Laboratory duplicates

Random laboratory duplicates should be prepared and analyzed ( 5%). 

Mori T. and Green D. H. (1978). Laboratory duplication of phase equilibria observed in natural garnet Iherzolites. J. Geol, 86 83-97. 

A QC assessment was done for all samples. De-ionized water field blanks were collected on seven different days to evaluate process contamination. Site duplicates were taken at eight sites to evaluate repeatability and site variation. Instrumental precision was constrained by analysis of laboratory duplicate solutions, and is typically less than 5%. Finally, standard reference material (SRM) water standards were analyzed with sample batches, to assess instrumental accuracy. 

Analysis of laboratory duplicates to measure analytical 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.)... 

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. 

Laboratory duplicates are field samples that are prepared and analyzed twice. 

Laboratories subsample two aliquots of a field sample from the same container and treat them as two separate samples. Typically, laboratory duplicates are prepared and analyzed with every 10 samples in trace element and inorganic analyses. This allows laboratories to calculate the RPD between the two results as a measure of analytical precision. Laboratory duplicates are rarely used in organic compound analysis. 

Depending on the analytical method and laboratory procedure, not all of these QC checks may be available in each data package. However, every preparation batch must contain at least one LCS as a measure of analytical accuracy and an LCSD or any other pair of laboratory QC check samples (a sample and a laboratory duplicate or an MS/MSD pair) as a measure of analytical precision. Sample data for which accuracy and precision cannot be determined are not data of known quality. 

Laboratory duplicate Inorganic compounds only 20% precision... 

To test the quality of the work of a commercial laboratory, duplicate analyses of a purified benzoic acid (68.8% C, 4.953% H) sample were requested. It is assumed that the relative standard deviation of the method is cr = 4 ppt for carbon and 6 ppt for hydrogen. The means of the reported results are 68.5% C and 4.882% H. At the 95% confidence level, is there any indication of systematic error in either analysis ... 

On December 31, 1954, Dr. H. Hugh Woodbury of the General Electric Laboratory duplicated my December 16 run and thus, to our knowledge, became the first man to duplicate the diamond synthesis claim of another. ... 

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. 

What is fascinating about Kelvin s doubts - and demonstrates how difficult it was for the conservation of heat doctrine to be abandoned - is that by the time he published this 1849 paper, he had in his own laboratory duplicated Joule s findings. In a letter of his, dated December 5, 1847, he writes ... 

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