Matrix spike duplicates

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. 

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 duplicate (one per 20 samples of each matrix type)... 

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... 

MS/MSD denotes matrix spike/matrix spike duplicate. 

Similar to an LCS, but in this case the actual sample analyzed is being spiked with the analytes of interest. Data will give an indication of possible matrix interferences, and relative percent differences (RPD) can be calculated (30%—50% depending on matrix and analyte). Matrix spikes and matrix spike duplicates (MS/MSD) should be run with each new matrix. 

Definitive quantitation by reanalyzing 10% samples determination of precision, accuracy, and confidence limits by analyzing 10% or 2 pairs of matrix spike duplicates (whichever is greater). 

Constraint-based Representation Scheme. The primary feature of the chemists ability to specify QC criteria based on the QA/QC Objective and other inputs is that the QC criteria are specified as a set of general constraints and limits which the data must adhere to. For example, for a PCB site with a QA/QC Objective level of QA2, the experts could specify constraints for the data such as "the matrix spike duplicate recoveries should be between 801 to 120Z", and that "the PCB detection level must be at least 1.5 ppm." Therefore, a constraint-based representation presents a natural mechanism to emulate the thought process of the chemists in developing QC criteria. 

Preparing the running QC surrogates, matrix spikes, and, in some cases, matrix spike duplicates per batch of samples. A batch is defined in EPA methods to be approximately 20 samples. These reference standard spikes serve to assess extraction efficiency where applicable. Matrix spikes and duplicates are often required in EPA methods. 

Matrix Spike Standard consists of a representative set of the targeted analytes whose percent recoveries are evaluated in the sample matrix. For example, if THMs were the targeted analytes, this reference standard would consist of one or more THMs such as chloroform, bromodichloromethane, and chlorodibromomethane. These compounds would be dissolved in a matrix-compatible solvent such as MeOH. A precise aliquot of this solution is added to a sample so that the effect of the sample matrix on the percent recovery can be evaluated. A second standard called a matrix spike duplicate is often required in EPA methods and is used to assess matrix recovery precision. 

For every batch of samples that have been digested, one blank, one matrix spike, and one matrix spike duplicate should also be prepared. For the matrix spike and matrix duplicate, designate one sample from the batch for these. 

Prepare a matrix spike and a matrix spike duplicate. The amount of spike should double the concentration found in the original sample. The spike recovery must be between 85% and 115% in order to verify the method. 

Include all calibration data, ICVs, and sample unknowns for both instrumental methods. Perform a statistical evaluation in a manner that is similar to previous experiments. Use EXCEL or LSQUARES (refer to Appendix C) or other computer programs to conduct a least squares regression analysis of the calibration data. Calculate the accuracy (expressed as a percent relative error for the ICV) and the precision (relative standard deviation for the ICV) from both instrumental methods. Calculate the percent recovery for the matrix spike and matrix spike duplicate. Report on the concentration of Cr in the unknown soil samples. Be aware of all dflution factors and concentrations as you perform calculations ... 

Spike approximately 200 mL of high-purity laboratory water that has been acidified with 1 1 HCl with approximately 2 mg of dode-cane note that most of the dodecane will float on top. This sample is called a matrix spike using terms flrst developed at the EPA. Spike a second 200-mL portion of acidified water with approximately 2 mg dodecane. This sample is called a matrix spike duplicate. Leave a third 200-mL portion of water unspiked and acidify. This sample is called a method blank. 

Pass the method blank, matrix spike, and matrix spike duplicate samples through the cartridges under vacuum. 

Matrix spike duplicate A second aliquot of the same matrix as the matrix spike that is spiked to determine the precision of the method. 

Compounds that contain halogens and are aromatic display response on both (e.g., chlorobenzene) detectors. Compounds that have a double bond, such as vinyl chloride, are ionized on the PID (11.7 keV), but show a much weaker response than on the Hall detector. Common quality control samples such as a method blank, a matrix spike and a matrix spike duplicate, and a laboratory control sample are required when analyzing samples by this method. A continuing calibration or check standard is injected every 12 h to verify the calibration. 

MSD Matrix spike duplicate mass-selective detector... 

Samples, which must contain a laboratory control sample (LCS) plus one matrix spike (MS) and matrix spike duplicate (MSD)... 

Matrix Spike Duplicate (MSD) Sample (Tier II only)—Every batch or 20 samples, whichever is more frequent, precision data is generated using a matrix spike duplicate. Acceptance criteria is 20 % RPD (relative percent difference) for the duplicate analyses. 

Matrix Spike and Matrix Spike Duplicate Samples— Add 1.0 mL of spiking solution to the sample just after the addition of the surrogate and prior to the addition of the acetone-hexane solvent. 

A Typical Analysis Sequence—A typical analysis sequence includes (a) reagent blank (optional), (b) CCS (1016/ 1260 mid standard), (c) method blank, (d) Samples 1 to 20, (e) matrix spike sample, and (f) matrix spike duplicate. 

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