When can you exclude calibration points?

Ask the Expert Question:
When is it permissible to exclude calibration points?

Expert Response:
Removal or replacement of calibration points (point(s)) from the middle of a calibration curve (i.e., points other than the highest or lowest) is not permitted unless an injection or instrument problem confined to that point was directly observed and can be clearly documented. In this case, the failed standard must be re-run within 24 hours and before any samples and inserted into the initial calibration. If that new point is not useful, recalibration is required.

Removal of points for individual analytes from levels other than the highest and lowest is not permitted in any event.

Formula for Calculating Conductivity Dilution in Water

Ask the Expert Question:

Can you advise me of the correct formula for diluting the salinity in water?

We have groundwater ingress in a tunnel at a reading of 4630 us/cm it is seeping into the tunnel at 5L/sec.  We need to reduce the salinity to at least 600us/cm using potable water.  The potable water has around 720us/cm content and will be available at 10L/sec.

Expert Response:

The formula for figuring out the dilution would be as follows.

(Ca  x  Qa) + (Cb  x Qb)

--------------------------------

          (Qa + Qb)

Where:

Ca = conductivity of liquid A

Qa = flow rate of liquid A

Cb = conductivity of liquid B

Qb = flow rate of liquid B

In this specific case, however, you will not be able to dilute the saline water to less than 600 us/cm.  The dilution water you are using has a salinity greater than 600 us/cm.  Any combination of a water with 4630 us/cm and a water with 720 us/cm will have a conductivity between those two extremes.  In order to dilute the saline water to 600 us/cm you would need dilution water that has a conductivity lower than 600 us/cm.

View Dr. Charlie Carter's expert profile

TestAmerica's New Methods and Capabilities

EPA Method 8260B SIM

Honolulu Laboratory

Method Application:

The method is used for a select group of analytes that drastically improves low level detection limits. The 82060B SIM method is ideal when running methanol preserved samples collected by incremental sampling methodology (ISM) for VOC analysis. The Honolulu laboratory can report Trichloroethylene (TCE) at 0.2ug/Kg.

Market Application:

The method is designed for those entities that perform incremental sub sampling for certain volatile chemicals of potential concern (COPC).

Hawaii's Department of Health (DOH) performed a characterization study with TestAmerica, on a U.S. Air Force base for subsurface contamination. The study focused on groundwater and soil gas data used in determining environmental risk hazards. In the investigation, core increment soil samples were extracted from contaminant locations and Single Ion Monitoring (SIM) analysis was applied, reducing the reported MDLs.

Advantages:

When performing an incremental sub sampling VOC process, field samples are preserved in methanol. This generally forces a dilution factor of 50, raising the reporting limits. The SIM approach allows the client to obtain reporting limits closer to the standard 8260 limits they expect, while performing the incremental sampling methodology.

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TPH Analysis GC Chromatogram Interpretation

Ask the Expert Question: 
Is there a way to distinguish whether TPH hits in a sample are from diesel, gasoline or mineral oil?

Expert Response:
The product causing the positive TPH results can generally be identified from the pattern of contamination present in the chromatogram provided the TPH was analyzed by method SW846 8015B or a similar Gas Chromatograph (GC) analysis.

Each of the petroleum products will show analytes in a generally well defined Carbon Number range (for example, gasoline is primarily from C4-C12, Diesel Fuel from C10 to C28, etc), and each of these products also have a very distinct distribution pattern within that carbon range. Identification is then based on both the carbon range and the actual distribution within that carbon range (there can be some overlap of the carbon number range for the various products). Our petroleum chemists are very experienced in evaluating these patterns and establishing the petroleum product present, and can evaluate the GC chromatograms from the analysis for identification.

It is also possible that the results are due to something other than petroleum products. The GC TPH methods are not necessarily specific for only petroleum products, but will include any compounds that elute within a defined Carbon Number range. Again, an evaluation of the chromatographs by a trained chemist can usually identify the cause of the positive results.

View Johnny Mitchell's expert profile

TestAmerica's New Methods and Capabilities

SW 8015B/ Iowa OA-2 Analyte Addition - Crude Oil
Cedar Falls Laboratory

Method Application:

This method is used to determine the total extractable hydrocarbons as Crude Oil present in a sample.

Market Application:

At the request of the Nebraska Department of Environmental Health, the laboratory validated this analyte using the IA-OA2 method. This request was made for the potential release of crude oil from a new oil pipeline being constructed in the state.

The Legislature recently introduced a bill that would require oil companies that own, operate, or manage a pipeline in Nebraska, to file an extensive application process with the state's Public Service Commission. This would require the submission of a pre-filed testimony, application framework, in addition to providing evidence of any environmental and economic studies of the proposed pipelines.

Advantages:

This method/analyte would use area of the entire chromatogram and compare it against a crude oil standard versus the traditional OA-2 comparing the chromatogram to individual regions of refined gasoline, diesel, and waste oil standards.

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