Pesticides method development

E. A. Hogendoorn, C. Verscliraagen, U. A. Th Brinkman and van P. Zoonen Coupled column liquid chr omatography for the tr ace determination of polar pesticides in water using dhect large-volume injection method development strategy applied to methyl isothiocyanate , Awn/. Chim. Acm 268 205-215 (1992). 

A method has been reported for the quantification of five fungicides (shown in Figure 5.39) used to control post-harvest decay in citrus fruits to ensure that unacceptable levels of these are not present in fruit entering the food chain [26]. A survey of the literature showed that previously [27] APCl and electrospray ionization (ESI) had been compared for the analysis of ten pesticides, including two of the five of interest, i.e. carbendazim and thiabendazole, and since it was found that APCl was more sensitive for some of these and had direct flow rate compatibility with the HPLC system being used, APCl was chosen as the basis for method development. 

The above examples can be extended to the majority of older and newer active substances described in, e.g., The Pesticide Manual and to numerous relevant metabolites featuring hydroxyl or carboxyl moieties or even for conjugates however, there remain various active substances and metabolites that still require careful and extensive method development. 

However, there is no general requirement that enforcement methods need to monitor all metabolites of an active ingredient. The primary purpose of enforcement methods is to detect violations of good agricultural practice. For this purpose, residue levels found in samples from the market (so-called Market Basket Surveys) have to be compared with MRLs, which are derived from residue concentrations found in supervised trials. It is not necessary for this comparison to be based on the total pesticide residue. Most often the choice of a single compound (e.g., parent or primary metabolite) as a marker of the total pesticide residue is more feasible. Method development and the later method application are much easier in that case. Only for intake calculation purposes, e.g., when the daily intake of pesticide residues (calculated from the results... 

A plefhora of methods developed for the determination of triazine compounds in water, soil, crops, biological fluids, etc., have been reported in the literature, and several excellent reviews are available for the interested reader. " More method papers are published on the determination of triazines in water than for all other sample matrices combined (water > soil > crop). The majority of the water method reports relate to the determination of parent triazine compounds plus compounds from one or more other chemical classes of pesticides (e.g., phenoxy acids, carbamates, pheny-lureas, acetanilides, acetamides, organophosphorus compounds, etc.) for generalized multi-residue screening or monitoring purposes. Addressed in other more selective... 

Accurate, precise and sensitive analytical methods are important to the collection of data needed for regulatory decisions about pesticide registration. This article describes the various components of analytical method development, validation and implementation that affect the collection of pesticide residue distribution data for regulatory assessment of environmental fate and water quality impacts. Included in this discussion are both the technical needs of analytical methods and the attributes of study design and sample collection needed to develop data that are useful for regulatory purposes. 

As more sensitive analytical methods for pesticides are developed, greater care must be taken to avoid sample contamination and misidentification of residues. For example, in pesticide leaching or field dissipation studies, small amounts of surface soil coming in contact with soil core or soil pore water samples taken from further below the ground surface can sometimes lead to wildly inaccurate analytical results. This is probably the cause of isolated, high-level detections of pesticides in the lower part of the vadose zone or in groundwater in samples taken soon after application when other data (weather, soil permeability determinations and other pesticide or tracer analytical results) imply that such results are highly improbable. 

A variety of formats and options for different types of applications are possible in CE, such as micellar electrokinetic chromatography (MEKC), isotachophoresis (ITP), and capillary gel electrophoresis (CGE). The main applications for CE concern biochemical applications, but CE can also be useful in pesticide methods. The main problem with CE for residue analysis of small molecules has been the low sensitivity of detection in the narrow capillary used in the separation. With the development of extended detection pathlengths and special optics, absorbance detection can give reasonably low detection limits in clean samples. However, complex samples can be very difficult to analyze using capillary electrophoresis/ultraviolet detection (CE/UV). CE with laser-induced fluorescence detection can provide an extraordinarily low LOQ, but the analytes must be fluorescent with excitation peaks at common laser wavelengths for this approach to work. Derivatization of the analytes with appropriate fluorescent labels may be possible, as is done in biochemical applications, but pesticide analysis has not been such an important application to utilize such an approach. 

Methods to determine exposure of pesticides to agricultural workers have developed over the last 30 years at a reasonably slow pace. Some of the first methods to determine agricultural worker exposure to pesticides were developed by Armstrong, Wolfe, and Durham1 as well as Poppendorf.2 Using these methods for research has resulted in the development of several axioms related to agricultural worker exposure to pesticides ... 

Di Corcia A, Marchetti M. 1992. Method development for monitoring pesticides in environmental waters liquid-solid extraction followed by liquid chromatography. Environ Sci Technol 26(1 ) 66- 74... 

Sorbent Methods. The sorbent methods developed in this program are listed in Table II. These methods are strictly for vapors of the listed pesticides. Complete methods are published in the "NISOH Manual of Analytical Methods (9,11). ... 

In food analysis, sensitivity is not the only requirement for analytical method development. Besides confirmation of the identity of pesticides, the identification of nontarget analytes is also important. One powerful tool is LC/MS, especially when it is combined with appropiate sample-treatment procedures it allows one to obtain detection limits adequate for trace-level analysis. Liquid chromatography-MS has demonstrated that it is an effective way to obtain both qualitative and quantitative information. 

Analysis. The Washington State urine samples were analyzed at the ARS Yakima Agricultural Research Laboratory and the North Dakota samples at the ARS Pesticide Degradation Laboratory at Beltsville, Maryland. The method used by both laboratories was a similar procedure based on a method developed at Yakima (Maitlen and Sell, unpub.). Several randomly selected urine samples were... 

There are 14 analytical methods developed by U.S. EPA for measuring common organic pollutants in air. These analytes include aldehydes and ketones, chlorinated pesticides, polynuclear aromatic hydrocarbons, and many volatile organic compounds. These methods may also be applied to analyze other similar substances. All these methods are numbered from TO-1 to TO-14 and based on GC, GC/MS, and HPLC analytical techniques. Method numbers, sampling and analytical techniques, and the types of pollutants are outlined in Table 1, while individual substances are listed in Table 2. 

All samples were assayed according to the method developed in our laboratories (6). After saponification of the fat, the pesticides were extracted into hexane. Since DDT is quantitatively dehydrohalogenated to DDE during alkaline hydrolysis, all results reported as DDE are the sum of DDT plus DDE. The hexane extracts were resolved and assayed in gas chromatographs equipped with electron capture detectors. In addition to columns packed with Dow 11 plus Epon coated on Fluoropak 80, at least one replicate from each sample was assayed on a column packed with 3% QF-1 on anakrom ABS. This latter column showed excellent resolution for dieldrin and DDE, as shown in Figure 1. 

Analytical methods and quality control of pesticides in developing countries... 

Kross, B.C., H.F. Nicholson and L.K. Ogilvie (1996). Methods Development Study for Measuring Pesticide Exposure to Golf Course Workers using Video Imaging Techniques, Appl. Occup. Environ. Hyg., 11, 1346-1350. 

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