Quadrupole systems

ToFs can also be used in combination with other mass analysers. Both hybrid sector and quadrupole systems are available. oaToF-MS has been interfaced to a quadrupole mass filter and hexapole gas collision cell, such as to allow recording of mass spectra and product ion spectra with good mass resolution (ca. 10000), high sensitivity, high mass range (ca. 10 000 Da) and high mass accuracy (<5ppm) [177,178]. QqToFMS may be fitted with API sources with flow-rates from nL... 

In 1995, when HPLC/MS/MS was becoming the premier tool for PK assays, chromatographic sample cycle times were typically 10 to 12 min. At 10 min per sample, 16 hr were required to process 96 samples. By 2000, scientists used shorter HPLC columns and per-sample cycle times decreased to 5 to 6 min. At 5 min per sample, it takes about 8 hr to assay one 96-well plate of samples. As a result, parallel HPLC became popular Korfmacher et al.154 described a two-column system and an MS vendor produced a triple quadrupole system designed to work with four HPLC columns.16155-158 Advances in fast chromatography continued and by 2005, sample cycle times of 1 to 2 min became common.21 87 159-161 At 2 min per sample, 3 hr are required to assay one 96-well plate of samples. 

To study dipole-dipole relaxation, one must distinguish between homonuclear and heteronuclear (unlike) spin-1 pairs. The latter gives rise to the so-called 3/2 effect.29 For an isolated pair of like spin-i nuclei (/= 1) separated by an intemuclear distance r, the treatment of spin relaxation is identical to that for a spin-1 quadrupole system. The Zeeman spin-lattice relaxation time T1Z and spin-spin relaxation time T2 are given, respectively, by... 

At present, the most powerful and promising interfaces for drug residue analysis are die particle-beam (PB) interface that provides online EI mass spectra, the thermospray (TSP) interface diat works well with substances of medium polarity, and more recently the atmospheric pressure ionization (API) interfaces that have opened up important application areas of LC to LC-MS for ionizable compounds. Among die API interfaces, ESP and ISP appear to be the most versatile since diey are suitable for substances ranging from polar to ionic and from low to high molecular mass. ISP, in particular, is compatible with the flow rates used with conventional LC columns (70). In addition, both ESP and ISP appear to be valuable in terms of analyte detectability. These interfaces can further be supplemented by preanalyzer collision-induced dissociation (CID) or tandem MS as realized with the use of triple quadrupole systems. Complementary to ESP and ISP interfaces with respect to the analyte polarity is APCI with a heated nebulizer interface. This is a powerful interface for both structural confirmation and quantitative analysis. 

V. A. Moskalenko, M. I. Vladimir, and S. P. Kozhukar, Self-Consistent Field Method in the Theory of the Glass State of Spin and Quadrupole Systems, Shtiintsa, Kishinev, USSR, 1990. 

All analytics should be performed on LC/MS systems in industrial labs very often ion traps or quadrupole systems are used. Single ion monitoring in either positive or negative mode (compound dependent) is used in HTS conditions. Local LC conditions (injection volume, mobile phase gradients) should be applied to accommodate variations in LC equipment. The selected LC column stationary phase can be used routinely in different labs (for example, C-18 phase selection is compound dependent). 

The choice of GC conditions employed was left to the discretion of the seven participating laboratories. Instrument types used in this study included three quadrupole systems and four magnetic sector instruments. One of the laboratories performed the analyses using both electron capture and mass spectral detection. Two laboratories performed the analysis at a high resolving power (RP > 10,000) while others used the mass spectrometer operating at nominal resolution. All laboratories performed the analysis under ECNI conditions... 

A simple method was described for the determination of simvastatin in human plasma in the range of 0.1-20 ng/ml, based in LC-MS detection of [M+Na] in SIM on a single quadrupole system [36]. No attention was paid to the possible conversion of simvastatin into its P-hydroxy acid. 

The above analysis is usually applied to spin- /2 systems but there is no reason why magnetisation transfer cannot be applied to quadrupole systems. If Xq is small the theory is identical to that given above, but if xq becomes significant the Hartmann-Hahn condition is modified to... 

Tandem mass spectrometers are either triple quadrupole systems (the collision cell is also a quadrupole) or quadrupole ion-trap spectrometers. A triple quadrupole mass spectrometry system is shown in Figure 32F-2. Here, the first quadrupole acts as a mass filter to select the ion of interest. This ion is then fragmented by collision with an inert gas in the collision cell. The final quadrupole mass analyzes the fragments produced. The triple quadrupole system can be operated in other modes. For example, if the first quadrupole is operated as a wide mass filter to transmit a wide range of ions and no collision gas is present in the collision cell, the instrument is operating as an LC/MS system. The instrument can be operated by scanning one or both quadrupoles to produce mass spectra of the fragments of ions selected by the first quadrupole as that quadrupole is scanned. 

Particularly in quadrupole systems spectral interferences may limit the power of detection as well as the analytical accuracy. This is shown by a comparison of a high- and a low-resolution scan of a mass spectrum (Fig. 123) [609, 610], In the first scan (A), the signals of 56Fe2+, 28Si+, 12C160+ and 2N are clearly separated, which is not, however the case in the quadrupole mass spectra. In the latter scan, interferences can be recognized from comparisons of the isotopic abundances. Also physical means such as the use of neon as an alternative discharge gas [611] can be used to overcome the spectral interference problem. 

Fig. S.4. Schematic view of a quadrupole system with stable (resonant ion) and unstable (non-resonant ion) ion trajectories. 

Lor analyses, two sets of HPLC conditions were used, depending on whether UV (285 nm) or MS (electrospray ionization on a triple quadrupole system) was to be used for detection. Lor MS detection, analyses were conducted using a 125 x 4 mm (5 pm) Lichrospher 60 RP-Select B column. Eluent A was 800 ml water/200ml acetonitrile/3.08 g ammonium acetate adjusted to pH 6.5 with acetic acid. Eluent B was 500 ml water/500ml acetonitrile/1.93 g ammonium acetate adjusted to pH 6.5 with acetic acid. The gradient was run at 0.5ml/min as follows from 0-25.0 min, 100% A from 25.0-35.0 min, 100% A-100% B from 35.0-45.0 min, 100% B from... 

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