IC-MS Coupling

Most commercial systems utilize a pneumatic, concentric nebulizer that typically consists of a 100-pm fused-sihca capillary, through which the column effluent is directed. A helium flow (1-3 L/min) drctimvents the end of this capillary. After nebuhzation, the solvent is evaporated from the droplets in the externally heated desolvation chamber. Temperature is generally kept at about 50-70 °C. As a result of the high pumping efficiency in the jet separator, the pressure in the desolvation chamber generally is sub-ambient, i. e. between 20 and 30 kPa. The design 

The most important characteristic of a particle-beam interface is the possibihty to obtain El spectra, which can be evaluated according to known rules and compared to those of spectra libraries. For obtaining a meaningful spectrum of a substance, an absolute amount of 10 to 100 ng is required. In 90% of all applications El ionization is applied in 20% of the applications El ionization is combined with chemical ionization in the positive ion mode. AH other Cl applications are carried out in the negative ion mode. 

A characteristic example for a successful coupling of an ion chromatograph to a mass spectrometer via a particle-beam interface is described by Hsu [114] who analyzed aromatic sulfonic acids in leachates. Hsu used an OmniPac PAX-500 multimode phase in the microbore format to separate the sulfonic acids. The compounds of interest were eluted with a mixture of NaOH and acetonitrile 

The corresponding mass spectrum of the main peak is shown in Fig. 7-55 (top) and compared to that of a respective standard (bottom). In both cases, the background signal has been subtracted. Smaller signals such as m/z 104 and m/z 186 correspond to p-xylenesulfonic acid, m/z 94 and m/z 158 to benzenesulfonic acid, which are both present as impurities. Although the application of a particle-beam interface is limited to analytes with a significant vapour pressure in the 

In the technique known as thermospray [108, 117, 118] volatile electrolytes dissolved in the eluant are nebulized out of a heated vaporizer tube. As a result of heating, the liquid is nebulized and partially vaporized. The capillary is heated under controlled conditions to avoid complete evaporation of the liquid in the capillary. Unvaporized solvent and sample are carried into the ion source as micro droplets or particles in a supersonic jet of vapour. By applying efficient pumping directly at the ion source, up to 2 mL/min of aqueous solvents can be introduced into the MS vacuum system. The ionization of volatile analytes takes place by means of ion-molecule reactions in the gas phase non-volatile samples may be ionized by direct ion evaporation processes from highly charged droplets 

An additional problem is the electrolytes that are used for separating ionic species on ion-exchangers. Such separations cannot be performed without 

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Analyses using an MS detector are also characterized by a very low matrix influence and are therefore ideally suitable for cases involving coelution, eluate interference, or sample matrix influence. This means that MS represents a real alternative to conventional IC detectors such as conductivity, electrochemical or UVA is detectors. Because of IC-MS coupling, direct quaUtative analysis of different species is possible. The mass-charge ratio is used for peak identification and resolving the molecular structure of the analyte. MS detection can be carried out in selected ion monitoring (SIM) or scan (m/z) mode. 

The ion spray liquid chromatography/mass spectrometry (LC-MS) interface coupled via a postsuppressor split with an ion chromatography (IC) has been used in the analysis of alcohol sulfates. The IC-MS readily produces the molecular weight while the tandem mass spectrometric detection IC-MS-MS provides structural information [305]. 

A few DBFs, such as bromate, chlorate, iodate, and chlorite, are present as anions in drinking water. As a result, they are not volatile and cannot be analyzed by GC/MS. They are also difficult to separate by LC, but will separate nicely using ion chromatography (IC). At neutral pH, HAAs are also anions and can be separated using 1C. A number of methods have been created for these DBFs using both IC/ inductively coupled plasma (ICF)-MS and IC/ESl-MS. Fretreatment to remove interfering ions (e.g., sulfate and chloride), along with the use of a suppressor column prior to introduction into the MS interface, is beneficial for trace-level measurement. 

In IC-MS systems, the core of the equipment is the interface. In fact, inside the interface evaporation of the liquid, ionization of neutral species to charged species and removal of a huge amount of mobile phase to keep the vacuum conditions required from the mass analyzer take place. Two main interfaces are used coupled to IC, namely electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI). In the ESI mode, ions are produced by evaporation of charged droplets obtained through spraying and an electrical field, whilst in the APCI mode the spray created by a pneumatic nebulizer is directed towards a heated region (400°C-550°C) in which desolvation and vaporization take place. The eluent vapors are ionized by the corona effect (the partial discharge... 

Ion Chromatography, IC Inductively Coupled Plasma Mass Spectrometry, ICP-MS... 

Figure 2.3 Experimental set-up for the IC/ICP-MS coupling (after Ingrand et al, 2002). Reprinted from Trends in Analytical Chemistry, Vol. 21, No. 1, Ingrand etal, Determination of bromate. .. , pp. 1-12,2002, with permission from Elsevier...

The most useful detection mode in IC seems to be MS. Because of its flexibility, this coupling method has numerous possible applications in ion analysis. IC coupled with spectrometric detector (IC-MS) is a modem determination method for quantitative and qualitative analysis. Similar analytes are separated by IC and subsequently detected by a mass spectrometer. Both ionic substances (anionic and cationic) and polar substances (e.g., organic acids or sugars) can be determined with this very sensitive detection system. 

These species can be determined by UV/Vis or amperometric detection, coupled with suppressed conductivity, or by hyphenated techniques such as ion chromatography-mass spectrometry (IC-MS) or ion chromatography-inductively coupled plasma-mass spectrometry (IC-ICP-MS). ... 

Seubeet a, and Nowak M (1998) Trace analysis of bromate in drinking waters by means of online coupling IC-ICP-MS. Fresenius J Anal Chem 360 777-780. 

Fig. 5. Strategies for isotope dilution analysis utilizing on-line coupling IC-ICP-MS. Shown is the separation of bromate and bromide by anion IC.The sample was 585 )Lll of a bottled water, spiked with bromate and a bromate isotope standard. The column, eluent and detection device are as described in Fig. 4. Shown are the mass traces form/z79 and 81 (dotted line) and the total time slice isotope ratio for m/z 79/81.

Like every analytical method on-line coupling IC-ICP-(AES,MS) suffers from several disadvantages and limitations ... 

The calibration of atomic spectrometers can be handled much easier than that of conventional IC detectors using the large dynamic range of ICP techniques. Those simple off-line calibrations had been used for ICP-AES and ICP-MS in on-line preconcentration applications. With its ability to decide between isotopes the ICP-MS is well suited for isotope dilution analysis (IDMS), a calibration tool which increases the accuracy, the results and saves time due to reduced calibration work. The use of IDMS in combination with on-line coupling methods allows a significant speedup of the usually to IDMS applied time consuming separation processes. 

Besides reversed-phase HPLC, IC has also been used to separate Hg species.111112 IC enables the direct separation of more polar and ionic species, so that sample pretreatment can be simplified. The coupling of IC with CV-ICP-MS allows very low detection limits to be obtained.112... 

GC, gas chromatography HPLC, high-performance liquid chromatography MS, mass spectroscopy AA, atomic absorption GFAA, graphite furnace atomic absorption ICP, inductively coupled plasma UV-VIS, ultraviolet-visible molecular absorption spectroscopy IC, ion chromatography. 

Metals contained in samples are determined by a wide variety of analytical methods. Bulk metals, such as copper in brass or iron in steel, can be analyzed readily by chemical methods such as gravimetry or electrochemistry. However, many metal determinations are for smaller, or trace, quantities. These are determined by various spectroscopic or chromatographic methods, such as atomic absorbance spectrometry using flame (FAAS) or graphite furnace (GFAAS) atomization, atomic emission spectrometry (AES), inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS), x-ray fluorescence (XRF), and ion chromatography (IC). 

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