Laboratory control sample duplicate

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. 

Laboratory control sample I laboratory control sample duplicate... 

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... 

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.)... 

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. 

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. 

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

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.)... 

It is important to point out that the quality of analytical results is not immediate it can only be achieved if an extensive set of measures are adopted and complied with. Therefore, in parallel to the development of the QA concept, QC systems were introduced as an important tool supporting the QA of chemical measurements. The QC process of examination of laboratory performance in time should always follow QA. QC thus comprises a set of operational techniques and activities used to check whether the requirements for quality are fulfilled. In practice, QC in an analytical chemistry laboratory implies operations carried out daily during the collection, preparation, and analysis of samples, which are designed to ensure that the laboratory can provide accurate and precise results. QC procedures are intended to ensure the quality of results for specific samples or batches of samples and include the analysis of reference materials (RMs), blind samples, blanks, spiked samples, duplicate, and other control samples.2... 

Examples of quality assurance protocols that are considered standard practice in any data collection scheme include the use of both internal control samples (e.g. use of field blanks and spikes6) and external quality assurance samples (e.g. duplicate samples of known concentrations sent to different laboratories) to determine the extent of intra- and interlaboratory variation. Ensuring that the data have not been compromised or corrupted may also require setting up accessible data archives of original paper or electronic records so that the accuracy of summaries of the data published in documents and articles can be verified. 

These blind control samples are in addition to any primary reference materials (PRM) that the laboratory may also analyse. For the G-BASE project, the BGS laboratories usually insert a PRM at the beginning and end of each batch of 500 samples. As G-BASE generally collects and analyses 2000—3000 samples each field campaign 8% of the samples is more than adequate to carry out quality control procedures. However, if sample numbers are <500, then it is recommended that the number of duplicates and replicates per hundred samples should be doubled. 

In laboratory studies of analytical variation, it is estimates of imprecision that are obtained. The more observations, the more certain are the estimates. Commonly the number 20 is given as a reasonable number of observations (e.g., suggested in the NCCLS guideline on the topic) To estimate both the within-run imprecision and the total imprecision, a common approach is to measure duplicate control samples in a series of runs. For example, one may measure a control in duplicate for more than 20 runs, in which case 20 observations are present with respect to both components. One may here notice that the dispersion of the means (x, ) of the duplicates is given as ... 

In precision charts (the range chart or R-chart), the data from duplicates are plotted with the vertical scale (ordinate) in units such as percent, and the horizontal scale (abscissa) in units of batch number or time. Usually the mean of the duplicates is reported and the difference between the duplicates, or range, is examined for acceptability. The mean and standard deviation are calculated from the data. It is common practice in analytical laboratories to run duplicate analyses at frequent intervals as a means of monitoring the precision of analyses and detecting out-of-control situations. This is often done for analyses for which there are no suitable control samples or reference materials available. 

Apart from these samples, some other quality control samples such as duplicate samples and equipment field blanks are used by different laboratories. Duplicate samples are taken from the same collection site to determine the variability of results for the same sample after the AMS analysis. Generally, one duplicate sample should be collected for every 20 samples. Equipment blanks are collected using laboratory-provided water, which has been run over the decontaminated soil sampling equipment. These samples are used to determine the efficiency of cleaning procedures for soil sampling equipment. 

Control limits for a properly working instrument Control limits for a properly standardized instrument Control limits for a correct set of test samples Control limits for duplicate reference values from another laboratory Control limits for agreement between NIRS analysis values and reference method values... 

The most useful methods for quality assessment are those that are coordinated by the laboratory and that provide the analyst with immediate feedback about the system s state of statistical control. Internal methods of quality assessment included in this section are the analysis of duplicate samples, the analysis of blanks, the analysis of standard samples, and spike recoveries. 

In a performance-based approach to quality assurance, a laboratory is free to use its experience to determine the best way to gather and monitor quality assessment data. The quality assessment methods remain the same (duplicate samples, blanks, standards, and spike recoveries) since they provide the necessary information about precision and bias. What the laboratory can control, however, is the frequency with which quality assessment samples are analyzed, and the conditions indicating when an analytical system is no longer in a state of statistical control. Furthermore, a performance-based approach to quality assessment allows a laboratory to determine if an analytical system is in danger of drifting out of statistical control. Corrective measures are then taken before further problems develop. 

The Production Department was not amused, because lower values had been expected. Quality Control was blamed for using an insensitive, unse-lective, and imprecise test, and thereby unnecessarily frightening top management. This outcome had been anticipated, and a better method, namely polarography, was already being set up. The same samples were run, this time in duplicate, with much the same results. A relative confidence interval of 25% was assumed. Because of increased specificity, there were now less doubts as to the amounts of this particular heavy metal that were actually present. To rule out artifacts, the four samples were sent to outside laboratories to do repeat tests with different methods X-ray fluorescence (XRFi °) and inductively coupled plasma spectrometry (ICP). The confidence limits were determined to be 10% resp. 3%. Figure 4.23 summarizes the results. Because each method has its own specificity pattern, and is subject to intrinsic artifacts, a direct statistical comparison cannot be performed without first correcting the apparent concentrations in order to obtain presumably true... 

The laboratories have a quality manager and quality section. The quahty section prepares all of the analytical quality control (AQC) standards for the laboratories, including spiked and duplicate samples. The quality section is a separate laboratory with a separate supply of deionized water, glassware, balances and chemicals. The latter, wherever possible, are purchased from a different source to those for the analytical sections. These actions ensure a more independent approach to quality control. 

For most of the laboratories, additional quality control (QC) samples were inserted within each batch of samples sent. These included sample site duplicates, sample splits for analytical duplicates, a suite of USGS-prepared standard reference materials (SRMs), and... 

While these are two separate and distinct activities, each must complement the other to ensure a quality program. Day to day quality control in the laboratory is the obligation of the chemist. The chemist develops the methods, calibrates the instruments, and with management approval develops the standard operating procedures for the laboratory. Quality control is running duplicate samples, reagent blanks, fortification samples, linearity checks and confirmatory analyses. 

A preparation batch is a group of up to 20 field samples, prepared together for the same analysis using the same lots of reagents and associated with common QC samples. In addition to field samples, a preparation batch must, at a minimum, include a method (extraction or digestion) blank, an LCS, and an LCSD. Other laboratory QC checks may be part of the preparation batch, such as an MS/MSD pair or a laboratory duplicate. If laboratory QC checks in a preparation batch meet the laboratory acceptance criteria, the batch is considered be in a state of control and every sample in it is acceptable, provided that individual QC checks are also acceptable. If the method blank and the samples in a preparation batch show contamination that makes sample results inconclusive or if the LCS and LCSD recoveries are not acceptable, the whole batch may be prepared again. 

Quality control procedures are generally established to provide checks on the data that have been collected to evaluate whether in fact the quality assurance procedures were followed and whether the data meet agreed-upon norms. Otherwise, it is difficult for the user to judge the integrity of a data set per se, because there may be few ways to tell that procedures were not followed or values properly recorded. Quality control measures can be linked to the quality assurance procedures. In the example given above for use of field blanks, spikes and duplicate samples, laboratories must provide evidence that their analysis of these samples meets acceptable statistical guidelines for accuracy and precision. Quality control can also simply involve careful analysis of a data set to determine whether it is internally consistent. 

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