
LS 6000 Scintillation System User’s Manual
PN 247971-F
7-2
How Sample Preparation Affects Results
Chemiluminescence
5. Plant extracts containing chlorophyll.
Interpretation of Results
Lum-Ex values provide an indication of what percent of the total CPM’s are due to
non-radioactive events. The significance of this Lum-Ex% depends on a number of factors
that you must evaluate. For example: How accurate must your answer be? Is the Lum-Ex%
the same in all the samples? Are small CPM differences between samples critical?
As a general rule, If the Lum-Ex value is 5% to 10% or greater, steps should be taken to
eliminate the problem (see the following section).
Reducing Single Photon Events
Many single photon events can be eliminated from samples by some very simple techniques.
Chemiluminescence from peroxides and alkaline pH can almost always be eliminated by the
addition of glacial acetic acid. Usually, 100 µL in 10 mL of cocktail is sufficient.
This same treatment sometimes works for chemiluminescence from tissue solubilizers. If this
does not eliminate the chemiluminescence, set the samples aside and monitor them hourly
until the chemiluminescence is sufficiently low.
Figure 7.11 shows the counts of a sample with chemiluminescence. This sample has no
radioactivity. Notice how the addition of acetic acid completely eliminates the random
coincidence counts after 5 minutes.
While there is no corresponding method for reducing photoluminescence, the effects
fortunately decay rather quickly. Generally, avoid exposing samples to sunlight or ultraviolet
light. If photoluminescence is suspected, let the vials sit in the counter for 30 to 60 minutes
before counting.
Figure 7.1 Chemiluminescence and Statics
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