Quantitative analysis pesticides

In 1994, Nam and King (68) developed a SFE/SFC/GC instrumentation system for the quantitative analysis of organochlorine and organophosphorus pesticide residues in fatty food samples (chicken fat, ground beef and lard). In this way, SFC was used as an on-line clean-up step to remove extracted material. The fraction containing pesticide residues is then diverted and analysed by GC. 

The principal limitation in the use of electrophoretic techniques is the lack of availability of suitable detection systems for quantitative analysis and unequivocal identification of pesticide analytes. Traditionally, either ultraviolet/visible (UVA IS) or fluorescence detection techniques have been used. However, as with chromatographic techniques, MS should be the detection system of choice. A brief comparison of the numbers of recent papers on the application of GC/MS and LC/MS with capillary elec-trophoresis/mass spectrometery (CE/MS) demonstrates that interfaces between CE... 

Consider the analysis of plant material for a pesticide residue by GC. Two grams of the material is chopped up and placed in a Soxhlet extractor (Chapter 11) and the pesticide quantitatively extracted into an appropriate solvent. Following this, the solvent is evaporated to near dryness and the residue is diluted to volume in a 25-mL flask. Then 2.5 pL of this solution and standards is injected in a GC with the following results ... 

Juan-Garcia, A., Font, G., and Pico, Y. (2005). Quantitative analysis of six pesticides in fruits by capillary electrophoresis-electrospray-mass spectrometry. Electrophoresis 26, 1550—1561. 

Figure 3. Flow chart showing the qualitative and quantitative analysis of a complex pesticide waste (2).

Low-volume sampling is typically used for quantitative analysis for specific compounds, such as pesticides, polychlorobiphenyls (PCBs), and organic acids. Large-volume sampling is used to simultaneously... 

Early studies using resins for isolation and analysis of trace organics, such as pesticides, PCBs, and organic acids, from small volumes of water showed excellent recovery and the potential of easy application to environmental samples. Isotherm studies in distilled water were used to define the sampling parameters for quantitative analysis of these compounds. Later, studies using resin samplers for large-volume environmental samples were extrapolated from the early low-volume resin work of Junk et al. (5,14) and Thurman et al. (27) (see Table I). 

Pesticides and Fungicides. Modern pure food regulations require that the food processor be responsible for their finished products. Since so many pesticides and fungicides are used in agriculture, their detection and quantitative analysis are difficult (5, 22). Organophosphorus and chlorinated hydrocarbons are the most common pesticides. When GLC is used for halogens, electron capture or microcoulometric detectors are used for phosphorus, a thermionic flame photometric detector is required. 

A method for the quantitative analysis of the OCPs in water using the HPLC technique of online trace enrichment was developed. The pesticides were concentrated onto an ODS column, and the analysis was performed on an ODS column with UV detection (47). 

The objective of an analytical measurement can be qualitative or quantitative. For example, the presence of pesticide in fish is a topic of concern. The questions may be Are there pesticides in fish If so, which ones An analysis designed to address these questions is a qualitative analysis, where the analyst screens for the presence of certain pesticides. The next obvious question is How much pesticide is there This type of analysis, quantitative analysis, not only addresses the presence of the pesticide, but also its concentration. The other important category is semiqualitative analysis. Here... 

In conclusion, it is obvious that chemical derivatization continues and will continue to play an important role in both qualitative and quantitative analysis of pesticides, their residues and metabolites. One of the major advantages being that derivatization gives an improvement in selectivity as a result of the formation of a characteristic derivative which responds selectively to certain GC and HPLC detectors. 

Specific areas where FTIR has provided valuable information include quantitative analysis of active material impurity identification in technical material analysis of volatile components from formulated material and the identification of metabolites. In this paper, we will discuss the results from these studies and describe some of the problems we encountered. We will also discuss some of the new developments in FTIR that might prove useful in pesticide analysis. 

Sensitivity limits must be improved for both quantitation and identification of pesticide residues. Although the former method is more sensitive than the latter, until recently most progress has been made in improving the sensitivity of quantitative analysis. Since there is a dependence between the two methods, sensitive methods of identification have... 

Tn recent years much concern has risen, especially in o Bcial regulatory circles, about the problem of misidentification or uncertain identification in pesticide residue analysis. Since the introduction of the electron-capture detector (EC) in 1960 (i) and its rapid exploitation for the determination of organochlorine residues by gas-liquid chromatography (GLC) (2) the combined EC-GLC system has become, from 1963, the most commonly used end-method for quantitative pesticide residue analysis. It was quickly discovered that even after the application of the more common clean-up techniques (3, 5, 4) EC-GLC interferences occurred not only from peak-overlap of the various pesticides themselves (6, 7) but also from extraneous contamination—e,g, the laboratory or... 

For some years (1987-1992), thermospray LC-MS was the most widely apphed LC-MS interface. It has demonstrated its potential in qualitative as well as quantitative analysis in mat r application areas, such as drugs and metabolites, conjugates, nucleosides, peptides, natural products, pesticides. A few examples are given below. 

The FBI has been widely apphed for identification, confirmation of identity as well as quantitative analysis in a variety of apphcation areas, especially in the analysis of pesticides. The interest of the US Envirornnental Protection Agency (US-EPA) in the use of the PBI for envirornnental monitoring of pesticides obviously contributed significantly to the proliferation of the system. 

Obviously, potential hazardous effects are not only related to pesticides, but possibly also to their metabolites in living systems and/or degradation products in the environment. Considerable attention has been paid in recent years to the characterization of degradation products of pesticides and to the monitoring and quantitative analysis of such compounds in environmental samples. Selected results and strategies are reviewed in this section. 

Quantitative analysis of the organophosphorous pesticides acephate, azinphos, chlorpyrifos, coumaphos, diazinon, isazofos, malathion, methamidophos, parathion, pirimiphos, and their O.O-dimethyl analogues in human urine using LC-MS-MS [143]. 

The recent development of commercial HPLC systems has provided a powerful instrumentation for the separation, characterization, identification, and quantitation of minute amounts of essential dietary components (68,69). Developments in hardware and packings for HPLC have overcome the problems of nonreproducible behavior and low efficiency separations previously associated with column chromatography (70). HPLC has already been applied to the quantitative analysis of analgesics, pesticides, and fat-soluble vitamins with precision and accuracy and a minimum of sample clean-up. Such instrumentation provides a rapid, accurate, and sensitive technique for the separation and analysis of subnanomole quantities of a wide range of complex high-molecular-weight, nonvolatile, thermally labile, compounds that are vital for metabolic and nutritional studies. 

Immunoassays offer much potential for rapid screening and quantitative analysis of pesticides in food and environmental samples. However, despite this potential, the field is still dominated by conventional analytical approaches based upon chromatographic and spectrometric methods. We examine some technical barriers to more widespread adoption and utilization of immunoassays, including method development time, amount of information delivered and inexplicable sources of error. Examples are provided for paraquat in relation to exposure assessment in farmworkers and food residue analyses molinate in relation to low-level detection in surface waters and bentazon in relation to specificity and sensitivity requirements built in to the immunizing antigen. A comparison of enzyme-linked immunosorbent assay (ELISA) results with those obtained from conventional methods will illustrate technical implementation barriers and suggest ways to overcome them. 

Quantitative analysis of pesticides is usually performed by high performance liquid chromatography (HPLC) and gas chromatographic (GC) techniques. 

GC-MS analysis is performed in SIM mode employing the analytical conditions reported in Table 6.11. Confirmation of the pesticide is established by the retention time of the target ion and the presence of three qualifier-to-target ion ratios (Table 6.12). Quantitative analysis is performed on the peak area ratio of the target ion divided by the peak area of the internal standard versus concentration of the calibration standards. 

Tsoupras et al. used 31p nmr to detect the presence of phosphate groups in the 22-adenosinemonophosphoric ester of 2-deoxy-ecdysone and 22-phospho-2-deoxyecdysone (34). Quantitative NMR has been used in several studies. Wayne et al. used 51p nmr for quantitative analysis of organophosphorous pesticides (35). Zon et al. used NW to study chemical and microsomal oxidation of cyclophosphamide ( ), and to determine the half-life of a cyclophosphamide analogue (37). 

Immunochemical methods are rapidly gaining acceptance as analytical techniques for pesticide residue analysis. Unlike most quantitative methods for measuring pesticides, they are simple, rapid, precise, cost effective, and adaptable to laboratory or field situations. The technique centers around the development of an antibody for the pesticide or environmental contaminant of interest. The work hinges on the synthesis of a hapten which contains the functional groups necessary for recognition by the antibody. Once this aspect is complete, immunochemical detection methods may take many forms. The enzyme-linked immunosorbent assay (ELISA) is one form that has been found useful in residue applications. This technique will be illustrated by examples from this laboratory, particularly molinate, a thiocarbamate herbicide used in rice culture. Immunoassay development will be traced from hapten synthesis to validation and field testing of the final assay. 

Figure 3.18 Chromatograms of a sample containing two compounds A and B, for which the UV spectra are different. According to the choice of detection wavelength, the chromatogram will not have the same aspect. On the right the chromatograms represent a mixture of several pesticides recorded at three different wavelengths which illustrates this phenomenon. In quantitative analysis therefore the response factors of each of the compounds must be determined prior to the analysis (cf Quantitative analysis, Chapter 4).

---