Laboratory control samples

Each vegefafion, soil or tissue sample was uniquely numbered and stored individually in a plastic Ziploc bag. Samples were frozen until shipped to laboratory facilities. Samples were shipped in coolers with dry-ice and were returned to freezers immediately upon receipt at the analytical laboratories. Control samples were stored separately from treated samples. 

Laboratories establish analytical precision for each method using a laboratory control sample (LCS) and laboratory control sample duplicate (LCSD). These samples are made at the laboratory with interference-free matrices fortified (spiked) with known amounts of target analytes. Interference-free matrices are analyte-free reagent water or laboratory-grade (Ottawa) sand. Precision is then calculated as the RPD between the results of the LCS and LCSD. Analytical precision depends on analytical method and procedure the nature of the analyte and its concentration in the LCS and LCSD and the skill of the chemist performing analysis. The RPD for interference-free laboratory QC samples is typically below 20 percent for soil and water matrices. 

Analytical laboratories establish the accuracy of the performed methods through the preparation and analysis of laboratory control samples, the same samples that are used for the determination of laboratory precision. Based on a statistical evaluation of the recoveries from these interference-free matrices, laboratories derive the recovery acceptance criteria, called laboratory control limits. 

Analysis of surrogate standards and laboratory control samples to measure analytical accuracy... 

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.)... 

Laboratory control sample I laboratory control sample duplicate... 

Laboratory control samples are analyte-free matrices (reagent water or laboratory-grade sand) fortified (spiked) with known concentrations of target analytes and carried throughout the entire preparation and analysis. Laboratories prepare and analyze these batch QC check samples at minimum frequency of one LCS/LCSD pair for every preparation batch of up to 20 field samples. Laboratory control samples serve two purposes ... 

Laboratory control sample/laboratory control sample duplicate Organic and inorganic compounds recovery as determined by laboratory control charts typical precision is 30% ICP-AES 75 to 125% recovery 20% precision AA 80 to 120% recovery 20% precision... 

The laboratories who do CLP analyses for inorganic constituents have to maintain an extensive Quality Assurance program. This includes analysis of duplicates, laboratory blanks, interference checks, and laboratory control samples. However, the prescribed Quality Assurance does not always transfer to the laboratory bench. Also at times, routine analytical procedures will not yield the chemical information that is necessary for aqueous modeling. The following points out when these problems occur and what steps the researcher needs to take to insure data adequate for modeling. 

Preparing and running laboratory blanks, laboratory control samples, and field and trip blanks. These blanks serve to assess whether or not samples may have become contaminated during sampling and sample transport. 

Analytical sample Any solution or media introduced into an instrument on which an analysis is performed, excluding instrument calibration, initial calibration verification, initial calibration blank, continuing calibration blank. The following are all analytical samples undiluted and diluted samples, predigestion spike samples, duplicate samples, serial dilution samples, analytical spike samples, postdigestion spike samples, interference check samples, laboratory control samples, preparation or method blank, and linear range analysis samples. 

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. 

An internal standard calibration with at least five levels is performed over the range of 5 p.g/mL to approximately 120 p,g/mL. Standards are prepared in methylene chloride. Because of the long list of compounds, laboratories often purchase commercially available mixes and dilute these to prepare the calibration standards. Quantification is based on the area of the primary quantitation ion (m/z) for each target compound and the average relative response factor of the calibration standards. The RSD of the relative response factors for each target compound must be less than 20%. A method blank, matrix spikes (MS and MSD), and the laboratory control sample (ECS) must accompany each batch of samples. Target compounds are identified by their retention time and their mass spectmm. Most compounds are reported down to 1 tig/L in water samples and 330 ppb in soil samples. 

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

Reporting iimit (RL) verification standard The minimum concentration that can be reported with a specified degree of confidence. The RL can be no lower than the concentration of the lowest initial calibration standard. Laboratory control sample (LCS) A multielement standard of known concentrations that is carried through the entire sample preparation and analysis procedure. This solution is used to verify method performance in an ideal sample matrix. 

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