ASSAYS
PerkinElmer Life and Analytical Sciences 71
Direct DPM Assays
The Direct DPM Assay
The Direct DPM Assay is a predefined assay which performs the DPM calculation
based on the Quench Indicating Parameter, SIS (Spectral Index of the Sample).
Since this assay comes pre-installed as part of the system, there is no need to
define individual assay parameters. This assay will calculate accurate DPM values
for single label beta or beta/gamma nuclides, including Tritium. Single-label
samples containing different beta nuclides may be counted in the same cassette.
When using the Direct DPM method, samples are evaluated as follows:
If the SIS value is greater than or equal to 40, then the DPM is reported with
no message on the printout.
If the SIS value is between 20 and 40, then the DPM is reported and the
sample is designated as indeterminate (I) on the printout.
If the SIS value is less than or equal to 20 and the sample is determined to
contain Tritium, the DPM is reported with no message on the printout.
If the SIS value is less than or equal to 20 and the sample is determined not
to contain Tritium, then the DPM is not reported and the sample is designated
as indeterminate on the printout.
Note: When a sample is designated as indeterminate on a printout,
the DPM reported may be valid if the sample is not heavily
quenched. Check the tSIE value of the sample to determine the
level of quench. If the tSIE is greater than 200, the DPM reported
is most likely accurate, within statistical counting error. The
accuracy is independent of cocktail density variation, vial size or
type, sample volume, color and chemical quench. Direct DPM is not
recommended for any background level samples counted for a
short time.
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