Laboratory control analyses

The control chart is set up to answer the question of whether the data are in statistical control, that is, whether the data may be retarded as random samples from a single population of data. Because of this feature of testing for randomness, the control chart may be useful in searching out systematic sources of error in laboratory research data as well as in evaluating plant-production or control-analysis data. ... 

Earlier in this chapter we considered the nature of chemical control (Section 5.1), the character and degree of automation (Section 5.2) with the choice between discontinuous and continuous analysis, the role of electroanalysis in automated chemical control (Section 5.3) and automated electroanalysis in laboratory control (Section 5.4). 

If the samples are to be brought back to a shore laboratory for analysis, contamination during analysis is more easily controlled. The analyst on shore must have confidence in the people taking the samples with the pressure on berth space and wire time on board ship, too often the samples are taken on a while you re out there, take some for me basis. Again, ideally, the analyst should at least oversee every part of the process, from the cleaning of the sampler to the final calculation of the amounts present. His confidence in the accuracy of the final calculation must decrease as he departs from the ideal arrangement. 

Laboratory Controls General Controls Testing of Intermediates and APIs Validation of Analytical Procedures Certificate of Analysis Stability Monitoring of APIs Expiry and Retest Dating Reserve/Retention Samples Validation... 

In our laboratory, control values that fall within 2 standard deviations of the mean are considered acceptable and require no further action. Any control values that are either greater than 2 standard deviations or trends require review by a laboratory director. The laboratory director decides whether the analysis of the complete batch or of specific samples needs to be repeated and initiates troubleshooting. 

In laboratory chemical analysis, where only minute samples may be available, only milligrams of material oi less are requited lor some forms of chromatography. Chromatography is widely used in pollution control technology. 

Laboratory controls (testing of intermediates and APIs, validation of analytical procedures, certificates of analysis, stability monitoring of APIs expiry dating, retention 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. 

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.)... 

Another tool that enables us to evaluate analytical accuracy of organic analyses is surrogate standards. These are compounds that do not naturally occur in the environment and that are similar in chemical nature and behavior to target analytes. In organic compound analysis, known amounts of surrogate standards are added to each sample prior to extraction. The comparison of surrogate standard recoveries to laboratory control limits permits the laboratory to monitor the efficacy of extraction and to measure the accuracy of analysis for each individual sample. 

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 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 ... 

Similar to LCS recoveries, surrogate standard recoveries should be monitored by the laboratory and plotted as control charts. The EPA recommends the use of in-house laboratory control limits for surrogate standards recoveries for all organic compound analyses (EPA, 1996a). The exception is the CLP SOW, which specifies these limits for soil and water analysis. Unless affected by matrix interferences, surrogate standard recoveries normally have relatively narrow control limits, 65-135 percent for most organic compound analysis. (Many laboratories, however, default to arbitrary limits of 50-150 percent for GC analyses, instead of using statistical control limits.)... 

GC/MS methods are the only published methods that include the surrogate standard recovery limit guidance. Similar to LCS, acceptance criteria for surrogate standard recoveries of all other organic analysis methods are the laboratory control limits. The limits for internal standard recovery in GC/MS analysis are specified by the method and cannot be changed by the laboratory. Acceptance criteria for matrix interference detection techniques in trace element analyses, discussed in Chapter 4.4.4.5, are also specified in the analytical methods. 

Documented testing procedures make the work in the laboratory controlled chemicals, reagents, samples, subsamples, analyses, and analysis results are traceable (chain-of-custody)... 

At least 10 % of the samples should be quality control samples. Blank sampling cartridges should be taken to the field and returned to the laboratory for analysis however, they should not be exposed to the air. Spiked sampling media may also be similarly transported as field controls. 

Once sampling is completed, sampling media should be placed immediately in appropriate clean, sealed containers and placed on ice or dry ice for return or shipment to the laboratory. The sealed containers should be placed in a freezer maintained at -20 °C or lower until extracted. Media should not be stored for more than about two weeks. Frozen extracts may be safely stored for 90d or more. At least 10% of the samples shonld be quality control samples. Blank media should be taken to the field, briefly removed from the containers to air, and then retnmed to the laboratory for analysis. 

Polymerization process control can benefit significantly from using online state estimation techniques. In general, online control of polymer properties such as molecular weight, MWD, copolymer composition, MI, density, etc. is difficult, mainly because of the lack of adequate online or in-process sensors. Therefore, many of these polymer property parameters are controlled indirectly by controlling first-level process variables such as temperature, pressure, and the flow rates of various reactants, solvents, and catalysts. When some deviations in polymer properties are detected through laboratory sample analysis, certain reactor variables need to be adjusted. Extensive plant experience might be required to make such process adjustments, or model-based online state estimator can be used. 

Properties to be controlled may not be measurable online fast enough to allow for a timely action by the manipulated variable. Such properties may have to be inferred from other measured properties. A column product purity or composition, for example, could be inferred from measured column temperatures on a number of trays. The required property is related to the measurements by inferential property correlations whose parameters must be determined. In the composition-temperature example, the correlation parameters are evaluated from measured temperatures and laboratory composition analysis, and are updated every time laboratory analyses become available. 

ACassurance is the quality assurance expert system that will be used by the MANAGER and the ANALYST to assist in the execution of a laboratory quality assurance program. Incorporated into this expert system are modules that will be used to provide instruction and advice to the laboratory personnel in carrying out their tasks and completing the analysis procedures. ACanalyst, the quality control and process control expert system, will comprise five modules that will be used in methods selection, process control, analysis, fault diagnosis, and quality control. 

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. 

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