Multi-matrix methods

For multi-analyte and/or multi-matrix methods, it is not possible to validate a method for all combinations of analyte, concentration and type of sample matrix that may be encountered in subsequent use of the method. On the other hand, the standards EN1528 andEN 12393 consist of a range of old multi-residue methods. The working principles of these methods are accepted not only in Europe, but all over the world. Most often these methods are based on extractions with acetone, acetonitrile, ethyl acetate or n-hexane. Subsequent cleanup steps are based on solvent partition steps and size exclusion or adsorption chromatography on Florisil, silica gel or alumina. Each solvent and each cleanup step has been successfully applied to hundreds of pesticides and tested in countless method validation studies. The selectivity and sensitivity of GC combined with electron capture, nitrogen-phosphorus, flame photometric or mass spectrometric detectors for a large number of pesticides are acceptable. 

In contrast to multi-analyte/multi-matrix methods, a more or less complete validation of methods with limited scope is possible. For this reason, TC 275 decided that... 

The sensitivity achieved (LOD) is not normally presented. It is recognized that different laboratories determine dissimilar values for this parameter and even within a laboratory the repeatability of the LOD is low. Most often, the lowest validated concentration gives an impression about the lowest levels that can be analyzed generally with acceptable results. A measure of selectivity is the intensity of blank results. This intensity is discussed by the participants of inter-laboratory validation studies. However, results are not reported and limits are not defined by CEN TC 275. The results of method validations of the several multi-residue/multi-matrix methods are not reported in the same way, but newer methods with limited scope generate analogous tables with validation results (as an example, see Table 7). 

In accordance to the EU Commission Decision, 40 samples per matrix are needed to asses CCa and CC/3. B. Julicher et al. have developed an in-house validation protocol to asses the detection capabilities [50], This approach is especially interesting for validating multi-matrix methods. 

EPA Methode 1613 (USA) Bestimmung der PCDD/PCDF (C14-C18) mit HRGC/HRMS Multi-Matrix-Methode u.a. Wasser, Boden, Schlamme keine Angaben US EPA (1990)... 

Abb. 5-13 FlieBschema fur die Bestimmung der PCDD und PCDF nach der Multi-Matrix-methode EPA 8280 [US EPA 1986],... 

Additional applications of the transfer matrix method to adsorption and desorption kinetics deal with other molecules on low index metal surfaces [40-46], multilayers [47-49], multi-site stepped surfaces [50], and co-adsorbates [51-55]. A similar approach has been used to study electrochemical systems. 

Owing to the complexity of multi-residue methods for products of animal origin, it is not possible to outline a simple scheme however, readers should refer to methods described in two references for detailed guidance (Analytical Methods for Pesticides in Foodstuffs, Dutch method collection and European Norm EN 1528. ) There is no multi-method specifically designed for body fluids and tissues. The latter matrix can be partly covered by methods for products of animal origin. However, an approach published by Frenzel et al may be helpful (method principle whole blood is hemolyzed and then deproteinized. After extraction of the supernatant, the a.i. is determined by GC/MS. The LOQ is in the range 30-200 ag depending on the a.i.). 

CEN requirements for widely accepted multi-matrix/multi-residue methods... 

Many experts in Europe have tested the methods of both standards with various pesticide-matrix combinations in their own laboratories. Consequently, the responsible working groups of CEN TC 275 concluded that these are the best methods available. Nevertheless, there is no complete validation of all possible pesticide-matrix combinations. However, for most multi-residue methods within the standards all those pesticides which had been successfully tested in method validation trials and/or proficiency tests are listed. Also, matrices which had been examined in ring tests are listed. 

If analytical methods are validated in inter-laboratory validation studies, documentation should follow the requirements of the harmonized protocol of lUPAC. " However, multi-matrix/multi-residue methods are applicable to hundreds of pesticides in dozens of commodities and have to be validated at several concentration levels. Any complete documentation of validation results is impossible in that case. Some performance characteristics, e.g., the specificity of analyte detection, an appropriate calibration range and sufficient detection sensitivity, are prerequisites for the determination of acceptable trueness and precision and their publication is less important. The LOD and LOQ depend on special instmmentation, analysts involved, time, batches of chemicals, etc., and cannot easily be reproduced. Therefore, these characteristics are less important. A practical, frequently applied alternative is the publication only of trueness (most often in terms of recovery) and precision for each analyte at each level. No consensus seems to exist as to whether these analyte-parameter sets should be documented, e.g., separately for each commodity or accumulated for all experiments done with the same analyte. In the latter case, the applicability of methods with regard to commodities can be documented in separate tables without performance characteristics. 

Specifically for triazines in water, multi-residue methods incorporating SPE and LC/MS/MS will soon be available that are capable of measuring numerous parent compounds and all their relevant degradates (including the hydroxytriazines) in one analysis. Continued increases in liquid chromatography/atmospheric pressure ionization tandem mass spectrometry (LC/API-MS/MS) sensitivity will lead to methods requiring no aqueous sample preparation at all, and portions of water samples will be injected directly into the LC column. The use of SPE and GC or LC coupled with MS and MS/MS systems will also be applied routinely to the analysis of more complex sample matrices such as soil and crop and animal tissues. However, the analyte(s) must first be removed from the sample matrix, and additional research is needed to develop more efficient extraction procedures. Increased selectivity during extraction also simplifies the sample purification requirements prior to injection. Certainly, miniaturization of all aspects of the analysis (sample extraction, purification, and instrumentation) will continue, and some of this may involve SEE, subcritical and microwave extraction, sonication, others or even combinations of these techniques for the initial isolation of the analyte(s) from the bulk of the sample matrix. 

Methods submitted include single- and multi-analyte methods for parent compounds and for degradates of concern. Pesticide regulatory methods are needed for each type of environmental matrix fate methods may be designed for soil, water, plant tissue, animal tissue or air, but are predominantly for soil and water. Analytical methods need to include a complete description of the procedure, materials and equipment in order to be completely reproducible. The methods should be practical and rapid and, to the extent possible while maintaining other quality objectives, inexpensive (often State and local regulatory agencies with few available resources need to utilize them). 

The overall process of method validation is illustrated in Figure I. However, the extent and scope of validation is governed by the applicability of the method. An in-house procedure requires a less exacting process than a method intended for multi-matrix and/or multi-laboratory use. For the latter methods, a full collaborative trial is necessary and is covered in Chapter 9. However, for many purposes validation is limited to either demonstrating that method performance criteria established during development are met under routine laboratory conditions and/or showing method equivalence (Figure 18). 

The theory of the multi-vibrational electron transitions based on the adiabatic representation for the wave functions of the initial and final states is the subject of this chapter. Then, the matrix element for radiationless multi-vibrational electron transition is the product of the electron matrix element and the nuclear element. The presented theory is devoted to the calculation of the nuclear component of the transition probability. The different calculation methods developed in the pioneer works of S.I. Pekar, Huang Kun and A. Rhys, M. Lax, R. Kubo and Y. Toyozawa will be described including the operator method, the method of the moments, and density matrix method. In the description of the high-temperature limit of the general formula for the rate constant, specifically Marcus s formula, the concept of reorganization energy is introduced. The application of the theory to electron transfer reactions in polar media is described. Finally, the adiabatic transitions are discussed. 

Validation is the determination of the attributes, or figures of merit, of an analytical method for one or more analytes in one or more sample matrices by one or more analysts in one or more analytical laboratories and the acceptance of the attributes as reasonable and useful by the users of the data. There are many levels of analytical method validation ranging from the validation of a method for a single analyte in a single matrix by a single analyst in a single laboratory to a multi-analyte, multi-matrix, multi-analyst, and multi-laboratory validation. 

In order to correlate the solid state and solution phase structures, molecular modelling using the exciton matrix method was used to predict the CD spectrum of 1 from its crystal structure and was compared to the CD spectrum obtained in CHC13 solutions [23]. The matrix parameters for NDI were created using the Franck-Condon data derived from complete-active space self-consistent fields (CASSCF) calculations, combined with multi-configurational second-order perturbation theory (CASPT2). 

At this point it must be mentioned that the term specificity is used interchangeably with selectivity, although in a strict sense specificity refers to methods which produce a response for a single analyte, whereas selectivity refers to methods that produce responses for a number of chemical entities, which may or may not be distinguished [1]. Selective multi-analyte methods (e.g. for different drugs of abuse in blood) should of course be able to differentiate all interesting analytes from each other and from the matrix. 

This multi-element method includes Cr. The sensitivity Is however influenced by the matrix components and the subsequent background emitted by major components. Particle Induced X-ray emission (PIXE) analysis with the aid of a Si (Li) detector is occasionally used for Cr determinations in biological specimens. The sensitivity is too low to measure the normal Cr content of biological fluids (I.e. less than reliable data for the 1 mg/kg amounts (Maenhaut et al., 1984). 

Runnqvist et al. reviewed the published PLE methods for antimicrobials, including multi-analyte methods. The methods are summarized and critically discussed. Regarding method optimization, the authors concluded that pressure may be less important while solvent composition and temperature are presumably the parameters that influence the extraction efficiencies to the greatest extent. Extraction temperature should be carefully determined since this parameter affects not only the absolute amounts extracted but also the degradation of analytes and the co-extraction of unwanted matrix components. ... 

However, the thin-fihn approximation may yield significant errors even for films a few tenths of nanometers thick [7]. Yamamoto and Ishida [44], based on the KK technique of Hansen and Abdou [465] for a multi-interface system, and Buffeteau and Desbat [452], based on the Abeles matrix method and the fast Fourier transform for the KK relations, suggested procedures for measuring the optical constants from IRRAS without employing the thin-film approximation. These techniques can yield the optical constants of both organic and inorganic ultrathin films with high accuracy if the film thickness and are known. 

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