Well scintillation counter with automatic sample changing and data processing. An inexpensive instrument incorporating consumer products

An automatic well scintillation counting system suitable for in-vitro assays with 125I has been designed with the express purpose of allowing effective operation and maintenance in laboratories in developing countries. The system incorporates comparatively simple components, notably two consumer products: A Kodak Carousel slide projector as sample changer and a Hewlett-Packard HP-97 programmable printing calculator as system controller and data processor. The instrument can accommodate 80 counting vials of dimensions 12 mm phi x 75 mm, or 40 vials of 16 mm phi x 100 mm. The calculator provides on-line control and data reduction with the mediation of an interface somewhat resembling that required between a scaler and a printer. Its program capacity is adequate for fairly complicated on-line operations, including, for example, deduction of concentration of hormone in unknown sample by interpolation from a standard curve in logit-log space, calculation of error in hormone concentration, and termination of counting when the counting error is reduced to a prescribed fraction of the composite of other random assay errors (as stored in the calculator's memory). This system is inexpensive, robust, and capable of being operated manually if automatic accessories fail. It could be improved in several ways, particularly by providing for operation from batteries and, no doubt in the immediate future, substitution of the next generation of cheaper and more powerful calculators for the calculator used at present. The instrument may be cost-effective in any small to medium-sized laboratory. (author)