Validation matrix effects

This ring test had been conducted with specially selected polar pesticides, and therefore the results are not representative of all pesticides. However, irrespective of this, the study clearly showed that validation smdies must be conducted with standards in a matrix. In recovery determinations, conducted with standards in a solvent, the analyst cannot be sure that a bad recovery is not masked by matrix effects. 

The use of a matrix blank is the simplest way to overcome a matrix effect, but the analyst must ensure that the matrix blank is uniform and does not change between sample sets. Acquiring a uniform blank matrix may be problematic if assays are conducted over an extended time period. Caution must be taken when an analysis, validated for one matrix or species, is used for a different tissue or species, because... 

Verification and/or validation EP14 evaluation matrix effects... 

The method development process with the multisorbent plate consists of three steps. In step 1, the sorbent chemistry and the pH for loading, washing, and elution are optimized. In step 2, optimization of the percentage organic for wash and elution and the pH of the buffer needed is carried out. Step 3 is validation the method developed from the results of the previous two steps is tested for linearity, limits of detection, quantitation of recovery, and matrix effects using a stable isotope-labeled analyte as an IS. 

In some cases, the signal is still influenced by the sample matrix despite peak purity, e.g., because of sample pre-treatment operations. If matrix effects are considered to be very unlikely, the following check can be skipped. They would still be discovered testing for accuracy. However, matrix effects lately discovered imply a lot of extra work, since the method must then be changed and validated once again. 

Jemal, M., Schuster, A., and Whigan, D. B. (2003). Liquid chromatography/tandem mass spectrometry methods for quantitation of mevalonic acid in human plasma and urine method validation, demonstration of using a surrogate analyte, and demonstration of unacceptable matrix effect in spite of use of a stable isotope analog internal standard. Rapid Commun. Mass Spectrom. 17, 1723-1734. 

ICP-AES was validated for the simultaneous determination of Al, B, Ba, Be, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Se, Sr and Zn in human serum in a clinical laboratory. The samples underwent digestion and yttrium was used as an internal standard. The LOD were as follows 0.002-0.003 (xM for Ba, Cd, Mn and Sr 0.014-0.07 (xM for Be, Co, Cr, Cu, Fe, Li, Ni, Pb and Zn and 0.2-0.9 (xM for Al, B and Se. The concentrations of Al, Be and Co in human serum were found to be above the LOD, while those of Cd, Cr, Ni and Pb were below the LOQ however, in case of acute intoxication with the latter elements the method is valid . Matrix effects were evaluated for ICP-AES analysis using solution nebulization and laser ablation (LA) techniques. The main matrix-related interferences stem from elements with a low second ionization potential however, these are drastically reduced when pure He is used as carrier gas. This points to Ar (the usual carrier) participation in the interference mechanism, probably by interacting with doubly charged species. ... 

Dams et al. [18] developed a validated quantitative LC-APCI-MS-MS method for simultaneous determination of multiple illicit drugs and their metabolites in oral fluid. This substrate is being increasingly popular for forensic applications as it provides information on recent use, similarly to blood plasma/serum, although it can be obtained with a simple, noninvasive, collection. Sample pretreatment, though limited to protein precipitation with acetonitrile, was sufficient to avoid matrix effect (see Figure 20.2). 

It may be important to consider the variability of the matrix due to the physiological nature of the sample. In the case of LC-M/MS-based procedures, appropriate steps should be taken to ensure the lack of matrix effects throughout application of the method, especially if the nature of the matrix changes from the matrix used during method validation. For Microbiological and immunoassay, if separation is used prior to assay for study samples but not for standards, it is important to establish recovery and use it in determining results. In this case, possible approaches to assess efficiency and reproducibility of recovery are ... 

In principle, methods should be validated for each type of matrix and for the extraction agent applied. Matrix effects may affect strongly the calibration (e.g. loss of signal, interferences). Standard addition techniques are, therefore, the only way to control the validity of the detection, but only if the addition is performed with the proper identical form of the compound to be determined. As stressed above, it is of primary importance to evaluate this linear range before starting the analysis so that the spiked levels remain in the linear range of the detector response (Quevauviller et al., 1996a). 

Eeckhaut AV, Lanckmans K, Sarre S, Smolders I, Michotte Y (2009) Validation of bioanalyti-cal LC-MS/MS assays evaluation of matrix effects. J Chromatogr B 877 2198-2207... 

Lindegardh N, Annerberg A, White NJ, Day NPJ (2008) Development and validation of a liquid chromatographic-tandem mass spectrometric method for determination of piperaquine in plasma stable isotope labeled internal standard does not always compensate for matrix effects. J Chromatogr B 862 227-236... 

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