Spectrometer Specifications

Commercially available FT NMR spectrometers (e g, Bruker, Vanan, GE, JEOL) are designated by their H operating frequency ranges (Table 5 4 1) Satisfactory nC NMR spectra of lignin can be obtained with 200 and 250 MHz spectrometers Higher field provides greater sensitivity and is used when enhanced sensitivity is a critical requirement The following instrument specifications are important 

Homogeneity of B (obtained by adjusting gradient coils or shimming). 

Sensitivity is defined by the signal-to-noise ratio of one acquisition on an 8% solution of ethylbenzene in CDC13. 

General operating conditions are described in the user s manual, including lists of commands, together with the program and microprogram sequences that are available. These sequences are periodically upgraded by the manufacturers. Once the NMR experiment and its sequence are selected, the operator has to choose the appropriate experimental parameters. 

Spectra are usually recorded with complete decoupling of protons by broadband noise decoupling. The general scheme of the sequence for a routine spectrum is illustrated in Fig. 5.4.5a and a set of recording values are listed in Table 5.4.2. 

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The tandem mass spectrometer consists of a mass spectrometer followed by a field-free collision chamber, followed by a second mass spectrometer. Specific ions... 

The GETFILE software is used in this volume to demonstrate its capabilities for converting various spectrometer specific data formats into the WINNMR format. It has been developed for data conversion and easy data transfer and must be installed if you wish to... 

A typical layout of an EPR spectrometer is shown in Fig. 15.5. While the general principles of operation and detection are the same for different spectrometers, specific steps may vary. The readers are encouraged to consult the manual and vendor regarding each individual spectrometer. Examples used in discussions below are based on a Bruker EMX X-band spectrometer that is equipped with an ER-041X microwave bridge and a high-sensitivity cavity (ER-4119HS, Bruker Biospin, Inc.). 

Ion transport from a continuous ion source to the extraction/acceleration region of the TOF-MS presents many of the challenges also associated with other mass spectrometers. Specifically, a means of efficiently focusing incoming ions into a beam of well-defined energy and spatial characteristics is required in order to achieve optimal performance for any mass analyzer. 

All of these techniques can, of course, be used simultaneously with chromatographic separation techniques. Methods that allow an improvement in the mass spectrometer specificity can thus be worthwhile alternatives to long procedures for sample preparation. However, quantitative analysis carried out directly on neat samples may undergo a matrix effect characterized by a variation in the sample response because of the effect of the matrix on the abundance of ions within the source. 

The list below defines most of the detector properties important to Raman applications, particularly for dispersive spectrometers. Specifications of particular devices will be discussed in subsequent sections. More specific definitions are provided for CCD detectors in Section 8.5.2. 

The mass spectrometer is theoretically capable of analyzing any gas in a mixture of gases with a speed, specificity, sensitivity, and accuracy that cannot be matched by other known means of analysis. However, the initial cost of the instrument and accessory equipment has thus far precluded its widespread use. Fowler and Hugh Jones described a mass spectrometer specifically for respiratory physiological studies. Extensive use has been made of this instrument (W6-W8). 

FT-IR spectrometers specifically manufactured for reflection microspectrometry are commercially available. Such spectrometers can be combined with most microscopes having infinity-corrected optics (in which the output from the Cassegrain objective mirror becomes parallel radiation). Since, in the infinity-corrected design, the output... 

Standard deviation is consistent with spectrometer specification... 

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