ENERGY PROGRAM NEWSLETTER

CONTACTS

Jamey McCord
jdmccord@usgs.gov

Quality Assurance

Quality - Control Process

The Energy Geochemistry Laboratory uses a three-tiered approach to QC.

1. The First Tier

Method Performance; QC samples are analyzed by lab personnel. At this level, lab personnel use the QC sample data to control the analytical process for each batch of samples. If the acceptance criteria are not met, the analysis is discontinued until corrected.

2. The Second Tier

Data Review and Blind Sample Programs; lab personnel use data from these programs to monitor method performance throughout the laboratory and for long term tracking.

3. The Third Tier

Performance-Evaluation Studies; These studies can managed by private labs, local, State, and Federal agencies, all external to the energy lab. Data from these studies can be used to compare laboratories or to select a laboratory for analytical work. Summary reports from many of these studies will be available on the Energy Geochemistry Laboratory web page.

First Tier: Method Performance

Energy lab personnel trying to determine elements in any sample evaluate two areas of performance: instrument and method. Accurate instrument operation can be verified by analyzing known standards at different concentrations.  Blank water, which has negligible concentrations of the constituents of interest, is also analyzed to evaluate and eliminate potential sources of bias.
The analyst uses QC samples to assess whether the method is working properly. Data produced from these samples are the most useful for customers to evaluate the labs entire analytical process. In addition to blank samples, standard reference materials are the primary tools for evaluating method bias and variability. Laboratory replicate data is also used to evaluated and obtain method variability information.

Standard Reference Materials (SRMs) SRM’s are obtained through internal and external sources. Examples (NIST, CANSPEX, USGS, and EPA) The SRM is thought to be sufficiently tested to be used to assess method performance. Several SRM’s of differing concentrations and elements are analyzed alongside everyday samples. The SRM data is evaluated to assess bias for each analysis. Additionally, as the data is compiled, long-term estimates of method variability can be obtained.

 

Laboratory Replicate (Duplicate). The environmental sample is split at the laboratory to provide information about variability. If the sample is split into identical sub-samples, then the replicate will provide information about variability inherent in the analytical process. However, true sample splits are often difficult to obtain. More frequently, the split samples will exhibit some differences because of sample homogeneity. The sample variability will often mask the sample processing and analytical variability.

Second Tier: Data Review and Blind Sample Programs

Data Review Program. All energy lab analytical results initially are stored in the Laboratory Information Management System data base. A QC check is done by the lab manager to review all analytical results in the data base. Examples of QA checks include the following:

• Duplicate within limits
• SRM’s fall within limits
• Internal Blinds
• Internal standards
• Historical trends checked if available
• Correlation is within limits
• Proper amount of QA used in Job

Blind Sample Programs. The blind sample programs are administered by internal and external personnel to the energy lab. The internal program quantifies bias caused by random laboratory contamination. The external blind checks method performance and reproducibility.

Blind Coal: 2006-1, 2006-2
Blind Ash: 2006-1, 2006-2

Third Tier: Performance-Evaluation Studies

The energy lab participates in the following national and international inter-laboratory performance-evaluation studies:

• USGS Branch of Quality Systems Evaluation Program for Standard Reference Samples;
• CANSPEX - 2007-2, 2007-3 ,2007-4 , 2008-1