The Importance of Quality Control Materials during Sample Analysis

Complete Article from Edition 44 APG eNewsletter

Article written by Tina Noble, Account Executive, APG

Analyzing quality control samples alongside “real” samples aids analysts in identifying laboratory errors such as proper functionality of laboratory instrumentation, contamination issues with glassware and equipment, sample preparation, and analyst evaluations.

Some common QC samples include:

Method Blank or Laboratory Reagent Blank – This is reagent water that has gone through the same procedure and has all the reagents as the other samples.  Method blanks are useful in determining contamination.

Duplicate – Two samples are analyzed side-by-side using the same procedural process and tested separately.  These samples are used to evaluate analytical or measurement precision.

Matrix Spikes or Laboratory Fortified Matrix– A spike sample is a “real” sample that has a known amount of analyte added to it.  The difference between the sample and the spiked sample is determined and the percent recovery is calculated.  Spikes help to determine if interferences are present.

Laboratory Control Sample or Laboratory Fortified Blank – This is a quality control sample that has a known amount of analytes present. 

Quality Control Sample - This is a quality control sample that has a known amount of analytes present.  It should be made from a different source of chemicals than what the calibration standards are made from.  This sample may be a proficiency testing sample or the laboratory’s own preparation of a standard mix.

In addition to having a documented true value of a known quality control standard, the following guidelines should also be met.

1. The quality control sample has a certified true value.  This allows the analyst to evaluate the accuracy of the analysis.
2. The quality control sample should be traceable to a NIST standard, if possible.
3. The quality control sample should have an EPA acceptance range.  This information provides assurance that the data generated in the analysis would be accepted by a regulatory agency.
4. The quality control standard should be accompanied by an interlaboratory acceptance range.  This data provides assurance that the results are comparable to the data generated by other laboratories running the same method.

A properly prepared and utilized quality control standard verifies the calibration and validates the unknown sample data.  For this reason, independently prepared quality control samples purchased from an accredited provider are essential to producing accurate and defensible data. 

APG’s quality control standards provide you with the perfect level of documentation and confidence that cannot be achieved when you prepare the standards yourself.  Should you have any questions regarding quality control standards or how to improve your quality system, feel free to contact Tina Noble at t.noble@apgqa.com.