Resolution magnetic sector

Collision/reaction cell technology (CCT/CRC) is a cheaper alternative for reducing the impact of interferences than is high-resolution magnetic sector ICP-MS. 

The determination of deviations in isotopic ratios requires very precise measurements. The combustion stage involved is usually carried out immediately before injection into the mass spectrometer. Some instruments have been developed that include a gas chromatograph in line with a tubular combustion oven (containing copper oxide at 800 C) and a low-resolution magnetic sector instrument. The mass spectrometer is equipped with a multicollector that allows recording at each individual mass (see Fig. 16.24). 

Concentrations of cadmium and lead were determined by isotopic dilution ICP-MS using two instruments a quad-rupole equipped with a collision cell and a high resolution (magnetic sector) ICP-MS. Results are presented in Table 2. 

The use of a high-resolution magnetic sector mass spectrometer, which can resolve the small difference in m/z for As" " at 74.922 from that of " °Ar Cl at 74.931, eliminates the chlorine interference. New collision-cell techniques, in which the atomized samples are mixed with a second gas (usually H2) in a reaction cell, also minimize this interference. Arsenic detection limits of a few ng have been reported in matrices containing 1,000 mg NaCl. The chlorine interference can also be avoided by preseparation using HG, GF, or chromatography. 

Eight samples of un-irradiated reactor pressure vessel (RPV) steel, two each from Trawsfynydd (TRA), Dungeness A (DNA), Sizewell A (SXA) and Bradwell (BWA) reactors were analysed. ICP-MS analysis was carried out using a high resolution magnetic sector instrument. Despite the sensitivity of this method, i.e. lower limit of detection (LLD) of around 8 pg g for procedural blanks, it failed to detect Li and achieved a detection limit of 80 ng g, which was well above the level of interest. However, the results were consistent and did show that the Li concentration was well below that found from the earlier analytical attempts (ICP-OES) and below the levels conservatively assumed in the waste inventory assessments. 

K.E. Jarvis, Determination of Lithium in Steel Samples by High Resolution Magnetic Sector ICP-MS, 7 December 2004, Viridian Partnership Report, for British Nuclear Group. 

Orthogonal extraction, improvements in TOF/MS resolution, and improvements in electronics have created a new application for TOF/MS in accurate mass measurements [70,71]. Accurate mass applications have traditionally been associated with high-resolution magnetic sector and FTMS systems. The ability to provide accurate mass measurements (+5 ppm) with more cost-effective instrumentation has created potential opportunities in the pharmaceutical industry. Such applications can offer improved selectivity for single-stage instrumentation and metabolite or impurity/degradation product identification, particularly when standard compounds are not available, such as in early drug discovery. 

Most mass spectrometers measure one m/z value at a time. A single channel ion detector is used for these instruments, either an electron multiplier or a Faraday cup. TOF, ion trap, and FTICR mass spectrometers have the ability to extract ions with many m/z values simultaneously, so simultaneous detection of these ions is desirable. One approach to multiple ion detection has been to use multiple detectors. Multiple detectors are also used for high-resolution magnetic sector MS instruments designed for very precise isotope ratio determination and for quantitative analysis using isotope dilution. Instruments with... 

Figure 10.31 Gas chromatogram of compounds in a sample of whiskey analyzed on a GCmate E high-resolution magnetic sector GC-MS instrument. [From JEOL Apphcations Note MS-1126200-A. Courtesy of JEOL USA, Inc., Peabody, MA (www.jeol.com).]...

Most manufacturers of ICP/MS instruments now offer a model that incorporates a collision cell. Interference reduction by sample purification, use of a collision cell (also called chemical resolution), and mass separation—are said to be orthogonal, i.e., gains in each method are independent and multiplicative with gains in the others. The ultimate instrument in this regard—a collision cell equipped, high resolution, magnetic sector MS—has not yet been built, but would enable the nearest approach yet to detection without interference of any isotope at ultra-trace levels. 

FIGURE 2.33 Double-focusing high-resolution magnetic sector mass spectrometer. 

Accurate isotope ratios often require high-precision mass spectrometers. Instruments capable of such high precision are either ICP-TOF-MS or high-resolution magnetic sector ICP-MS instruments of either the single detector or multicollector type. An excellent fundamental... 

Two types of mass spectrometers are mainly used for GC/MS work magnetic sector mass spectrometers, and quadrupole mass filters. There seems to be no clear preference for one or the other t e of instrument. For GC/MS usually low resolution spectra are sufficient. The molecular peak and the fragment peaks form a typical pattern that can either be interpreted by experience or by comparison of the unknown spectrum in the llbraiy. However, If the comparison method falls in identification of the unknown spectrum, a high resolution magnetic sector field mass spectrometer is needed. 

Figure 2.195 High resolution magnetic sector analyser, mass resolution at 10000 at 10% valley (TCDD isotope pattern).

---