Instrumentation simplicity

The field of bioanalysis remains dominated by HPLC, despite the fact that several other chromatographic forms have been interfaced to MS, which include gas chromatography, supercritical fluid chromatography, and capillary electrophoresis. The popularity of RP-LC stems from its instrumental simplicity, wide scope of application, and relative ease of method development. This section primarily focuses on RP-LC, with attention also given to the recent resurgence in normal-phase methods (NP-LC). 

To date, the Raman method has been used with commercial Raman probes and microscopes, predominantly in the backscattering collection mode (see Figure 12.1), although in a number of specialist laboratories a 90° collection geometry is also used [1]. While the backscattering mode is used mainly for its instrumental simplicity and ease of use, this approach permits the effective depth discrimination of Raman signals in these media only at shallow depths [1]. Consequently, as... 

The application of capillary SFC to such complex mixtures clearly benefits from the use of selective detectors such as the mass spectrometer. As is shown in the next section, the cosdiina-tion of SFC with mass spectrometry has many of the same advantages of instrumental simplicity and flexibility as GC-MS. 

The method of molecular absorption has been used for Br atoms in the author s laboratory to check the stoichiometry of the titration reaction, Br + CINO -> BrCl + NO. It has also been used to measure the kinetics of radiative and nonradiative third-order recombination of Br atoms, and to follow [Br] in the bimolecular disproportionation of two BrO radicals these were shown to decay by the reaction BrO -f BrO -> 2Br -f- O2. It appears that vibrational relaxation of Bra, which might affect the method, was complete under the conditions used. One advantage of the molecular absorption method is its relative instrumental simplicity. However, the method is clearly inapplicable to any system in which interfering absorption by transients, reactants or products can occur. 

During this time there was a controversy between open tubular and packed column SFC. There was a widespread belief that carbon dioxide was much more polar than it actually is. Carbon dioxide is roughly as polar as pentane but probably in a different solvent family. Initially, efforts to extend SFC to more polar solutes were limited by the (largely unrecognized) low polarity of carbon dioxide, since there was also a reluctance to abandon the inherent instrumental simplicity of pressure programming a pure fluid. 

In spite of the instrumental simplicity of cyclic voltammetry, the method is surprisingly versatile and an experienced researcher can obtain a considerable amount of information on the basis of just recording a single CV. A large number of different electroanalytical techniques have been applied to the research on conducting polymers, from the chronoamperometric method to AC impedance methods, However, the methods rest only on the electrochemical characteristics of the polymer and naturally the information obtained is rather restricted. 

FTDI. The authors remarked that the instrumental advances and the associated open-source project recently reported can spread out the use of this universal detector for food analysis. Furthermore, the inherent portability of the C D system could make it an ideal instrument for on-site food testing. One example that combines creativity and the instrumental simplicity of this home-made conductivity detection is the analysis of monoalkyl carbonates in carbonated alcoholic beverages (sparkling wine, beer, and mixed drinks) [151]. By using two detectors, the authors not only demonstrated the presence of monoethyl carbonate (MFC) in the selected drinks but also proposed that the low pH values were responsible for the larger concentrations of MEC observed in lager beer and mixtures of rum and cola. In addition, the possibility to control not only a C D detector but also a series of valves using open-source software (Arduino) has been recently demonstrated [152]. 

Probably the simplest mass spectrometer is the time-of-fiight (TOP) instrument [36]. Aside from magnetic deflection instruments, these were among the first mass spectrometers developed. The mass range is theoretically infinite, though in practice there are upper limits that are governed by electronics and ion source considerations. In chemical physics and physical chemistry, TOP instniments often are operated at lower resolving power than analytical instniments. Because of their simplicity, they have been used in many spectroscopic apparatus as detectors for electrons and ions. Many of these teclmiques are included as chapters unto themselves in this book, and they will only be briefly described here. 

Simplicity Compared to most of the instrumentation currently in use, colorimetric tubes have no moving parts. 

Mechanical manometers are the oldest, simplest, and most reliable pressure measurement instruments. They have some disadvantages, which is one reason the use of electrical manometers is expanding. Their simplicity and fundamental nature can, however, be an advantage. 

The Munsell book standards corresponding to the limiting colors may even serve as material standards for industrial color control. In a material standard system the sample is compared with a standard by eye without the use of any meter or optical instrument. The success and popularity of these systems are largely due to their simplicity of application. The ability of the human eye to compensate for various illuminants and surroundings makes it possible for this system to give results even under mediocre conditions. The most critical work with material standards requires carefully controlled observing conditions. 

Brain et al. [137] reported a tandem mass spectrometry (MS-MS) procedure by which a direct measurement from an n-pentane extract of a surfactant is possible. This procedure is excellent from the standpoint of sensitivity and simplicity of sample preparation but is not commonly applied because of the need of an MS-MS instrument. 

Because of its simplicity the orifice meter is commonly used for process measurements, and this instrument is suitable for providing a signal of the pressure to some comparator as indicated in Figure 6.1. 

The advantage of the ToF instrument, in addition to its simplicity, is its fast scanning capability and for this reason it is increasingly being encountered in LC-MS instrumentation, particularly when fast analysis or high chromatographic resolution is involved. 

Seligson s group (95) has published a similar turbidimetric procedure but used nephelometry to measure continuously the effect of lipase on the light scattering of an olive oil emulsion. The instrumentation and approach is the same as that described above for the nephelometric determination of amylase. The method according to the authors is fast and precise with good specificity and sensitivity. The short time required for analysis makes it suitable for emergency use. The technical simplicity permits this method to be easily automated, and it appears to be the lipase method of choice. 

Compounds that are radioactive can be located on a preparative layer by contact film autoradiography, electronic autoradiography, and storage phosphor screen imaging [21-23]. These methods differ in terms of factors such as simplicity, speed, sensitivity, and resolution, and the method of choice depends on the available equipment, reagents, and instrumentation. All are nondestructive, and the detected compounds can be recovered without change for later studies. 

This yields an estimate for the bias (intercept) a and slope b needed to correct predictions yg from the new (child) instrument that are based on the old (parent) calibration model, b. The virtue of this approach is its simplicity one does not need to investigate in any detail how the two sets of spectra compare, only the two sets of predictions obtained from them are related. The assumption is that the same type of correction applies to all future prediction samples. Variations in conditions that may have a different effect on different samples cannot be corrected for in this manner. 

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