s [ Pobierz całość w formacie PDF ]

this is possible. One of the most common faults of a laboratory is that calibrators and controls
are not subject to hydrolysis, or some other pre-treatment.
G-5 E Does the laboratory establish a valid calibration for each quantitative assay?
Spectrophotometry _____
Gas chromatography _____
High performance liquid chromatography _____
Gas chromatography-mass spectrometry _____
Liquid chromatography-mass spectrometry _____
Linearity of the procedure should be established by using at least three positive calibrators.
The concentration of the calibrators should be such that they bracket the anticipated
concentration of the specimens. If the concentration of the specimen exceeds the
concentration of the highest calibrator, the specimen should be diluted and re-extracted if
accurate quantitation is required. Otherwise the specimen should be reported as having a
concentration greater than the highest calibrator. If the concentration of the specimen should
be less than that of the lowest calibrator, an additional calibrator should be set up which falls
below the expected range of the analyte and the specimen re-extracted, or the analyte reported
as being less than the value of the lowest calibrator. A matrix blank or negative control should
also be run to ensure that no significant analyte signal is contributed by the reagents or sample
v. 020223
25
matrix.
For assays that are performed routinely, it is acceptable for the laboratory to perform a single
point calibration, as long as controls are run that bracket the expected concentration range of
the analyte. In this case the laboratory must document the linearity of the assay over the
expected concentration and validate this linearity periodically. This validation should occur at
least every six months.
G-6 E If the laboratory uses historical calibration for an assay, are calibrators and/or controls
run with each batch of specimens for analysis to check stability of the calibration?
Spectrophotometry _____
Gas chromatography _____
High performance liquid chromatography _____
Gas chromatography-mass spectrometry _____
Liquid chromatography-mass spectrometry _____
It is acceptable for laboratories to use historical calibration curves if they have demonstrated
and documented the linearity and precision of the curve over time. If they do use historical
curves, then they must validate the calibration by using controls with each batch of specimens.
These controls should be such that they validate the calibration over the entire range of the
curve. Although, it is better to use controls for this purpose, it is acceptable for the laboratory
to validate the calibration by analyzing calibrators as long as these cover the entire range.
G-7 E Are appropriate criteria established for the acceptability of calibration data?
Spectrophotometry _____
Gas chromatography _____
High performance liquid chromatography _____
Gas chromatography-mass spectrometry _____
Liquid chromatography-mass spectrometry _____
There are a variety of procedures for establishing the acceptability of calibration data, and
these are often listed as options within data reduction software included with modern
analytical instruments. Most commonly, laboratories use linear regression and define
acceptability based on the  r value. Typically, values of greater than 0.98 are acceptable with
non-deuterated internal standards and, for mass spectrometry, greater than 0.99 with deuterated
internal standards. For frequently run assays, it may be valuable to monitor the slope of the
calibration line. A significant deviation from the historical slope may indicate a problem with
the assay.
Other procedures include back calculating the concentrations of calibrators based on the
response factor of the previous calibrator(s) within that run, selection of the best curve fit (not
necessarily a linear response) and use of first or second derivatives (for spectrophotometry).
Regardless of which the laboratory uses, the SOP should clearly indicate which procedure is
used for which analyte and the criteria for acceptance.
If the laboratory uses more than three calibration points, the SOP must clearly indicate how
many points can be deleted and under what circumstances. The SOP should also address
v. 020223
26
which results can be reported after calibrators are deleted.
G-8 I Does the laboratory use an internal standard for qualitative analysis?
Gas chromatography _____
High performance liquid chromatography _____
Gas chromatography-mass spectrometry _____
Liquid chromatography-mass spectrometry _____
It is recommended that laboratories use internal standards for chromatographic assays that are [ Pobierz całość w formacie PDF ]