HPLC with MS detectors

Non-elemental mass spectrometry has been increasingly used with HPLC for speciation studies. Tandem mass spectrometry (mass spectrometry-mass spectrometry, MS-MS) has been of particular interest in this area. In this type of system, two mass analysers are needed and it is used as a method of achieving fragmentation of ions generated in the ion source. Arsenic has been speciated by HPLC with ion spray MS-MS (Corr and Larsen, 1996) and Miermans et al. (1997) studied the application of various ionisation methods for the analyses of triphenyltin compounds by MS-MS. 

The thermospray, particle beam electrospray (ES) (Fig. 4.4) and atmospheric pressure chemical ionisation (APCI) have been used in HPLC-MS-MS. The ES and APCI are both atmospheric pressure ionisation systems. The column effluent is nebulised and ionised in the atmospheric pressure region and the ions are then 

A heated pneumatic nebuliser is used to produce the aerosol in APCI and the ions are produced by ion-molecule reactions initiated by corona discharges in the ion source region. White et al. (1998) found atmospheric pressure ionisation MS and LC-ICP-MS to be complementary techniques. 

In thermospray interfaces, the column effluent is rapidly heated in a narrow bore capillary to allow partial evaporation of the solvent. Ionisation occurs by ion-evaporation or solvent-mediated chemical ionisation initiated by electrons from a heated filament or discharge electrode. In the particle beam interface the column effluent is pneumatically nebulised in an atmospheric pressure desolvation chamber this is connected to a momentum separator where the analyte is transferred to the MS ion source and solvent molecules are pumped away. Magi and Ianni (1998) used LC-MS with a particle beam interface for the determination of tributyl tin in the marine environment. Florencio et al. (1997) compared a wide range of mass spectrometry techniques including ICP-MS for the identification of arsenic species in estuarine waters. Applications of HPLC-MS for speciation studies are given in Table 4.3. 

The ICP-MS detector offers excellent selectivity and sensitivity for HPLC and HPLC-ICP-MS is a rapidly expanding technique. The high sensitivity of this method means that sample preparation steps are simplified and pre-concentration steps tend not to be necessary. Isotopic dilution measurement techniques can also be used to improve accuracy at low concentrations. Heumann et al. (1994), for example, could determine iodate concentrations in the range of 0.5-20 ngml-1 with RSDs of 2%. 

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