Sample Uptake Research Articles

Sonic Spray Nebulizer for Inductively Coupled Plasma Atomic Emission Spectrometry

A novel nebulizer called a sonic spray nebulizer (SSN) was developed to introduce microliter sample solution for ICP-AES with a high nebulization efficiency. At a sample uptake rate of 50 m l min–1, the detection limit of ICP-AES with the SSN is comparable to that with a conventional concentric nebulizer (CCN) at a typical sample uptake rate of 850 m l min–1. The absolute sensitivity of the SSN was improved by an average factor of 13, compared to that of the CCN. The SSN system is capable of introducing a sample solution at a rate as low as 1 m l min–1 with a relative standard deviation (RSD) of about 2%; therefore, the SSN nebulizer should be very useful for introducing biological or other samples in very limited volumes.

Feasibility of Sampling Vapors of Compounds with Low Volatility by Permeation

Lindane was used as the model of low vapor pressure compounds for the study of the feasibility of sampling vapors of such compounds by permeation. A constant source of lindane vapor, a dynamic exposure chamber, and a sampler for the chamber air were all based on the permeability of polyethylene (PE) to the vapor. Lindane-saturated air was contained in a glass vial with a thin PE membrane septum; the other side of the film was exposed to the supply air for the chamber. This kept the downstream face at virtually zero. The chamber concentration was monitored for several months by a grab sampler using a polyurethane foam (PUF). The samplers were ∼2 mL autoanalyzer vials with a PE septum backed by PUF sorbent. All operations to this point were conducted in a controlled temperature room. From the chamber concentration and the sampler uptake of lindane it was possible to calculate the coefficient of diffusion (D) for the combination, lindane vapor and a polyethylene membrane (lindane·PE). Using this value for D,...

Determination of selenium in urine by inductively coupled plasma mass spectrometry: interferences and optimization

The aim of this study was to develop a method for selenium determination in urine and examine the influence of sensitivity enhancement reagents, instrument parameters, internal standards and the salt content of the urine matrix on the determination. Several carbon-containing solutions (methanol, ethanol, propanol, butanol, glycerol, acetonitrile and acetic acid) were examined for their sensitivity enhancement effect. Enhancement factors up to six were obtained and were dependent on the nebulizer gas flow and rf power. There was no important difference in the enhancement effects of these solutes when the nebulizer gas flow rate was optimized for each solute. The influences of sample uptake rate, nebulizer flow rate and rf power were examined in multivariate experiments. The nebulizer gas flow rate and rf power were found to be interdependent, but the sample pump flow rate was independent of the other parameters. The sensitivities of different selenium species (selenite, selenate, selenomethionine and trimethylselenonium iodide) were equal during the experiments in different enhancement solutes and when analysed with the optimized parameter settings. The influence of the urine matrix and different salts on four selenium isotopes were examined. It was concluded that only 82 Se was usable for quantitative determination in urine as the blank at mass 82 was close to zero. The blank values at masses 76, 77 and 78 varied considerably and differently with different salts and salt concentrations. Yttrium, indium and gallium were compared for their use as internal standards. There was no difference in the efficiency of these internal standards and they were all usable. The accuracy of the method was determined using the NIST SRM 2670 Toxic Metals in Freeze-dried Urine (certified value 0.030±0.008 mg l –1 ). The result was 29.4±1.0 µg l –1 (n=8) and the precision was 3.4%. In synthetic urine diluted 1+1, the limit of detection was 0.9 µg l –1 and the limit of determination was 2.2 µg l –1 .

Microliter Sample Introduction Technique for Microwave-Induced Plasma Mass Spectrometry

Nitrogen-MIP-MS has an advantage over conventional inductively coupled plasma mass spectrometry (ICPMS) in that it is free from Ar-related spectral interference when measuring the concentration of elements, for example As and Se. Therefore, MIP-MS is a powerful technique for simultaneous determination of multiple elements. However, the ionization efficiencies in the MIP are lower for elements with high values of ionization potential (IP). Our goal was to improve the sensitivity of MIP-MS for As and Se by optimizing the sample introduction technique. A new nebulizer, called the sonic spray nebulizer (SSN), was developed to introduce a liquid sample into the MIP-MS with a flow rate at the microliter per minute level. Our results showed that plasma characteristics could be significantly affected by the sample introduction method used. Compared with a conventional concentric nebulizer (CCN), the detection limits were improved. By using a sample uptake rate that was only one-seventh of that for the CCN, i.e., a SSN rate of 50 μL/min, detection limits were improved by a factor of about 7 for As, Se, and Au, which have very high IP values. Detection limits were also improved for Te, Be, Zn, Sb, and Cd but remained almost the same for elements with low ionization potentials. A mechanism that accounts for this sensitivity enhancement was discussed. Typically, relative standard deviation was found to be less than 2%. In addition, the formation of oxide ions of rare earth elements was reduced by a factor of more than 100 when the SSN was used. The SSN system is capable of introducing samples at a rate as low as 1 μL/min with good precision, which is highly desirable in many cases.

Thermospray nebulizer as sample introduction technique for microwave plasma torch atomic emission spectrometry

A thermospray nebulizer was used as a sample introduction device for microwave plasma torch (MPT) atomic emission spectrometry (AES). Experimental parameters, including the power supplied to the MPT, the flow rates of support and carrier gases, the observation height, the sample uptake rate, the thermospray working temperature, the temperature of the aerosol spray chamber and cooling water were optimized. Under optimum conditions, the relative standard deviation (RSD) of 10 measurements for 21 elements is in the range 0.3–2.0%. The detection limits were improved in comparison with the ultrasonic nebulizer as sample introduction technique for MPT–AES. The inclusion of 20% methanol into the MPT showed there is no effect on the stability of MPT discharge. The technique can thus be held to have the potential for interface to reverse-phase HPLC systems.

Studies on parameters of inductively coupled plasma spectrometer

Analytical aspects of different adjustment of parameters of an inductively coupled plasma atomic emission spectrometer (ICP‐AES) were investigated. The ICP‐AES was a LABTAM 8440M (now called GBC) spectrometer. Since at many times, the elemental concentration of the analyte is near to the detection limit, the lowest possible detection limit has to be reached. When the signal‐to‐background ratio (SBR) is maximized, the detection limit is the smallest. This is the reason why the effects of each adjustable parameters on the signal‐to‐background ratios were investigated. Seven adjustable parameters can be analyzed in this equipment: (i) viewing height, (ii) forward power, (iii) sample gas, (iv) coolant gas, (v) auxiliary gas, (vi) flushing gas, and (vii) sample uptake flow rates. Furthermore aerosol distribution by droplet size and nebulization efficiency were also examined applying three different sample gas flow rates and four elements [iron (Fe), magnesium (Mg), manganese (Mn), and nickel (Ni)]. The alkali metals with low excitation energy [potassium (K), lithium (Li), and sodium (Na)] were detectable in higher regions of the plasma, some alkali‐earth and transition metals with medium excitation energy [calcium (Ca), srontium (Sr), and copper (Cu)] were well detectable in medium height, whereas the maximum signal‐to‐background ratios of the other elements with relatively high excitation energy [e.g. cadmium (Cd), Ni, and phosphorus (P)] reached in lower regions of the plasma. On the basis of results the compromised viewing height for all the elements is found 5 mm, the optimum sample gas flow rate 1.14 dm3 min‐1 and the forward power 1200 W. Change of coolant and auxiliary gas flow rates has not changed the signal‐to‐background ratios significantly. Consequently the optimum argon flow rates in aspect of consumption of argon are the possible lowest flow rates, where plasma remains stable. For coolant and auxiliary gas flow rates these values are 10 dm3 min‐1 and 0.1 dm3 min‐1, respectively. Changing the rate of peristaltic pump (i.e. sample uptake rate) the signal‐to‐background ratios increase to 4‐ or 5‐fold of the original values, therefore the optimum sample uptake rate is considered 4 cm3min‐1. Increase of flushing gas flow rate has not changed the signal‐to‐background ratios significantly, except in case of sulfur (S) and P, because of oxygen (O2) absorption from the air. When analysis of S and P content is necessary, 0.13 dm3min‐1 and 0.2 dm3 min‐1, respectively, of flushing gas flow rate is recommended to use.

Determination of metals in saline and biological matrices by axial inductively coupled plasma atomic emission spectrometry using microconcentric nebulization

An axial inductively coupled plasma atomic emission spectrometer equipped with a commercially available microconcentric nebulizer (MCN) was evaluated for the determination of metals in saline and biological samples. The performance of the MCN was optimized regarding the sample uptake rate and nebulizer pressure in terms of signal intensity and signal-to-background ratio. The effect of increasing salt concentrations was also studied. The results were compared with those obtained with a standard concentric glass nebulizer (CGN) for sample volumes, sensitivity and stability. The MCN was shown to reduce the sample consumption from several milliliters to a few hundred microliters for multi-element analyses. The analytical performance with the MCN was generally poorer than with the CGN, but the magnitude of the effects is element dependent. For the 18 elements studied, the detection limits range from 0.05 µg l–1 (Mn) to 30.48 µg l–1 (Ca) for the CGN and from 0.13 µg l–1 (Mn) to 173.66 µg l–1 (Na) for the MCN. Increasing the salt concentration decreases both the sensitivity and signal stability obtained with both nebulizers, but the effects are more pronounced for the MCN. The method was further evaluated by analyzing three BCR reference materials: CRM 63 Milk Powder, CRM 185 Bovine Liver and CRM 278 Mussel Tissue. Overall, the results obtained with both nebulizers showed good agreement with the certified values.

Speciation of organic selenium compounds by reversed-phase liquid chromatography and inductively coupled plasma mass spectrometry. Part I. Sector field instrument with low mass resolution

The speciation of selenocystine, selenocystamine, selenomethionine and selenoethionine was studied by on-line coupling of high performance liquid chromatography with inductively coupled plasma mass spectrometry with hydraulic high pressure nebulization (HHPN) for sample introduction employing a double-focusing magnetic sector field mass spectrometer in order to achieve the utmost sensitivity. Reversed-phase chromatography was applied to separate the organic Se compounds. The eluent was 30 mm ammonium buffer adjusted to pH 3.0 in methanol-water (5+95 v/v). The operating conditions for chromatographic separation (pH of the mobile phase, methanol content of the mobile phase, pH of the sample and sample uptake rate) were carefully optimized. With the developed procedure, detection limits below 0.02 ng ml –1 were achieved, so that even low pg levels could be detected when applying sample volume of 200 μl.

High resolution inductively coupled plasma mass spectrometry for the trace determination of plutonium isotopes and isotope ratios in environmental samples

S. Stürup, H. Dahlgaard and S. Chen Nielsen, J. Anal. At. Spectrom., 1998, 13, 1321 DOI: 10.1039/A806408C

Spatial Characterization of Emission Intensities and Temperatures of a High Power Nitrogen Microwave-induced Plasma

The spatial characterization of a high power nitrogen microwave-induced plasma (N 2 -MIP), using an Okamoto cavity, was undertaken. The plasma operating conditions were fixed during all the experiments at a microwave frequency of 2.45 GHz, an incident power of 1.3 kW, a plasma gas flow rate of 11.0 l min -1 , a carrier gas flow rate of 1.0 l min -1 and a sample uptake rate of 1.6 ml min -1 . A Ca solution was used to measure the emission intensity distribution for both Ca atom and ion lines in the N 2 -MIP, and an Fe solution was used to determine the excitation temperature distribution of the N 2 -MIP, which was obtained by using a Boltzmann plot under the assumption of LTE. In addition, rotational temperature measurements were carried out using the N 2 + (0–0):B 2 Σ u + →X 2 Σ g + band. Because the H β line (486.13 nm) could not be excited in the N 2 -MIP, measurement of the electron number density was carried out by a method involving the Saha equation using both the emission intensity ratio (Ca II:Ca I) and the excitation temperature of the N 2 -MIP. The degree of ionization of various elements in the N 2 -MIP was also calculated. The spatial characteristics of the N 2 -MIP were compared with those of the Ar-ICP.

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.

Universal calibration for analysis of organic solutions by inductively coupled plasma atomic emission spectrometry

The petrochemical industry needs analytical methodology for the determination of trace elements in a variety of hydrocarbons and organic solvents, some highly volatile. The authors have previously demonstrated the use of an ultrasonic nebulizer (USN) coupled to a microporous membrane desolvator (MMD) for direct ICP-AES analysis of hydrocarbons and solvents of boiling-point well below 100 °C. Removal of the organic matrix by the USN/MMD was sufficient not only for good ICP operability but for the nearly complete elimination of calibration bias between the various solvent systems. This suggested the concept of ‘universal calibration’, a single analytical calibration valid for ICP-AES analysis of multiple organic solvent systems. Universal calibration is important for the analysis of refinery/chemical plant streams which demonstrate temporal variability in composition and volatility. The present study extended the scope of previous work by using a longer (140 mm) MMD for more complete matrix removal. With this system, direct analysis of pentanes is practical with sample uptake rates of 1–3 ml min–1 and detection limits similar to aqueous solution analysis with USN. Using 140 mm MMD USN/ICP-AES it is possible to establish a single calibration for direct trace element analysis of gasoline, refinery naphtha streams and volatile organic solvents. Corrections for differences in sample nebulization efficiency can be made by prior calibration or with the use of an internal standard.

Determination of rare earth elements in wine by inductively coupled plasma mass spectrometry using a microconcentric nebulizer

A method for the direct determination of REEs in undiluted wine by ICP-MS was developed. The performance of a microconcentric nebulizer (MCN) was optimized regarding the nebulizer gas flow rate and sample uptake rate for all the REEs in terms of signal intensity and signal-to-noise ratio. The effect of ethanol on the sensitivity was also studied. Possible spectral interferences were identified and are discussed in detail. The MCN was shown to reduce the sample consumption to 30–50 µl min–1 and to decrease the matrix signal suppression by a factor of 2–5 in comparison with a de Galan nebulizer. Polyatomic interferences were found to be negligible except for those of BaO on 151Eu, 153Eu and 155Gd and of 139La16O on 155Gd. Data obtained with three different ICP-MS instruments were compared. Several wines from different vineyards in France, California and Australia were analysed for REEs. The REE concentration patterns showed inter-continental and inter-regional variations, whereas no difference was observed for different vintages from the same vineyard over a period of several years.

Fundamental studies on pneumatic generation and aerosol transport in atomic spectrometry: effect of mineral acids on emission intensity in inductively coupled plasma atomic emission spectrometry

The mechanism of the mineral acid interference has been studied in ICP-AES. For this study five mineral acids have been evaluated (HCl, HNO 3, HClO 4, H 2SO 4 and H 3PO 4) in four concentrations (0, 0.5, 5 and 30%). In order to investigate this interference emission signal, sample uptake rate, primary and tertiary drop size distributions, total analyte transport rate and excitation temperature have been measured. From the results obtained, it seems that this interference is contributed by a reduction of the analyte transport rate and, also, by a decrease in the plasma temperature. The degree of the contribution to the interference of each one of these causes depends on the type of acid and sample uptake mode. The physical properties of the acid solutions are in the origin of the interference. These physical properties modify the sample uptake rate and/or the primary drop size distribution of the aerosols. The acids evaluated can be classified in two groups. The first group would consist of HCl, HNO 3 and HClO 4, and the second one of H 2SO 4 and H 3PO 4. In natural uptake mode the interference is mainly due to changes in sample uptake rate, and in controlled uptake mode to changes in primary drop size distribution of the aerosols. In both sample uptake modes a density-effect may appear on increasing acid concentration. All these factors tend to decrease the analyte transport rate and, hence, the emission signal. Finally, a cooling effect of the plasma due to a higher load of acids is superimposed to these causes. We think that from this study the mineral acid interference in ICP-AES, with pneumatic nebulization, should be better understood.

Characterization of aerosols produced by pneumatic nebulizers for inductively coupled plasma sample introduction: effect of liquid and gas flow rates on volume based drop size distributions

The effect of liquid sample uptake rate and nebulizer gas flow rate on analyte transport rates and volume based primary and tertiary drop size distributions were studied for two pneumatic, concentric nebulizers with a Scott type spray chamber. Experimentally measured Sauter mean diameters and spans were compared to those predicted by an empirical model. One of the two nebulizers produced analyte transport rates that were a factor of two or more higher than the other nebulizer under all uptake rate and gas flow rates studied, despite that the nebulizers were of the same model. When the sample uptake rate is increased 400% (from 0.4 to 2.0 ml/min) the aerosol transport rate increased by only 60 to 68%. Losses of aerosol of all drop sizes due to secondary and tertiary processes result in a decrease in the sample transport efficiency as the uptake rate is increased. When the nebulizer gas flow rate was increased from 0.4 to 1.0 l/min the analyte transport rate increased more than a factor of five. The increase in analyte transport rate (and efficiency) as the gas flow rate was increased from 0.4 to 0.6 or 0.7 l/min was due to both a larger volume of small primary aerosol drops produced and less severe losses of drops due to secondary and tertiary processes. The relative increase in volume of small primary aerosol drops produced when the nebulizer gas was increased from 0.6 or 0.7 to 1.0 l/min was similar to the relative increase in analyte transport rate. The higher transport rates produced by one of the two nebulizers was due to a higher production/loss ratio due to secondary and tertiary processes for drops of all sizes less than 20 μm in diameter rather than differences in the volume of primary aerosol contained in small drops.

Simultaneous reduction of arsenic and lead to hydrides by sodium tetrahydroborate(III) for inductively coupled plasma-atomic emission spectrometry: An investigation into the reaction medium

Nitroso R salt and potassium ferricyanide, in hydrochloric acid, have been used as the reaction medium for simultaneous generation of arsine and plumbane, combined with inductively coupled plasma-atomic emission spectrometric detection. Both of the reagents enhance the lead signal and neither reagent inhibits the arsenic signal, provided that the potassium ferricyanide is mixed on-line with the analyte solution. Potassium iodide, which is used to prereduce As(V) to As(III), does not interfere with plumbane generation in both reaction systems. Various parameters affecting the signals have been studied, and the hydrochloric acid-potassium ferricyanide system has proved to be a better reaction medium. Detection limits of lead and arsenic are 1.1 and 2.8 ng/ml, respectively, have been obtained in the HClK 3 Fe(CN) 6 system at a sample uptake rate of 1.5 ml/min.

Thermospray device of improved design for application in ICP-MS

A new thermospray device for sample introduction in ICP-MS has been developed. Three design principles were followed in order to minimize blank values which originate from chemical erosion of the utilized materials: the aerosol comes exclusively in contact with chemically inert materials; a fused silica capillary is used instead of the usually applied steel capillary; and a double desolvation system is applied for an effective reduction of the solvent load to the plasma. With careful optimization of the temperature of the capillary, aerosol gas flow rate, sample uptake rate, operation of the desolvation system and the ICP, a considerable improvement was achieved. Blank values in the mass region of Fe, as appear with steel capillaries, were reduced by orders of magnitude, so that this important region became accessible for analytical determination with satisfying detection limits. Sensitivity was improved by a factor of about 20 for the elements measured in comparison with two commercial pneumatic nebulization systems and ICP-MS instruments with low and high resolution. Standard deviations of ⩽3.8%, and about 10 times lower detection limits in the mean were achieved for a variety of elements in comparison with pneumatic nebulization. In spite of remaining restrictions from blank values, detection limits at pg ml–1 levels and below were realized for several elements.

Automated simplex optimization for monochromatic imaging inductively coupled plasma atomic emission spectroscopy

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), the electronic section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by a diskette with data files and text files with the hardcopy paper in Word for Windows 2.0 and ASCII format, and a disclaimer. The text details the purpose of the work, and the appendix provides essential information for accessing the diskette and using programs and data. An automated simplex optimization program was written in an attempt to relieve the monotonous human effort required to optimize an inductively coupled plasma atomic emission spectroscopic (ICP-AES) instrument. The program controls the operating conditions of a solid-state ICP while a monochromatic imaging spectrometer collects two-dimensional response images. In the work described in this article, four of the most important ICP operating parameters are optimized automatically: radio frequency (rf) power, intermediate Ar flow rate, nebulizer flow rate and sample uptake rate. Optimization of these parameters is based first on the response of the Ca II net signal and, independently, on the response of the Ca II net signal-to-background noise ratio ( S N B ). Since the best height and off-axis positions of the designated response are known from the optimal two-dimensional response image, two spatial parameters are indirectly optimized through use of a CCD camera. Optimal operating conditions are reported for the CA II net signal and Ca II S N B as well as the Mg II Mg I ratio.

Application of an electrospray-interface as a new nebulizer for inductively coupled plasma atomic emission spectrometry

An electrospray nebulizer was constructed for possible use as an interface for micro-HPLC and ICP-AES. The sample uptake rate was 10 μl min −1. To allow the transport of the aerosol to the plasma, the highly positively charged droplets produced by the electrospray were neutralized. To test the performance of the interface, methanoi and methanol/water (8:2, v/v) solvent test solutions of metal-acetylacetonates were nebulized. Concentration detection limits obtained with this interface were worse than those obtained with thermospray or conventional pneumatic nebulizers. However, due to the low uptake rate, the absolute detection limits were considerably lower. No signal drift was observed when nebulizing the methanol test solution over l h. The extra-column peak broadening caused by the interface is not satisfactory and only acceptable when coupling to a micro-HPLC packed column with an inner diameter no smaller than 1 mm.

Trace analysis in high matrix aqueous solutions using helium microwave induced plasma mass spectrometry

The practical aspects of a He microwave induced plasma (MIP) mass spectrometry system for the determination of As, Se, Br and I in biological samples were investigated. A prototype instrument with a toroidal helium MIP coupled to a quadrupole mass spectrometer was used. Liquid samples were analysed by pneumatic nebulization with a Meinhard nebulizer without desolvation. The plasma was operated at 380 W with 3.6 l min–1 cooling gas, 0.8 l min–1 nebulizer gas, 0.6 l min–1 intermediate gas and 0.5 ml min–1 sample uptake rate. Arsenic, Se, Br and I showed linearity of more than 4 orders of magnitude. The detection limits (3s) were determined for 75As, 78Se, 79Br and 127I, and were 0.05, 0.25, 0.30 and 0.07 µg l–1, respectively. The influence of Na and K on the response of As was less than 20% up to concentrations of 1000 mg l–1. Analysis of 3% HCl causes an interference at a concentration of 1 µg l–1 of As, analysis of 1000 mg l–1 of Ca causes an interference at a concentration of 2 µg l–1 of As. Both of these elements in the solution cause significant interference in the determination of 75As, due to the formation of the 40Ca35Cl polyatomic ion. Biological reference materials (liver, muscle, milk, flour, diet and fish) and different fish samples were analysed for As and Se after high-pressure ashing with HNO3. Bromine was found to be a good internal standard for these elements. The results obtained with the He-MIP showed good agreement with the certified values for most of the materials investigated. Bromine and I were determined after alkaline digestion with tetramethylam-monium hydroxide. The determination of Br was complicated by severe memory effects. The results obtained for the few available reference materials showed acceptable agreement with the certified values.