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Thin-Layer Radiochromatography - Raytest

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A Field Guide to In stru men ta tion<br />

Figure 6. AR-2000 TLC imaging scanner<br />

(courtesy of Bioscan Inc.).<br />

for automatic measurement, data<br />

evaluation, and report printing. It scans<br />

along one trace from start to front and<br />

then goes to the next preprogrammed<br />

trace position and scans that trace with<br />

individual nuclide settings. The<br />

V-shaped bismuth germanate (BGO-V)<br />

crystal scintillation probe detector,<br />

mounted in tungsten shielding, can be<br />

automatically energy calibrated using a<br />

137 Cs standard, and many energy<br />

windows can be preprogrammed for<br />

various nuclides. Collimators of 3 mm<br />

(stainless steel) and 5–20 mm (tungsten)<br />

size are available to optimize resolution<br />

and sensitivity for gamma detection in<br />

different energy ranges (0–60, 60–150,<br />

150–250, 250–450, and >450 keV)<br />

depending on the radioactive compound.<br />

Up to 80 sample traces can be<br />

programmed in terms of location, scan<br />

speed, etc., in both directions on two 20<br />

� 20 cm plates. Specifications include<br />

energy 0–2000 keV, activity<br />

10–100 000 Bq, sensitivity 20 Bq for<br />

99m Tc, resolution 2 mm for 99m Tc, linearity<br />

10 5 , and decay correction. A single<br />

chromatogram can be displayed live on<br />

the screen of a connected PC, and<br />

multiple traces can be displayed in 3<br />

dimensions. Peak integration can be<br />

performed manually or automatically,<br />

and measurement and data handling are<br />

digital (single event counting). A typical<br />

scan of a TLC zone containing a gamma<br />

radiolabeled compound is shown in<br />

Figure 8. Beta/positron detection can be<br />

made using an optional Geiger-Mueller<br />

(GM) detector ( 3<br />

H is not detected).<br />

<strong>Raytest</strong> miniGITA Star<br />

The miniGITA Star (Figure 9) is a<br />

scanner for gamma and beta/positron<br />

radiation from TLC zones that is similar<br />

to the GITA. The major differences are<br />

that the scan area is 5 � 20 cm and only<br />

one trace can be made at a time in the X<br />

direction. The BGO-V crystal has a 3 �<br />

25 mm entry window and is 25 mm high,<br />

and the tungsten shielding has an outside<br />

diameter of 70 mm.<br />

<strong>Raytest</strong> RITA Star<br />

The RITA Star beta radiation TLC<br />

analyzer (Figure 10) has a position<br />

sensitive proportional gas flow counter<br />

detector with an active length of 200 mm<br />

and active width of 20, 15, 10, 3, or<br />

1 mm controllable by exchange of the<br />

diaphragm. The sensing element is gold<br />

plated for easy cleaning and long life.<br />

For measurement of low energy betas<br />

from 3 H, the counting tube is used open<br />

(without any window) and is placed as<br />

close as possible to the radioactive TLC<br />

zone. Therefore, the detector rests on the<br />

surface of the layer in order to close the<br />

counting chamber and reduce gas<br />

leakage, and the gold-plated tungsten<br />

counting wire can be accurately aligned<br />

for optimum results. The entrance<br />

window is closed for 14<br />

C and other beta<br />

emitting nuclides. The counting tube is<br />

automatically moved to measure traces<br />

of multiple chromatograms on a layer.<br />

2D thin-layer chromatograms are<br />

measured by assembling individual<br />

one-dimensional traces. Data collection,<br />

analysis, and documentation meet GLP<br />

requirements. Two 20 � 20 cm plates can<br />

be measured at once.<br />

The RITA Star is designed for<br />

maximum sensitivity for low energy<br />

emitting nuclides such as 3<br />

H, 14<br />

C, 35<br />

S, 33<br />

P,<br />

and 32 P. Sensitivity and resolution values<br />

are 100 dpm/peak and 0.5 mm for 3 H,<br />

and 10 dpm/peak and 1 mm for 14<br />

C,<br />

respectively, and the dynamic range is<br />

10 6 . Background is 80 cpm/200 mm.<br />

Position deviations of the counting tube<br />

are less than 0.5 mm over the 200 mm<br />

length. The counting gas is 90% Ar and<br />

10% methane (P10 gas) with a<br />

0.5–1 L/min flow rate.<br />

Gamma and positron emitting<br />

nuclides such as 125<br />

I, 99m<br />

Tc, and 18<br />

F are<br />

detected more sensitively using the<br />

GITA or miniGITA Star.<br />

<strong>Raytest</strong> MARITA Star<br />

The MARITA Star (Figure 11) is an<br />

automatic single-trace instrument for<br />

measurement of one 5 � 20 cm TLC<br />

plate. The same position sensitive<br />

Figure 7. GITA gamma TLC scanner<br />

(courtesy of <strong>Raytest</strong>).<br />

JOURNAL OF AOAC INTERNATIONAL VOL. 92, NO. 1, 2009. � Copyright 2009 by AOAC INTERNATIONAL. Reprinted with permission.

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