10.7 Blank Analyses10.7.1 Summary.

10.7 Blank Analyses
10.7.1 Summary. To monitor for possible laboratory contamination, laboratory method blanks are analyzed
at least once in a 24-hour analytical sequence. All steps in the analytical procedure are performed on the blank using all reagents, standards, equipment, apparatus, glassware, and solvents that would be used for a sample
analysis.
A laboratory method blank (LMB) is an unused, certified canister that has not left the laboratory. The blank
canister is pressurized with humidified, ultra-pure zero air and carried through the same analytical procedure as
a field sample. The injected aliquot of the blank must contain the same amount of internal standards that are
added to each sample.
10.7.2 Frequency. The laboratory method blank must be analyzed after the calibration standard(s) and
before any samples are analyzed.
Whenever a high concentration sample is encountered (i.e., outside the calibration range), a blank analysis should
be performed immediately after the sample is completed to check for carryover effects.
10.7.3 Procedure. Fill a cleaned and evacuated canister with humidified zero air (RH >20 percent, at 25EC).
Pressurize the contents to 2 atm.
The blank sample should be analyzed using the same procedure outlined under Section 10.8.
10.7.4 Calculations. The blanks are analyzed similar to a field sample and the equations in Section 10.5.4
apply.
10.7.5 Technical Acceptance Criteria. A blank canister should be analyzed daily.
The area response for each internal standard (IS) in the blank must be within ±40 percent of the mean area
response of the IS in the most recent valid calibration.
The retention time for each of the internal standards must be within ±0.33 minutes between the blank and the
most recent valid calibration.
The blank should not contain any target analyte at a concentration greater than its quantitation level (three times
the MDL as defined in Section 11.2) and should not contain additional compounds with elution characteristics
and mass spectral features that would interfere with identification and measurement of a method analyte.
10.7.6 Corrective Action. If the blanks do not meet the technical acceptance criteria, the analyst should
consider the analytical system to be out of control. It is the responsibility of the analyst to ensure that
contaminants in solvents, reagents, glassware, and other sample storage and processing hardware that lead to
discrete artifacts and/or elevated baselines in gas chromatograms be eliminated. If contamination is a problem,
the source of the contamination must be investigated and appropriate corrective measures need to be taken and
documented before further sample analysis proceeds.
If an analyte in the blank is found to be out of control (i.e., contaminated) and the analyte is also found in
associated samples, those sample results should be "flagged" as possibly contaminated.