Sample handling matrix effects

Raman provides easy sampling, whereas IR spectroscopy frequently needs some form of sample preparation. Materials which are difficult to handle in IR (highly viscous liquids, solids requiring pellets, mulls, or diffuse reflectance) are often easily measured by Raman. Unlike IR reflectance spectra, Raman spectra of solid samples are not affected by sample properties such as particle size. A significant difference with infrared absorption spectroscopy is that the Raman signal is emitted from the sample. Consequently, matrix effects are seldom as severe in RS as they are with mid-IR and NIR. Water may be used as a solvent with no loss in signal or resolution. Glass, even tinted, does not interfere with the Raman spectra. 

Nondestructive radiation techniques can be used, whereby the sample is probed as it is being produced or delivered. However, the sample material is not always the appropriate shape or size, and therefore has to be cut, melted, pressed or milled. These handling procedures introduce similar problems to those mentioned before, including that of sample homogeneity. This problem arises from the fact that, in practice, only small portions of the material can be irradiated. Typical nondestructive analytical techniques are XRF, NAA and PIXE microdestructive methods are arc and spark source techniques, glow discharge and various laser ablation/desorption-based methods. On the other hand, direct solid sampling techniques are also not without problems. Most suffer from matrix effects. There are several methods in use to correct for or overcome matrix effects ... 

Interferences have been handled, traditionally, by the use of a matrix compensation response curve. Basically, the system is a series of standard additions to samples of a matrix and the use of these supplementations as the standards in a response curve. Thus, the recoveries of antibiotics, affected positively or negatively, can be corrected for matrix effects over a wide range of concentrations. Absolute recoveries are, of course, determined against standards in buffer. 

Assay application. At this point major differences appear between the historical use of clinical immunoassays and the potential applications of environmental and pesticide immunoassays. Most clinical assays have been applied to simple or well defined and consistent matrices such as urine or serum. In contrast, most matrices likely to be analyzed for pesticides are more complex, less well defined, and more variable. The potential for serious problems with matrix effects in the environmental field is far greater than most clinical immunoassays have encountered. The application of immunoassays to environmental analysis requires sampling strategies, cleanup procedures, and data handling fundamentally similar to those presently in use in any good analytical lab. The critical factor in the success of immunochemical technology will likely be competence... 

Additional problems are encountered with petroleum hydrocarbons due to the wide range in volatility, solubility and matrix effects. Knowledge of holding times should also be considered. Likewise, sample handling procedures within the laboratory will have a profound effect on the test result i.e. drying and crushing samples will lose volatile species, whereas a GC characterisation of a wet (as received) soil may sometimes show an unusually high aromatic content due to relative solubility effects. 

Several investigators have used neutron activation analysis (NAA) to determine the aluminium content of biological specimens both with and without some chemical processing. Instrumental neutron activation analysis involves the bombardment of a sample with neutrons and the measurement of the radioactivity induced by nuclear reactions. No chemical processing is required. Upon activation Al (100% isotopic abundance) forms the radioactive AI nuclide by a (n,y) reaction. There are a number of attractive features in this technique which include excellent sensitivity with relative independence from matrix effects and interferences. Also, there is relative freedom from contamination since the sample is analyzed directly with minimal handling. One major problem is the need to... 

Static headspace gas chromatography is a mature and reliable technique it is considered the technique of choice for the analysis of ethanol in biological samples, and is therefore jrresent in the vast majority of forensic laboratories around the world with the qualified personnel to operate it however, the applicability of this technique is not limited to this test and can be used for the analysis of various substances with minimal modifications, providing proper calibration and proper handling of matrix effects, excellent validation parameters, along with a clean injection. So, with this technique, various substances can be analyzed without the need of additional methods, and that would allow forensic laboratories to expand the number of cases they can take care of, with a minimal investment. 

The results of the experiments with bentonite and leachate reported in the literature have helped our understanding of the properties of bentonite, and its attenuating potential of some pollutants. However, it is very difficult to reproduce environmental conditions in the laboratory so that some of the results obtained cannot be readily extrapolated to real situations. It is difficult to compare data obtained with different experimental settings and to take into account the possible artefacts that may be caused by leachate handling, storage conditions and sample preparation techniques before analysis. Griven the interferences and leachate matrix effects commonly observed during leachate analysis, the reliability of the data obtained must also be carefully considered (DeWalle et al. 1981 Daly Farooq 1982 Lund et al. 1992). 

Regular LLE procedures are mostly implemented prior to UHPLC and present several benefits in terms of sample cleanup and enrichment. This technique is well adapted to LC-MS analysis because proteins and salts are extensively excluded, which minimizes any matrix effect and/or ion suppression and allows for very low detection limits with good recovery and precision (45). However, LLE usually includes long handling steps, which are not in line with UHPLC throughput. 

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