Performance spectrometers

The study of these contributions either as a subject in itself or for the purpose of obtaining more accurate values for the isomer shift requires the combination of a high performance spectrometer and an extensive data reduction effort using a digital computer. 

Ibach H 1990 Electron Energy Loss Spectrometers the Technology of High Performance (Berlin Springer)... 

All kinetic measurements were performed using UV-vis spectroscopy (Perkin Elmer 2, 5 or 12 photo spectrometers) as described in Chapter 2. 

In the process of performing a spectrophotometric determination of Ee, an analyst prepares a calibration curve using a single-beam spectrometer, such as a Spec-20. After preparing the calibration curve, the analyst drops the cuvette used for the method blank and the standards. The analyst acquires a new cuvette, measures the absorbance of the sample, and determines the %w/w Ee in the sample. Will the change in cuvette lead to a determinate error in the analysis Explain. 

The Z-spray inlet causes ions and neutrals to follow different paths after they have been formed from the electrically charged spray produced from a narrow inlet tube. The ions can be drawn into a mass analyzer after most of the solvent has evaporated away. The inlet derives its name from the Z-shaped trajectory taken by the ions, which ensures that there is little buildup of products on the narrow skimmer entrance into the mass spectrometer analyzer region. Consequently, in contrast to a conventional electrospray source, the skimmer does not need to be cleaned frequently and the sensitivity and performance of the instrument remain constant for long periods of time. 

For example, if a carbonaceous sample (S) is examined mass spectrometrically, the ratio of abundances for the carbon isotopes C, in the sample is Rg. This ratio by itself is of little significance and needs to be related to a reference standard of some sort. The same isotope ratio measured for a reference sample is then R. The reference ratio also serves to check the performance of the mass spectrometer. If two ratios are measured, it is natural to assess them against each other as, for example, the sample versus the reference material. This assessment is defined by another ratio, a (the fractionation factor Figure 48.2). 

The choice of a particular mass spectrometer to perform a given task must take into account the nature of the substances to be examined, the degree of separation required for mixtures, the types of ion source and inlet systems, and the types of mass analyzer. Once these individual requirements have been defined, it is much easier to discriminate among the large number of instruments that are commercially available. Once suitable mass spectrometers have been identified, the final choice is often a case of balancing capital and running costs, reliability, ease of routine use, after-sales service, and the reputation of the manufacturer. 

Preprocessor. A device in a data-acquisition system that performs a significant amount of data reduction by extracting specific information from raw signal representations in advance of the main processing operation. A preprocessor can constitute the whole of a data-acquisition interface, in which case it must also perform the data-acquisition task (conversion of spectrometer signal to computer representation), or it can specialize solely in data treatment. 

Edx is based on the emission of x-rays with energies characteristic of the atom from which they originate in Heu of secondary electron emission. Thus, this technique can be used to provide elemental information about the sample. In the sem, this process is stimulated by the incident primary beam of electrons. As will be discussed below, this process is also the basis of essentially the same technique but performed in an electron spectrometer. When carried out this way, the technique is known as electron microprobe analysis (ema). 

Xps ndAes Instrumentation. The instmmentation required to perform xps and aes analyses is generally sophisticated and expensive (19). The need for UHV conditions in order to retain surface cleanliness for a tractable period of time was mentioned above. Beyond this requirement (and the hardware that accompanies it), the most important components of an electron spectrometer system are the source, the electron energy analyzer, and the electron detector. These will be discussed in turn below. 

Atr—ftir can be readily performed on most commercial ftir spectrometers through the use of an attachment for atr spectroscopy. These devices provide ir-transparent internal reflection elements that are typically made of Ge, KRS-5, ZnSe, or ZnS. These internal reflection elements are made of materials that are of extremely high purity to avoid losses from absorption by impurities in these devices. Coupling of a thin film or surface sample to one of these reflection elements is accompHshed by pressing the sample against the element while acquiring the spectmm. 

In addition, the appHcation of the mass spectrometer (ms) as a detector for gas—Hquid chromatography has made the positive identification of peaks possible. High performance Hquid chromatography (hplc), which involves various detectors, can be used to measure hydrophilic and hydrophobic organic compounds in water. 

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