A versatile low-cost laboratory computer network.

An inexpensive but powerful computer network particularly suited to the research laboratory is discussed. The primary advantages of the system are low cost, flexibility, freedom of choice of manufacturer, and convenience of upgrading. The principal limitations are speed of data transfer and the requirement for a certain level of skill during setting up. The system operates with both the CP/M and MP/M operating systems, but the principles of operation are generally applicable.

Selection of spectral windows for plasma atomic-emission spectrometry.

A program has been developed to evaluate the number of spectral windows required to perform elemental analysis by ICP-AES, given a certain spectral window width. The data indicate that photodiode array systems (sequential slew scan) with as few as 7 or 8 acquisitions (windows) might be viable. With smaller windows, approaching in size those used by direct-reading spectrometers, it appears that conventionally designed spectrometers with photomultiplier tube detectors could use between 29 and 37 windows to determine 59 elements. This indicates that a general purpose direct-reading spectrometer may be feasible.

Laboratory data-acquisition capabilities of microcomputers.

Some microcomputers have been evaluated in terms of their features and capabilities for basic laboratory data-acquisition tasks. The systems studied include the SDK-80 (8080), SDK-85 (8085), and KIM-1 (6502) single-board microcomputers, and the PET consumer/hobby-market microcomputer. Data-acquisition software benchmarks were tested on all the systems, and inexpensive analogue-to-digital and digital-to-analogue hardware subsystems were developed for the PET. The acquisition rates for 10-bit data under machine-language control range from 15 to 25 kHz, but under high-level (BASIC) language-control drop to about 100 Hz.

Laboratory data-acquisition capabilities of microcomputer high-level languages.

A comparison is made of the efficiency and precision of various high-level languages in data-acquisition programs for microcomputers.

Online standard additions calibration of transient signals for inductively coupled plasma mass spectrometry.

An online standard additions calibration method for transient signals in ICPMS is demonstrated in which a small volume of standard is injected as a spike into the sample/carrier stream, overlaying the analyte peak. This technique provides the advantages of conventional standard additions but requires only a single sample run. The method corrects for matrix effects and is suitable for transient signals in which the severity of the matrix effect changes over the analyte peak. The method uses a peak-fitting program to determine the area of the underlying peak and is shown to be effective for the determination of trace metal concentrations in both a high ionic strength matrix and in a biological matrix (urine). Eight analytes with concentrations in the range of 0.82-233.2 mug L-1 in urine were simultaneously determined using a standard spiking solution of 75 mug L-1 injected through a 100-muL loop. The measured concentrations for analytes free of spectral interferences agreed with the certified values, and the precision achieved was comparable to that achieved by the certifying agency. Using a conventional cross-flow nebulizer and Scott-type spray chamber, the accuracy obtained for online standard additions calibration was within 2%, and the precision was within 5%.

Design and operation of a capsule-based microwave digestion system.

A high-pressure microwave digestion system has been designed based on the concept of using large-bore tubes as digestion vessels and capsules as a vehicle for sample introduction. Many of the design aspects are dictated by the use of a relatively large (8.4 mm o.d., 25 mm long) capsule, which in turn dictates the inner tube dimensions. A variety of materials were studied for use as the tubing material. PFA was selected as the best material for a demonstration arrangement. The cycle of operation involves insertion of the capsule by a flexible rod followed by addition of digestion reagent and then a heating/cooling/venting cycle for removal of gases. When the digestion is completed, the system removes the liquid with the same flexible rod and then cleans itself. The system is highly automated with computer-controlled venting, cooling, and reagent addition. Data indicate that performance is similar to that expected of a conventional microwave oven operated at the same temperatures.