Inductively-coupled plasma separation techniques

Nickel also is deterrnined by a volumetric method employing ethylenediaminetetraacetic acid as a titrant. Inductively coupled plasma (ICP) is preferred to determine very low nickel values (see Trace AND RESIDUE ANALYSIS). The classical gravimetric method employing dimethylglyoxime to precipitate nickel as a red complex is used as a precise analytical technique (122). A colorimetric method employing dimethylglyoxime also is available. The classical method of electro deposition is a commonly employed technique to separate nickel in the presence of other metals, notably copper (qv). It is also used to estabhsh caUbration criteria for the spectrophotometric methods. X-ray diffraction often is used to identify nickel in crystalline form. 

At present, inductively coupled plasma mass spectrometry provides a unique, powerful alternative for the determination of rare earths in natural samples [638,639]. Nevertheless, its application to the determination of rare earths at ultratrace concentration level in seawater is limited, because highly saline samples can cause both spectral interferences and matrix effects [640]. Therefore, a separation of the matrix components and preconcentration of the analytes are prerequisites. To achieve this goal, many preconcentration techniques have been used, including coprecipitation with... 

A hyphenated technique, the coupling of ion chromatographic separation (DX-100, DIONEX) and inductively coupled plasma mass spectrometric detection (ELAN-5000, PERKIN-ELMER) was used for the speciation... 

Analytes must be liberated from their associated solvent molecules as well as be ionized to allow mass separation. Several ionization methods enable ion production from the condensed phase and have been used for the coupling of CE to MS. Among them, atmospheric pressure ionization (API) methods, matrix-assisted laser desorption/ionization (MALDI), and inductively coupled plasma (ICP) ionization are mainly used. API techniques are undoubtedly the most widespread ionization sources and cover different analyte polarity ranges. 

A striking feature of the ILs is their low vapor pressure. This, on the other hand, is a factor hampering their investigation by MS. For example, a technique like electron impact (El) MS, based on thermal evaporation of the sample prior to ionization of the vaporized analyte by collision with an electron beam, has only rarely been applied for the analysis of this class of compounds. In contrast, nonthermal ionization methods, like fast atom bombardment (FAB), secondary ion mass spectrometry (SIMS), atmospheric pressure chemical ionization (APCI), ESI, and MALDI suit better for this purpose. Measurement on the atomic level after burning the sample in a hot plasma (up to 8000°C), as realized in inductively coupled plasma (ICP) MS, has up to now only rarely been applied in the field of IE (characterization of gold particles dissolved in IE [1]). This method will potentially attract more interest in the future, especially, when the coupling of this method with chromatographic separations becomes a routine method. 

The quasi-simultaneous separation and determination of lanthanides and actinides by ion chromatography inductively coupled plasma mass spectrometry combined with the isotope dilution technique and the further use of ion chromatography for the determination of fission products and actinides in nuclear applications are described by Betti et ul.10 48 68... 

Egorov, O. B., O Hara, M. J., Farmer, O. T., Ill, and Grate, J. W., Extraction chromatographic separations and analysis of actinides using sequential injection techniques with on-line inductively coupled plasma mass spectrometry (ICP MS) detection, Analyst, 126, 1594-1601, 2001. 

Multi-element determination of dissolved metals at ultratrace level may be performed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). U.S. EPA s Methods 200.8 and 1638 present a methodology for measuring trace elements in waters and wastes by the above technique. Sample is acid digested and the solution is introduced by pneumatic nebulization into a radio-frequency plasma. The elements in the compounds are atomized and ionized. The ions are extracted from the plasma through a differentially pumped vacuum interface and separated by a quadrupole mass spectrometer by their mass to charge ratios. The mass spectrometer must have a resolution capability of 1 amu peak width at 5% peak height. 

Centrifugation alone is not sufficient to separate Np solid material from the solution (j) ). Thus, the Np solution concentrations and oxidation state analyses were determined from aliquots filtered through approximately 1.8 nm pore-size Centriflo membrane cones (Amicon Corp., Lexington, MA). Each filter cone was pretreated with an initial aliquot of the suspension to be filtered. Tests using successive filtration confirmed that no significant amounts of Np were being sorbed by the filter cones. The solutions were alpha counted by liquid scintillation techniques. Major cations in the solutions were determined by inductively coupled plasma spectrometry (ICP) analyses. 

Inductively coupled plasma-mass spectrometry (ICP-MS) is a powerful technique that uses an inductively coupled plasma as an ion source and a mass spectrometer as an ion analyzer. It can measure the presence of more than 75 elements in a single scan, and can achieve detection limits down to parts per trillion (ppt) levels for many elements—levels that are two or three orders of magnitude lower than those obtained by ICP-AES (Keeler 1991). It is more expensive than ICP-AES and requires more highly skilled technical operation. Aluminum levels in urine and saliva were detected down to 0.02 g/mL and in blood serum to 0.001 g/mL using ICP-MS (Ward 1989). Speciation studies have employed ICP-MS as a detector for aluminum in tissue fractions separated by size-exclusion chromatography (SEC) with detection limits of 0.04 g/g in femur, kidney and brain (Owen et al. 1994). 

HPLC units have been interfaced with a wide range of detection techniques (e.g. spectrophotometry, fluorimetry, refractive index measurement, voltammetry and conductance) but most of them only provide elution rate information. As with other forms of chromatography, for component identification, the retention parameters have to be compared with the behaviour of known chemical species. For organo-metallic species element-specific detectors (such as spectrometers which measure atomic absorption, atomic emission and atomic fluorescence) have proved quite useful. The state-of-the-art HPLC detection system is an inductively coupled plasma/MS unit. HPLC applications (in speciation studies) include determination of metal alkyls and aryls in oils, separation of soluble species of higher molecular weight, and separation of As111, Asv, mono-, di- and trimethyl arsonic acids. There are also procedures for separating mixtures of oxyanions of N, S or P. 

Techniques can be classified into two main categories those that detect total metal concentrations and those that detect some operationally defined fraction of the total. Methods which detect total concentrations such as inductively coupled plasma spectrometry, neutron activation analysis, atomic absorption spectrometry and atomic emission spectrometry have no inherent speciation capabilities and must be combined with some other separation technique(s) to allow different species to be detected (approach A in Fig. 8.2). Such separation methods normally fractionate a sample on the basis of size, e.g. filtration/ultrafiltration, gel filtration, or a combination of size and charge, e.g. dialysis, ion exchange and solvent extraction (De Vitre et al., 1987 Badey, 1989b Berggren, 1989 1990 Buffle et al., 1992). In all instances the complexes studied must be relatively inert so that their concentrations are not appreciably modified during the fractionation procedure. 

ICP-MS is a multielement technique that is suitable for trace analysis it offers a long linear range and low background for most elements. ICP-MS is a technique where the ions produced in inductively coupled plasma are separated in a mass analyzer and detected. The sample solution is fed into a nebulizer by a peristaltic pump. The nebulizer converts the liquid sample into a fine aerosol that is transported into the plasma by an Ar gas flow. In the plasma the sample is evaporated, dissociated, atomized, and ionized to varying extents. The positive ions and molecular ions produced are extracted into the mass analyzer. Detailed descriptions of the ICP-MS technique can be found in a number of textbooks.13,14... 

All raw and treated coals were analyzed at Ames Laboratory for trace, major, and minor elements using energy-dispersive x-ray fluorescence (XRF), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), and atomic absorption spectrophotometry (AA). General analytical procedures employed for each of these techniques are discussed separately below. 

The combination of capillary zone electrophoresis or CIEF with inductively coupled plasma (ICP) MS promises a powerful tool for metal speciation. The on-line hyphenation of these techniques resulted in short separation times (10 min) and a subsequent detection step lasting 100 s. Standard mixtures and body fluids such as human milk and serum have been studied [65],... 

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