Thin-Layer Radiochromatography - Raytest

A Field Guide to In stru men ta tion
Figure 6. AR-2000 TLC imaging scanner
(courtesy of Bioscan Inc.).
for automatic measurement, data
evaluation, and report printing. It scans
along one trace from start to front and
then goes to the next preprogrammed
trace position and scans that trace with
individual nuclide settings. The
V-shaped bismuth germanate (BGO-V)
crystal scintillation probe detector,
mounted in tungsten shielding, can be
automatically energy calibrated using a
137 Cs standard, and many energy
windows can be preprogrammed for
various nuclides. Collimators of 3 mm
(stainless steel) and 5–20 mm (tungsten)
size are available to optimize resolution
and sensitivity for gamma detection in
different energy ranges (0–60, 60–150,
150–250, 250–450, and >450 keV)
depending on the radioactive compound.
Up to 80 sample traces can be
programmed in terms of location, scan
speed, etc., in both directions on two 20
� 20 cm plates. Specifications include
energy 0–2000 keV, activity
10–100 000 Bq, sensitivity 20 Bq for
99m Tc, resolution 2 mm for 99m Tc, linearity
10 5 , and decay correction. A single
chromatogram can be displayed live on
the screen of a connected PC, and
multiple traces can be displayed in 3
dimensions. Peak integration can be
performed manually or automatically,
and measurement and data handling are
digital (single event counting). A typical
scan of a TLC zone containing a gamma
radiolabeled compound is shown in
Figure 8. Beta/positron detection can be
made using an optional Geiger-Mueller
(GM) detector ( 3
H is not detected).
Raytest miniGITA Star
The miniGITA Star (Figure 9) is a
scanner for gamma and beta/positron
radiation from TLC zones that is similar
to the GITA. The major differences are
that the scan area is 5 � 20 cm and only
one trace can be made at a time in the X
direction. The BGO-V crystal has a 3 �
25 mm entry window and is 25 mm high,
and the tungsten shielding has an outside
diameter of 70 mm.
Raytest RITA Star
The RITA Star beta radiation TLC
analyzer (Figure 10) has a position
sensitive proportional gas flow counter
detector with an active length of 200 mm
and active width of 20, 15, 10, 3, or
1 mm controllable by exchange of the
diaphragm. The sensing element is gold
plated for easy cleaning and long life.
For measurement of low energy betas
from 3 H, the counting tube is used open
(without any window) and is placed as
close as possible to the radioactive TLC
zone. Therefore, the detector rests on the
surface of the layer in order to close the
counting chamber and reduce gas
leakage, and the gold-plated tungsten
counting wire can be accurately aligned
for optimum results. The entrance
window is closed for 14
C and other beta
emitting nuclides. The counting tube is
automatically moved to measure traces
of multiple chromatograms on a layer.
2D thin-layer chromatograms are
measured by assembling individual
one-dimensional traces. Data collection,
analysis, and documentation meet GLP
requirements. Two 20 � 20 cm plates can
be measured at once.
The RITA Star is designed for
maximum sensitivity for low energy
emitting nuclides such as 3
H, 14
C, 35
S, 33
P,
and 32 P. Sensitivity and resolution values
are 100 dpm/peak and 0.5 mm for 3 H,
and 10 dpm/peak and 1 mm for 14
C,
respectively, and the dynamic range is
10 6 . Background is 80 cpm/200 mm.
Position deviations of the counting tube
are less than 0.5 mm over the 200 mm
length. The counting gas is 90% Ar and
10% methane (P10 gas) with a
0.5–1 L/min flow rate.
Gamma and positron emitting
nuclides such as 125
I, 99m
Tc, and 18
F are
detected more sensitively using the
GITA or miniGITA Star.
Raytest MARITA Star
The MARITA Star (Figure 11) is an
automatic single-trace instrument for
measurement of one 5 � 20 cm TLC
plate. The same position sensitive
Figure 7. GITA gamma TLC scanner
(courtesy of Raytest).
JOURNAL OF AOAC INTERNATIONAL VOL. 92, NO. 1, 2009. � Copyright 2009 by AOAC INTERNATIONAL. Reprinted with permission.