Advanced Techniques in Gas Chromatography-Mass Spectrometry (GC-MS-MS and GC-TOF-MS) for Environmental Chemistry

• Publisher: Elsevier
• Year: 2013
• ISBN:
  9780444626240
• Topic: Sciences physiques
• Subtopic: Spectroscopie et analyse du spectre

Gas chromatography mass spectrometry (GC-MS) has been the technique of choice of analytical scientists for many years. The latest developments in instrumentation, including tandem mass spectrometry (MS-MS) and time-of-flight (TOF) detectors, have opened up and broadened the scope of environmental analytical chemistry.

This book summarizes the major advances and relevant applications of GC-MS techniques over the last 10 years, with chapters by leading authors in the field of environmental chemistry. The authors are drawn from academia, industry and government.

The book is organized in three main parts. Part I covers applications of basic GC-MS to solve environmental-related problems. Part II focuses on GC-MS-MS instrumentation for the analyses of a broad range of analysis in environmental samples (pesticides, persistent organic pollutants, endocrine disruptors, etc.). Part III covers the use of more advanced GC-MS techniques using low- and high-resolution mass spectrometry for many applications related to the environment, food and industry.

• Summarizes the major advances of GC-MS techniques in the last decade
• Presents relevant applications of GC-MS techniques
• Covers academic, industrial and governmental sectors

Part I: Advances in GC–MS and GC–MS–MS. Environmental Applications

Outline

Chapter 1 Gas Chromatography–Mass Spectrometry Techniques for Multiresidue Pesticide Analysis in Agricultural Commodities

Chapter 2 Microextraction Techniques Coupled to Advanced GC–MS Techniques for Analysis of Environmental Samples

Chapter 3 Determination of Pesticide Residues in Environmental and Food Samples Using Gas Chromatography–Triple Quadrupole Mass Spectrometry

Chapter 4 Environmental Odor Pollution

Chapter 5 Injection Port Derivatization for GC/MS–MS

Chapter 6 High-Throughput Analysis of PPCPs, PCDD/Fs, and PCBs in Biological Matrices Using GC–MS/MS

Chapter 7 GC–MS Applied to the Monitoring of Pesticides in Milk and Blackberries and PAHs in Processed Meats of Colombia

Chapter 8 Applications and Strategies Based on Gas Chromatography–Low-Resolution Mass Spectrometry (GC–LRMS) for the Determination of Residues and Organic Contaminants in Environmental Samples

Chapter 9 Determination of Pyrethroid Insecticides in Environmental Samples by GC–MS and GC–MS–MS

Chapter 10 GC–MS–MS for the Analysis of Phytoestrogens in the Environment

Chapter 1

Gas Chromatography–Mass Spectrometry Techniques for Multiresidue Pesticide Analysis in Agricultural Commodities

Jon W. Wong, Douglas G. Hayward and Kai Zhang, U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Regulatory Science, College Park, Maryland, USA

Abstract

Multiresidue methods are the most common approaches to analyze pesticide residues because the pesticide application on an agricultural commodity is usually not known. Since there are hundreds of pesticides available, it is essentially impractical to apply individual single residue analysis for every pesticide in various types of food products. The challenge is to process a sample using a single procedure or a limited number of procedures that can identify and quantitate as many pesticides with varying physical and chemical properties as possible that could potentially be present in a wide variety of agricultural matrices. Over the past 20 years, capillary gas chromatography–mass spectrometry (GC–MS) has played a major role in the analysis of pesticides in foods. Despite the increasing popularity of liquid chromatography–mass spectrometry (LC–MS), GC–MS is still widely used because of its affordability, ruggedness, and effectiveness in multiresidue pesticide procedures. GC–MS is primarily used to analyze a variety of thermally stable and volatile or semivolatile pesticides as well as other industrial contaminants such as PCBs, dioxins, brominated flame retardants, and related persistent organic pollutants in diverse food matrices that currently cannot be analyzed by conventional LC–MS methods. This chapter will attempt to account the past and present use and the future of multiresidue procedures that utilize a variety of GC–MS systems and platforms for the analysis of pesticide residues in foods and related agricultural products.

Keywords

Multiresidue pesticide methods; Gas chromatography–mass spectrometry; Quadrupole ion trap; Quadrupole mass filter; Triple quadrupole mass spectrometry; Time-of-flight mass spectrometry

1 Gas Chromatography

Gas chromatography was developed in the 1950s when James and Martin [1] reported the separation of organic and fatty acids from mixtures using nitrogen as the carrier gas and 10% steric acid in silicone/diatomaceous earth as the stationary phase [2]. Since its development, tremendous advancements and improvements in the hardware, software, and consumables have established GC as an important analytical tool in the isolation of chemical constituents from complex matrices prevalent in the food, flavor and fragrances, petroleum and chemicals, environmental, and biological and medical disciplines [3]. Fused silica capillary columns of diverse stationary phases and column dimensions have since replaced packed columns due to their superior separation efficiency and resolution. The pneumatics and microfluidic devices, built into current GCs, allow for precise control of gas flows that provides not only reliable chromatographic retention times [4] but also introduce a variety of sample injection and maintenance techniques such as large volume or programmed temperature vaporization (PVT) injection [5], column backflushing [6], and advanced GC procedures such as multidimensional (GC × GC), low pressure, and fast capillary gas chromatography [7–10] techniques. The integration and use of the computer in today’s GC aids in the optimization of instrumental conditions, enables for efficient acquisition and storage of chromatographic (and mass spectra) data, and provides the speed to quantitatively and qualitatively process the data using various software algorithms and programs. The combination of these technological advances has made it possible to couple sampling devices such as headspace, thermal desorption, solid-phase microextraction, stir bar sorptive extraction as well as automated sample preparation workstations, to allow for increased sample throughput and further diversity of GC and gas chromatography–mass spectrometry (GC–MS) applications.

2 Gas Chromatography with Element Selective Detection for Multiresidue Pesticide Analysis

The first significant work of multiresidue pesticide procedures by Mills [11] applied paper chromatography using a chromogenic reagent (silver nitrate/hydrogen peroxide in 2-phenoxyethanol and acetone) to stain the paper as a means to detect organochlorine pesticides and reported “it is possible to rapidly identify and approximately measure residual of commonly used pesticides in a variety of foods and feeds.” Identification with paper chromatography depended on the number and size of the developed spots and difficulties arose due to streaking and resolving spots of pesticides with similar migration times. In a follow up on his work, Mills et al. [12] replaced paper chromatography with a GC equipped with a Coulson coulometric detector for the separation and detection of 21 organochlorine pesticides, demonstrating one of the first published application of detectors used for GC analysis for pesticides.

Many GC detectors prior to mass spectrometry were of the element selective types, namely, so because detection was dependent on the presence and detection of element heteroatoms in the molecular makeup of the analyte that formed specific ions or emissions when combusted and became ideally suited for pesticide analysis. Commonly used universal GC detectors were the thermal conductivity (TCD) and flame ionization (FID) detectors [13–15] because of their abilities to produce signal responses from the carbon–hydrogen content of the analyte. The TCD signal response is a result of changes in the temperature and electrical resistance when the analyte from the GC effluent comes in contact with a conductivity cell. The FID signal results when the C–H-containing analyte is combusted in a flame jet creating ions which are collected at an electrode to produce the response. The detectors generally used for the GC analysis of pesticides are electron-capture (ECD) [16,17], electrolytic conductivity (ELCD) [18], nitrogen–phosphorus (NPD) [19], and flame photometric [20], which were effective due to their selectivity and sensitivity for halogens (especially chlorine), nitrogen, phosphorus, sulfur, or a conjugated moiety such as an aromatic ring that were present in organochlorine and organophosphorus pesticides that were commonly used at the time [12,21–23]. Some of these detectors have been modified such as the micro-electron-capture (μECD) and pulsed flame photometric [24] and are of still in use today because of their improved selectivity and sensitivity [25,26]. The ELCD and the closely related halogen-specific detector (XSD) [27–29] are currently used to analyze organochlorine pesticides and have been useful to detect phthalimide fungicides such as captan, captafol, and folpet [30,31], notoriously difficult pesticides to analyze by MS because of their thermal instability under GC conditions and the inability to produce stable fragments with MS. As a result of the availability of these different detector types, many multiresidue pesticide procedures based on gas chromatography coupled with element selective detection for the analysis of foods were developed at several regulatory and private laboratories [21,32,33]. Despite the increasing use of GC–MS, the addition of an element selective detector to the GC–MS or a stand alone GC-element selective detector can be used to compliment GC–MS or enhance the GC–MS performance in the detection or confirmation of difficult pesticides in complex food and agriculture-based matrices [24,30,34–38].

3 Capillary GC–MS

Pesticide confirmation with GC-element selective detection is determined by cross-referencing the retention indices or comparing the variations in the retention times of each pesticide using two different columns of stationary phases of varying polarities [26,39,40]. This practice has since been replaced because MS has become the primary detector of use in most laboratories and is more reliable for identification or confirmation. Today, criteria for pesticide presence from a sample are based on MS technology [41–45]. Due to the separation and resolution capabilities of GC, an analyte is isolated as it undergoes fragmentation typically by electron ionization (EI) in the mass spectrometer to generate a spectrum based on mass-to-charge (m/z) ratios. The analyte can be unambiguously identified based on the chromatographic retention time and the unique spectral fragmentation pattern of the mass spectrum in full-sc...