Decision-theoretical formulation of the calibration problem

The choice of calibration policy is of basic importance in analytical chemistry. A prototype of the practical calibration problem is formulated as a mathematical task and a Bayesian solution of the resulting decision problem is presented. The optimum feedback calibration policy can then be found by dynamic programming. The underlying parameter estimation and filtering are solved by updating relevant conditional distributions. In this way: the necessary information is specified (for instance, the need for knowledge of the probability distribution of unknown samples is clearly recognized as the conceptually unavoidable informational source); the relationship of the information gained from a calibration experiment to the ultimate goal of calibration, i.e., to the estimation of unknown samples, is explained; an ideal solution is given which can serve for comparing various ways of calibration; and a consistent and conceptually simple guideline is given for using decision theory when solving problems of analytical chemistry containing uncertain data. The abstract formulation is systematically illustrated by an example taken from gas chromatography.     

A computer-enhanced pH study of the formaldehyde–sulphite clock reaction

The formaldehyde-sulphite clock reaction was studied using an Orion SA 720 pH/ISE meter interfaced to an IBM PC. The laboratory software ‘ASYST’ was employed to facilitate data acquisition and data treatment. Experimental pH profiles thus obtained for the first time were simulated by invoking a theoretical model based on the reaction mechanism suggested by Burnett [1]. The variation of rate constants with compositions of reaction mixtures was also discuseed in light of the empirical expression proposed by Bell and Evans [2] for instantaneous rate constant of the clock reaction.     

A simple flow-injection method for the determination of blood glucose using a Technicon immobilized enzyme coil

The applicability of a single-channel flow-injection system with immobilized enzyme coil (Technicon) and UV detection to the determination of glucose is described. The method was used for a pure glucose solution and for serum. The detection limit was 0.10 mM, the rate of determination was 20-40 per hour and the precision was satisfactory. The system is very simple and practical when many analysis are to be determined periodically.     

Development and analytical performance of an automated screening method for cannabinoids on the Dimension clinical chemistry system

A fully automated, random access method for the determination of cannabinoids (UTHC) was developed for the Dimension AR and XL clinical chemistry systems. The method utilizes Abuscreen ONLINE reagents and a multianalyte liquid calibrator containing 11-nor-Δ⁹-THC-9-carboxylic acid. Within-run and total reproducibility, determined using NCCLS protocol EP5- T2, was less than 0.6% and 1.6% CV, respectively, at all concentrations. Calibration stability was retained for at least 30 days. An extensive evaluation of non-structurally related drugs and various physiological substances indicated lack of interference in the method. No sample carry-over was observed following a specimen containing 1886 ng/ml 11-nor-Δ⁹-THC-9-carboxylic acid. A 99.1% agreement (N = 445 samples) was found between an EMIT based method on the aca discrete clinical analyser and the Dimension UTHC method.Dimension clinical chemistry system and aca discrete clinical analyser are registered trademarks of Dade International.     

A simple,automated device for the precise addition of liquids

Metering liquid reagents into reaction mixtures in a controlled and reproducible manner has often been a problem in synthetic chemistry. Carrying out the real simultaneous addition of two or more liquid reagents (concurrent additions) is even more inconvenient. Difficulties increase when addition volumes become small, when addition times become long, or when the reagents are corrosive or air-sensitive. We have constructed and tested an inexpensive, automated device for the slow, precise delivery of liquid reagents into laboratory-scale reaction mixtures. Controlled by a standard personal computer, this slow adder can accommodate liquid volumes from hundreds of microlitres to litres and addition times from minutes to days. Its glass and Teflon construction makes it useful for nearly all reagents. By using multiple slow adders, true concurrent addition of several liquids can be easily achieved.