高效液相色谱-气相色谱在线联用同时测定土壤中饱和烃和芳香烃

doi:10.3724/SP.J.1123.2021.02011

摘要/Abstract

摘要：

为加强对土壤中石油烃类污染物的风险管控,生态环境部已将石油烃类列为土壤中的重点监测项目。石油烃源于石油与合成油,是涵盖一定碳数范围的碳氢化合物,主要分为饱和烃和芳香烃两大类。芳香烃通常是高度烷基化的单环、双环与多环芳烃,其对人和动物的毒性较饱和烃大很多,因此,仅仅测定土壤中总石油烃含量难以准确评估其环境毒性。目前环境领域的标准方法尚未区分土壤中饱和烃和芳香烃。该研究针对土壤样品的基质干扰特点,对样品的提取和净化环节进行了优化,并且应用高效液相色谱-气相色谱在线联用(HPLC-GC)技术,建立了同时测定土壤中饱和烃和芳香烃的方法。其中,提取方法选择正己烷-乙醇(1∶1, v/v)以固液比1∶4常温振荡提取1 h,然后水洗去除乙醇,取正己烷层提取液净化;净化方法选择自制硅胶柱,以正己烷-二氯甲烷(8∶2, v/v)洗脱;洗脱液经浓缩注入HPLC-GC分析,以内标法同时测定试液中的饱和烃和芳香烃,方法的定量限为0.4 mg/kg。该方法经过土壤石油烃标准物(SQC-116)验证,测定值在证书提供的可信区间内,相对误差(RE)为10.6%,相对标准偏差(RSD)为1.4%,说明方法准确可靠且精密度达到分析要求。最后,该文采用建立的方法检测了北京地区的5个土壤样品,结果表明:5个样品均含有饱和烃(C₁₀~C₄₀),其含量范围为3.3~32.1 mg/kg;其中4个样品中检出芳香烃(C₁₀~C₄₀),其含量范围为0.8~4.3 mg/kg;此外,通过谱图分析还可以初步判别烃类物质的污染来源。

关键词: 高效液相色谱-气相色谱在线联用, 饱和烃, 芳香烃, 土壤

Abstract:

To strengthen regulation for mitigating the risk posed by petroleum contaminants in soil, the Ministry of Ecology and Environment of the People’s Republic of China has classified petroleum hydrocarbons as a key monitoring item for regulatory contamination monitoring. Petroleum is principally derived from petroleum and synthetic fuels, which contain an extremely high content of hydrocarbon compounds that have varied boiling points. These compounds are chemically classified primarily as saturated and aromatic. Aromatic hydrocarbons are typically highly alkylated monocyclic, bicyclic, and polycyclic, which are more toxic to human and animal life than saturated hydrocarbons. Because of the significant toxicological differences among the various hydrocarbons, it is difficult to accurately assess their environmental toxicity by only determining the total content of petroleum in soil. However, there are no analytical methods for the simultaneous determination of saturated hydrocarbons and aromatic hydrocarbons in soil according to Chinese standards.
In this study, extraction and purification procedures were completely optimized depending on the matrix of the soil samples. The advanced analytical technique of on-line high performance liquid chromatography-gas chromatography (HPLC-GC) was performed after sample preparation for the simultaneous determination of saturated hydrocarbons and aromatic hydrocarbons in soil. For the extraction, n-hexane/ethanol (1∶1, v/v) was chosen as the extraction solvent. The ratio of solid sample (soil) to the solvent was chosen as 1∶4, and extraction was performed once at room temperature, for 1 h. Water was then added and mixed to remove ethanol from the extracts, and the upper n-hexane layer was separated; thus, the petroleum hydrocarbons in the samples were completely extracted. However, the oils and fats in the matrix of the soil sample were also simultaneously extracted. Because of the limited retention capacity of the HPLC column, the presence of oils, fats, and other interferents would affect the subsequent determination of saturated hydrocarbons and aromatic hydrocarbons. Therefore, an additional purification step is required before sample injection into the HPLC-GC equipment. In this study, purification was performed using a lab-made silica gel column, which is commonly used for the determination of saturated hydrocarbons and aromatic hydrocarbons in food. The purification column was conditioned and eluted with an 8∶2 ratio (v/v) of n-hexane to dichloromethane after sample loading. Subsequently, the eluent was concentrated and injected into the HPLC-GC equipment for analysis. The flame ionization detector (FID) is ideal for petroleum hydrocarbons quantification because of its nearly identical responses to all hydrocarbons; hence, with the FID, reference standards are not required for quantification, and internal standards are typically used for quantifying the total hydrocarbon content. In this study, cyclohexylcyclohexane (Cycy) and 2-methylnaphthalene (2-MN) were used as internal standards for determining the saturated and aromatic hydrocarbons, respectively. The limit of quantification (LOQ) of this proposed method was 0.4 mg/kg. Moreover, the suitability of the method was verified by comparing the obtained content against the soil petroleum hydrocarbon standard (SQC-116); the measured value was found to be within the credible interval provided by the standard. The relative error (RE) was 10.6% with a relative standard deviation (RSD) of 1.4%, which indicates that the proposed method is accurate and reliable, and the precision meets analytical requirements. Finally, the method was applied to the determination of hydrocarbons in five soil samples from the Beijing area. Saturated hydrocarbons (C₁₀-C₄₀) were detected in all five samples, with contents ranging from 3.3 to 32.1 mg/kg, while aromatic hydrocarbons (C₁₀-C₄₀) were detected in four samples, with contents ranging from 0.8 to 4.3 mg/kg.
HPLC-GC combines the high selectivity of HPLC with the high separation efficiency of GC, and as demonstrated in this study, can be used for the simultaneous determination of saturated and aromatic hydrocarbons in soil. The source of hydrocarbon contamination can also be preliminarily identified by chromatographic analysis.

Key words: on-line high performance liquid chromatography-gas chromatography (HPLC-GC), saturated hydrocarbons, aromatic hydrocarbons, soil

中图分类号:

O658

刘玲玲, 李冰宁, 武彦文. 高效液相色谱-气相色谱在线联用同时测定土壤中饱和烃和芳香烃[J]. 色谱, 2021, 39(8): 905-912.

LIU Lingling, LI Bingning, WU Yanwen. Simultaneous determination of saturated and aromatic hydrocarbons in soil by on-line high performance liquid chromatography-gas chromatography[J]. Chinese Journal of Chromatography, 2021, 39(8): 905-912.

图/表 7

图1 不同溶剂提取同一土壤样品中饱和烃的HPLC-GC谱图

Fig. 1 HPLC-GC chromatograms of saturated hydrocarbons (SH) in the same soil sample extracted using different solvents Cycy: cyclohexylcyclohexane; Cho: 5α-cholestane.

表1 提取级数对同一土壤样品中饱和烃(C10~C40)测定的影响

Table 1 Influence of extraction time on the determination of SH (C10-C40) in the same soil sample

Extraction time	Contents/(mg/kg)				RSD/%
Extraction time	1	2	3	Average	RSD/%
1	14.0	13.8	13.8	13.9	0.8
2	14.3	15.1	14.2	14.5	3.4

图2 饱和烃和芳香烃(AH)混合标准溶液通过硅胶柱净化后以正己烷-二氯甲烷(8∶2, v/v)混合溶剂洗脱的结果

Fig. 2 Elution order of mixed standard solution containing SH and aromatic hydrocarbons (AH) through the SPE column packed with silica gel and a solvent mixture of n-hexane and dichloromethane (8∶2, v/v) 5B: pentylbenzene; MN: methylnaphthalene; TBB: tri-tert-butylbenzene; Per: perylene.

图3 SH/AH混合标准溶液经硅胶柱净化后的HPLC-GC谱图

Fig. 3 HPLC-GC chromatograms of mixed standard solution of SH/AH purified by the SPE column packed with silica gel

图4 n-C10~n-C40正构烷烃混合溶液的HPLC-GC谱图

Fig. 4 HPLC-GC chromatogram of n-alkane (C10-C40) standards

表2 土壤样品中饱和烃和芳香烃(C10~C40)的含量

Table 2 Contents of SH and AH (C10-C40) in soil samples

Sample No.	SH/(mg/kg)	AH/(mg/kg)	Aromatics ratio/%
1	6.6	1.0	13.2
2	32.1	4.3	11.8
3	3.3	<0.4	-
4	13.8	1.1	7.4
5	11.8	0.8	6.3

图5 两个土壤样品中SH和AH的HPLC-GC谱图

Fig. 5 HPLC-GC chromatograms of SHs and AHs in two soil samples

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