Bench-top Instruments

Quadrupole mass spectrometers are generally bench-top instruments, of relatively low cost, easy to manage and widely used for routine analysis. 

Newer techniques for measuring the refractive index allow for instantaneous, real-time measurement in process streams, or alternatively, a special continuous-flow sample well can be installed on bench top instruments. Small, pocket-sized refractometers also make held measurement very simple and reliable. Fiber optic sensors find uses in biomedical applications. 

In addition to these collision/reaction cell instruments, since 2002 Thermo Fisher Scientific has been selling the XSeries ICP-MS with a hexapole collision cell (developed from ThermoElemental PQExel ICP-MS) as a bench top instrument on the analytical market. A special ion extraction system in Thermo s XSeries", ion optics together with a hexapole collision cell to minimize the interference problem in ICP-MS, provides the lowest background signals for ICP-QMS (< 0.5 cps). 

The OPCW mobile laboratory equipment has been selected to allow operation of a GC/MS laboratory on site, aiming at a performance similar to the one of a stationary laboratory using a standard bench top instrument. However, restrictions in the selection and operation of the equipment (i.e. protection of confidential information) and issues related to logistics/transport of the laboratory equipment cause certain limitations, which are described in the paragraphs below. 

Modern multimeters maybe equipped with memory possibilities, and/or interfaces to a personal computer by infrared, IrDA, or serial link, RS-232, or an instrument bus such as IEEE. Modern portable DMMs may have accuracies as good as 0.025%, whereas nowadays bench-top instruments reach accuracies in the single-digit parts per million figures. 

There are many types of mass spectrometer, from high-resolution double-focusing instruments, which can distinguish molecular and fragment masses to six decimal places, to bench-top machines with a quadrupole mass detector which can resolve masses up to about m/z = 500, but only in whole-number differences. Routinely you are most likely to encounter data from bench-top instruments and therefore only this typie of spectrum will be considered. 

Advances in TOF/MS technology, such as reflectron ion optics, delayed ion extraction, and orthogonal ion acceleration, have given rise to bench-top instrumentation with resolution capabilities in excess of that obtained by quadra-pole MS systems. Each of these devices limits or corrects the kinetic energy spread of ions with identical m/ ratios. 

Mass spectrometry is becoming the most common detector for the analysis of VOCs in soil samples, particularly as bench top instruments have increased in performance and decreased in price. Very often, the nature of the contaminants present is unknown and MS is used to identify individual compounds in the sample. Mass spectrometry may be used either in full scan mode or selected ion monitoring, depending on the nature of the compounds to be analysed and whether or not identification and quantitation are required. The use of selected... 

Traditionally, a sample was taken from a tank, vat or pipe and carried to a laboratory remote from the process for analysis on conventional bench top instruments. This takes time and when results are finally available the process may have been halted unnecessarily or, worse, have continued for a number of hours when results may have indicated that it needed to be stopped and remedial action taken. To avoid such costly delays, there has been a drive to bring the instruments to the process rather than the other way aronnd. There are a nnmber of ways of taking samples from a process for assay (Figure 9.1) ... 

Another more elaborate pyrolysis—chromatography—apparatus was described by MacLaury and Schroll (146), which permitted heating rates from 5 C/m to 5000°C/S. It consisted of a Chemical Data Systems geological sample and analysis system and a gas chromatograph. This system is a self-contained bench-top instrument that provides a means of trapping volatiles from a DSC 100 Pyroprobe solids pyrolyzer. The Pyroprobe uses a platinum... 

Which is better, GC-MS or immunoassay This is a question often asked about plant hormone quantification. GC-MS, which is now more widely available since the Introduction of bench-top instruments, has the advantage that it not only provides quantification of the hormone by the isotope dilution method, but also confirms the identity of the compound concerned by comparison of its spectrum with that of a standard. However, once validated for a particular tissue, immunoassay has the advantage that many samples can be analysed very quickly. Both techniques require sample pre-purification, often by the same methods. A more recent development is a powerful combination of the two technologies which uses the antibody immobilised on a polymer support as a method of affinity-purifying the hormones (together with interfering substances) from plant extracts prior to analysis by GC-MS. Immunoaffinity chromatography is discussed in the next section. 

Bench top MWDXRF analyzers were used in this study. Measurements were performed in two different laboratories. Five different bench top instruments were used in the XOS R D laboratory and one instrument was used for measurements acquired in a refinery lab. 

An in-house Found robin study was conducted using the ultra-low-sulfur diesel crosscheck samples from the ASTM D2 study group. Five bench top instruments were used with a different operator for each instrument. Calibration standards from different conunercial sources were used for the calibration of these instruments. There were a total of 8 diesel samples from the crosscheck program. NIST SRM2723a was added to frie 8-sample group so a total of 9 samples were used in the study. Two successive repeat measurements were made for each sample on each analyzer. The measurement results are hsted in Table 6. 

The goal of this programme was a bench-top instrument that could eventually be deployed in the field or on a plant, for routine automatic analysis of a gaseous sample stream for a few components at the 1 ppm to 100% concentration level. At the start of the project an overview was taken of the commercial spectrometer designs that had appeared on the market during previous years (Chapter 5). Their common feature was the use of microwave sweepers based on frequency stabilised BWO sources, gas samples maintained at Pa pressures and modulated by high electric fields, calibration by bridge spectrometry, and operation in the 10-40 GHz band. All these features led to cumbersome and expensive systems that were versatile but required specialised skills to operate them. 

Although the TMS derivatives are applicable to a very wide range of analytes, care must be taken to avoid exposure to moisture. They have another major handicap for the GC—MS of compounds with multiple derivatizable functional groups the molecular weight is increased by 72 daltons for each TMS group added (Table 1). As the m/z range of the majority of bench-top instruments is 0-650 or 0-800, one can quickly obtain derivatives which produce important ions outside this range, so that only partial mass spectra are recorded. In such cases, acylation or methylation (see Sections 4 and 5, below, and Chapters 2, 3 and 5) may be preferred. 

The research process is a long-term commitment and requires high standards in the results from the very beginning. The quality of the results relies on competent analytical chemists, but also on the availability of good instrumentation, which is often evident in the laboratories of the research intensive pharmaceutical industry. Separation techniques, especially LC, have had an enormous impact on pharmaceutical analysis. The combination of LC with MS has now extended the possibilities of the techniques as qualitative and quantitative data can be obtained online. The availability of less-expensive bench-top instruments operated by nonspecialists has changed the situation considerably. 

However, the continual development of new bench-top instruments provides potential for the future use of this method. 

Bench-top Instruments Component Quantification during a Chemical Reaction... 

Centrifuge for 10 min using a bench-top instrument. K is essential that a spark-proof centrifuge is used for this purpose. 

In recent years mass spectrometers have become increasingly robust, compact and less expensive, at least on a gathered information/price basis. Bench-top instruments are available with either quadrupole or ion trap mass filters. Applying single-ion monitoring (SIM) of a few characteristic fragments of the halocarbon molecules, the sensitivity is equal to or better than that of the ECD. 

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