Operator, environmental, and method errors often include sources of contamination. In an increasing, more exacting analytical landscape in pursuit of parts-per-billion (ppb)-level analytes, it is very important not only to understand the sources of error and contamination but how to reduce them. During the dawn of analytical instruments, the laboratories tested for a select number of compounds or elements at parts-per-thousand levels. Modern instrumentation now has increased the number of compounds and elements to be quantitated and lowered the analytical threshold to sub-part-per-billion levels where 1 ppb is equivalent to 1 s in 32 years! In this type of testing environment even low parts-per-billion levels of contamination can cause large errors in quantitation. In this guide, we look at all of the most common sources of contamination and error in an analytical process from the water used in the laboratory to the inherent mistakes and error caused by laboratory equipment and operators.
General Principles and Practices
Laboratories should follow a general regime of three runs each of wash–rinse runs, blank runs, and sample runs, as well as single runs of sample plus spike, and standard or spike runs without sample to use as a control solution to evaluate recovery.
Analysts must realize that the cleanliness and accuracy of their procedures, equipment, and dilutions affect the quality of the standards and samples. Many laboratories will dilute CRMs to use across an array of procedures and techniques. This in-house dilution of CRMs can be a savings to the laboratory but in the final analysis can be a source of error and contamination.
CRM manufacturers design standards for particular instruments to obtain the highest level of accuracy and performance for that technique. They also use calibrated balances, glassware, and instruments to ensure the most accurate standards are delivered to customers. Certifications such as ISO 9000, ISO 17025, and 17034 assure customers that procedures are being followed to ensure quality and accuracy in those standards. After those CRMs are in chemists’ hands, it is then their responsibility to use all possible practices to keep their analysis process free from contamination and error.
- ASTM D1193-06(2018), Standard Specification for Reagent Water, (ASTM International, West Conshohocken, Pennsylvania, 2018) www.astm.org.
- SPEX CertiPrep Webinar, “Clean Laboratory Techniques,” https://www.spexcertiprep.com/webinar/clean-laboratory-techniques.
- SPEX CertiPrep Application Note, “Analysis of Laboratory Water Sources for BPA and Phthalates,” https://www.spexcertiprep.com/knowledge-base/files/AppNote_BPALabWater.pdf.
- SPEX CertiPrep Application Note, “Understanding Measurement: A Guide to Error, Contamination and Carryover in Volumetric Labware, Syringes and Pipettes,” available via the SPEX CertiPrep website as a downloadable PDF.
- J.R. Moody and R. Lindstrom, Anal. Chem. 49, 2264 (1977).
Patricia Atkins is a Senior Applications Scientist with SPEX CertiPrep in Metuchen, New Jersey. Direct correspondence to: [email protected]
How to Cite This Article
P. Atkins, Cannabis Science and Technology 1(4), 40-49 (2018).