Quality control (QC) results render meaningful the results of analytical tests. Essential QC measures (described in Part 1000) include method calibration, reagent standardization, assessment of each analyst’s capabilities, analysis of blind check samples, determination of the method’s sensitivity (method detection level or quantification limit), and daily evaluation of bias, precision, and the presence of laboratory contamination or other analytical interference. The details of these procedures, their performance frequency, and expected ranges of results should be formalized in a written Quality Assurance Manual and standard operating procedures (SOPs).
Some of the methods in Part 6000 include specific QC procedures, frequencies, and acceptance criteria. These are considered the minimum quality controls needed to perform the method successfully; additional QC procedures can and should be used. If the QC criteria listed in this section exceed those listed in the individual methods, the criteria in this section must also be included. Some regulatory programs may require further QC or have alternative acceptance limits.
Each method typically includes acceptance-criteria guidance for precision and bias of test results. If not, the laboratory should determine its own criteria via control-charting techniques. Evaluate bias using recoveries from laboratory-fortified blanks (LFBs). Evaluate precision by analyzing duplicate or spiked duplicate samples. Additional acceptance criteria guidance may be provided by program- or project-specific requirements.
To help verify the accuracy of calibration standards and overall method performance, participate in an annual or preferably semi-annual analytical program of single-blind QC check samples (QCS), ideally provided by an external entity. Such programs are sometimes called proficiency testing (PT)/performance evaluation (PE) studies. An unacceptable result on a PT sample is often a strong indication that a test protocol is not being followed accurately. Investigate circumstances fully to find the cause. In many jurisdictions, participation in PT studies is a required part of laboratory certification and accreditation.