Sample matrices

Analyte(s) Sample matrix Sample preparation" Eirst EC mode Subsequent EC mode(s) Detection" Reference... 

In the push out test [93], the fiber is pushed into the matrix rather than being pulled out. The test allows the measurement of two quantities, Fdcb (the force at which debonding occurs) and F/., (the force needed to push the fiber through the matrix sample if it is thin enough). The bond shear strength Tdeb is calculated using the shear lag theory ... 

Morphology of the anionically synthesized triblock copolymers of polyfp-methyl-styrene) and PDMS and their derivatives obtained by the selective chlorination of the hard segments were investigated by TEM 146). Samples with low PDMS content (12%) showed spherical domains of PDMS in a poly(p-methylstyrene) matrix. Samples with nearly equimolar composition showed a continuous lamellar morphology. In both cases the domain structure was very fine, indicating sharp interfaces. Domain sizes were estimated to be of the order of 50-300 A. 

Table 5.15 Relative signal responses from various injection volumes for the LC-MS-MS analysis of a wheat forage matrix sample. Reprinted from J. Chromatogr., A, 907, Choi, B. K., Hercules, D. M. and Gusev, A. L, Effect of liquid chromatography separation of complex matrices on liquid chromatography-tandem mass spectrometry signal suppression , 337-342, Copyright (2001), with permission from Elsevier Science...

Table 5.16 LC-MS-MS signal responses" obtained from wheat forage matrix samples using various mobile-phase additives (injection volumes of 50 p,l). From Choi, B. K., Hercules, D. M. and Gusev, A. I., LC-MS/MS signal suppression effects in the analysis of pesticides in complex environmental matrices , Fresenius J. Anal. Chem., 369, 370-377, Table 2, 2001. Springer-Verlag GmbH Co. KG. Reproduced with permission...

Cruz, R. B. and Loon, J. C. van "A Critical Study of the Application of Graphite-Furnace Non-Flame Atomic Absorption Spectrometry to the Determination of Trace Base Metals In Complex Heavy-Matrix Sample Solutions". Anal. Chlm. Acta (1974), 72, 231-243. 

The pure substances are provided with a statement of the purity and serve as authentic reference compounds to prepare calibration solutions for measurement of trace levels of the compound in natural matrix samples. 

Stability Assessment In general there is no formal stability study prior to the certification of a natural matrix S RM. H owever, the stability of the certified analytes is monitored on a regular basis, typically every 1-3 years depending on the analytes, as the SRMs are analyzed as control samples during the analyses of similar matrix samples. A recent study of PAHs in frozen mussel tissue over nearly 10 years found no significant changes in the concentrations of the measured PAHs (Schantz et al. 2000). 

Although accepted by lUPAC and ACS, the k s /m" definition is hard to implement and does not take either variability in method efficiency or matrix effects into consideration. This would be rectifiable if the calibration curves were prepared from control matrix samples fortified at different concentrations (within one order of magnitude of an estimated LOD). 

Analyte(s) Matrix Sample preparation Instrumentation Recovery data summary Ref. 

The injection standards of carfentrazone-ethyl must be in acetonitrile. Other solvents (e.g., ethyl acetate) lead to poor chromatography following injection of matrix samples. This can lead to apparent enhanced recoveries of analyte in the fortified samples. 

Conditioning the GC system with matrix samples before the actual run of the set is recommended to establish stable analytical conditions for the analytes. The GC... 

Optimizing the GC instrument is crucial for the quantitation of sulfentrazone and its metabolites. Before actual analysis, the temperatures, gas flow rates, and the glass insert liner should be optimized. The injection standards must have a low relative standard deviation (<15%) and the calibration standards must have a correlation coefficient of at least 0.99. Before injection of the analysis set, the column should be conditioned with a sample matrix. This can be done by injecting a matrix sample extract several times before the standard, repeating this conditioning until the injection standard gives a reproducible response and provides adequate sensitivity. 

Matrix samples, where appropriate, are processed by grinding with dry-ice either in a food processor or a Hobart-Cutter mixer and stored in zipper-locking storage bags, allowing the dry-ice to sublime. All processed samples are then stored frozen (<0 °C) until used for fortification and analysis. 

All fortified (spiked) matrix samples are prepared in the laboratory at the same concentration. Laboratory spikes are immediately put into cold storage. Trip and fleld spikes are kept cold and sent to the fleld. The trip spikes will accompany sample shipments. The fleld spikes are stored and transported in the same manner as the trip spikes. When practical, air should be pulled through fleld spikes in the same manner as actual fleld samples being taken at the time of the study. 

A reference substance can be either the formulated test substance suspended in water or the technical or analytical grade active ingredient of the test substance dissolved in a solvent. The reference substance is normally used to fortify field matrices to develop information on the field storage stability of the active ingredient. Reference substances should be prepared at the analytical facility where the matrix samples are to be analyzed. Methods to prepare reference substances for field use will be discussed later. 

Field fortification of worker exposure matrix samples (a) Purpose for having field fortification samples... 

Such field-fortified matrix samples are absolutely necessary as a part of any worker exposure or re-entry study in order for the behavior of the active ingredient to be... 

The make-up of a sef of held fortification samples at each fortification event should be considered. Usually, a triplicate set of matrix samples fortified af a low concenfra-tion of fesf active ingredient and a triplicate set of matrix samples fortified at a high... 

Another consideration when planning field fortification levels for the matrices is the lowest level for fortification. The low-level fortification samples should be set high enough above the limit of quantitation (LOQ) of the analyte so as to ensure that inadvertent field contamination does not add to and does not drive up the field recovery of the low-fortification samples. Setting the low field fortification level too low will lead to unacceptably high levels of the analyte in low field spike matrix samples if inadvertent aerial drift or pesticide transport occurs in and around where the field fortification samples are located. Such inadvertent aerial drift or transport is extremely hard to avoid since wind shifts and temperature inversions commonly occur during mixer-loader/re-entry exposure studies. 

The time at which all matrix samples are fortified, the time that the air pumps are turned on and off, and the time that all matrix samples are processed after weathering should be recorded in the raw data. 

Weigh 20 g of homogenized sample into a 300-mL tail-form beaker. Begin recovery samples at this point by fortifying the control tissue matrix samples. Add 120 mL of acetone, and homogenize the mixture for approximately 5 min followed by the addition of 60 mL of laboratory-grade water with another 2 min of homogenization. 

Weigh 5.0 g of frozen homogenized sample into a 120-mL tail-form glass bottle. Begin recovery samples at this point by fortifying the control tissue matrix samples. 

Sample matrix Sample preparation Analytical method Detection limit Accuracy Reference... 

Analytical chemistry is a critical component of worker safety, re-entry, and other related studies intended to assess the risk to humans during and subsequent to pesticide applications. The analytical aspect takes on added significance when such studies are intended for submission to the U.S. Environmental Protection Agency and/or other regulatory authorities and are thus required to be conducted according to the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) Good Laboratory Practice (GLP) Standards, or their equivalent. This presentation will address test, control, and reference substance characterization, use-dilution (tank mix) verification, and specimen (exposure matrix sample) analyses from the perspective of GLP Standards requirements. 

It is largely without debate that the term "reference substance" includes those chemical and biological materials that are used as standards in a study (i.e., those materials used for response comparison purposes, such as analytical reference standards). Normally, one thinks of reference substances as just referring to specimen (sometimes referred to as "matrix samples") analyses, but the characterization of test, control, and reference substances (see... 

---