Plasma emission spectrometer chromatographs

In contrast to gas chromatographic separations, which require the preparation of volatile derivatives of tin compounds, separations carried out by means of HPLC do not necessarily require preparations of derivatives. HPLC has been used in conjunction with several detection techniques, including photometers, atomic absorption spectrometers and direct current plasma emission spectrometers after hydride generation. Some recent studies have involved fluorimetric detection (Kleibohmer and Cammann, 1989) and hydride generation AAS. The latter has been applied to the quantification of TBT in coastal water. 

The beryllium acetylacetonate is separated in a gas chromatograph and injected into the helium plasma emission spectrometer. The detection limit is lOpg in a 30mL water sample and the standard deviation was 4.1% at lOng of beryllium. 

Measurement and control of low-flow rates are a requirement in such applications as fuel cells, purging, bioreactors, leak testing, and controlling the reference gas flow in chromatographs or in plasma-emission spectrometers. The most traditional and least expensive low-flow sensor is the variable-area flowmeter. It has a high rangeability (10 1) and requires little pressure drop. Due to its relatively low accuracy, it is limited to purge and leak-detection applications. 

Plasma Emission Spectrometer as a Detector for Gas and Liquid Chromatographs... 

Fig. 2.4. Chromatogram of a solution containing arsenite, arsenate, methylarsonic acid, dimethylarsinic acid, phenylarsonic acid, selenite, and phosphate recorded with an ARL 34000 simultaneous inductively coupled argon plasma emission spectrometer as the multi-element-specific detector [Hamilton PRP-1 resin-based reverse-phase column, Waters Associates Inc. Model 6000A high pressure liquid chromatograph, 0.1 ml injected flow rate 1.5 ml min", mobile phases 0.002 M aqueous HTAB at pH 9.6 to 250 sec, 99/1 (v/v) H2O/CH3COOH 250-1100 sec, 90/10 (v/v) H20/dimethylformamide 1100-1700 sec. ICP As 189.0 nm, P 241.9 nm, Se 203.9 nm, integration time 5 sec]. Redrawn from Spectrochimica Acta [11] by permission of Pergamon Press and the authors.

Inductively coupled argon plasma emission spectrometers of the sequential or simultaneous type were used very little as detectors for gas chromatographs [28]. The detection limits for metals in these systems approached the low nanogram levels. However, the detection limits for... 

Common gas chromatographic detectors that are not element- or metal-specific, atomic absorption and atomic emission detectors that are element-specific, and mass spectrometric detectors have all been used with the hydride systems. Flame atomic absorption and emission spectrometers do not have sufficiently low detection limits to be useful for trace element work. Atomic fluorescence [37] and molecular flame emission [38-40] were used by a few investigators only. The most frequently employed detectors are based on microwave-induced plasma emission, helium glow discharges, and quartz tube atomizers with atomic absorption spectrometers. A review of such systems as applied to the determination of arsenic, associated with an extensive bibliography, is available in the literature [36]. In addition, a continuous hydride generation system was coupled to a direct-current plasma emission spectrometer for the determination of arsenite, arsenate, and total arsenic in water and tuna fish samples [41]. 

Fig. 2.7. Chromatograms of purified and impure methanolic extracts from crab meat and of a distilled water solution of S3mthetic arsenobetaline with an ARL 34000 simultaneous inductively coupled argon plasma emission spectrometer as the arenic-specific detector. [Hamilton PRP-1 column, Waters Associates high pressure liquid chromatograph, conditions as in ref [11], Redrawn from Chemoaphere [68] by permission of Pergamon Press and the authors.

A rapid method of analysis of organo-tin compounds in sediment and biological CRMs was developed (Pereiro et al., 1997). Ethylated butyltin compounds were separated isothermally on a multicapillary (MC) gas chromatographic column in less than 30 s as compared with 5-10 min on a regular capillary column. The MC column consisted of a bundle of about 900 1 m-long, 40 mm i.d. coated capillaries. The column was connected to a microwave-induced plasma atomic emission spectrometer. Phenyltin compounds were also included in the procedure. Detection limits of MBT, DBT and TBT were about 0.2ngml 1 (as tin). 

The gas chromatograph may be interfaced with atomic spectroscopic instruments for specific element detection. This powerful combination is useful for speci-ation of different forms of toxic elements in the environment. For example, a helium microwave induced plasma atomic emission detector (AED) has been used to detect volatile methyl and ethyl derivatives of mercury in fish, separated by GC. Also, gas chromatographs are interfaced to inductively coupled plasma-mass spectrometers (ICP-MS) in which atomic isotopic species from the plasma are introduced into a mass spectrometer (see Section 20.10 for a description of mass spectrometry), for very sensitive simultaneous detection of species of several elements. 

In Fig. 12.20 are shown schematically the chief hybridizations possible between chromatography and various spectrometric techniques. The simplest configuration (Fig. 12.20a) involves the linkage between the column and the spectrometer detection zone via a suitable interface —the information is obtained from the spectrometer only. This configuration is one of the commonest in GC-MS [42-44], HPLC-MS [45], HPLC-plasma emission (ICP, MIP) [46], SFC-MS [47] and HPLC-NMR [48] hybridizations. In the configuration In Fig. 12.20b, the typical non-destructive detector (thermal conductivity In GC and UV-visible In HPLC) of the chromatograph provides an ordinary chromatogram ... 

With a few exceptions, most of the detectors used in GC were invented specifically for this technique. The major exceptions are the thermal conductivity detector (TCD, or katharometer) that was preexisting as a gas analyzer when GC began, and the mass spectrometer (or mass selective detector, MSD) that was adapted to accept the large volumes and the fast scan rates needed for GC peaks. Most recently, other spectroscopic techniques like IR and atomic plasma emission have been coupled to the effluent from gas chromatographs, serving as GC detectors. 

The association of a spectrometer with the liquid chromatograph is usually for the purpose of structure elucidation of the eluted solute, a procedure that will be discussed in a later chapter. The association of tui atomic spectrometer with the liquid chromatograph, in contrast, is almost exclusively for the specific detection of the metalic and semi-metalic elements. The atomic spectrometer is a highly specific detector, and for element detection perhaps more so than the electrochemical detector. However, in general, a flame atomic absorption spectrometric (AAS) system is not as sensitive. If an atomic emission spectrometer or an atomic fluorescence spectrometer is employed then multi-element detection is possible. The inductively coupled plasma spectrometer can also, under some circumstances, provide multi-element detection but all three instruments are extremely expensive particularly in terms of an LC detector. It follows that most LC/AAS combinations employ a flame atomic absorption spectrometer or occasionally an atomic spectrometer fitted with a graphite furnace. Furthermore the spectrometer is usually set to monitor one element only, throughout the development of any given separation. 

Argon plasmas are used in optical emission spectrometry to atomise and ionise elements leading to the emission of characteristic spectral lines. Hence, a plasma torch (7-8 000 K) can be used for ionisation in mass spectrometry. Ions produced in the plasma are introduced into the mass analyser through a small orifice (called a skimmer) placed in the axial direction. Because the mass spectrometer is operated under a vacuum, the ions are sucked into the mass analyser through the skimmer. An aqueous solution of the sample can be aspirated into the plasma or, alternatively, the plasma can be placed at the exit of a gas chromatograph (e.g. speciation of organo-metallic compounds by GC/ICP-MS). Since all chemical bonds are broken in the plasma, the only accessible information is that concerning the concentration of monoatomic ions (Fig. 16.19). 

The same compounds have also been examined by Urasa et al. [50], who coupled an ion chromatograph to a DCP atom emission spectrometer2 by connecting the column end capillary with the nebulizer of the spectrometer, which was slightly modified [51]. A principle problem of DC plasma detection is the relatively low sensitivity, which may be attributed to the inadequate efficiency of the nebulization and to the sample dilution during the chromatographic process. The dilution effect alone accounts for a reduction... 

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