Low Count Rate With ULTIMA Gold MV

Problem
The researcher’s sample preparation consisted of 2.0 mL
of acetonitrile and 1.0 mL water added to 7.0 mL of
ULTIMA Gold MV.
After observing low counts, the researcher varied the
preparation techniques and recorded the following data:
Table 1.
Acetonitrile
(mL)
Water
(mL)
ULTIMA Gold
MV (mL)
Activity
Detected
2
0
7
15,000 CPM
2
1
7
5,000 CPM
ULTIMA Gold MV can accept 1.0 mL of water in 7.0 mL
of cocktail. In addition, it can accept 2.0 mL of acetonitrile in 7.0 mL of cocktail. However, when you try to
add both 1.0 mL of water plus 2.0 mL of acetonitrile
in 7.0 mL of cocktail an unstable mixture is formed
which rapidly separates into two layers.
From the observed results obtained in Table 1, it can be
concluded that the activity present is aqueous soluble
and when this mixture is prepared, the activity ends
up in the highly quenched lower aqueous phase.
Recommendations
1. Increase the volume of ULTIMA Gold MV to 15.0 mL
and keep the samples at their present levels. This
will yield a stable, reproducible mixture.
2. Refine new sample preparation techniques using
glass vials to ensure any cloudiness or separations
can be easily observed. Plastic vials can be used
when the method is refined.
Discussion
ULTIMA Gold MV was specifically formulated for the
rapid uptake of aqueous and non-aqueous samples.
Due to its low viscosity and high counting efficiency
the cocktail is ideal for counting small volume samples
in miniature vials (hence the name ULTIMA Gold MV,
signifying Micro Volume).
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007902_22
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N O T E
A researcher was preparing samples and performing
standard LSA counting using plastic vials and
PerkinElmer’s ULTIMA™ Gold MV (part number
6013159), a member of the ULTIMA Gold family of
modern, safer cocktails. Unfortunately, the researcher
was observing lower than expected 3H count rates and
suspected that he may have exceeded the practical
sample loading for this cocktail.
A P P L I C A T I O N
L S C C O C K TA I L S
LSC in Practice
Low Count Rate With ULTIMA Gold MV