Nebulisers high efficiency

FTD Flame thermoionic detector HEN High-efficiency nebuliser... 

A further study by the Olesik group [138] used an interface with a laminar flow in the direction of the detector. The interface was a stainless-steel tee with the capillary threaded through the colinear ends of the tee. A sheath electrolyte was delivered through the lower arm of the tee with a peristaltic pump. Both a high efficiency nebuliser (HEN) and a concentric glass nebuliser were used in the study the former was used with a conical spray chamber and the latter with a Scott double-pass spray chamber. Increasing the sheath electrolyte flow-rate enabled the laminar flow to be eliminated, therefore improv-... 

Liu, H., Clifford, R.H., Dolan, S.R and Monaser, A. (1996) Investigation of a high-efficiency nebuliser and thimble glass frit nebuliser for elemental analysis of biological materials by ICP-AES, Spectochimica Acta, Part B, 51, pp27—40. 

A pneumatic cross-flow micronebuliser has been described for use in ICP-MS. The high efficiency cross-flow micronebuliser (HECFMN) has a narrow capillary placed inside the conventional sample capillary. The inner diameter of the nebuliser gas nozzle is reduced with respect to the conventional cross-flow design. Due to the characteristics of this device, the free liquid uptake rate (i.e. about 9 p-L/min) is lower than that found for either a conventional cross-flow nebuliser (i.e. 1900 pL/min) or concentric pneumatic micronebulisers (i.e. from about 30 to 100 pL/min). This fact makes the HECFMN attractive for CE ICP-MS interfaces. ... 

Sensitivity and detection limits of ICP-MS are governed by the absolute amount of analytes introduced to the plasma per time unit. Hence, sample transport efficiency of the ICP-MS introduction system will critically affect detection limits in CE-ICP-MS. A general drawback of CE is that concentration-based detection limits are limited by the small sample injection volumes and the electrophoretic peak width. Interfaces employing nebulisers in combination with spray chambers yield analyte transport efficiencies of < 100%, depending on the nebuliser and solution flow rate. Consequently, the sensitivity of CE-ICP-MS can be improved by using introduction systems with 100% aerosol transport efficiency, such as the direct injection nebuliser and the direct injection high-efficiency nebuliser. ... 

Another low-flow nebuliser used for coupling ICP-MS to chromatographic columns is the high-efficiency nebuliser (HEN). This device has a small capillary and is used with a spray chamber. Compared to pneumatic nebulisers, the HEN operates more efficiently at very low solution uptake rates. Micro-HPLC-HEN-ICP-MS coupling was applied to the speciation of five arsenic compounds. The HEN operated most efficiently at sample uptake rates of 40 pL/min and was shown to have excellent absolute detection limits. A possible drawback of the HEN, as for all low-flow nebulisers, is the poor tolerance in nebuhsing highly concentrated solutions. 

ES ionisation can be pneumatically assisted by a nebulising gas a variant called ionspray (IS) [129]. ESI is conducted at near ambient temperature too high a temperature will cause the solvent to start evaporating before it reaches the tip of the capillary, causing decomposition of the analyte during ionisation and too low a temperature will allow excess solvent to accumulate in the sources. Table 6.20 indicates the electrospray ionisation efficiency for various solvents. 

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. 

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. 

Chemical interference is practically non existent as a result of the high temperature of the plasma. On the other hand, physical interference may be observed. This stems from variations in the sample atomisation speed which is usually due to changes in nebulisation efficiency caused by differences in the physical properties of the solutions. Such effects may be caused by differences in viscosity or vapour tension between the sample solutions and the standards due, for example, to differences in acidity or total salt content. The technique most commonly used to correct this physical interference is the use of internal standards. In this technique a reference element is added at an identical concentration level to all the solutions under analysis, standards, blank and samples. For each element, the ratio of simultaneous measurements of the lines of the element and the internal standard is then determined in order to compensate for any deviation in the response of the plasma. If the internal standard behaves in the same way as the element to be determined, this method can be used to improve the reliability of the result by a factor of 2 to 5. It can also, however, introduce significant errors because not all elements behave in the same way. It is thus necessary to take care when using it. Alternatives to the internal standard method include incorporating the matrix into the standards and the blank, sample dilution, and the standard addition method. 

The advantage of using APDC is the metal salts are readily soluble in most organic solvents and will separate them from high concentrations of other solutes that could cause difficulties in nebulisation and atomisation. Large bulk of aqueous sample may be extracted efficiently into a smaller volume of an organic solvent and this can be further... 

The determination of sodium, potassium, calcium and magnesium in soil extracts [57] illustrates the implementation of this approach in a flow injection system. As these analytes are present in relatively high concentrations in the assayed samples, additions of diluent confluent streams were needed to increase dispersion. However, the total flow rate of the stream reaching the spectrometer was also increased, thus impairing nebulisation efficiency. This was circumvented by removing part of the sample carrier stream and the sampling rate was increased. In spectrophotometry, similar restrictions have been observed, especially when the increase in total flow rate impairs the development of relatively slow chemical reactions. 

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. 

---