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over if it uses automatic pipetting/diluting equipment?
Very often the larger laboratories will use automatic pipetting/diluting equipment or automated
analyzers (such as the Hitachi 717 or the Olympus AU800). Because these instruments are
used to analyze specimens that can contain large concentrations of analyte, it is important that
the laboratory has validated this potential for carryover and taken corrective action if it occurs.
An example of appropriate corrective action is reanalyzing consecutive positives with a
negative control between them, when the first positive urine has a higher concentration than
the carryover limit.
F-6 D If the laboratory uses radioimmunoassay, does it determine background counts before
each run or daily, including the background in each well of a multi-well counter?
For RIA analyses, counting efficiency and statistical biases should be determined on a regular
basis and background counts should be determined on a daily basis or whenever the testing is
performed. These values should be entered in a record book to monitor changes in instrument
performance.
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Section G: CHROMATOGRAPHY, MASS SPECTROMETRY AND
SPECTROPHOTOMETRY - GENERAL QUESTIONS:
G-1 E Are the analytical protocols used for the chromatography based assays appropriate?
The protocols used should be sufficiently comprehensive to satisfy the mission of the
laboratory. For example, it would be inappropriate for a laboratory to indicate they performed
drug screening on a medical examiner case when testing was only based on immunoassay,
even if any positive findings were subsequently confirmed by mass spectrometry (unless the
report included a statement indicating the limitations of the screen). The laboratory should also
have the capability to quantitate an adequate range of drugs in blood and other specimens with
an acceptable degree of accuracy and precision, sufficient for the mission of the laboratory,
recognizing that some tests may have to be sent out to a reference laboratory.
G-2 I Does the laboratory prepare quantitative calibrators and controls using an appropriate
matrix?
Spectrophotometry _____
Thin layer chromatography _____
Gas chromatography _____
High performance liquid chromatography _____
Gas chromatography-mass spectrometry _____
Liquid chromatography-mass spectrometry _____
It is important that an appropriate matrix be used, since for some analytes recovery is very
matrix-dependent. For some forensic toxicology procedures, providing an appropriate matrix
is no more difficult than for any other test. Typical examples include tissue homogenates,
expired blood bank blood or plasma or urine. For others the matrix may be unique (e.g.
decomposed tissues, bone, hair or nails) and providing a matrix blank can be very difficult. In
such cases the laboratory should select the one that is closest to the specimen being analyzed.
For example when hair is analyzed the digestion medium would be acceptable as a matrix
blank.
It may be acceptable to analyze specimens of differing matrix against a common calibration, if
matrix-matched controls are run at the same time, or if it has been demonstrated using the
same or a similar analyte, that the assay is not significantly matrix-sensitive. For example, it
may be acceptable to analyze a serum specimen for lorazepam against a blood-based
calibration, if it had already been shown that there was relatively little difference between the
results obtained for diazepam (for example) in blood versus serum in the same or a similar
assay.
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G-3 E For qualitative and quantitative assays, does the laboratory analyze calibrators and/or
controls with each batch of specimens?
Spectrophotometry _____
Thin layer chromatography _____
Gas chromatography _____
High performance liquid chromatography _____
Gas chromatography-mass spectrometry _____
Liquid chromatography-mass spectrometry _____
Comments:
Case specimens should never be assayed in isolation. At least one calibrator or control should
be processed at the same time, in order to ensure the veracity of the extraction process. For
example, to ensure that if the sample tested negative, a calibrator or control should be
extracted and run simultaneously to demonstrate that there were no analytical deficiencies.
See the question relating to historical calibrations.
G-4 E Does the laboratory analyze calibrators and controls in the same manner as unknowns?
Spectrophotometry _____
Thin layer chromatography _____
Gas chromatography _____
High performance liquid chromatography _____
Gas chromatography-mass spectrometry _____
Liquid chromatography-mass spectrometry _____
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