Samples check

A final component of a quality control program is the certification of an analyst s competence to perform the analysis for which he or she is responsible. Before an analyst is allowed to perform a new analytical method, he or she may be required to successfully analyze an independent check sample with acceptable accuracy and precision. The check sample should be similar in composition to samples that the analyst will routinely encounter, with a concentration that is 5 to 50 times that of the method s detection limit. 

BRM-2 highlighted the distinction between primary (certified) and secondary (e.g. check samples for proficiency testing) RMs. 

Check sample, n - a single pure compound, or a known, reproducible mixture of compounds whose spectrum is constant over time such that it can be used as a quality or validation or verification sample during an instrument performance or function test. 

QC check samples are being tested by the defined procedures, at the required frequency and there is an up-to-date record of the results and actions taken where results have exceeded action limits. 

Step 5 Off-line method or analyzer development and validation This step is simply standard analytical chemistry method development. For an analyzer that is to be used off-line, the method development work is generally done in an R D or analytical lab and then the analyzer is moved to where it will be used (QA/ QC lab, at-line manufacturing lab, etc.). For an analyzer that is to be used on-line, it may be possible to calibrate the analyzer off-line in a lab, or in situ in a lab reactor or a semiworks unit, and then move the analyzer to its on-line process location. Often, however, the on-line analyzer will need to be calibrated (or recalibrated) once it is in place (see Step 7). Off-line method development and validation generally includes method development and optimization, identification of appropriate check samples, method validation, and written documentation. Again, the form of the documentation (often called the method or the procedure ) is company-specific, but it typically includes principles behind the method, equipment needed, safety precautions, procedure steps, and validation results (method accuracy, precision, etc.). It is also useful to document here which approaches did not work, for the benefit of future workers. 

Samples were also taken from the geoduck beds for PSP analysis ( 3). Spot check samples were taken, with results indicating that high levels existed only in the viscera of the clam. Of all samples taken, only one sample of body meat taken near Gravina Island (Ketchikan, 1980) revealed PSP levels above the quarantine limit of 80 mg/100 g for human consumption. 

Residue-testing laboratories might also need to review their sample preparation processes and consider modifying or eliminating tissue homogenization prior to residue extraction. Suppliers of proficiency-testing services should also question whether certain drugs are appropriate to include in such studies. For example, liver spiked with sulfaquinoxaline, sulfadiazine, or sulfamerazine is not suitable for preparation of spiked interlaboratory check samples or reference materials. 

This example illustrates that there is no guarantee that results are reliable, even if they are obtained by "accredited " laboratories using accepted procedures. A good way to assess the reliability of a lab working for you is to provide the lab with blind samples—similar to your unknowns—for which you know the right answer, but the analyst does not. If the lab does not find the known result, there is a problem. Periodic blind check samples tire required to demonstrate continuing reliability. 

Performance test samples (also called quality control samples or blind samples) are a quality control measure to help eliminate bias introduced by the analyst knowing the concentration of the calibration check sample. These samples of known composition are provided to the analyst as unknowns. Results are then compared with the known values, usually by a quality assurance manager. 

For quality assessment of an analytical process, a control chart could show the relative deviation of measured values of calibration check samples or quality control samples from their known values. Another control chart could display the precision of replicate analyses of unknowns or standards as a function of time. 

Poor reproducibility Inadequate pressurization/equilibration Ensure samples are heated and pressurized for the same amount of time Make sure crimp seal is on tightly Check sample homogeneity... 

Step 9 Method maintenance Incorporate the new method or analyzer into the existing method maintenance systems for the site, to ensure that the method as practiced continues to meet the technical requirements for as long as it is in use. This is done by the receiver. Method maintenance systems may include check sample control-charting, intra-and/or inter-lab uniformity testing, on-site auditing, instrument preventive maintenance (PM) scheduling, control-charting the method precision and/or accuracy, etc. 

Twenty-eight of fifty-four samples purchased were found to have coatings made from polyester resins and so their contents were analysed for TPA and IPA. Analysis was by GC-MS after extraction and derivatisation to form the dimethyl esters of TPA and IPA. Included in the analytical quality assurance steps taken was participation in a check-sample exercise whereby four samples were supplied by a second laboratory and analysed blind. The performance of the testing laboratory was assessed from the accuracy and precision of their measurements and was demonstrated to be acceptable. 

Sample Custodians track sample custody within the laboratory. Other laboratory section personnel check samples in and out of cold storage using internal COC Forms or a checkout logbook. One container with soil may be used for multiple analyses the same is true for some types of water analyses. As one analysis has been completed, the sample is returned back to cold storage to be taken out again for the next analysis. 

The laboratory detects measurement errors by comparing the accuracy and precision of sample and laboratory QC check sample analysis to acceptance criteria. If results do not meet the criteria, the laboratory identifies the reason and takes corrective action, such as the following ... 

When justified, manual integration may be conducted for standards, samples, and QC check samples. The manner in which manual integration is conducted is based on professional judgment of the analyst experienced in chromatographic analysis. If a need for manual integration arises, the analyst will select a proper technique, conduct the manual integration, and document it in the sample file. Once a manual integration technique has been selected, it must be consistently used for the similarly affected peaks in all subsequent analyses. 

The use of LIMS makes internal review process rapid, reliable, and concurrent with data reporting. While Tier 1 reviewers typically work with hardcopy data, Tier 2 reviewers often access appropriate LIMS modules and review sample and QC data before final results are printed. They will also review the accompanying laboratory documentation that is available in hardcopy form only. Computerized confirmation of numeric acceptance criteria, such as the recoveries of laboratory QC check samples or surrogate standards, significantly reduces time and effort during review. Tier 3 Review is usually conducted on a hardcopy final data after analytical results and support documentation have been compiled into a single package. 

The laboratory uses QC check samples for the calculations of the primary DQIs (accuracy and precision). In addition, QC check samples enable laboratories to monitor the secondary DQIs, such as memory effects and recovery. The purpose and frequency of analysis of the laboratory QC check samples are summarized in Table 4.8. 

Different regulatory methods have different requirements for the type and frequency of analysis of laboratory QC check samples. That is why it is important to specify these requirements in the SAP. 

Table 4.8 The purpose of laboratory QC check samples Purpose Frequency of analysis...

Preparation and analytical batches must be clearly identified with a unique number in laboratory bench sheets, notebooks, and computer systems. The same applies to QC check samples associated with each batch. During data quality assessment, the data user will determine the quality of the field sample data based in the results of the batch QC check samples that are part of the preparation and analytical batches. The data user will examine batch QC check samples first and, if they are acceptable, will proceed to individual sample QC checks. A complete examination of these QC checks will enable the data user to evaluate the quantitative DQIs (accuracy and precision). A combination of acceptable batch QC checks and individual QC checks makes the data valid on condition that the qualitative DQIs (representativeness and comparability) are also acceptable. 

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 ... 

Step 4—Evaluate laboratory QC check sample results... 

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. 

---