Mass Spectrometry Instrument Parameters

Instrument parameters were optimised for each experiment to provide the highest relative signals. For experiments requiring colhsion induced activation, the voltage apphed in the trap region was optimised such that minimal secondary fragmentation of ejected ions occurred (Table 2.8). 

Denatured KS spectra obtained from acylation experiments were subjected to minimal smoothing and noise reduction. The spectra were deconvoluted using the transform function of MassLynx, taking an average of aU charge states. Relevant peak intensities were recorded and converted into the concentration of [KS-SH] and [KS-acyl] respectively. Data was recorded in triplicate, and an average taken for kinetic plots. 

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Christman et al. [72] gave details of procedures for extraction, clean-up, and concentration of samples of soil prior to the determination of their content of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans by gas chromatography and by gas chromatography-mass spectrometry. Instrumental parameters are also included. Some typical results are tabulated. 

Contemporary GC/mass spectrometry instruments are greatly aided by computers, which can control various instrumental parameters, provide data reduction, and compare acquired mass spectra with the extensive libraries of many thousands of previously recorded spectra. 

A second problem in whole molecule mass spectrometry is that fluctuations in ion current may introduce substantial errors. Recall that ions of different m/z are not measured simultaneously in whole molecule mass spectrometry. If the ion current is not stable (and it commonly fluctuates in El sources), then after first peak (say m/z = 112 in our example) is measured, and instrumental parameters are changed in order to focus the next peak (m/z = 114) on the collector, the ion current of this second peak may no longer correspond to that existing at the time the first peak was measured. One can try to switch the detector from peak to peak more rapidly but that shortens the collection time for each peak, fewer ions will be counted, and errors in counting statistics will increase. Normally this problem is dealt with by statistical... 

Using the three measured ratios, Ca/ Ca, Ca/ " Ca and Ca/ " Ca, three unknowns can be solved for the tracer/sample ratio, the mass discrimination, and the sample Ca/ Ca ratio (see also Johnson and Beard 1999 Heuser et al. 2002). Solution of the equations is done iteratively. It is assumed that the isotopic composition of the Ca- Ca tracer is known perfectly, based on a separate measurement of the pure spike solution. Initially it is also assumed that the sample calcium has a normal Ca isotopic composition (equivalent to the isotope ratios listed in Table 1). The Ca/ Ca ratio of the tracer is determined based on the results of the mass spectrometry on the tracer-sample mixture, by calculating the effect of removing the sample Ca. This yields a Ca/ Ca ratio for the tracer, which is in general different from that previously determined for the tracer. This difference is attributed to mass discrimination in the spectrometer ion source and is used to calculate a first approximation to the parameter p which describes the instrumental mass discrimination (see below). The first-approximation p is used to correct the measured isotope ratios for mass discrimination, and then a first-approximation tracer/sample ratio and a first-approximation sample CeJ Ca... 

Benkestock, K. Sundqvist, G. Edlund, P. O. Roeraade, J. Influence of droplet size, capillary-cone distance and selected instrumental parameters for the analysis of noncovalent protein-ligand complexes by nanoelectrospray ionization mass spectrometry. J. Mass Spectrom. 2004, 39,1059-1067. 

Many of the compositional parameters utilized as independent variables in the work cited above represented derived coal properties rather than fundamental chemical features. Further, variables traditionally used are often highly correlated with each other (for example volatile matter and hydrogen). As pointed out by Neavel (34) / this limits the utility of such parameters in correlational models. Instrumental techniques such as pyrolysis/mass spectrometry (35.36 C-n.m.r, FTIR, and... 

G. Wang, R.B. Cole, Solution, gas-phase, and instrumental parameter influences on charge-state distributions in electrospray ionization mass spectrometry. In R.B. Cole (Ed.) Electrospray Ionization Mass Specrmmerty, Wiley, New York, 1997, pp. 137-174. 

As analytical and bioanalytical methods must be validated before using them for routine sample analysis and after changing method parameters (see Chapter 8), instruments such as liquid chromatography coupled with mass spectrometry (LC-MS) or tandem mass spectrometry (LC-MS/MS), which are utilized to perform the analysis, should be calibrated and qualified. In addition, an instrument s performance should be tested for suitability prior to use on practically a day-to-day basis. 

Gas Chromatography-Mass Spectrometry. A Finnigan 4500/Incos instrument with a 30-m X 0.32-mm i.d. capillary column coated with SP-B-5 was used. The GC parameters were as follows injector, 270 °C column oven temperature programmed, 50 °C (0.1 min, hold) 15 °C/min to 100 °C, 5 °C/min to 270 °C internal standard, anthracene-djo helium flow, 3.0 mL/min sample size, 3.0 /xL. MS conditions were as follows El, 70 eV scan (m/z), 35-650 daltons source temperature, 250 °C filament current, 0.5 A sensitivity, 10-8 A/V. (NOTE When the name of a compound is followed by (confirmed) , it means that the standard material was analyzed for confirmation under conditions identical to those of the sample when the name is followed by (tentative) , it means that the mass fragmentography showed the best fit (>80 ) based on the National Bureau of Standards [NBS] library computer search.)... 

A critical review of the inherent limitations of modern PFA analytical methods is available in Martin et al. [18], but some examples are discussed here. For quantitative determination, the HPLC system is often interfaced to a Micromass or Sciex tandem mass spectrometer operated in the negative ion electrospray mode. Instrumental parameters are optimized to transmit the [M - H] ion for all analytes (Table 5). When possible, multiple daughter ions are monitored, but quantitation is generally based on a single product ion (Table 5, Fig. 4). In the electrospray tandem mass spectrometry (ES MS/MS) system, the 499 Da -> 80 Da transition can provide a stronger signal than... 

F. Laborda, M. J. Baxter, H. M. Crew, J. Dennis, Reduction of polyatomic interferences in inductively coupled plasma mass spectrometry by selection of instrumental parameters and using an argon-nitrogen plasma effect on multi-element analyses, J. Anal. Atom. Spectrom., 9 (1994), 727-736. 

Mass spectrometry has become more useful In the support of electronic development and manufacturing processes. Fourier transform mass spectrometry, the latest advance in this analytical method, Is another step forward in versatility, sensitivity and reproducibility in analytical characterization, qualification and quantification of raw materials and contaminants as used in electronic devices. A review will be provided of basic instrument hardware and interfacing, significant operating parameters and limitations, and special inlet systems. Emphasis will be placed on material evaluation, process control and failure analysis. Data handling will be reviewed using appropriate examples encountered in material and failure analysis. 

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