Reference Material / Samples - A material containing known quantities of target analytes in solution or in a homogeneous matrix. It is used to document the bias of the analytical process.
Stock Solution - A solution containing an analyte that is prepared using a reference material traceable to EPA, NIST, or a source that will attest to the purity and authenticity of the reference material. A stock solution is diluted to make calibration standards or working standards.
Working Standards - Dilutions of stock standard solutions are prepared for daily use in the testing laboratory. “Working standards” are used to prepare laboratory and matrix spikes and may be prepared at several different dilutions from a common stock standard. Working standards are diluted with solutions that ensure the stability of the target analyte.
Spikes – A spike sample is a “real” sample that has a known amount of analyte added to it. The difference between the sample and the spiked sample is determined and the percentage (%) recovery is calculated. Spikes help to determine if interferences are present. Generally, 85% to 115% recovery is acceptable.
Known / Check Sample – This is a sample that has a known amount of analyte in it. The sample can be made in-house or it can be from an outside source. If it is made in-house, it should be made from a different source of chemicals than what the test standards are made from. The value of the known sample should fall within the result range of the other samples. Knowns help determine the accuracy of an analysis.
Blind / Double Blind Samples - A blind sample is known to the technical staff as a check sample, but the composition is unknown. A double-blind sample is completely unknown to the technical staff and is used to eliminate any possible bias in the results, from knowing the location or composition of the check sample. Blind and double-blind samples are usually reserved for formal quality control appraisals.
Laboratory Control Sample / Blank Spike - A laboratory control sample free of the target analytes or interference, that is spiked with verified amounts of analytes — or a material containing known and verified amounts of analytes. The LCS/blank spike sample is processed through the entire analytical method including any extraction, digestion or any other preparation procedure.
The primary purpose of the laboratory control sample is to demonstrate that the laboratory can perform the overall analytical approach in a matrix free of interferences (e.g., in reagent water, clean sand, or another suitable reference matrix) and its analytical system is in control.
It is either used to establish intra-laboratory or analyst-specific precision and bias (or accuracy), or to assess the performance of a portion of the measurement system. Results are expressed as a percentage recovery.
Laboratory Control Sample Duplicate - A laboratory control sample duplicate (LCSD) is an additional replicate of the LCS. LCS and LCSD results are generated to monitor the accuracy and precision of the analytical process on a purified material Following LCS and LCSD recovery results, the Relative Percent Difference (RPD) is reported for each analyte. In addition to RPD, which is a measurement of reproducibility, we provide control limits for LCS-LCSD recovery ranges for each analyte to evaluate our performance.
Matrix Spike- A matrix spike (MS) is a sample prepared by adding a known amount of the target analyte to an environmental sample in order to increase the concentration of the target analyte. The MS is used to determine the effect of the matrix on a method's recovery efficiency and is a measure of accuracy. Poor spike recoveries for MS-MSD samples could mean your sample matrix is causing matrix interference issues.
- Matrix effects are the manifestations of non-target analytes or physical and chemical characteristics of a sample that impair quantification of the target analyte (i.e., prevent the compound or element of interest from being effectively quantified by the test method). Matrix effects typically adversely impact the reliability of the quantification. A matrix effect can cause either high or low bias.
Matrix Spike Duplicate - A matrix spike duplicate (MSD) consists of an aliquot of the same environmental sample to which known quantities of the target analytes are added in the laboratory. Both the MS and MSD samples are analyzed exactly like an environmental sample within the lab batch. The purpose of analyzing the MS and MSD samples is to determine whether the sample matrix contributes bias to the analytical results, and to measure precision of the duplicate analysis.
Surrogate Spike - Surrogates spikes are typically used to measure the performance of organic testing by Gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), and high-performance liquid chromatography (HPLC). Surrogate spikes of known concentrations are added to primary samples, which are then analyzed and reported. The surrogate recoveries assess sample matrix interference effects and laboratory performance. The analytes selected as surrogates mimic the behavior of the target analytes throughout sample preparation and analysis but are not normally found in the environment.
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