Sample-changers, automatic

Beta particle calibration sources span energies from about 100 to 3,000 keV for proportional counters, and down to a few keV for liquid scintillation counters. In this experiment, a low-background, gas-flow, end-window proportional counter with automatic sample changer for alpha- and beta-particle counting is calibrated. Beta-particles sources are counted with pulse-height discrimination to eliminate interference from alpha particles the discriminator may be turned off when no alpha particles are present. 

Low background gas-flow, end window proportional counter with automatic sample changer for alpha and beta counting (or equivalent counting system)... 

An automatic sample changer (ASC) often is an option for a spectrometer. The operator sets the samples into the rack of the ASC and predefines the experiments, which are then performed with automatic homogeneity adjustment, processing,... 

For those who have access to the necessary equipment, neutron activation analysis is a convenient method for the determination of the average concentrations of trace elements in polymers. The fact that very little sample preparation is necessary contributes to its high reliability and reduces the risk of contamination to a minimum. Accuracies of 5% or better can be achieved when the concentrations are well above the detection limits. Analysis for about a dozen elements can be completed in less than an hour. To detect the elements with long-lived radioactive isotopes, about ten days are needed. If a number of samples are to be analysed, they can be irradiated simultaneously and counted sequentially using an automatic sample changer. 

Gamma-ray cylindrical sources The point source is mounted at the end of a plastic rod (diameter 9 mm). A disc can be fitted to this rod to facilitate its use in automatic samples changer. These sources are particularly suited for the calibration of well-type Nal(Tl) scintillation counters. 

Figure 8. Manifold for the determination of total amino acids by FIA (29). Key S, an automatic sample changer F, a filter fluorimeter (Turner Model 111) and R, the 1,2-henzenedicarbaldehyde reagent used as the carrier stream.

To limit random errors which could be associated to short term instabilities of the spectrometer, a given spectrum is repeated three times. Using an automatic sample changer, three vanillin samples can therefore be studied in 24 hours. 

Automation is one important prerequisite for high-throughput methods. Automated routines are nowadays available from nearly all companies. This equipment also comprises automatic pipeting as well as automatic sample changers. As this is particularly helpful for proteomics studies where-due to the digestion with different proteases a large number of samples is obtained, the clear focus is so far on proteins and no commercial Lipidomics MALDI-based platform is available so far (Wenk 2005). 

Commercial X-ray spectrometers may be equipped with automatic sample changers for unattended analysis of multiple samples. Computer-controlled spectrometers permit... 

The sample cassette is moved into position, either manually or with the automatic sample changer. In position, the sample is spun, generally at about 30 rpm, to homogenize the surface presented to the X-ray beam. 

The second commonly available system is a detector coupled to an automatic sample changer. In this arrangement, planchets or disks from a stack of 30 or 50 are fed individually by tray to the location beneath the detector window. The controlling computer sets the counting time of typically 10 to 100 min, moves the tray, and records the time and accumulated counts. The computer also controls whether alpha or beta particles or both are measured and whether samples are to... 

Finally, the use of nuclear instrumentation in the NAA process has proved to be unusually well-suited to automation. Large numbers of samples may be simultaneously irradiated, their gamma-ray spectra determined by an apparatus consisting of automatic sample-changer coupled to a germanium detector with tape or disk readout, processed by mass computational methods. This results in very rapid multielement data accumulation, requiring computer storage and manipulation, as will be evident in the section below devoted to Provenience research. 

Physical effects may be controlled in practice by frequent measurement of standards, rinsing nebulizers with solvent after each sample and performing operations at a constant rate. Automatic sample changers can improve results by performing these operations reproducibly. Partial clogging of the nebulizer uptake tube may be the main source of error remaining, as it may not be noticed until the next standard measurement. 

Commercial instruments are equipped with automatic sample changers. These are of various types and sizes, permitting either controlled loading of samples with sequential access or X-Y random access. 

---