Detector mass spectrometry

The use of mass spectrometry (MS) as a detection system is inevitable in the evolution of any separation method, especially CE where the liquid flow rate ( 1 ml/min) is compatible with conventional mass spectrometers. The combination of a high-efficiency liquid-phase separation technique, such as capillary electrophoresis, with MS detection provides a powerful system for the analysis of complex mixtures. Analyte sensitivity and the mass spectrum obtained depend on the electrospray ionization (ESI) voltage, ion-focusing parameters, and buffer composition. In general, the greatest sensitivity is obtained by employing conditions that facilitate desolvation and minimize cluster formation.47 Three ways of interfacing for CE-MS 

The first approach to interfacing CE with MS was reported by Smith et al.48 when they incorporated the electrospray ionization (ESI) technique introduced by Dole et al.66 This development was based on the recognition that it is not necessary for the detection end of the CE capillary to be immersed in the buffer reservoir as conventionally practiced, as long as it is biased negative of the cathode potential (assuming a cathodic detector end). The ESI was created directly at the terminus of the CE capillary, avoiding any postcolumn region that would contribute to extracolumn band spread or analyte adsorption. A quadrupole mass filter was combined with ESI to produce the first on-line MS detection with capillary electrophoresis. 

A coaxial CF-FAB interface was applied to the coupling of CE with tandem MS. A pair of coaxial fused silica capillary columns were used to deliver, independently, the microcolumn effluent and the FAB matrix directly to the FAB probe tip face. The advantages of the system are that the composition and flow rates of the two liquid streams can be independently optimized, the FAB matrix does not affect the microcolumn separation process, and peak broadening is minimized because the two streams do not mix until they reach the tip of the FAB probe, where ion desorption occurs. 

An interface has been connected to a high-resolution double-focusing mass spectrometer applied to the analysis of mixtures of both chemically synthesized peptides and peptides obtained from proteolytic digests of proteins. Detection limits of about 35 fmol were reported. Reinhold et al.73 described the on-line coupling of CE and MS using a CF-FAB system in 

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The recent development and comparative application of modern separation techniques with regard to determination of alkylphosphonic acids and lewisite derivatives have been demonstrated. This report highlights advantages and shortcomings of GC equipped with mass spectrometry detector and HPLC as well as CE with UV-Vis detector. The comparison was made from the sampling point of view and separation/detection ability. The derivatization procedure for GC of main degradation products of nerve agents to determine in water samples was applied. Direct determination of lewisite derivatives by HPLC-UV was shown. Also optimization of indirect determination of alkylphosphonic acids in CE-UV was developed. Finally, the new instrumental development and future trends will be discussed. 

Total-ion-current trace A plot of the total number of ions reaching the mass spectrometry detector as a function of analysis time. 

In recent years, also the number of articles concerning HILIC stationary phases has enormously increased, especially as regards the hydrophilic interactions that resolve some important problems separation and resolution of less retained compound in reversed phase chromatography. With this novel stationary phase, where the silica surface is covered with cross-linked diol groups to increase polar selectivity in hydrophilic conditions, is possible obviate to the use of normal phase with high water content. This allows facilitating the interfacing with sensible and selective detection instruments, such as mass spectrometer with ESI source. The HILIC stationary phase was often chosen to interface the mass spectrometry detector, because it would be... 

Many applications for ion analysis use a UV detector with indirect detection, though other electrochemical, laser-induced fluorescence (LIE), or mass spectrometry detectors have been described. The main advantage of UV detection is its availability on commercial instruments and that both UV-absorbing and non-UV-absorbing analytes may be detected. Nowadays, electrochemical detectors are also available specific background electrolytes (BGEs) must be used and the detector has to be adapted to existing CE instruments. 

Having optimised the efficiency of a chromatographic separation the quality of the chromatography can be controlled by applying certain system suitability tests. One of these is the calculation of theoretical plates for a column and there are two other main parameters for assessing performance peak symmetry and the resolution between critical pairs of peaks. A third performance test, the peak purity parameter, can be applied where two-dimensional detectors such as diode or coulometric array or mass spectrometry detectors are being used. The reproducibility of peak retention times is also an important parameter for controlling performance. 

The availability of commercial bench-top mass spectrometry detectors for HPLC is facilitating the development of HPLC-MS methods for many analytes. This is more common in pharmaceutical than food applications. As is generally the case, mass spectrometry is first being applied to standard solutions and relatively simple samples before being applied to more complex food matrices. A standard mixture of ten vitamers, AA, DHAA, PN, PL, PM, thiamine, nicotinic acid, nicotinamide, pantothenic acid and biotin, were recently determined by HPLC-particle beam... 

After optimization of the method, the following analytical conditions were used silica capillary with stationary phase HP-5MS (30 m x 0.25 mm internal diameter, 0.25 pm film thickness) column gradient temperature started at 80 °C and increased at a rate of 10 °C/min to 280 °C injection temperature was fixed at 250 °C and helium was used as a carrier gas with constant flow rate of 1 mL/min. A mass spectrometry detector with single quadrupole was used as analyzer, operated at 150 °C with an acquisition scan rate of 50-800/n/z. 

Historically microdialysis samples, collected in a discontinuous way, have been analysed by high-performance hquid chromatography using various types of detectors, the most common types being UV, electrochemical, fluorescence and mass spectrometry detectors. 

The Inductively Coupled Plasma-Mass Spectrometry Detector... 

Some new specialised detectors are mass spectrometry detectors (MS), evaporating light scattering detectors (ELSC) and atom specific detectors. They all have in common that the mobile phase stream has to be split to secure a safe operation of the fragile detection system. As pointed out earlier, the eluent stream can be split by active and passive principles. For certain applications, mainly in the isolation of impurities with unknown structures in the mg range, the combination of these detectors to preparative equipment is of high value. As soon as the diameter of the... 

A mass spectrometry detector (MSD) which consists of a low resolution mass spectrometer, cf. Chapter 16) can be placed to the outlet of the column. A fragmentation spectrum of each eluted compound is obtained. From the total ionic current... 

SP-2401" and 3% SP-2250. ° Detectors used by EPA standards procedures, include photoionization (PID)," electron capture (ECD)," Eourier transform infrared spectrometry (PTIR), " and mass spectrometry detectors (MSD)." ° Method 8061 employs an ECD, so identification of the phthalate esters should be supported by al least one additional qualitative technique. This method also describes the use of an additional column (14% cyanopropyl phenyl polysiloxane) and dual ECD analysis, which fulfills the above mentioned requirement. Among MSDs, most of the procedures employ electron impact (El) ionization, but chemical ionization (CI) ° is also employed. In all MSD methods, except 1625, quantitative analysis is performed using internal standard techniques with a single characteristic m/z- Method 1625 is an isotope dilution procedure. The use of a FTIR detector (method 8410) allows the identification of specific isomers that are not differentiated using GC-MSD. 

Mass Spectrometry Detectors One of the most powerful detectors for (i(. is the mass spectrometer. Ma.ss spectrometers and applications of mass spectrometry are discussed in( haptcrs 11 and 20. The combination of OC with mass spcctionictry Ls... 

Barnes, J.H., IV Hieftje, G.M. Denton, M.B. SperUne, R. Koppenaal, D.W. Baringa, C. A mass spectrometry detector array that provides truly simultaneous detection. Am. Lab 2003, October, 15. 

Analysis of fumonisins in corn-based food by liquid chromatography withfluorescence and mass spectrometry detectors. Food Chemistry, 112, pp. 1031-1037, ISSN 0308-8146... 

The detector type will vary depending on the application however, the most commonly used systems are diode array UV/Vis. Other detectors are available, such as electrochemical and mass spectrometry detectors. Detectors used will vary depending on the type of chromatography and the type of analyte required to be detected (e.g., when carrying out ion exchange chromatography, an electrochemical detector is required because a UV/Vis detector will not detect the ions). This will be discussed further in Chapter 5. 

Dugo, R, M. Herrero, T. Kumm, D. Giuffrida, G. Dugo, and L. Mondello, 2008. Comprehensive normal-phase X reversed-phase liquid chromatography coupled to photodiode array and mass spectrometry detectors for the analysis of free carotenoids and carotenoid esters from mandarin. L Cfmmgtogi 1189 196-206. 

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