Direct Injection High Efficiency Nebulizer Research Articles

Detection of nanoparticles by single-particle ICP-MS with complete transport efficiency through direct nebulization at few-microlitres-per-minute uptake rates.

Measurement of nanoparticle (NP) concentration and size by single-particle inductively coupled plasma mass spectrometry (spICP-MS) usually requires the use of a NP reference material to determine the loss of NPs and/or ions during their transport from the sample solution to the detection system. The determination of this loss, qualified as nebulization efficiency (ηNebulization) and/or transport efficiency (ηTransport), is time-consuming, costly and lacks reliability. Nebulization of the NPs directly into the plasma (without a spray chamber) results in ηNebulization = 100% and is thus a promising strategy to avoid these calibration steps. In this work, we used the μ-dDIHEN introduction system: a demountable direct injection high-efficiency nebulizer (dDIHEN) hyphenated to a flow-injection valve and a gas displacement pump. For the first time with a continuous flow nebulizer, complete transport efficiency was reached (i.e. ηTransport = 100%). Operated at a very low uptake rate (as low as 8μLmin-1), the μ-dDIHEN accurately and reproducibly determined average diameters of Au-, Ag- and Pt-NPs, in full agreement with their reference values. It was also successfully tested for Au-NPs in complex matrices, such as surface waters. spICP-MS analyses with the μ-dDIHEN sample introduction system only require a dissolved standard calibration to determine NP average diameter (dNPs in nm) and number concentration (NNPs) from the simplified set of equations: [Formula: see text] and [Formula: see text]Graphical abstract.

Piloted Liquid Spray Flames: A Numerical and Experimental Study

ABSTRACT Liquid-fuel spray flames are the primary mode of energy conversion in many high-power-density practical combustion devices. As compared to gaseous fuels, the phase change in liquid-fuel spray flames complicates the environment for laser-based combustion diagnostics and formulating predictive computational models. In this work, we present in-situ, non-intrusive measurement strategies and predictive models for combustion and carbon monoxide (CO) formation in piloted liquid-methanol spray flames. Resolving CO is essential to understand the incomplete oxidation of liquid hydrocarbon fuels and subsequent soot formation. A modified, flat-flame McKenna burner fitted with a direct-injection high-efficiency nebulizer (DIHEN) is used to produce piloted liquid-methanol spray flames. Hydroxyl (OH) planar laser-induced fluorescence (PLIF) is used for characterizing the reaction zones and temperature profiles of liquid-spray flames and two-dimensional (2D) images of CO are obtained via two-photon laser-induced fluorescence (TPLIF) using ultrashort, femtosecond-duration (fs) laser pulses. A three-dimensional (3D) computational model comprised of compressible continuous gas phase using unsteady Reynolds-averaged Navier-Stokes (URANS) in conjunction with two-way coupled Eulerian-Lagrangian spray modeling approach and partially-stirred reactor combustion model has been adapted to the modified McKenna burner. The computational model predicts the general trends of OH, temperature and CO profiles well at certain heights above the burner surface. Limitations of experimental measurements and strategies for improved model predictions pertaining to distributions of droplet sizes, pilot flame temperature, and the coflow temperature are discussed.

CO Imaging in piloted liquid-spray flames using femtosecond two-photon LIF

Abstract Liquid-spray flames are encountered in many practical combustion devices such as gasoline direct injection and diesel engines, gas turbine combustors as well as industrial furnaces. As opposed to gaseous fuels, additional phase-change steps present in liquid sprays not only complicate the overall combustion process, but also make in-situ, laser-based combustion diagnostics challenging. In particular, the formation of carbon monoxide (CO) due to incomplete fuel-air mixing and partial oxidation becomes a major challenge. In this study, we apply femtosecond, two-photon laser-induced fluorescence (fs-TPLIF) to measure CO concentration in piloted liquid-spray flames, taking into account possible signal interferences in the 230.1-nm, B1Σ+←X1Σ+ excitation scheme. A modified, flat-flame McKenna burner fitted with a direct-injection high-efficiency nebulizer (DIHEN) was used to produce piloted liquid-methanol spray flames. Although single-laser-shot OH-PLIF images show the presence of strong turbulent interactions in the core region, shot-averaged OH-PLIF images indicate that near the nozzle-exit region, the primary reaction takes place in an annular region around the droplet cloud, in general. A detailed spectroscopic study reveals that the signal interference at 460 nm originating from the second-order scattering of the excitation laser, which becomes approximately an order of magnitude stronger than CO fluorescence spectral lines near the nozzle exit region. The specific spectral filtering scheme introduced in our recent work is proved to be capable of suppressing interferences primarily originating from C2 Swan-band emissions. Two-dimensional CO maps along with OH-PLIF flame structure data provide key insights into the CO formation in piloted liquid-spray flames, while providing critical validation datasets for advanced computational models.

A Low-cost Demountable Direct Injection High-Efficiency Nebulizer for Inductively Coupled Plasma Mass Spectrometry

We developed a low-cost,demountable direct injection high-efficiency nebulizer(DIHEN) for inductively coupled plasma mass spectrometry(ICP-MS).It consisted of an enlarged microconcentric nebulizer based body,a tapered capillary(0.25 mm i.d.and 0.37 mm o.d.,30 μm i.d.and 40 μm o.d.at the tip),a hollow stainless steel tubing(0.5 mm i.d.and 2.0 mm o.d.) and two adapters made from polytetrafluoroethylene(PTFE),which were assembled by epoxy resin.The tapered capillary was reproducibly fabricated according to a flame-heated two-step drawing method.After immerging into boiling water,the epoxy resin became soft and the components could be taken apart simply.Then the broken or blocked sample capillary was replaced by a new tapered capillary with the same dimensions and then they were assembled again.The optimal sensitivity was obtained when the gas flow rate was 0.27 L/min with a sample uptake rate of 50 μL/min and a forward power of 1500 W.The sensitivities,detection limits and precisions of the homemade DIHEN under optimal operating conditions are similar,or better than those obtained with the MicroMist nebulizer,to some extent,though the polymeric ion levels of the former are higher than those of the latter.The utility of the homemade DIHEN for the analysis of small-volume samples was demonstrated by microscale flow injection analysis of Pt in serum samples.Then the homemade DIHEN was further utilized to couple microchip electrophoresis to ICP-MS for iodine speciation.The cost of the homebuilt DIHEN is about 1% price of the commercial Meinhard DIHEN,and the demountable construction permits that the blocked or broken sample capillary could be conveniently renewed with the same capillary in dimensions,obtaining low cost and easy maintenance.

Interfacing a microchip-based capillary electrophoresis system with a microwave induced plasma spectrometry for copper speciation

Abstract A microchip-based capillary electrophoresis (µCE) system was interfaced with a microwave induced plasma optical emission spectrometry (MIP-OES) to provide copper species separation capabilities. This system uses an extremely low flow demountable direct injection high efficiency nebulizer (D-DIHEN) sited directly at the liquid exit of the chip. A supplementary flow of buffer solution at the channel exit was used to improve nebulization efficiency. A small evaporation chamber has been incorporated into the interface in order to prevent the losses associated with traditional spray chambers, allowing the entire aerosol sample to enter the plasma. Syringe pumps were used to manipulate the flow rate and flow direction of the sample, buffer, and supplementary buffer solution. Sample volumes of 25 nL can be analyzed. With application of an electric field up to 500 V cm−1, species such as Cu(II) and Cu(EDTA)2− were separated in acidic solution within 90 s using a 26 mm long separation channel etched in a glass base. Resolution of the Cu(II) and Cu(EDTA)2− peaks was 1.1 using the chip-based µCE-MIP-OES system.

MC‐ICP‐MS Isotope Measurements with Direct Injection Nebulisation (d‐DIHEN): Optimisation and Application to Boron in Seawater and Carbonate Samples

We report here an optimisation of the demountable direct injection high efficiency nebuliser (d‐DIHEN) for isotopic measurements with a Neptune (ThermoFisher Scientific, Bremen, Germany) multi‐collector inductively coupled plasma‐mass spectrometer (MC‐ICP‐MS) and describe a method for boron isotopic ratio determination. With direct injection nebulisation 100% of the analyte was introduced into the ICP‐MS plasma and wash times were drastically reduced for elements such as boron and thorium. Compared to the classical stable introduction system (SIS: double Scott/cyclonic spray chamber), sensitivity for boron was 2–5 times higher with d‐DIHEN and wash times up to ten times shorter. Repeatability of 11B/10B sample‐calibrator bracketing measurements reached 0.25‰ (2s) for seawater and coral samples. Method accuracy and reproducibility were tested on mixed reference solutions having δ11B values in the ranges −90 to +40‰ and −2 to +2.5‰, demonstrating our ability to distinguish δ11B values with differences of only 0.25‰. The international seawater reference material NRCC NASS‐5 (National Research Council, Ottawa, Canada), analysed in different sessions over a 10‐month period, yielded an average δ11B value of +39.89 ± 0.25‰, in the upper range of previously published seawater values. A comparison between δ11B determined by d‐DIHEN MC‐ICP‐MS and positive‐TIMS (P‐TIMS) for four modern corals showed an excellent agreement (with bias of less than 0.4‰).

Effect of solvent dilution on the ICP-AES based silicon sensitivity, the aerosol characteristics and the resulting organic solution properties in the analysis of petroleum products

The effects of the solvent dilution factor on the physical properties of the resulting organic solutions, the aerosol characteristics and the silicon sensitivity were studied in ICP-AES for four different petroleum products by using near total sample consumption systems. The four samples were two gasoline products having very different volatilities along with a kerosene and a diesel sample. Petroleum product samples were diluted with xylene using four sample dilutions; 1:2, 1:5, 1:10 and 1:50. The sample introduction systems were a single pass spray chamber associated with a micronebulizer and a demountable Direct Injection High Efficiency Nebulizer (d-DIHEN). A cyclonic spray chamber also associated with a micronebulizer was taken as the reference system. Silicon was used as the test element, because it has been previously demonstrated that the ICP-AES Si sensitivity was significantly modified according to its chemical form. Silicon was spiked in each diluted solution with the same concentration to test sensitivity. When considering the dilution factor as the key variable, it was found that for the two gasoline samples and the kerosene one, the higher this variable, the lower the sensitivity. This result was explained in terms of changes in the solution volatility and/or in the aerosol characteristics. It was also observed that the total sample consumption systems were less sensitive to changes in the properties of the resulting organic solutions than the system based on the cyclonic spray chamber. However, for the latter chamber, the properties of the resulting organic solution had a marked influence on the extent of the effect of the silicon chemical form on the sensitivity. This fact demonstrated the appearance of an undefined interaction between the analyte and the organic solution during the aerosol transport step. However, both the single pass spray chamber and the d-DIHEN mitigated this effect for all the samples.

Original use of a direct injection high efficiency nebulizer for the standardization of liquid fuels spray flames

It is of practical importance to lead laboratory-scale experiments allowing a better understanding of the impact of commercial fuels composition on the formation of combustion residues such as soot particles. To this end, a hybrid burner has been designed recently to burn high-speed sprays of small liquid fuel droplets. It consists of a Holthuis (previously McKenna) burner originally equipped with a direct injection high efficiency nebulizer for the atomization of liquid hydrocarbons. A detailed description of this original setup is given in this paper. A priori estimations of atomization and evaporation times and length scales are then proposed and compared with experimental data. Droplet-size distribution measurements obtained in nonreacting conditions using a Malvern Spraytec particle sizer are presented and compared with values estimated by calculation. Cold sprays contours and liquid jet lengths in flames determined by Mie scattering at 532 and 1064 nm, respectively, are also presented. The results discussed in this work indicate that the hydrodynamic characteristics of the sprays generated with our system are relatively independent of the physical properties of fuels leading to comparable flames with identical liquid jet lengths, dimensions, and global structure. This feature facilitates an accurate comparison of flames burning various liquid hydrocarbons, which is of interest to emphasize differences in pollutants emissions and to highlight chemical effects for soot formation analysis.

Potential Primary Measurement Tool for the Quantification of DNA

An automated sample introduction system, utilizing a demountable direct injection high-efficiency nebulizer (d-DIHEN), is successfully incorporated for the first time with an inductively coupled plasma optical emission spectrometer (ICP-OES) for the measurement of the phosphorus content in acid-digested nucleotides and deoxyribonucleic acid (DNA). With this experimental setup, the solution uptake rate and volume are reduced from 170 to 30 microL min(-1) and from 10 to 2.4 mL, respectively, thereby reducing the required DNA sample mass for solutions containing 3 microg g(-1) P from 300 to 72 microg of DNA, in comparison to previous analyses in our laboratory using a glass concentric nebulizer with cyclonic spray chamber arrangement. The use of direct injection also improves P (I) 213.617 nm sensitivity by a factor of 4 on average. A high-performance (HP) methodology in combination with the previous sample introduction system and ICP-OES provides simultaneous, time-correlated internal standardization and drift correction resulting in relative expanded uncertainties (% U) for the P mass fractions in the range of 0.1-0.4 (95% confidence level) for most of the thymidine 5'-monophosphate (TMP), calf thymus DNA (CTDNA), and plasmid DNA (PLDNA) analyses. The d-DIHEN with HP-ICP-OES methodology allows for the quantification of DNA mass at P mass fractions as low as 0.5 microg g(-1), further reducing the required DNA mass to 12 microg, with small uncertainty (< or = 0.4%). This successful approach will aid in the development and certification of nucleic acid certified reference materials (CRMs), particularly for these samples that are typically limited in volume.

Heated-spray chamber-based low sample consumption system for inductively coupled plasma spectrometry

A systematic study about the effect of the heating of a modified version of the so-called Torch Integrated Sample Introduction System (TISIS) has been performed. The results showed that when working at liquid flow rates of 20–40 µl min−1, it was possible to raise the chamber wall temperature up to 100 °C without degradation of plasma thermal characteristics. Furthermore, a sheathing gas stream was added to the spray chamber so as to improve the aerosol transport towards the plasma. Under these conditions, sensitivity enhancements ranging from 8 to 15 with regard to those found under standard conditions (i.e., with neither chamber heating nor sheathing gas inlet) were reached for the different ionic and atomic emission lines studied. As a result, limits of detection at 20 µl min−1 were improved by a factor between 2.5 and 13. These LODs were only 1.7 to 2 times lower than for a cyclonic spray chamber at an uptake rate of 1 ml min−1. Two direct injection nebulizers were used for comparison: the conventional direct injection high efficiency nebulizer (DIHEN) and its demountable version (d-DIHEN). When TISIS was used under standard conditions quite similar results were found as those provided by d-DIHEN, although at low nebulizer gas flow rates (i.e., 0.1 l min−1), the DIHEN gave rise to higher sensitivities. However, by heating the TISIS chamber at 100 °C, sensitivities were enhanced by a factor up to one order of magnitude with respect to both the DIHEN and d-DIHEN. The result was ascribed both to the production of a finer tertiary aerosol and to the improved plasma excitation conditions. Furthermore, lower limits of detection were encountered for the hot chamber as compared to direct injection nebulizers. Hence, the developed system could be considered to be very promising for the analysis of very low liquid sample volumes through ICP techniques.

Minimization of the effect of silicon chemical form in xylene matrices on ICP-AES performance

It has been shown previously that the influence of the silicon chemical form could be minimized in ICP-AES by using high efficiency sample introduction systems. In this work, the effects of two of the most different silicon chemical forms have been minimized in ICP-AES by using near total sample consumption systems. The two tested devices have been a single pass spray chamber equipped with wall heating (heated torch integrated sample introduction system, h-TISIS) and a demountable direct injection high efficiency nebulizer (d-DIHEN). A room temperature TISIS and a cyclonic spray chamber have been taken as the reference systems. Solutions containing silicon as six different compounds in xylene have been prepared and analyzed through ICP-AES. It has been observed that, at low liquid flow rates, the h-TISIS improves the sensitivity and the limits of detection as compared to the d-DIHEN. In contrast, shorter wash-out times are obtained for the d-DIHEN. As regards to the effect of the silicon chemical form, h-TISIS and d-DIHEN have minimized it with respect to a conventional cyclonic spray chamber.

Direct injection nebulizer with replaceable capillary for micro samples analysis by inductively coupled plasma-optical emission spectrometry

The analytical performance of a low cost direct injection high efficiency nebulizer (DIHEN) with replaceable capillary is evaluated and compared with a high efficiency nebulizer HEN-cyclonic spray chamber arrangement for sample introduction at lower solution uptake rates in inductively coupled plasma optical emission spectrometry (ICP-OES). The system allows the use of a replaceable capillary and optimization of the aerosol generation. The study was performed in terms of the main analytical figure of merits (i.e., sensitivity, limits of detection and signal stability) for plain water solutions and matrix effects caused by nitric acid and sodium in ICP-OES. In general, the DIHEN with replaceable capillary offers better sensitivities than the HEN-Cyclonic system and for some elements, improved detection limits (DL) in the range of 1.1–3.8 ng · mL−1 for Ba, Mg, Zn 206.2–200 nm and Zn 213.8–856 nm were obtained. Strontium’s DL was comparable with both systems and those for Cd and Mn were slightly worse. Short-term precision for this unit is not as good as the HEN-Cyclonic system, but being less than 2%, it can still be considered acceptable. It was more susceptible to changes in matrix composition, being ca. 18% the acid depressive effect and 7% due to sodium with the DIHEN compared to the conventional nebulizer-spray chamber arrangement (13 and 3% acid and sodium depressive effect, respectively). The utility of the developed unit is explored analyzing three certified materials (bovine liver, rice and wheat flours) and the experimental results are within the certified values. The ability of the DIHEN with replaceable capillary to analyze real micro samples (samples reconstituted in 150 µL deionized water) was demonstrated by the determination of Ca, Cd, Cu, Mg, Mn, Sr, and Zn in individual scorpion venoms samples. One of the main advantages over other arrangements is that it can be easily constructed in the laboratory.

Determination of As, Cd, Pb, and Hg in urine using inductively coupled plasma mass spectrometry with the direct injection high efficiency nebulizer

The application of the large-bore direct injection high efficiency nebulizer (LB-DIHEN) for the determination of arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg) in urine by inductively coupled plasma mass spectrometry (ICP-MS) is described. The LB-DIHEN is compared with the standard method using a concentric pneumatic nebulizer and cyclonic spray chamber. In addition to the toxicological significance of As, Cd, Pb, and Hg, these elements represent a cross-section of analytical issues including spectral interferences (e.g., 40Ar 35Cl + on 75As + and 98Mo 16O + on 114Cd +) and memory effects (Hg). In this study, the low sample consumption of the LB-DIHEN is used to reduce the volume of urine needed for analysis, and to reduce the volume of final diluted sample required for analysis. Eliminating the spray chamber and reducing the dead volume of the nebulizer reduces memory effects, especially for analytes such as Hg. The Dynamic Reaction Cell (DRC) is used in this study to attenuate the background level of ArCl + in spite of the increase in the solvent load and, in turn, the urine matrix (chloride) delivered to the plasma by the LB-DIHEN. This is the first report on coupling the LB-DIHEN to a standard autosampler for unattended sample analysis. The robustness of direct injection nebulization for routine analysis and the issues associated with automation of the sample introduction process are discussed. Although the figures of merit (sensitivity, limit of detection, and precision) determined for both nebulizers are slightly poorer for the LB-DIHEN than for the concentric pneumatic nebulizer, there is not a clinically significant difference between the results for both sample introduction systems. The accuracy of results is assessed using archived urine materials that are circulated by several different proficiency testing (PT) programs and external quality assessment schemes (EQAS). Results obtained using the LB-DIHEN were within the acceptable range established by a consensus pool generated using different methods, none of which are likely to be using direct injection nebulization. Internal quality control sample results obtained using the LB-DIHEN were compared to those obtained using the conventional nebulizer. Reported results were similar for both nebulizers. Thus, these results show that the LB-DIHEN is certainly feasible for the analysis of urine specimens.

Speciation analysis of mercury and lead in fish samples using liquid chromatography–inductively coupled plasma mass spectrometry

A liquid chromatography–inductively coupled plasma mass spectrometric (LC–ICP-MS) method for lead and mercury speciation analysis was described. Sample containing ionic lead and mercury compounds was subjected to liquid chromatographic separation before injection into the direct injection high efficiency nebulizer (DIHEN, 170-AA). The species studied include inorganic lead (Pb(II)), trimethyl lead (trimethyl-Pb), triethyl lead (triethyl-Pb), inorganic mercury (Hg(II)), methyl mercury (methyl-Hg) and ethyl mercury (ethyl-Hg), which were well separated by reversed-phase liquid chromatography with a C18 column as the stationary phase and a pH 2.8 solution of 0.2% (v/v) 2-mercaptoethanol, 1 mg L −1 ETDA, 174.2 mg L −1 sodium 1-pentanesulfonate and 12% (v/v) methanol as the mobile phase. The lead and mercury species in biological tissues were quantitatively extracted, into 10 g L −1 EDTA and 0.2% (v/v) 2-mercaptoethanol solution taken in a closed centrifuge tube and kept on water bath, using microwaves at 65 °C for 2 min. The spike recovery of individual lead and mercury species determined by spiking the samples with suitable concentration of lead and mercury mixture standard were between 93% and 99%. The detection limits of the species studied were in the range 0.1–0.3 μg Pb L −1 and 0.2–0.3 μg Hg L −1. The procedure has been applied for the speciation analysis of two reference samples namely NRCC DOLT-3 Dogfish Liver and DORM-2 Dogfish Muscle and a swordfish sample obtained locally. The sum of the concentrations of individual species has been compared with the certified values for total lead and mercury to verify the accuracy of the method. The precision between sample replicates was better than 10% with LC–DIHEN-ICP-MS method.

Nano-HPLC-inductively coupled plasma mass spectrometry for arsenic speciation

A nano-high performance liquid chromatography-inductively coupled plasma mass spectrometry (nano-HPLC-ICPMS) method is developed, using a demountable direct injection high efficiency nebulizer (d-DIHEN), to reduce sample and mobile phase consumption, minimize organic waste generation, decrease analysis time, and enhance separation efficiency. A HPLC column (50 mm × 0.3 mm id), packed with 3.5 μm C18 material, is explored for chromatographic separation of five arsenic species naturally present in the environment or introduced as a pollutant: sodium (meta)arsenite [As(III)], arsenic acid [As(V)], dimethylarsenic acid (DMA), disodium methylarsenate (MA), and p-arsanilic acid (p-ASA). A fast chromatographic separation of five arsenic species is achieved in less than 12 min at a solution flow rate of 0.9 μL min−1 using a 50 nL sample injection. The HPLC-ICPMS interface provides well defined flow injection profiles at various concentrations, giving a correlation coefficient of 0.999 for each individual arsenic species calibration curve. Precision values for peak height and area of five arsenic species range from 0.5 to 6.5% RSD and absolute detection limits are within 0.4 to 5.4 pg arsenic, which are comparable to previously reported data at higher solution uptake rates (20 μL min−1 to 1 mL min−1) and larger sample injection volumes (20–100 μL).

Comparison of aerosol properties and ICP-MS analytical performance of the Vulkan direct injection nebuliser and the Direct Injection High Efficiency Nebuliser

Monodisperse polymer particles consisting of DVB and styrene-copoly-DVB were successfully synthesized by photoinitiated precipitation polymerization with 2,2'-azobis(2-methylpropionitrile) (AIBN) as initiator. A focused 150 W xenon short arc lamp was used to radiate the sample mixtures. The size of the particles ranged from 1.5 to 4 m and could be varied by changing the monomer concentration between 2 and 10% (v/v) and by means of the time of polymerization. By using photoinitiation instead of thermal initiation, it was possible to avoid coagulum and arrive at spherical particles with an exceptionally high monodispersity for particles of this size range (polydispersity index < 1.02) and with monomer loadings well above 5%.

Direct solution introduction using conventional nebulizers with a short torch for plasma mass spectrometry

A new torch, a shortened version of a standard demountable torch, is proposed for facilitating direct injection of liquid samples into an inductively coupled plasma mass spectrometer using conventional and micro-pneumatic nebulizers. The proposed arrangement reduces the cost of the direct injector nebulizer by a factor of 5, typically from $2000 to $400, although a different torch is required. The analytical performance of the high efficiency nebulizer-short torch arrangement is compared to that obtained with the direct injection high efficiency nebulizer interfaced to the conventional torch. Optimum operating conditions for the high efficiency nebulizer-short torch arrangement are generally similar to those of the direct injection high efficiency nebulizer: high RF power (1500 W), low nebulizer gas flow rates (0.09 L/min) and low solution uptake rates (5–85 μL/min). Sensitivity with the high efficiency nebulizer-short torch system at 85 μL/min is improved by a factor of 2.4 on average compared to the direct injection high efficiency nebulizer, while precision values (%RSD) and detection limits are generally comparable or slightly degraded (on average by a factor of 1.7), respectively. Sensitivity is also better at lower solution uptake rates (5 μL/min) by factors ranging from 2 ( 82Se) to 7 ( 59Co) compared to the direct injection high efficiency nebulizer. Additionally, the %RSD values are better at 5 μL/min, ranging from 3.5% to 6.0% for the high efficiency nebulizer-short torch combination compared to 4.7 to 9.1% for the direct injection high efficiency nebulizer. The utility of the high efficiency nebulizer-short torch arrangement is demonstrated through the microscale flow injection analysis of Cr-DNA adducts and the analysis of four certified reference materials (Lyphochek urine metals control, SRM 1515: Apple Leaves, SRM 1570a: Spinach Leaves, SRM 1577b: Bovine Liver). Peak to peak precision values ( N = 3) for the microscale flow injection analysis-high efficiency nebulizer-short torch system is 3.1% and 3.7% based on peak areas and heights, respectively, at a solution uptake rate of 85 μL/min. Good agreement is obtained between certified and measured concentrations for several elements across the mass range (e.g., Al, V, Mn, As, Cd, Pb, U). The proposed system is novel because it potentially offers a lower-cost and a more universal arrangement for improved direct solution introduction in plasma mass spectrometry using off-the-shelf commercial nebulizers.

Noise characteristics and analytical precision of inductively coupled plasma mass spectrometry using a Vulkan direct injection nebuliser for sample introduction

Noise and precision of ion count rate measurements were characterised for ICP-MS using a Vulkan direct injection nebuliser (Vulkan DIN) for sample introduction. For comparison, experiments were also carried out using a direct injection high efficiency nebuliser (DIHEN). The Vulkan DIN gave considerably higher relative white noise compared with the DIHEN, −40.3 compared with −45.8 dB, and measurements of aerosol characteristics showed that this was a result of broader size distribution and larger mean size of droplets for the Vulkan DIN. At a liquid flow rate of 85 μL min−1, the aerosol volume fraction constituted by droplets with a diameter smaller than 10 μm was only 5% for the Vulkan DIN compared to 38% for the DIHEN, and the Sauter mean diameter was 30.2 and 11.1 μm, respectively. Compared with the DIHEN, interference noise from a peristaltic pump was very small with the Vulkan DIN because at the liquid flow rate giving maximum sensitivity, the analyte signal intensity was not much affected by changes in liquid flow rate. Although this had a positive effect on precision, it indicated that the plasma is cooled by large droplets that do not positively contribute to the analyte signal intensity. For analytical precision data it was evident that with the Vulkan DIN, precision was limited by the high white noise in the frequency range 0.4–500 Hz, but for the DIHEN there were relatively large contributions from 1/f and/or interference noise to the observed precision. When using integration times of 1000 ms or longer, the DIHEN did, however, appear to give slightly better precision for most of the isotopes tested. For comparison, precision data was also generated when using a conventional spray chamber sample introduction system and it was found that, with a 3000 ms integration time, both direct injection nebulisers gave better precision for most isotopes. Although analytical precision is impressive, the results in this paper also show that both direct injection nebulisers produce aerosols that are far from ideal for the types of ICPs currently used in commercial instruments.

Down-scaling narrowbore LC-ICP-MS to capillary LC-ICP-MS: a comparative study of different introduction systems

Narrowbore high performance liquid chromatography (HPLC) was scaled down stepwise to capillary HPLC employing 2.1, 1 and 0.32 mm id separation columns. Provided that each column was operated at optimum chromatographic conditions (eluent velocity, injection volume) and provided that system connection (tubing, unions) was optimal, the influence of different HPLC-ICP-MS interfaces on extra column dispersion could be investigated. Several pneumatic nebulizers i.e. PFA-ST, MCN6000, AriMist, direct injection high efficiency nebulizer (DIHEN), CEI-100 and a costume made PFA005 nebulizer were tested. It could be shown that the contribution to extra column dispersion is minimal for the DIHEN interface. As a major advantage most of the microbore and capillary hyphenations were not prone to signal suppression due to organic solvents. The 1 mm id microbore set-up employing flow rates of 60 μL min−1 offered the best compromise in terms of sensitivity, peak dispersion, resolution, peak asymmetry and compatibility with organic solvent.

In Situ Visualization and Characterization of Aerosol Droplets in an Inductively Coupled Plasma

Laser-scattering techniques are utilized for the first time to visualize the aerosol droplets in an inductively coupled plasma (ICP) torch from the nebulizer tip to the site of analytical measurements. The resulting images provide key information about the spatial distribution of the aerosol introduced by direct injection and conventional sample introduction devices: (1) a direct injection high-efficiency nebulizer (DIHEN); (2) a large-bore DIHEN; and (3) a MicroFlow PFA nebulizer with a PFA Scott-type spray chamber. Moreover, particle image velocimetry is used to study the in situ behavior of the aerosol before interaction with the plasma, while the individual surviving droplets are explored by particle tracking velocimetry. Directly introduced aerosols are highly scattered across the plasma torch as a result of their radial motion, indicating less than optimum sample consumption efficiency for the current direct injection devices. Further, the velocity distribution of the surviving droplets demonstrates the importance of the initial droplet velocities in complete desolvation of the aerosol for optimum analytical performance in ICP spectrometries. These new observations are critical in the design of the next-generation direct injection devices for lower sample consumption, higher sensitivity, lower noise levels, suppressed matrix effects, and developing smart spectrometers.