Early instrumentation

World War 11 produced the seeds for mid-range infrared instruments. Synthetic rubber produced to replace supplies lost due to the German naval presence needed to be analyzed. Industrial infrared instruments were first developed for this purpose. Postwar research showed that the mid-range region of the spectrum was more suited to structural elucidation instead of quantitative work. 

With the explosion of organic synthesis, infrared spectrometers became common in almost every laboratory for the identification of pure materials and structure elucidation. With the appearance of commercial ultraviolet/visible (UV/Vis) instruments in the 1950s to complement the mid-range IRs, little was done with near infrared. 

It is no coincidence, then, that several companies specializing in NIR equipment should spring up in nearby communities of Maryland over the years [12]. In fairness, Dickey-John produced the first commercial NIR filter-based instrument and Technicon (now Bran + Leubbe) the first commercial scanning (grating) instrument. Available instruments and the principles of operation of each type are covered in a later chapter. However, before looking at the hardware, it is necessary to understand the theory. 

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Valve voltmeters were widely used in the past, but have been replaced by transistor voltmeters. With instruments of this type it is possible to achieve an input resistance of 50 MQ or more, the current required to operate the instrument being of the order of 10" A. The early instruments had a tendency to zero drift on the lower ranges, but this has been overcome in the modern transistor types. Such instruments are most often used to make potential readings in extremely high-resistance electrolytes. The accuracy of such instruments is of the order of 2% full-scale deflection. It is necessary to ensure that both types are so designed that they do not respond to alternating currents. 

Recently a decreased level of CE activity has been noticed with a shift of attention towards other separation techniques such as electrochromatography. CE is apparently not more frequently used partly because of early instrumental problems associated with lower sensitivity, sample injection, and lack of precision and reliability compared with HPLC. CE has slumped in many application areas with relatively few accepted routine methods and few manufacturers in the market place. While the slow acceptance of electrokinetic separations in polymer analysis has been attributed to conservatism [905], it is more likely that as yet no unique information has been generated in this area or eventually only the same information has been gathered in a more efficient manner than by conventional means. The applications of CE have recently been reviewed [949,950] metal ion determination by CE was specifically addressed by Pacakova et al. [951]. 

Photographic plates used in early instruments have now been abandoned because they are slow, non-reproducible and their response is nonlinear with ion intensity (low dynamic range). However, the principle of simultaneous detection is very attractive. Spark source Mattauch-Herzog spectrographs have long used this detection system. 

The evolution of Raman spectroscopy from a spectroscopic novelty, to a complementary technique in niche applications, to an analytical powerhouse, has closely paralleled the advancement of enabling technologies. While a simple block diagram of the components of a Raman spectrometer shown in Figure 1.1 would still be comparable to the very early instruments built by C.V. Raman [1], the improvement in functionality of each component has dramatically increased the impact of Raman spectroscopy in areas where it was... 

This chapter deals with two main issues Why PAC is done and how it is done. The history of PAC is discussed from the perspective of its early origins in petrochemicals. Further, aspects on early instrument development are presented. Why PAC is done is easy to answer to increase the bottom line via improved production efficiency. The benefits of PAC have already been mentioned - all of which impact a company s bottom line. How... 

As modem scientific instruments become ever more sophisticated, concealing their electronics within unexciting black (or grey) boxes, older instruments become all the more fascinating. An early instrument used in the analysis of solutions was the hydrometer, or in Lavoisier s term the chemist s balance for fluids . The various forms of this instrument and some of its applications over the period 1770-1810 have been discussed.297 While most designs were produced to determine the concentrations of alcoholic solutions, variants were marketed for use with a wide range of other liquids. Among these instruments was the urinometer, and an early version was described by William Prout.298... 

Beginning in 1953 with the first commercial NMR spectrometer, the early instruments used permanent magnets or electromagnets with fields of 1.41, 1.87, 2.20, or 2.35 T corresponding to 60, 80, 90, or 100 MHz, respectively, for proton resonance (the usual way of describing an instrument). 

Temperature Control. In most of the early instruments, the columns were exposed to ambient conditions, and no provision was provided for ther-mostating them. More recently it has become clear that there are advantages to controlling the temperature, and some analyses are markedly improved at elevated temperatures. For example, higher temperatures provide faster kinetics, lower solvent viscosities, and decreased adsorption. Newer instruments provide this capability, and thermostatic jackets are commercially available for retrofitting on older ones. 

Sodium and other alkali metals are easily ionized and need special caution. Early instruments were usually fitted with an air-propane burner that yielded a cooler flame, that is, less energy rich, hence giving rise to lesser ionization. Modern instruments do not usually have this facility rather, they use an air-acetylene flame that results in a standard upward curve as the ionization decreases with increasing concentration of the analyte. In such cases, ionization has to be counteracted by modifying the sample solution. Another metal with a high ionization potential is added in large quantities, for example, 1000 pg g-1, to the... 

Its successor, used for all early instruments designed to measure electrical currents, and still used in ammeters and voltmeters today, is the d Arsonval144 galvanometer (Fig. 10.28) developed by d Arsonal and Deprez145 in the 1880s, which consists of a permanent magnet B0/ within... 

Spectrometer — Spectrometers are instruments to record spectra, i.e., intensity (or absorbance) versus wavelength or versus frequency of electromagnetic radiation. The interaction of matter with electromagnetic radiation can be studied in absorption or in emission mode. In the former case electromagnetic radiation (used as probe) is interacting with matter. (The term spectroscope refers to the early instruments where the spectra were observed with the eye. Although in all modern experiments the spectra are measured and recorded, the term spectroscope is still used synonymously to spectrometer.)... 

Emission interference was common in many early instruments which were accessories for UV/visible spectrophotometers, which operated in most instances on a d.c. system. The interference was caused by emission of the element at the same wavelength as that at which absorption was occurring. All modem instruments use a.c. systems which are of course blind to the continuous emission from the flame. However, if the intensity of the emission is high, the noise associated with the determination will increase, since the noise of a photomultiplier detector varies with the square root of the radiation falling upon it. 

One limitation of the technique is the energy resolution obtainable. Early instrumentation only had a resolution of the order of 1 eV, although modem instruments achieve a resolution of 0.1 eV. These are much lower than the... 

Early instruments employed low (forward) angle laser light scattering (LALLS) but these have been replaced by multi-angle instruments. MALLS instruments use Lorenz-Mie (often referred to as Mie) theory or Fraunhofer diffraction theory. 

In early instruments, the detectors consisted of a series of half rings [143,144] (Figure 10.8) so that a matrix equation developed. Sliepcevich and co-workers [145,146] inverted this equation to obtain the particle size distribution. The equation was solved by assuming the distribution fitted a standard equation and carrying out an iteration to obtain the best fit. A matrix inversion was not possible due to the large dynamic range of the coefficients and experimental noise that could give rise to non-physical results. An inversion procedure that overcame these problems was developed by Philips [147] and Twomey [148] that eliminated the need to assume a shape for the distribution curve. 

So-called hybrid mass spectrometers include a combination of two different types of mass spectrometers in a tandem arrangement. The combination of a magnetic sector mass spectrometer with a quadrupole mass spectrometer was an early instrument of this type. More popular is the combination of a quadrupole for MSI and a TOF for MS2, As with TOF/TOF, these instruments are presently used mainly for proteomics research but could eventually find applications in the clinical lab. These mstruments are unable to perform true precursor ion scans or constant neutral loss scans. Commercial examples of this type of instrument include the qTOF by Waters Micromass and the QSTAR by Apphed Biosystems/MDS Sciex. 

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