount of alkaline aqueous solution was added to the test system during extraction to improve the extraction efficiency because aniline and benzidine compounds are weakly alkaline substances.When the pH of the extracted water phase was greater than 12,relatively good recoveries were obtained.Next,a mixed solvent of ethyl acetate-methylene chloride(1∶4,v/v)was added to extract the target compounds via oscillation for 20 min.The solid phase was discarded via centrifugation,and the aqueous and organic phases were transferred to a liquid separation funnel for further separation.Finally,the organic phase was retained.This pretreatment process prevents the co-extraction of acidic compounds or other impurities,thereby enhancing the purification ability of the method.Solid phase extraction(SPE)is generally recommended for soil extraction and purification.A preliminary test showed that compared with other columns,the Florisil SPE column could better retain the target substances and exhibited higher elution efficiency.After purification,the organic phase was concentrated to 1 mL using a nitrogen blower.The analytes were analyzed by gas chromatography-mass spectrometry using a capillary column(DB-35MS,30 m×0.25 mm×0.25μm).The temperature program was optimized to separate the target compounds at the baseline.Specifically,the initial oven temperature was set to 60℃,held for 2 min,increased to 130℃at a rate of 5℃/min,increased to 300℃at a rate of 30℃/min,and held for 4 min.The injector and ion source temperatures were 250 and 300℃,respectively.Aniline-d_(5) and acenaphthene-d_(10) were used as the internal standards for quantification.The effects of antioxidant addition,extraction solvent type,salting out,and other factors on extraction efficiency were investigated.The results showed that the method performed well under the optimized experimental conditions when actual soils were used as real sample matrices.The accuracy and precision of the proposed method were verified.A total of 14 aniline and benzidine compounds demonstrated good linearities in the range of 0.5-100 mg/L.The method detection limits(MDLs)ranged from 0.02 to 0.07 mg/kg,and the limits of quantification(LOQs)ranged from 0.08 to 0.28 mg/kg.The target compounds were spiked at contents of 1 and_(10) mg/kg.The spiked recoveries of the 14 targets in actual soils were 62.9%-101%,and the relative standard deviations(RSDs)of six precision tests were 3.8%-10.3%.The proposed method effectively inhibited the oxidation of aniline and benzidine compounds during extraction,and the target compounds exhibited high recoveries and good stabilities in the presence of three phases.Moreover,the operating procedure was simple and easy to implement.The proposed method was applied to the soil collected from an industrial enterprise in Jiangsu province that was suspected to be contaminated with aniline,and two aniline compounds were detected.The developed method requires a small sample size,and the preservation step is simple and effective.In addition,it can be applied to various types of actual soils.The method meets the requirements of current soil pollution risk control standards for aniline and benzidine compounds in soils.