A simple high-speed recording colorimeter system.

Abstract

The rapid and continuous increase in microbiological assays requested of the routine clinical laboratory has created physical problems by the sheer number of tubes involved. One of the major difficulties is associated with the reading of large numbers of cultures with conventional instruments.In those assays where it is the rate of growth that is being measured, eg, Lactobacillus casei folate assays, standards and tests should theoretically be measured simultaneously. Therefore, in practice, all the cultures to be compared with one set of standards should be read in the shortest possible time. With commercial colorimeters we have found that to read a batch of 500 cultures took two technicians approximately two hours. The method was very prone to copying errors which were not easily determined and the arithmetical processing of the figures was both time consuming and tiring.In order to alleviate these problems we have devised a simple system which enables large numbers of repetitive readings to be made rapidly with consistent accuracy. Used in conjunction with a vortex mixer over 500 tubes an hour can be read by one person. A foot switch is used to control the flow of samples and the recording of colorimeter readings, leaving both hands free to mix specimens and move the probe. The system (Fig. 1) is made more versatile by using flow cells of different light-path lengths, eg, a 2 mm cell enabled six-day Euglena gracilis vitamin B12 assays to be read undiluted. A simple base-board and graticule chart reader enables results to be calculated rapidly.