The Journal of Automatic Chemistry最新文献

The analytical performance of the Dimension XL clinical chemical system was evaluated. The XL is the latest addition to the Dimension family of instruments; it is a random access analyser with a throughput up to 740 tests/hour. Regression analysis of method comparison studies with Dimension AR yielded slopes of 0.93 to 1.03 and correlation coefficients >/=0.96 for 28 assays. Excellent precision performance was also observed. New instrument features of the XL are discussed.

An automated system to perform liquid-liquid extraction in monosegmented flow analysis is described. The system is controlled by a microcomputer that can track the localization of the aqueous monosegmented sample in the manifold. Optical switches are employed to sense the gas-liquid interface of the air bubbles that define the monosegment. The logical level changes, generated by the switches, are flagged by the computer through a home-made interface that also contains the analogue-to-digital converter for signal acquisition. The sequence of operations, necessary for a single extraction or for concentration of the analyte in the organic phase, is triggered by these logical transitions. The system was evaluated for extraction of Cd(II), Cu(II) and Zn(II) and concentration of Cd(II) from aqueous solutions at pH 9.9 (NH(3)/NH(4)Cl buffer) into chloroform containing PAN (1-(2-pyridylazo)-2-naphthol) . The results show a mean repeatability of 3% (rsd) for a 2.0 mg l(-1) Cd(II) solution and a linear increase of the concentration factor for a 0.5mg l(-1) Cd(II) solution observed for up to nine extraction cycles.

The Environmental Protection Act has created a growing need for the measurement and assessment of trace emissions to the environment. This encompasses three main areas of ground, water and the atmosphere. The need to achieve lower emissions has placed a large burden on analytical techniques, particularly in the areas of trace analysis to ppb and ppt levels. Chromatographic techniques are widely used for assessment and measurement of emissions in all three areas. Enhanced detectors using mass spectrometry principles are available to lower detection limits, but these are expensive. Standard chromatography detectors can be used for trace analysis, but this often leads to extensive sample preparation stages to achieve low detection limits. This paper describes the techniques developed by Thomas Swan & Company to introduce a cost effective way of lowering detection limits. The approach taken meets both BATNEEC and BPEO constraints.

This paper provides some initial considerations into the design and function of the Data Librarian. The first part (Liscouski, J., 1997, Journal of Automatic Chemistry, 19, 193-197) described the need for the Librarian.

pH is frequently measured in laboratories, but to have confidence in the results it is necessary to know that it was measured properly. For an electrode to give accurate results it must be treated well and calibrated correctly. In this paper, an automated system for pH measurement is described; the system uses the operational pH scale and calibrates using two or three buffer solutions, taking proper account of the effects of temperature on the system. The system can be programmed with standard methods and procedures to ensure that the electrode gives the best possible performance. Calibrations and measurements within the system are reproducible, and the automated system is more robust than the manual pH meter, and requires less operator time.

The basic requirement for a good calibration is representative data. This paper outlines techniques for selecting samples from an existing population. The concept of factorial designs is explained, and three ways of applying experimental design to generate representative data are described. These are: to vary the experimental conditions; focus on some of the parameters of interest directly (reference values); to vary the underlying conditions which generate consistent variations in the spectra,for example production factors. Finally the paper gives an example of the use of the concept of experimental design to pick out samples from a population.

The formulae for calculation of carry-over and sample interaction are derived for the first time in this study. A scheme proposed by Thiers et al. (two samples of low concentration followed by a high concentration sample and low concentration sample) is verified and recommended for the determination of the carry-over coeffcient. The derivation demonstrates that both widely used schemes of a high concentration sample followed by two low concentration samples, and a low concentration sample followed by two high concentration samples actually measure the sum of the carry-over coeffcient and sample interaction coefficient. A scheme of three low concentration samples followed by a high concentration sample is proposed and verified for determination of the sample interaction coeffcient. Experimental results indicate that carry-over is a strong function of cycle time and a weak function of ratio of sample time to wash time. Sample dispersion is found to be a function of sample time. Fitted equations can be used to predict the carry-over, absorbance and dispersion given sample times, and wash times for an analytical system. Results clearly show the important role of intersample air segmentation in reducing carry-over, sample interaction and dispersion.

An apparatus that operates with an isotope-ratio mass spectrometer to automatically perform nitrogen isotope analyses by the Rittenberg technique was modified to permit the use of nitrous oxide (N(2)O) instead of Freon (CCl(2)F(2) or CHClF(2)) for the purging of air prior to hypobromite oxidation of ammonium-N to N(2) in a plastic microplate. Analytical performance was unaffected by the modifications. Up to 768 samples can be processed in a single loading, at a rate of 6 to 12 samples/h. Within the range of 0.2 to 20 atom % (15)N, isotope-ratio analyses of 50 to 200 mug of N using the automated Rittenberg apparatus (ARA) with a double-collector mass spectrometer were accurate to within 0.7%, as compared to manual Rittenberg analyses of 1 mg of N using the same mass spectrometer with a dual-inlet system. Automated analyses of 20mug of N were accurate to within 2%, and automated analyses of 10 mug of N were accurate to within 7%. The relative standard deviation for measurements at the natural abundance level (10 analyses, 20-200 mug of N) was < 0.04 %.

This technical note explains the disadvantages of manual solid phase extraction (SPE) techniques and the benefits to be gained with automatic systems. The note reports on a number of general and highly specific applications using the Sample Preparation Unit OSP-2A.