Analysis of forensic samples can often involve the use of sophisticated instruments. While the presence of even minute quantities of a compound can be detected, the data can be suspect and legally inadmissible unless it can be demonstrated that the instrument was functioning properly. In a proper sample analysis, various quality control procedures need to be included along with the samples. One critical aspect is the inclusion of a reference sample.
A reference sample is a sample that is comprised of a similar matrix as the forensic sample. For example, if a forensic sample is a water-based solution, the reference sample must be a water-based solution. In addition, a reference sample contains a precisely defined amount of a target compound or microorganism.
Analysis of a reference sample should yield, within defined limits, the quantity of the target agent. If the analysis precision is faulty, then the reliability of the equipment and/or the operator is questioned.
For example, a microbiological reference sample will contain a defined number of living bacteria (such as Escherichia coli ). The sample is rapidly shipped to the laboratory and must be analyzed within a defined time (typically 48 hours). The results are sent back for evaluation and determination of the laboratory's performance.
Reference samples are commonly used in accreditation procedures, which are designed to verify that a laboratory is competent to perform the analyses. Achieving and maintaining accreditation adds credibility to a laboratory's performance and makes it less likely that the legal admissibility of sample analyses will be questioned.
In the United States, the American Board of Forensic Technology maintains a laboratory accreditation program in forensic toxicology . Proficiency testing involves the analysis of reference samples for the detection, identification and quantitative analysis of alcohol, various drugs, and toxins in biological matrices including urine and blood .
Other reference samples are available, depending on the analytical capability of the lab. Examples include DNA and metal ions.
Other countries have their own reference sample programs. For example, the Standards Council of Canada oversees the reference sample-mediated accreditation program that includes the six Royal Canadian Mounted Police forensic laboratories located across the country.
Laboratories that participate in reference sample-mediated accreditation programs are required to analyze a determined number of samples each year. This schedule ensures that the lab's equipment and personnel are continually proficient.
see also Analytical instrumentation; Control samples; Quality control of forensic evidence.