Matrix spiked

BRM3 identified the need for producing different levels of an analyte in a given matrix (spiked standards) to address matrix related measurement problems in foods. 

Soxhlet, sonication, supercritical fluid, subcritical or accelerated solvent, and purge-and-trap extraction have been introduced into a variety of methods for the extraction of contaminated soil. Headspace is recommended as a screening method. Shaking/vortexing is adequate for the extraction of petroleum hydrocarbons in most environmental samples. For these extraction methods, the ability to extract petroleum hydrocarbons from soil and water samples depends on the solvent and the sample matrix. Surrogates (compounds of known identity and quantity) are frequently added to monitor extraction efficiency. Environmental laboratories also generally perform matrix spikes (addition of target analytes) to determine if the soil or water matrix retains analytes. 

Quality Assurance/Quality Control. QA/QC measures included field blanks, solvent blanks, method blanks, matrix spikes, and surrogates. Percent recovery was determined using three surrogate compounds (nitrobenzene-d5, 2-fluorobiphenyl, d-terphenyl-diQ and matrix spikes (naphthalene, pyrene, benzo[ghi]perylene) the recoveries ranged from 80 to 102%. Separate calibration models were built for each of the 16 PAHs using internal standards (naphthalene-dg, phenanthrene-dio, perylene-di2). Validation was performed using a contaminated river sediment (SRM 1944) obtained from NIST (Gaithersburg, MD) accuracy was <20% for each of the 16 analytes. 

Analysis of a matrix-matched reference material, or typical matrix spiked with reference material, or typical test material with quantity value with known measurement uncertainty established by another method... 

The matrix spike recovery may be defined in two different ways (1) one method determines the percent recovery only for the standard added to the spiked sample, as followed by U.S. EPA, and (2) the other method calculates the percent recovery for the combined unknown sample and standard. Spike recovery calculated by both these methods would give different values. 

There are two types of control charts accuracy chart and precision control chart. Accuracy control charts are prepared from the percent spike recoveries data obtained from multiple routine analysis. Precision control charts may be prepared from the relative percent difference (RPD) of analyte concentrations in the samples and their duplicate analytical data. Alternatively, RPDs are calculated for percent recoveries of the analytes in the matrix spike and matrix spike duplicate in each batch and twenty (or any reasonable number of data points) are plotted against the frequency or number of analysis. If the samples are clean and the analytes are not found, the aliquots of samples must be spiked with the standard solutions of the analytes and the RPD should be determined for the matrix spike recoveries. Ongoing data quality thus can be checked against the background information of the control chart. Sudden onset of any major problem in the analysis can readily be determined from the substantial deviation of the data from the average. 

The precision and accuracy data are not available for all the urea pesticides listed in the Table 2.19.3. However, a matrix spike recovery between 70 and 130% and a RSD below 30% should be achieved for aqueous samples. Samples should be spiked with one or more surrogates. Compounds recommended as surrogates are benzidine-d8, 3,3-dichlorobenzidine-d6, and caffeine-15N2. Surrogate concentrations in samples or blank should be 50 to 100 pg/L. 

To establish reasonable acceptance criteria for accuracy during planning, we should obtain statistical laboratory control limits from the laboratory that will perform analysis for the project samples. We should also be aware of matrix interferences in environmental samples that may reduce the accuracy of analysis. As part of QC procedures, to estimate the effects of matrix interference on accuracy, laboratories perform the accuracy determinations on environmental samples, known as matrix spike (MS) and matrix spike duplicate (MSD). These fortified samples enable the laboratory to detect the presence of interferences in the analyzed matrices and to estimate their effect on the accuracy of sample analysis. (In the absence of matrix interferences, an additional benefit from MS/MSD analysis is an extra measure of analytical precision calculated as the RPD between the two recoveries.)... 

Matrix spike (one per 20 samples of each matrix type)... 

The laboratory will introduce the required internal and surrogate standards through the septum with a small gauge syringe and then place the vials on the autosampler for analysis. Matrix spikes will be prepared in a similar manner. 

Laboratory QC data are classified as batch QC data and individual sample QC data. For all types of analysis, batch QC data originate from laboratory blanks, laboratory control samples, matrix spikes, and laboratory duplicates. Individual sample QC data in organic compound analysis are obtained from surrogate and internal standard recoveries. Matrix interference detection techniques (serial dilution tests, postdigestion spike additions, and MSA tests) are the source for individual sample QC checks in trace element analysis. (Chapter 4.4.4.5 addresses the trace element matrix interference detection techniques and the associated acceptance criteria.)... 

Determines the effects of matrix interferences on Depends on the project DQOs analytical accuracy of a sample together with matrix spike determines analytical precision... 

Matrix spikes are field samples spiked with known concentrations of target analytes and carried throughout the entire preparation and analysis. The MS/MSD spiking solutions are usually the same as used for the preparation of LCS/LCSD. 

Matrix spikes enable the data user to evaluate the extent of matrix interference effects on the recovery of target analytes and to draw conclusions on the accuracy of environmental sample data. Soils of certain lithological composition have a tendency to retain chemicals, a property that is often demonstrated by MS/MSD recovery data. Such information may be particularly important for the projects where sample concentrations are compared to action levels. Low recoveries from certain soil types may render results inconclusive and warrant a different sampling or analysis approach. That is why matrix spikes provide meaningful data only if performed on the project samples. 

We should collect additional sample volumes and instruct the laboratory to use them for at least one MS analysis for every 20 field samples, especially for soil from uncharacterized sites. Otherwise, the laboratory may furnish the data on a randomly selected batch matrix spike prepared on a sample collected for a different project. Obviously, this batch matrix spike will not provide any useful information on matrix effects at another site. 

Matrix spike/matrix spike duplicate Organic and inorganic compounds recovery as determined by laboratory control charts precision of 30% for water and 50% for soil is typical for environmental samples ICP-AES 75 to 125% recovery 20% precision AA 80 to 120% recovery 20% precision... 

If project-specific matrix spike data are available, the chemist evaluates them to establish the effects of matrix interferences on the accuracy and precision of project sample analysis. Similar to LCS/LCSD recoveries, MS/MSD recoveries are monitored at the laboratory as control charts these recoveries, however, are not used as acceptance criteria for qualifying the data for the whole batch. The RPD between the MS and MSD results is an additional measure of analytical precision that may be used when the LCS/LCSD precision has failed or is not available. 

MS/MSD denotes matrix spike/matrix spike duplicate. 

Maximum Contaminant Level method detection limit matrix spike... 

Matrix effects play an important role in the accuracy and precision of a measurement. Sample preparation steps are often sensitive to the matrix. Matrix spikes are used to determine their effect on sample preparation and analysis. Matrix spiking is done by adding a known quantity of a component that is similar to the analyte but not present in the sample originally. The sample is then analyzed for the presence of the spiked material to evaluate the matrix effects. It is important to be certain that the extraction recovers most of the analytes, and spike recovery is usually required to be at least 70%. The matrix spike can be used to accept or reject a method. 

For example, in the analysis of chlorophenol in soil by accelerated solvent extraction followed by GC-MS, deuterated benzene may be used as the matrix spike. The deuterated compound will not be present in the original sample and can easily be identified by GC-MS. At the same time, it has chemical and physical properties that closely match those of the analyte of interest. 

Often, the matrix spike cannot be carried out at the same time as the analysis. The spiking is carried out separately on either the same matrix or on one that resembles the samples. In the example above, clean soil can be spiked with regular chlorophenol and then the recovery is measured. However, one should be careful in choosing the matrix to be spiked. For instance, it is easy to extract different analytes from sand, but not so if the analytes have been sitting in clay soil for many years. The organics in the soil may provide additional binding for the analytes. Consequently, a matrix spike may be extracted more easily than the analytes in real-world samples. The extraction spike may produce quantitative recovery, whereas the extraction efficiency for real samples may be significantly lower. This is especially true for matrix-sensitive techniques, such as supercritical extraction. 

Determination of the optimum time for which the SPME sorbent will be in direct contact with the sample is made by constructing an extraction-time profile of each analyte(s) of interest. The sorption and desorption times are greater for semi volatile compounds than for volatile compounds. To prepare the extraction-time profile, samples composed of a pure matrix spiked with the analyte(s) of interest are extracted for progressively longer times. Constant temperature and sample convection must be controlled. Stirring the... 

Field matrix spikes can be carried out by adding a known amount of a spike solution with a known concentration to a rephcate sample. Spike recoveries can be used to identify which compounds are consistently under or over reported or which compounds are variable in their recoveries. This is particularly relevant to the analysis of organic contaminants. 

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