Laboratory Quality Assurance

The Radiation Safety Academy is committed to providing our clients expedited services while not compromising accurate and defensible results. The Analytical Services Division undergoes rigid internal and external quality control tests, and has an extensive quality assurance plan.

Quality Control Types for Sampling

There are 4 basic types of quality control (QC) samples which the Academy uses to ensure defensible results. Although we are not at this time NELAC certified, the Analytical Services Division’s protocols are measured against NELAC standards.

Sample Types:

Blank

A blank sample is the most basic of QC samples. It is essentially a sample of the same geometry, volume, media type, etc. of the unknown samples but has no activity. Blank samples obtain 2 values. First, it allows a minimum detectable activity (MDA) for each sample to be calculated. Background values will vary and are a function of the constituents of the sample. For example, a sample using a 7 mL glass container would have less background than a 20 mL glass container due to the amount of K-40 found in glass. Secondly, blank samples allow the laboratory to ensure their equipment is not contaminated which would yield Type I errors or errors which result in positive counts but are not really radioactive. Blank QC samples are utilized for every batch of samples and come free of charge. If you have samples which are out of the ordinary, please send a similar sample which is known to be free of radioactivity and we will use that as the batch blank.

Duplicates

Duplicate samples are primarily used with liquid samples. However, if homogenization of a sample is implemented rigorously, then solid samples can also use duplicates. A duplicate sample is a sample that has 2 consecutive aliquots extracted from it but is prepared through the same process as the master and counted separately. Take a water sample for LS counting as an example. The preparer aliquots 1 mL of sample into a 7 mL container and prepares it, the preparer then aliquots another mL from the same sample and places into a separate 7 mL vial. The 2 samples (master and duplicate) are then counted under the same conditions and a percent difference is calculated. Utilization of duplicates ensures the preparation technique is not flawed.

Spikes

Spiking samples is the oldest of QC samples and are only used with liquid samples. This technique induces a known amount of radioactivity into a sample and a percent recovery is obtained. Many factors influence results of a sample when counting for radioactivity such as quench in LS counting. If a spike is implemented, the radioactivity added will undergo the same quenching properties as the unknown sample would. As a result, the efficiency of the unknown sample will be the same as the spiked sample. This QC sample measures the accuracy of the laboratory’s conversion process from cpm to activity.

Laboratory Control Sample

A laboratory control sample combines the values of a spike and duplicate sample. Laboratory control samples can also only be used with liquid samples. It is a process by which the laboratory has pre-made stock solutions of radioactivity and takes an aliquot of the stock solution. The aliquot is prepared through the same process as the unknown samples and percent difference is obtained. The LCS goes through the preparation process so the protocol is measured and it has actual known activity so the calibration protocol is also measured.