Nebulisers conventional

As the vast majority of LC separations are carried out by means of gradient-elution RPLC, solvent-elimination RPLC-FUR interfaces suitable for the elimination of aqueous eluent contents are of considerable use. RPLC-FTTR systems based on TSP, PB and ultrasonic nebulisa-tion can handle relatively high flows of aqueous eluents (0.3-1 ml.min 1) and allow the use of conventional-size LC. However, due to diffuse spray characteristics and poor efficiency of analyte transfer to the substrate, their applicability is limited, with moderate (100 ng) to unfavourable (l-10pg) identification limits (mass injected). Better results (0.5-5 ng injected) are obtained with pneumatic and electrospray nebulisers, especially in combination with ZnSe substrates. Pneumatic LC-FI1R interfaces combine rapid solvent elimination with a relatively narrow spray. This allows deposition of analytes in narrow spots, so that FUR transmission microscopy achieves mass sensitivities in the low- or even sub-ng range. The flow-rates that can be handled directly by these systems are 2-50 pLmin-1, which means that micro- or narrow-bore LC (i.d. 0.2-1 mm) has to be applied. 

The extension of inductively coupled plasma (ICP) atomic emission spectrometry to seawater analysis has been slow for two major reasons. The first is that the concentrations of almost all trace metals of interest are 1 xg/l or less, below detection limits attainable with conventional pneumatic nebulisation. The second is that the seawater matrix, with some 3.5% dissolved solids, is not compatible with most of the sample introduction systems used with ICP. Thus direct multielemental trace analysis of seawater by ICP-AES is impractical, at least with pneumatic nebulisation. In view of this, a number of alternative strategies can be considered ... 

Advances in TIMS-techniques and the introduction of multiple collector-ICP-MS (MC-ICP-MS) techniques have enabled the research on natural variations of a wide range of transition and heavy metal systems for the first time, which so far could not have been measured with the necessary precision. The advent of MC-ICP-MS has improved the precision on isotope measurements to about 40 ppm on elements such as Zn, Cu, Fe, Cr, Mo, and Tl. The technique combines the strength of the ICP technique (high ionization efficiency for nearly all elements) with the high precision of thermal ion source mass spectrometry equipped with an array of Faraday collectors. The uptake of elements from solution and ionization in a plasma allows correction for instrument-dependent mass fractionations by addition of external spikes or the comparison of standards with samples under identical operating conditions. All MC-ICP-MS instruments need Ar as the plasma support gas, in a similar manner to that commonly used in conventional ICP-MS. Mass interferences are thus an inherent feature of this technique, which may be circumvented by using desolvating nebulisers. 

Standard addition calibration is more robust and reliable than conventional external calibration, but is more time consuming and costly if it is applied separately for each sample. A major advantage of standard addition is the correction of multiplicative matrix effects such as alteration of nebulisation efficiency. The intensities of all samples (and spiked samples) change by the same factor, which leads to an altered calibration slope. However, for additive... 

The on-line interface of flow manifolds to continuous atomic spectrometric detectors for direct analysis of samples in liquid form typically requires a nebuliser and a spray chamber to produce a well-defined reproducible aerosol, whose small droplets are sent to the atomisation/ionisation system. A variety of nebulisers have been described for FAAS or ICP experiments, including conventional cross-flow, microconcentric or Babington-type pneumatic nebulisers, direct injection nebuliser and ultrasonic nebulisers. As expected, limits of detection have been reported to be generally poorer for the FIA mode than for the continuous mode. 

On-line coupling between a gas chromatograph and an atomic spectrometry detector is fairly simple. Typically, the output of the CG capillary column is connected to the entrance of the atomisation-ionisation system simply via a heated transfer line. When separation is performed by liquid chromatography (EC), the basic interface is straightforward a piece of narrow-bore tubing connects the outlet of the EC column with the liquid flow inlet of the nebuliser. Typical EC flow rates of 0.5-2 ml min are within the range usually required for conventional pneumatic nebulisation. 

Schramel [103] discusses the conditions for multi-element analysis of over 50 trace elements, giving detection limits. Wolnik [104] described a sample introduction system that extends the analytical capability of the inductively coupled argon plasma/polychromator to include the simultaneous determination of six elemental hydrides along with a variety of other elements in plant materials. Detection limits for arsenic, bismuth, selenium and tellurium range from 0.5 to 3 ng/ml and are better by at least an order of magnitude than those obtained with conventional pneumatic nebulisers, whereas detection limits for the other elements investigated remain the same. Results from the analysis of freeze-dried crop samples and NBS standard reference materials demonstrated the applicability of the technique. Results obtained by the analysis of a variety of plant materials are presented in Table 7.10. 

Where appropriate these methods of atomisation will be discussed again in the later chapters describing applications. These elements may be determined by conventional nebulisation systems with severely reduced sensitivity. 

Lipworth, B. J., Sims, E. J., Taylor, K., Cockburn, W., and Fishman, R. (2005), Dose-response to salbutamol via a novel palm sized nebuliser (aerodose inhaler), conventional nebuliser (pari LC plus) and metered dose inhaler (ventolin evohaler) in moderate to severe asthmatics, Br. J. Clin. Pharmacol, 59, 5-13. 

Varner A, Busse W 1996 Are you undertreating inflammation in asthma Journal of Respiratory Disease 17 656-668 Viel L 1999 Therapeutic efficacy of inhaled fluticasone propionate in horses with chronic obstructive pulmonary disease. In Proceedings of the 45th American Association of Equine Practitioners Annual Convention, Albuquerque, NM, pp. 306-307 Votion D, Ghafir Y, Munsters K et al 1997 Aerosol deposition in equine lungs following ultrasonic nebulisation versus jet aerosol delivery system. 

Vapor generation techniques The generation of gaseous analytes from the sample and their introduction into atomisation cells for subsequent absorption spectro-metric determination offers a number of advantages over the conventional sample introduction by pneumatic nebulisation of the sample solution. These include the elimination of the nebuliser, the enhancement of the transport efficiency, which approaches 100 %, and the presentation of a homogenous sample vapor to the atomiser. The most common and versatile techniques for the formation of volatile compounds are the hydride generation technique and the cold vapor technique. 

Capillary electrophoresis and atomic emission spectroscopy (CE-AES) Capillary electrophoresis (CE) is a rapidly emerging tool for many routine cHnical and pharmaceutical appHcations. Due to the high separation efficiency of the CE, this combination aUows the speciation of elements even in rather complex matrices such as human serum. A challenge for this hyphenation is the interface compatible with the low flow rate of CE, which can be as litde as a few nL min, compared with a typical sample introduction rate of 1 mL min into the fCP. Most interfaces reported in the Hterature contact the CE via a suitable Pt contact in a sheath buffer flow, which is mixed with the CE effluent, e. g. in a PEEK tee. As the total flow is significantly increased by the make-up flow, a conventional nebuliser can be used for sample introduction. 

Devadason 8G, Everard ML, Linto JM, Le 8ouef PN. Comparison of drug delivery from conventional versus Venturi nebulizers. Eur Respir J 1997 10 2479-2483. Wilson D, Bumiston M, Moya E, Parkin A, 8mye 8, Robinson P, et al. Improvement of nebulised antibiotic delivery in cystic fibrosis. Arch Dis Child 1999 80 348-352. 

Devadason SG, Everard ML, Linto JM, Le Souef PN. Comparison of drug delivery from conventional versus Venturi nebulisers. Eur Respir J 1997 10 2479-2483. 

A horizontally mounted ICP torch forms the basis of the ion source. Sample introduction is via a conventional nebuliser optimised for general-purpose solution analysis and suitable for use with both aqueous and organic solvents. 

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