Hollow Fiber Liquid Phase Microextraction And Its Application In Gas Chromatography

In real-world sample analysis, some problems are often encountered:(i) the concentration of the target analytes in samples is extremely low; (ii) the original existing forms of samples are unsuitable for direct analysis by the subsequent analytical instrument, and (iii) the possible interference results from the complex sample matrix. To solve above-mentioned problems, various sample pretreatment techniques have been employed and the development of novel sample pretreatment techniques has arose great interest and become a hot topic in the field of analytical sciences. At present, sample pretreatment techniques is towards the direction of miniaturization, simplification and extremely low solvent consumption. Liquid phase microextraction (LPME) is one of such novel sample pretreatment techniques, which integrates extraction, preconcentration and sample introduction into a single step with simple apparatus, easy operation and little solvent consumption. As one of the operation modes of LPME, hollow fiber (HF)-LPME utilizes a hollow fiber to stabilize and protect the extraction solvent, exhibiting an extra good clean-up ability of sample matrix because the micro-pores of the fiber prevent large molecules and particles from entering into the extraction phase. Besides, it can shorten the extraction time due to higher stirring rate allowed in HF-LPME. Therefore, HF-LPME has attracted more and more attention in analytical community.Gas chromatography (GC) is one of the most powerful techniques for trace/ultratrace analysis due to its significant advantages including good separation efficiency, high selectivity, low detection limits and simple operation. Additionally, it is worthy to mention that the injection volume of GC matches the volume of extraction solvent in LPME, which makes the combination of GC with LPME very convenient.The aim of this dissertation is to systematically investigate the effect of various parameters (such as extraction solvent, stirring rate and extraction temperature, etc.) on HF-LPME; to study the extraction behaviors of various target analytes (neutral and ionizable compounds) in HF-LPME procedure; to make a comparison of the characteristics of different extraction modes of LPME; and to develop a series of new methods by combining HF-LPME with GC for the analysis of environmental pollutants, illegal drugs and food additives in environmental, biological and food samples. The major contents are described as follows:(1) A method based on HF-LPME-GC-flame ionization detection (FID) was developed for the determination of trace chloro-and bromobenzene compounds in environmental water samples. Type of extraction solvent, extraction time, extraction temperature, stirring rate and ionic strength were investigated and optimized to obtain the best extraction efficiency for target analytes. Under the optimal conditions, the limits of detection (LODs, S/N=3) for the six target compounds (chlorobenzene, bromobenzene, m-chlorotoluene,1, 2-dichlorobenzene,1,2,4-trichlorobenzene and 1,3,5-tribromobenzene) were in the range of 2.38-9.48μg/L with the enrichment factors (EFs) of 101.7-146.1 folds. To validate the proposed method, real water samples collected from East Lake and Yangtze River were analyzed and the recoveries of 81.5-107.7% were obtained.(2) Taking amphetamine (AP), methamphetamine (MP), methylenedioxyamphetamine (MDA), methylenedioxymethamphetamine (MDMA), caffeine and ketamine (KT) as the target analytes, a novel method of HF-LPME-GC-FID was proposed for illegal drug analysis in urine samples. Under the optimal conditions, the LODs for the six target analytes were ranged from 0.008 mg/L (AP and KT) to 0.082 mg/L (MDA) and the RSDs (n=7) were in the range of 6.9-14.1% with the EFs of 5-227 folds. The proposed method is simple, effective, sensitive and low-cost, and provides a much more accurate and sensitive detection platform over commonly used techniques (such as immunological assay) for drug abuse analysis.(3) The simultaneous determination of seven preservatives including sorbic acid (SA), benzoic acid (BA), dehydroacetic acid (DA) and p-hydroxybenzoic acid methyl, ethyl, propyl and butyl esters (MP, EP, PP and BP) in beverage samples was realized by the means of HF-LPME-GC-FID. Orthogonal array design (OAD) was applied to optimize the extraction conditions of HF-LPME including type of organic solvent, extraction time, extraction temperature, stirring speed and salt concentration. Under the optimal conditions, the RSDs (n=7) of 5.2-12.5% with EFs of 26-124 was obtained for target analytes, and the LODs ranging from 0.03 mg/L (PP) to 0.52 mg/L (SA) demonstrated the application feasibility of the proposed method in real sample analysis. The method of HF-LPME-GC-FID was applied to sauce and beverage samples analysis and the recoveries ranging from 73.0-115.7% with RSDs of 0.1-15.4% were obtained.(4) Two methods of HF-LPME and dispersive liquid-liquid microextraction (DLLME) have been critically compared for the analysis of organosulphur pesticides (OSPs) in environmental and beverage samples followed by GC-flame photometric detection (FPD). Both methods were found to be simple, fast, efficient, and inexpensive. Compared with HF-LPME, DLLME exhibited less extraction time, suitability for simultaneous batch analysis and higher enrichment factors for simple samples such as water samples. While for the analysis of complicated matrix samples such as soil and beverage samples, HF-LPME was demonstrated to be more robust and more suitable. Both methods were applied to the analysis of six OSPs in different waters, soil and beverage samples, and no target OSPs was found in these samples. The recoveries of 81.7-114.4% were obtained for HF-LPME-GC-FPD and 78.5-117.2% for DLLME-GC-FPD.(5) Direct HF-LPME and in-situ derivatization HF-LPME combined with GC were proposed and compared for the determination of trace heroin and its metabolites (including codeine, morphine, acetylcodeine,6-monoacetylmorphine) in urine samples. Under the optimal conditions, the LODs for target analytes obtained by direct HF-LPME-GC-FID and direct HF-LPME-GC-MS were 1.5-72.9μg/L and 1.4-24.5μg/L with EFs of 17.5-139.1, respectively. The LODs and the EFs of target analytes obtained by in-situ derivatization HF-LPME-GC-FID were 5.3-24.8μg/L and 4.9-22.3 folds, respectively. In-situ derivatization HF-LPME-GC-FID was simple, fast and no special equipment required, while the provided LODs for target analytes were not obviously improved over those obtained by direct HF-LPME-GC-FID, possibly due to low derivatization efficiency. Direct HF-LPME-GC-FID was applied for the determination of heroin and its metabolites in urine samples from abused suspects, and the recoveries of 68.1-99.1% were obtained.