Spraying Detection systems

Several authors [386,387] have discussed the spectroscopic and nonspectroscopic (matrix) interferences in ICP-MS. ICP-MS is more susceptible to nonspectroscopic matrix interferences than ICP-AES [388-390]. Matrix interferences are perceptible by suppression and (sometimes) enhancement of the analyte signal. This enhanced susceptibility has to be related to the use of the mass spectrometer as a detection system. In fact, since both techniques use the same (or comparable) sample introduction systems (nebulisers, spray chambers, etc.) and argon plasmas (torches, generators, etc.), it is reasonable to assume that, as far as these parts are concerned, interferences are comparable. The most severe limitation of ICP-MS consists of polyatomic... 

Attainable detection limits depend on the amount of analyte that enters the ICP per second, the efficiency of aerosol conversion into analyte ions in the ICP, and the transmission efficiency of ions from the plasma to the MS detector. The detection limits also depend on the variation of the background and the integration time. Typical pneumatic nebulizer/spray chamber systems operated at sample uptake rates from 0.1 to 2.0 mL/min introduce an amount of analyte equivalent to that in 10 to 30 JiL/min of sample solution into the ICP. At a sample uptake rate of 1 mL/min, only 1% to 2% of the analyte enters the plasma most of the sample is lost in the spray chamber and exits through the drain. Concentration based detection limits can be improved by approximately a factor of 10 by using a high-... 

It is important to stress that these tests represent presumptive evidence for a vinyl ether containing phosphoglyceride (plasmalogen), but not a final proof of structure. Other tests that can be used in conjunction with the above qualitative detection systems are the phosphorus spray and sulfuric acid char... 

Liquid nebulization as a means of obtaining aerosols is commonly used for activities such as drug administration, hair spraying or perfume application [1,2]. Direct nebulization of a liquid phase containing the target analytes has been widely used in analytical chemistry for sample insertion into some detection systems (particularly atomic spectrometers). The main purpose of analytical nebulizers is to insert the maximum possible amount of sample, and hence of analyte, in the form of aerosol consisting of very small droplets, into the detection system. 

Penicillins on TLC plates are usually detected by iodine vapour [2,105,106] or a starch iodine spray [57,107], although amino penicillins such as amoxicillin can also be detected with ninhydrin [9,106], Investigations of alternative detection systems claimed advantages of sensitivity, selectivity or stability of the spot for chloroplatinic acid [108], iodic acid [109] and chloranil [110]. 

Spatially variable applications of herbicide can be made in fallow or widely spaced row-crops, such as maize or soya beans, by using spectral reflectance type detectors to determine the presence of weeds, and to actuate a spray application system directly. This approach has been developed commercially both in Australia (Felton, 1995), and in the USA, and considerable savings in herbicide use have been demonstrated - see also Chapter 3. The same approach has recently been developed in Europe for use in amenity areas, where the presence of weeds in pavements and gravel paths can be detected by systems working on spectral characteristic criteria. 

Highly nonpolar compounds such as fatty acids, glycerides, alkanes, and some lower terpenoids require simple nonpolar solvent systems (e.g., cyclohexane, hexane, pentane, diethyl ether.hexane mixtures) and may be difficult to detect by UV (i.e., no chromophore) or by spray detection (use charring reagents, e.g., vanillin-sulfuric acid). 

Visualization is either by viewing the developed plate under ultraviolet light or by spraying the developed plate with a dilute methanolic sulfuric acid solution and application of heat. System 4 with sulfuric acid spray detection is the most useful system because non-UV absorbing impurities are detectable. 

Another way to speed up HPLC that does not interfere with the existing gradient separation method is by parallel operation of several HPLC columns. The development in this direction started a couple of years ago when fast gradient separation was first combined with mass spectrometry-based detection. Parallel column operation was achieved by a single pumping system and a splitter tee that transferred the gradient flow onto two HPLC columns. The effluent of the two columns was simultaneously sprayed into a modified ion spray interface of a quadrupole mass spec-trometer. From the overlay chromatogram both desired and previously known compounds were identified after their molecular ions were filtered from the total ion current (TIC). In this first system, however, it was difficult to enhance the parallelization, and the detection system created a bottleneck. ... 

A similar mass spectrometric detection system is available commercially and is realized by a multiplexing electrospray inlet in combination with a time-of-flight (TOF) mass spectrometer that has a sufficiently high data acquisition rate. Like the above-described optical switch, the effluent of the HPLC channels is nebulized in individual probe tips and sprayed toward a rotating cylinder with a slit. By stepping this slit very rapidly from one probe tip to another, again a data acquisition rate of approximately one spectrum per channel can be reached in 1 second. Unlike the multiplex PDA detector, this multiplex mass spectrometric detector is normally connected to a HPLC system by a flow splitter. ... 

The functioning of these sprinklers can be initiated by an electronic detection system, or by heat-sensitive valves at each sprinkler head. When a fire is detected, a spray (or more recently, a mist) of water is emitted. The water absorbs the heat of the fire through a phase change to steam and thus arrests the combustion cycle. In certain appHcations where oil fires are expected, such as in restaurant kitchens, a special foam or gel replaces the water in the system. 

Several parameters have to be determined for achieving the optimum conditions when using iodine-azide reaction as the detection system in TLC pH (Fig. 2), the concentration of spray solution, and the influence of iodine and iodide ions on the course of iodine-azide reaction. 

Densitometric analysis coupled with iodine-azide reaction as a detection system is relatively difficult to conduct owing to background disappearance. There are two processes behind this iodine sublimation from a plate area and uninduced iodine-azide reaction proceeding outside a spot. Addition of potassium iodide to the spray solution lowers... 

Since shortly after its inception in 1955, AAS has been the standard tool employed by analysts for the determination of trace levels of metals. In this technique a fine spray of the analyte is passed into a suitable flame, frequently oxygen-acetylene or nitrous oxide-acetylene, which converts the elements to an atomic vapour. Through this vapour is passed radiation at the right wavelength to excite the ground state atoms to the first excited electronic level. The amount of radiation absorbed can then be measured and directly related to the atom concentration a hollow cathode lamp is used to emit light with the characteristic narrow line spectrum of the analyte element. The detection system consists of a monochromator (to reject other lines produced by the lamp and background flame radiation) and a photomultiplier. Another key feature of the technique involves... 

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