The ability to quantify levels of target analytes in biological samples accurately and precisely, in biomonitoring, involves the use of highly sensitive and selective instrumentation such as tandem mass spectrometers and a thorough understanding of highly variable matrix effects. Typically, matrix effects are caused by co-eluting matrix components that alter the ionization of target analytes as well as the chromatographic response of target analytes, leading to reduced or increased sensitivity of the analysis. Thus, before the desired accuracy and precision standards of laboratory data are achieved, these effects must be characterized and controlled. Here we present our review and observations of matrix effects encountered during the validation and implementation of tandem mass spectrometry-based analytical methods. We also provide systematic, comprehensive laboratory strategies needed to control challenges posed by matrix effects in order to ensure delivery of the most accurate data for biomonitoring studies assessing exposure to environmental toxicants.

Optical determination of the exact concentration of any given colloidal suspension of nanoparticles (NP) is complicated by the relative scarcity of NP-specific extinction coefficients and the rigor and expense of determining these constants experimentally. The discrete dipole approximation (DDA) theoretical technique allows for facile determination of NP energetic properties, therefore relating the extinction intensity provided by DDA to the extinction coefficient needed to determine the concentration of NP solutions would be extremely beneficial. We experimentally determine the extinction coefficients for a range of gold nanosphere and gold nanorod sizes, supplement these values with available literature values, and then use the Discrete Dipole Approximation theoretical technique to model the optical properties of each of these nanoparticles. We then develop a relationship between the theoretical extinction intensity provided by DDA and the extinction coefficients obtained experimentally. These relationships will allow future users to accurately predict extinction coefficients that are specific to the exact dimensions of the gold nanosphere or gold nanorod in question. Use of these relationships will greatly reduce both the time-scale and the cost of determining nanoparticle extinction coefficients by circumventing the need for costly, time-consuming analytical experiments.

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We have developed a rapid, high-throughput, accurate, multiresidue method for the analysis of selected organophosphorus and pyrethroid pesticides in a variety of food samples suitable for use in public health and epidemiologic investigations of high-use pesticides using modifications of existing methods. The procedure involves a pesticide extraction from the food sample with acetonitrile followed by a salting-out with NaCl and cleanup of the extract with a multilayer solid-phase extraction cartridge composed of a Supelclean ENVI-CARB-II top layer and a primary-secondary amine bottom layer separated by a polyethylene frit. To evaluate the method, we performed fortification studies at 50, 100, and 200 ng/g for 3 organophosphorus and 4 pyrethroid pesticides in 16 different foods. Instrumental analysis was carried out by capillary gas chromatography with electron-capture detection (GC-ECD). Confirmatory analysis was performed by GC coupled with mass spectrometry (MS) in the selected-ion monitoring (SIM) mode. Average recoveries for each fortification level ranged from 49 to 146% with 80% of recoveries between 80 and 120%.