Cross-flow Nebulizer Research Articles

The effect of nitric acid concentration and nebulizer gas flow rates on aerosol properties and transport rates in inductively coupled plasma sample introduction

An investigation of the influence of nitric acid on the aerosol generation and transport processes for an inductively coupled plasma (ICP) sample introduction system consisting of a cross-flow nebulizer and a Scott-type double pass spray chamber is described. Two important results are presented. (1) Aerosol and analyte transport rates decrease similarly when the nitric acid concentration is increased from 0 to 25% (v/v). This suggests that changes in analyte transport rates are due mainly to changes in aerosol transport through the spray chamber rather than changes in the relative analyte concentration in the tertiary aerosol compared with the bulk sample solution. (2) The relative decrease in transport rates as the nitric acid concentration is increased from 0 to 25% (v/v) is dependent on nebulizer gas flow rate. At low nebulizer gas flow rates, there is a dramatic decrease in the analyte and aerosol transport rates for a change from 0 to 2% (v/v) nitric acid and then little change as the nitric acid concentration is increased to 25% (v/v). At high nebulizer gas flow rates, there is a continuous decrease in the analyte and aerosol transport rates as the nitric acid concentration is increased from 0 to 25%. The nebulizer gas flow rate affects the ‘robustness’ of ICP-OES or ICP-MS signals to changes in acid concentration both through plasma condition ‘robustness’ and the susceptibility of the aerosol transport rate to variation in acid concentration. Changes in tertiary aerosol properties are more dramatically affected by changes in acid concentration than primary aerosol properties. Acid-dependent changes in the analyte and aerosol transport rates are likely most affected by changes in liquid aerosol density and evaporation rates. Evaporation is most efficient for 0% HNO 3 solutions and least efficient from 25% HNO 3 solutions and contributes to changes in the relative liquid density of aerosols. From the data described here, the acid-dependent changes in aerosol properties appear to occur predominantly during the transport of aerosol through the spray chamber. Similar effects should occur with other solutions (e.g. 5% w/w NaCl) whose density and water vapour pressure change significantly with concentration.

Validation of the determination of copper and zinc in blood plasma and urine by ICP MS with cross-flow and direct injection nebulization

The simultaneous determination of copper and zinc in human plasma and urine by inductively coupled plasma mass spectrometry (ICP MS) is discussed. The performances of a cross-flow nebulizer and a direct-injection nebulizer (DIN) were compared. Flow-injection-DIN-ICP MS analysis of clinical samples using 1–2 μl samples was optimized. Isobaric interferences were discussed and were demonstrated to be eliminated for the 65Cu and most of the Zn nuclides. The need for standard addition to compensate for signal suppression in the case of some serum samples was indicated. Results obtained by ICP MS using calibration with aqueous standard solutions were found to be in good agreement with those obtained by flame AAS for a batch of real blood plasma and urine samples. The methods developed were validated by analysis of several standard reference materials.

Determination of Iodine in Food-related Certified Reference Materials Using Wet Ashing and Detection by Inductively Coupled Plasma Mass Spectrometry

E. H. Larsen and M. B. Ludwigsen, J. Anal. At. Spectrom., 1997, 12, 435 DOI: 10.1039/A607581I

Evaluation of a commercially available microconcentric nebulizer for inductively coupled plasma mass spectrometry

The performance of a commercially available microconcentric nebulizer (MCN-100, CETAC Technologies, USA) operated at flow rates ranging from ⩽0.001 up to 0.65 ml min–1 was evaluated using a Perkin-Elmer Sciex ELAN 5000 ICP-mass spectrometer. The observations made were compared with those for the standard GemTip cross-flow nebulizer. Registration of signal behaviour plots (signal intensity as a function of the nebulizer gas flow rate) at different rf powers and at different sample uptake rates allowed firstly, a systematic optimization of the operation parameters, and secondly, a comparison of the signal behaviour observed when using both types of nebulizer. The stability of the MCN-100 was evaluated at different sample uptake rates and the occurrence of memory effects was checked for a number of elements. Also, the level and the behaviour of oxide and doubly charged ions was studied. Furthermore, the susceptibility to matrix effects was investigated using synthetic matrices of different origin (acid, organic and high salt content) and it was demonstrated that, generally, matrix effects observed with both nebulizers are comparable and the MCN-100 can be used with NaCl concentrations up to 4 g l–1 without capillary blocking. Finally, it is illustrated that the MCN-100 can be applied at sample flow rates of < 5 µl min–1, as are encountered when coupling capillary zone electrophoresis to ICP-MS for elemental speciation studies.

Influence of the sample introduction system on acid effects in inductively coupled plasma atomic emission spectrometry

Influence of the aerosol formation and transport on acid effects has been studied in inductively coupled plasma atomic emission spectrometry in order to elucidate the decrease in the analyte intensity. To separate the role of the ionization and excitation conditions from that of the sample introduction, operating conditions have been set-up to obtain a constant ratio of the ionic line to atomic line intensity of magnesium. A 27 MHz crystal-controlled generator and a 40 MHz tuned-line generator were used to verify the possible influence of the generator type. Once the ionization and excitation conditions were kept constant, the influence of the sample introduction system could be assessed by using the Mg I 285 nm line. Perchloric acid up to a concentration of 50% (v/v) has been used as the test acid. The CII 725.662 nm line was also used to assess the amount of chlorine reaching the plasma. Several pneumatic nebulizers were used: Meinhard concentric nebulizers, a Perkin Elmer cross-flow nebulizer, and a Perkin Elmer cone-spray nebulizer. Depressive effects resulting from the perchloric acid depended on the nebulizer type, the carrier gas flow rate and the spray chamber design. Droplet size of the primary and tertiary aerosol were measured. At perchloric acid concentrations higher than 1% (v/v), results suggested that the depressive effect on the Mg line intensity cannot only be explained by a change in the aerosol density but also by a variation in the analyte concentration in the fraction of aerosol that reached the plasma. A careful selection of the sample introduction system components and parameters could minimize the acid effects. Results were compared with those obtained with an ultrasonic nebulizer associated with a desolvation system. Acid effects were more important for the ultrasonic nebulizer than for the pneumatic nebulizers and were explained by a reduction in the production of aerosol.

Determination of fission products and actinides in spent nuclear fuels by isotope dilution ion chromatography inductively coupled plasma mass spectrometry

An Elan 5000 inductively coupled plasma mass spectrometry (ICP-MS) instrument was modified for its installation in a glove-box for the analysis of radioactive materials. An ion chromatographic system was coupled to the ICP-MS instrument. The chromatographic pump was set outside the box while the injection valve and separation column were installed inside the box coupled directly to the cross-flow nebulizer. Performance characteristics of the modified ICP-MS system were evaluated regarding long-term stability, optimum plasma and ion lens conditions, sensitivity and detection limits, polyatomic ions, mass discrimination, detector dead time and uranium matrix interferences. Chromatographic methods were developed for the separation of fission Cs from Ba, for the lanthanide elements (La to Gd) and for the actinides (U to Cm) in order to eliminate isobaric interferences. Isotope dilution analysis was applied for the determination of selected fission products and actinides in spent nuclear fuels after ion chromatographic separation.

Determination of ultratrace metals in biological standards by inductively coupled plasma atomic emission spectrometry with ultrasonic nebulisation

Ultratrace cadmium, cobalt, nickel and lead in biological standard samples were determined by inductively coupled plasma atomic emission spectrometry with ultrasonic nebulisation without removal of any matrix. The operating conditions of the ultrasonic system were examined in detail, together with the performance of the system. An internal standard method was essential to obtain accurate analytical results. The transport efficiencies of analyte (manganese) and solution to a plasma with the ultrasonic system were measure, and compared to those with a cross-flow nebuliser.

Evaluation of Thermospray and Cross-Flow Pneumatic Nebulization as Means of Interfacing a Flame Infrared Emission (FIRE) Radiometer to a High-Performance Liquid Chromatograph

A cross-flow pneumatic nebulizer and a thermospray nebulizer were each studied as a means of interfacing a flame infrared emission (FIRE) radiometer to a high-performance liquid chromatograph (HPLC). Both nebulizers introduced significant quantities of liquid mobile phase into the FIRE burner, necessitating modifications to the basic burner design and causing temperature changes in the hydrogen/air flame used as the FIRE source. Tailing in the trailing edge of the peak profiles was also observed with the use of pneumatic nebulization and attributed to dead volume present in the nebulizer spray chamber. Flame background caused by the combustion of carbon-containing mobile phases was also a problem, but could be avoided when the FIRE radiometer was operated in the carbon mode by using water as the mobile phase. Flame background from carbon-containing mobile phases could also be electronically subtracted by using a dual-channel, chlorine-specific FIRE radiometer to selectively determine mixtures of chlorinated hydrocarbons in the presence of a chlorine-free mobile phase. Background subtraction had the added advantage of improving the detection limits for organochlorine compounds by a factor of approximately 3. Detection limits for FIRE/HPLC using pneumatic nebulization and the single-channel FIRE radiometer in the carbon mode were estimated as 3.7 μg s−1 (5.5 × 102 μg) for acetic acid and 0.80 μg s−1 (1.2 × 102 μg) for ethanol with water as the mobile phase. FIRE/HPLC detection limits using thermospray nebulization and a dual-channel FIRE radiometer in the chlorine-specific mode were estimated as 6.2 μg s−1 (3.7 × 102 μg) for methylene chloride and 9.7 μg s−1 (5.8 × 102 μg) for carbon tetrachloride with a combustible mixture of 49% acetonitrile, 20% methanol, 30% water, and 1% acetic acid as the mobile phase.

The conespray nebulizer for inductively coupled plasma atomic emission spectrometry

A version of the conespray nebulizer proposed by Sharp has been designed and evaluated for routine liquid sample introduction for inductively coupled plasma atomic emission spectrometry (ICP-AES). The short-term analytical precision was better than 1% RSD with the conespray nebulizer using both simple aqueous solutions and solutions containing a matrix of 10% NaCl. The long-term %RSD (about 8 hr) was typically about 1% with simple (low matrix) solutions. The precision and stability of the analytical signal while nebulizing solutions with a 10% NaCl matrix during continuous runs were not distinguishable from the case when simple solutions were used. Sensitivity and detection limit data collected for the conespray nebulizer at a solution flow rate of 2 ml min and the cross-flow nebulizer at 1 ml min showed similar performance for these figures of merit. Wash-in and wash-out times for the conespray nebulizer were 9 and 40 s, respectively. Generally, this version of the conespray nebulizer provided similar overall performance to the best of the currently available Babington style nebulizers such as the V-groove nebulizer.

Coupling of HPLC and ICP-AES for speciation

The cross-flow nebulizer and the thermospray vaporizer can both be used as an interface for coupling high performance liquid chromatography with inductively coupled plasma-atomic emission spectrometry. The dispersion and the peak asymmetry are acceptable for both. With the thermospray system the sensitivity is threefold higher and the fraction of methanol in methanol/water mixtures introduced into the plasma can be as high as 75%, compared with 25% for the cross-flow nebulizer. Initial results obtained for the speciation of selenium in (CH 3) 3Se +, SeO 3 2− and SeO 4 2− are promising.

Small spray chamber for inductively coupled plasma atomic emission spectrometry and its evaluation by a digital signal sampling technique

The practical performance of a small single-barrel spray chamber was evaluated with special regard to the response time attained for the discrete nebulisation technique in inductively coupled plasma atomic emission spectrometry. The precision, sensitivity and response times obtained with chambers of various sizes were compared by digital signal sampling and processing using a personal computer. For a precise comparison, two parallel chamber systems, each having an individual chamber, cross-flow nebuliser and drain trap, were switched alternately with a 3-way valve with the plasma on. One system was equipped with the chamber being investigated and the other with a fixed chamber as a reference. The small chamber, 1.8 cm i.d. and 5 cm in length, was recommended for discrete nebulisation, because of its faster response and better precision compared with a chamber of a size normally available commercially. The small chamber also showed good performance characteristics with continuous nebulisation.

Effects of the Nature of the Solvent and Solutes on the Response of a Light-Scattering Detector

Abstract The effects of the nature of the solvent and solutes on the response of an evaporative light scattering detector (ELSD) are discussed. Data have been measured for six solutes with seven different solvents using concentric and cross-flow nebulizers. The experimental results suggest that the influence of the solvent on the properties of a dried aerosol are not properly accounted for by the equation of Nukiyama and Tanassawa. A modification of the droplet size distribution of the aerosol takes place, probably during the vaporization of the solvent. The amount of scattered light depends strongly on the molar absortivity of the solute at the light beam wavelength. Accordingly, the detector response depends on the properties of the solvent and the solute. The ELSD is not a mass detector and calibration is required for quantitative analysis.

Myers-Tracy signal compensation in inductively coupled plasma atomic emission spectrometry with high dissolved solids solutions

A preliminary study has been made of the use of Myers-Tracy signal compensation in inductively coupled plasma atomic emission spectrometry (ICP-AES). It was found that significant improvements in precision, in some instances up to ten-fold, could be obtained in comparison with normal ICP-AES operation. Matrix effects caused by the presence of up to 10%m/V potassium chloride were reduced by the use of signal compensation. However, deviations from standard plasma conditions are required to optimise the effect of ratioing to the internal standard. A comparison of the performance of a high dissolved solids nebuliser and a cross-flow nebuliser showed that the former provides better precision in a potassium chloride matrix in the determination of manganese and copper. Nevertheless, Myers-Tracy signal compensation was found to improve the precision performance of both nebulisers.

Electrothermal vaporization for sample introduction into a three-electrode direct current argon plasma

The direct current plasma (DCP) configuration developed by Elliott has been shown to be an excellent source for analytical atomic emission spectrometry. The application of DCP excitation for atomic emission (AES) measurements of trace metals has, during the past 10 years, enhanced the versatility of AES as an analytical technique. In normal use, sample is pumped continuously into a ceramic cross-flow nebulizer, and the resulting aerosol is transported to the excitation region of the plasma. This approach is satisfactory for routine analyses, but under special circumstances benefits may be obtained from the use of electrothermal vaporization (ETV) sample introduction. In this study the adaptation of the commercial electrothermal vaporization system is explored for sample introduction into the three-electrode DCP. The ETV technique reduces the sample volume required for analysis and is especially convenient for volumes in the 5-20 ..mu..L range. Recent studies of aerosol approaching the plasma indicate that elimination of the solvent by ETV may permit more efficient introduction of the sample directly into the excitation region of the DCP than with conventional nebulization. Three elements chosen for this feasibility investigation (aluminum, copper, and manganese) cover a range of vaporization and excitation conditions and illustrate problems expected in analyticalmore » applications. For each element the effects of carrier gas flow rate and observation region were investigated using 1 ..mu..g/mL solutions. The conditions providing the best signal-to-background ratio were employed to measure the calibration function and estimate the detection limit. 8 references, 4 figures, 1 table.« less

Experimental Characterization of Aerosol Production, Transport, Vaporization, and Atomization Systems. Part II: Factors Controlling Aerosol Size Distributions Produced

The effects of nebulization conditions on the size characteristics of the aqueous aerosol produced have been investigated for a cross-flow nebulizer. It is shown that the nebulizer gas flow rate does not affect the upper limit mean sizes of the aqueous droplets transported from the nebulization chamber but that the mean size of the analyte-containing aerosol itself is affected. Model equations are presented descriptive of the effects of gas flow rate and analyte concentrations on analyte aerosol size characteristics.

Flow injection analysis with inductively coupled plasma-atomic emission spectroscopy: critical comparison of conventional pneumatic, ultrasonic and direct injection nebulization

The analytical figures of merit observed under flow injection analysis (FIA) conditions of a direct injection nebulizer (DIN) interfaced to an inductively coupled plasma-atomic emission spectroscopy (ICP-AES) facility were found to be comparable to or better than conventional pneumatic nebulization in terms of limits of detection, reproducibility and interelement effects. The DIN offered clog-free operation and part per billion limits of detection for 30μl sample injection volumes and carrier stream consumption rates in the range of 100–200μl min −1. The relative detection limits observed were generally comparable to those obtained for: (a) FIA introduction of 200μl or continuous sample introduction into a conventional cross flow nebulizer; and (b) FIA introduction of 500μl or continuous sample introduction into an ultrasonic nebulizer. Absolute and relative detection limits were comparable to or within the range of values reported for electrothermal vaporization-ICP-AES and comparable or superior to those reported for the graphite cup, direct insertion-ICP-AES. The reported absolute detection limits for the graphite-rod direct insertion approach ranged from comparable values to superior by a factor of 30. At the normal compromise observation height (20 mm), the interelement effects, to the extent they were observable, were comparable in magnitude for both the DIN and conventional cross-flow pneumatic nebulizer.

Evaluation of ICP atomic fluorescence for the determination of mercury

Using a commercial atomic fluorescence instrument that employs an ICP as an atomization cell, a pulsed mercury hollow cathode lamp produced an unsatisfactory detection limit of only 0.5 mg l −1. Consequently, the hollow cathode lamp was replaced with a mercury vapor lamp operating in the pulsed mode. Using this source and sample introduction by pneumatic crossflow nebulization, a detection limit of 0.03 mg l −1 and an upper linearity limit of 300 mg l −1 were achieved. For lower level mercury determinations, a continuous cold vapor generator was developed that interfaces with the instrument to leave the nebulizer intact. The generator allows mercury to be determined with a detection limit of 0.2 μg l −1 while up to eleven other elements are simultaneously determined in the conventional manner. The cold vapor generator can also be used with the plasma off for single element mercury determinations. In this mode, a detection limit of 0.04 μg l −1 was achieved.

Screening for selected toxic elements in urine by sequential-scanning inductively-coupled plasma atomic emission spectrometry

A rapid screening method for nine elements (Se, As, Cr, Zn, Cd, Pb, Ni, Mn, and Cu) in human urine is described. A sequential-scanning inductively-coupled plasma atomic emission spectrometer, incorporating a cross-flow nebulizer, was used. Internal standardization with yttrium compensated for the differences between the aqueous calibration standards and the undiluted urine specimens. Accuracy was evaluated with aqueous (NBS SRM 1643a, EPA 378-13, and EPA 476-3) and urine (NBS SRM 2670 and Fisher Urichem Level II) reference and control materials. Detection limits for the system were evaluated from analyses of normal urine materials found to contain low levels of the elements investigated.

A study of designs of a cross flow nebulizer for ICP atomic emission spectrometry

Effects of some design parameters of a cross flow nebulizer on nebulization characteristics are described. The performance in ICP work is compared with that of a commercially available concentric nebulizer.

The determination of some nebulizer characteristics

An indirect method for measuring nebulizer characteristics is described in detail and is indirectly compared with a direct method described in the literature. Nebulizer characteristics for various cross-flow and concentric nebulizers are compared. The precision of the present indirect method is inferior to that of direct methods, but the accuracy tends to be the same. The efficiencies of cross-flow and concentric nebulizer systems for ICP systems are typically 1–3% and the aerosol concentration tends to be higher for cross-flow nebulizers.