Discrete Sample Introduction Research Articles

Discrete micro-volume suspension injection to microwave induced plasma for simultaneous determination of cadmium and lead pre-concentrated on multiwalled carbon nanotubes in optical emission spectrometry

A discrete sample introduction system (DSIS) for the direct micro-volume nanomaterials (NMs) suspension injection has been developed toward the simultaneous determination of Cd and Pb pre-concentrated (by dispersive micro solid-phase extraction (DMSPE)) on oxidized multiwalled carbon nanotubes (MWCNTs) to microwave induced plasma optical emission spectrometry (DMSPE-DSIS-MIP OES). On-axis low-volume spray chambers with flow focusing micro nebulizer (continues mode) and v-groove type pneumatic nebulizer (discontinues mode) for microliter-volume suspension introduction were tested.A univariate approach and the simplex optimization procedure were used to achieve optimized conditions and derive analytical figures of merit. Minimum dead volume, high nebulization and suspension transport efficiency were obtained by using miniaturized spray chamber/v-groove pneumatic nebulizer interface for 10 μL suspension injection in discontinues mode (at 0.5 mL min−1 pump speed).Analytical performance of DMSPE-DSIS-MIP OES method was characterized by determination of the limits of detection (0.7 and 0.1 ng mL−1 for Cd and Pb, respectively) and precision ranged from 6% to 8%. Quantitative data obtained for water reference materials (ERM-CA011b and SRM 1643e) were in good agreement, according to the t-test, for a confidence level of 95%, with the corresponding reference values, proving the potential of this analysis system for trace analysis via MIP OES. The proposed method had been successfully applied for the determination of Cd and Pb in water real samples.

Discrete Sample Introduction Module for Quantitative and Isotopic Analysis of Methane and Other Gases by Cavity Ring-Down Spectroscopy

Carbon dioxide (CO2) and methane (CH4) are natural and anthropogenic products that play a central role in the global carbon cycle and regulating Earth's climate. Applications utilizing laser absorption spectroscopy, which continuously measure concentrations and stable isotope ratios of these greenhouse gases, are routinely employed to measure the source and magnitude of atmospheric inputs. We developed a discrete sample introduction module (DSIM) to enable measurements of methane and CO2 concentrations and δ13C values from limited volume (5-100 mL) gas samples when interfaced with a commercially available cavity ring-down spectroscopy (CRDS) analyzer. The analysis has a dynamic range that spans six orders of magnitude from 100% analyte to the lower limit of instrument detection (2 ppm). We demonstrate system performance for methane by comparing concentrations and δ13C results from the DSIM-CRDS system and traditional methods for a variety of sample types, including low concentration (nanomolar CH4) seawater and high concentration (>90% CH4) natural gas. The expansive concentration range of the field-portable DSIM-CRDS system can measure enhances analytical performance for investigating methane and CO2 dynamics and, potentially, other gases measured by laser absorption spectroscopy.

Extraction induced by microemulsion breaking as a novel tool for the simultaneous determination of Cd, Mn, Pb and Sb in gasoline samples by ICP-MS and discrete sample introduction

This study reports a simple and efficient method for the simultaneous determination of Cd, Mn, Pb, and Sb at trace levels in gasoline samples by discrete sample introduction in inductively coupled plasma mass spectrometry (ICP-MS), employing the extraction induced by microemulsion breaking as a sample preparation method. In this work, a microemulsion was formed by mixing 0.7 mL of the gasoline sample with 0.28 mL of ethanol and 0.02 mL of 7 mol L−1 HNO3 solution. Afterwards, 0.1 mL of ultrapure water was added to induce microemulsion breaking. This lead to the formation of two different phases: (i) a top organic phase and (ii) a bottom aqueous phase that contained acid, ethanol and the extracted analytes. After that, 20 μL of the bottom phase (extract) was collected, and the analyte concentrations were determined by discrete sample introduction in ICP-MS. Calibration curves with 20 μg L−1 of Rh as an internal standard were set up to each analyte in the range from 1 up to 10 μg L−1, wherein the standard solutions were prepared in the matrix-matched extract (70:25:5, ethanol: deionized water: 7 mol L−1 HNO3 solution). The optimization of the EIMB conditions was carried out by analyzing the effects of the parameters that could affect the extraction efficiency, such as the relation between the nature of the alcohol and the proportion of the volumes of the microemulsion constituents (sample, HNO3 and alcohol), acid concentration, and the water volume used for the microemulsion breaking. The following limits of detection relative to the amount of sample were obtained: 0.03 (Cd), 0.49 (Mn), 0.07 (Pb) and 0.02 (Sb), all of them in μg L−1. The accuracy of the method was evaluated by the analysis of spiked samples, because no certified gasoline reference material is available. The average recoveries achieved for every analyte ranged from 96% to 114%. The developed methodology was successfully applied to the determination of these metals in five commercial gasoline samples.

Novel preconcentration technique using bis(2-ethylhexyl) hydrogen phosphate (HDEHP) loaded porous polytetrafluoroethylene (PTFE) filter tube as a sorbent: Its application to determination of In(III) in seawater by ICP-MS with air segmented discrete sample introduction

Novel preconcetration method involving porous polytetrafluoroethylene (PTFE) filter tube impregnated bis(2-ethylhexyl) hydrogen phosphate (HDEHP) as a sorbent was studied to establish it as a practical preconcentration method for ultra trace analysis with ICP-MS. A 1 ng portion of In(III) in 1000 ml of matrix free solution or 700 ml of synthetic seawater was quantitatively complexated with HDEHP adsorbed onto porous PTFE filter tube by passing the solution through the micro pore of the filter tube. Preconcentrated In(III) was then quantitatively recovered provided that the elution, which consists of a cyclical filtering 0.1 ml of 8 mol dm −3 hydrochloric acid through the filter tube for 1 min; therefore, up to 10000- and 7000-fold of enrichment was attained for matrix free solution and synthetic seawater, respectively. To introduce a 0.1 ml of the eluted solution to ICP-MS, flow injection method with air segmented discrete sample introduction (ASDI) was also studied by using manually operated simple valve system. By using ASDI, good linearity of calibration curve ( r = 0.99997) was observed from 0.01 to 5.0 ng ml −1 of In(III). Good reproducibility was also shown in measurements of 0.1 ml of 5 ng ml −1 of In(III) (R.S.D. = 1.9%, n = 5). The average recovery and R.S.D. of the results for the five duplicates determination of 0.1 ng of In(III) spiked to 200 ml of synthetic seawater were 99 and 2.4%, respectively. The method was applied to the determination of In(III) in coastal seawater sampled at north east of Hachijyo Island, Japan; using 200 ml of sample, 2000-fold preconcentration of In(III) was performed within 30 min for five samples. The analytical detection limit and the blank were 9.8 and 21 pg l −1, respectively. The average concentration was determined to be 96 pg l −1, and R.S.D. of the results was 3.7% ( n = 3).

Quantitation of Trace Metals in Liquid Samples by Dried-Droplet Laser Ablation Inductively Coupled Plasma Mass Spectrometry

A new, discrete sample introduction approach based on laser ablation (LA) is described for the quantitation of several trace metals in aqueous samples by ICPMS. Dried microdroplets of sample, previously mixed with a sodium acetate matrix, were quantitatively ablated from a polystyrene substrate. Calibration via the method of standard additions or isotope dilution provided accurate results for Ni, Cd, and Pb in drinking water and Se in a yeast extract. Compared to conventional solution nebulization, LA sample introduction provided a 2-7-fold enhancement in absolute sensitivity and transport efficiency of 2-14% for the elements examined. Estimated detection limits are 1-7-fold poorer for the dried-droplet LA technique, primarily a result of degraded precision arising from counting statistics limitations for discrete sample introduction. On the basis of the several-second half-width of the resulting transient signals, sample throughput can be in the range of 250 samples per hour. Additionally, integration of the transient signal should eliminate contributions to elemental fractionation from the LA step. Dried-droplet LA-ICPMS offers several advantages over its counterpart, ETV-ICPMS, with respect to background intensity, throughput, and ease of desorption.

Compensation for matrix effects in ICP-AES by using air segmented liquid microsample introduction. The role of the spray chamber

The combination of sample injection into an air carrier stream (i.e., air segmentation) with a low sample consumption system has been evaluated for the analysis of microsamples through ICP-AES. A PFA micronebulizer has been coupled to: (i), a double pass spray chamber; (ii), a Cinnabar cyclonic spray chamber; and (iii), a torch integrated sample introduction system, TISIS. Three matrices have been studied: in addition to water two concentrated acid solutions (2 mol l−1 nitric acid and 1.7 mol l−1 acetic acid) and Na 5,000 µg ml−1. A simulation of the evolution of the drop size distributions of the aerosols with time was carried out in order to evaluate the extent of solvent evaporation inside the chamber. The total mass of solvent evaporated inside the chamber was estimated and it was concluded that, at 25 °C, about 4–6 s residence time were required to promote the maximum evaporation of the solvent. In order to ensure this, discrete sample introduction into an air carrier stream (i.e., air segmentation) was used. Narrow peaks (i.e., with a full width at half maximum, FWHM, as short as 10 s) were obtained for a 10 µl injected sample. The peaks found for the Cinnabar and TISIS were narrower than those for the double pass spray chamber. More importantly, the interferences caused by inorganic as well as organic matrices were less severe in discrete than in continuous mode. The theoretical simulations allowed explanation of these results in terms of the enhancement of the solvent evaporation both for water and matrices in this operating mode. The enhanced solvent evaporation with respect to the situation in continuous mode minimized differences in analyte transport towards the plasma induced by these compounds. Despite this, in discrete mode a residual matrix effect was found that was attributed to the aerosol transport process. Internal standardization (IS) was applied to transient signals and the interferences were compensated for in virtually all the cases. Good results were obtained for the four emission lines taken as internal standards (i.e., Mg 280.270, Co 228.616, Cr 205.552 and Cu 324.754). However, for acetic acid and a few lines, IS was not efficient for removing interferences. The methodology was validated by analyzing two reference solid samples of foods (i.e., bovine liver and mussel tissue). By using Cd 214.438 as internal standard and under discrete mode 100% recoveries were found.

Optimization of the evaporation cavity in a torch integrated sample introduction system based ICP-AES system. Applications to matrix and transient effects, analysis of microsamples and analysis of certified solid samples

Results corresponding to the optimization of the aerosol evaporation cavity of the previously published torch integrated sample introduction system (TISIS) are shown in the present work. A micronebulizer (i.e., MicroMist) operated at liquid delivery rates in the 20–200 µl min−1 range was used throughout. Theoretical calculations suggested that the TISIS chamber allowed the evaporation of a significant fraction of the solvent contained in primary aerosol, while the remaining droplets first impacted against its inner walls and then evaporated. The cavity dimensions (i.e., length and inner diameter) were optimized in terms of sensitivity and memory effects. The results demonstrated that the longer the cavity, the higher the sensitivity, whereas an increase in its diameter did not significantly modify the aforementioned parameters. The optimized TISIS cavity, with a conical shaped end, proved to significantly shorten the wash-out times with respect to a double pass spray chamber and a low inner volume cyclonic type one (i.e., a Cinnabar spray chamber). Besides, the TISIS was used for discrete sample introduction of very low sample volumes (i.e., from 0.3 to 32 µl). The peaks found were narrower and higher than those provided by a double pass spray chamber. Matrix effects caused by sodium, acetic acid and ethanol solutions were less severe for TISIS than for the double pass and the Cinnabar spray chambers, while transient effects caused by nitric acid solutions almost disappeared when using the TISIS. As a result of the mitigation of the interferences, the recoveries found for three certified solid samples while calibrating with plain water standards were closer to 100% for the TISIS than for double pass and mini cyclonic spray chambers.

Application of internal standardization in ICP-QMS through discrete sample introduction methodologies

Non-spectral matrix effects in ICP-MS are often corrected by the method of internal standardisation. In the case of discrete sampling a common algorithm refers to the ratio of either maxima or areas of both analyte and internal standard peaks. The current work describes a protocol for internal standardisation across the transient peak based on the calculation of analyte-to-internal standard ratio for every scan sweep. Thus, a new converted function, Every Sweep Internal Standardisation (ESIS) ratio versus time, is obtained. One required merit is a dynamic estimation of variable matrix influence. Three discrete sampling systems coupled to an ICP-QMS instrument have been studied (i.e., flow injection, air segmented discrete introduction and injection into an air carrier). Two internal standard introduction modes (i.e., continuous and pulse) have been evaluated. For continuous mode, the ESIS function has a profile similar to the sample injection peak while for the pulse mode it has approximately constant values only within a limited time interval. The ESIS zone of stability for the tested sampling systems has been critically evaluated. By ESIS protocol lower RSDs have been found than the common internal standardisation. The matrix correction efficiency achieved with ESIS ranged between 96%–105%, 94%–106% and 93%–110% for an alcoholic beverage (alcohol content up to 40%), high salt content solution (NaCl up to 3%) and moss sample, respectively.

Determination of calcium, iron and manganese in moss by automated discrete sampling flame atomic absorption spectrometry as an alternative to the ICP–MS analysis

An automated, fast and reliable procedure has been developed for flame atomic absorption analysis of Ca, Fe and Mn in moss. The method is suitable for routine analysis of a large number of moss samples and allows sequential determination of all three elements in the same solution. In order to inhibit the matrix interference on Ca and to level the diverse analytical behaviour of the moss matrix, approximately 1% La was added to both samples and standard solutions as well. An integrated system of ‘sandwich-type’ air segmented discrete sample introduction and flame atomic absorption detection (ASDI–FAAS) was successfully applied. It works at ‘solvent-air-sample-air-solvent’ mode, which tolerates the introduction of high salt content solutions, reduces reagent and sample consumption and allows the application of data treatment models to pseudo-steady state signals for bettering the repeatability. For moss samples containing high Ca and Fe concentrations, equivalent procedure was used by turned on 45° burner head without worsening the analytical characteristics. Concerning these three elements, the method is suggested as a cheaper, easier and more trustworthy alternative with a better precision to the inductively coupled plasma–mass spectrometry (ICP–MS) one. The ASDI–FAAS results were used for selection of appropriate isotopes and correction procedures for ICP–MS determination. Both methods show good agreement of the Ca, Fe and Mn results that correspond to the moss reference materials tested.

A novel sample introduction system for microwave-induced plasma optical emission spectrometry

A newly developed micro-sampling technique using a discrete sample introduction system (DSIS) has been demonstrated for simultaneous multi-element analysis by microwave-induced plasma optical emission spectrometry (MIP-OES). A microliter volume of sample solution (20 μl) is manually inserted into a Teflon microsampling device and subsequently pumped at low solution uptake rates of <100 μl min −1 to a Meinhard-type concentric nebulizer and then into a 250-W helium plasma. The performance of DSIS-MIP-OES was demonstrated by the determination of major (Na, K, Ca, Mg), minor (Cu, Fe, Zn) and trace (Sr) elements in two clinical standard certified reference materials (serum, hair). Standard microaddition procedures were used to minimize possible matrix interference. The detection limit (3σ) obtained was 10, 30, 50, 100, 10, 5, 20 and 40 ng ml −1 for Ca, Cu, Fe, K, Mg, Na, Sr and Zn, respectively. The method offers relatively good precision (RSD ranged from 5 to 14%) and microsampling capability. Agreement between analytical results and certified values for the test elements was good. The method could be useful as a routine clinical laboratory procedure.

Coupling continuous flow systems to instruments based on discrete sample introduction

The interfaces between low-pressure continuous sample treatment systems and high-level information instruments such as gas chromatographs, capillary electrophoresis equipment and graphite furnace atomic spectroscopic instruments, which are characterized by conventional discrete sample introduction devices, are presented. The present and future developments are discussed of (directly) linking real samples and those analytical equipments with the main objective of avoiding or minimizing manually implemented preliminary operations of the analytical process.

Air Segmented Discrete Introduction in Inductively Coupled Plasma Mass Spectrometry

An assessment of some advantages and disadvantages of ICP-MS analysis using air segmented discrete sample introduction was performed. Air segmented discrete introduction (ASDI) was effected with two small air bubbles placed between the sample and the washing solvent and was carried out by an in-house built device. Sampling by ASDI was compared with continuous introduction and flow injection, testing 12 isotopes simultaneously (27Al, 55Mn, 63Cu, 64Zn, 75As, 103Rh, 114Cd, 115In, 130Te, 133Cs, 205Tl, 208Pb). The main benefit of the ASDI mode is the elimination of dispersion, leading to sensitivity enhancement at the same injection frequency and long-term stability compared with flow injection. Although small volumes (104–300 µl) were injected, slightly increased signals (‘hyper signals’) were observed with ASDI compared with continuous nebulization. Hyper signals up to 15% were observed for isotopes with low and medium ionisation potentials (<7.7 eV) and a variety of masses. For the elements tested at a 104 µl injection, the ASDI-ICP-MS detection limits were improved by a factor of ≈3 (peak maximum) compared with the same volume introduced by flow injection and were similar to those of continuous sample introduction.

Determination of CO 2( g) by enhancement of luminol—cobalt(II) phthalocyanine chemiluminescence: Analysis of atmospheric air and human breath

Two related continuous-flow sensing strategies are presented for the determination of CO 2( g) in gas mixtures. A continuous monitoring scheme is described for the determination of the analyte in atmospheric air, and a discrete sample introduction approach for the determination of the same analyte in human breath. The same chemical system is used in both cases, which is based on the CO 2( g) enhancement of luminol chemiluminescence in the absence of added oxidant and in the presence of cobalt(II) phthalocyanine complex as rate modifier. A specially designed reaction cell is at the heart of these determinations. The main analytical virtues of these approaches are simplicity, fast response, and a wide linear concentration range amenable to determination (in log-log relationships from about 50 ppm to 800 ppm v/v, and from 1% to 100% v/v CO 2( g).

Characterization of a new single-bore high-pressure pneumatic nebulizer for atomic spectrometry—II. Discrete sample introduction in flame atomic absorption spectrometry

A study has been made of the analytical behaviour, with discrete sample introduction, of a new high-pressure pneumatic nebulizer as part of sample introduction systems in flame atomic absorption spectrometry. The nebulizer possesses a single bore for the gas and liquid flows. In comparison to the standard Meinhard nebulizer and under identical conditions, the new nebulizer exhibits a greater relative sensitivity (up to 4.5 times) that increases the lesser the gas flow and the greater the liquid flow. Precision is similar with both nebulizers, the detection limits being lower for the pressure nebulizer. The memory effect is likewise of the same order of magnitude for both nebulizers. The pressure nebulizer has also proven satisfactory when working with high salt content or organic solutions

Aerosol Interfacing Effects on Discrete Sample Introduction Coupled with Spectrometric Detection

Aerosol techniques are commonly employed to interface discrete sampling techniques (flow injection analysis and liquid chromatography) with various detectors. The effects of these interfaces on discrete signals have not been described, nor has a rationale been established for presumed differences in band broadening due to aerosol-phase extra-column volume, compared to liquid-phase extra-column volume. In this report, the effects of laminar flow through several transport geometries on signal recovery and band broadening for both wet and desolvated aerosols are investigated. Data presented for the conditions studied indicate that signal losses with linear systems are primarily affected by gravitational settling. Increases in residence time lead to larger losses. Centrifugal effects, which lead to higher losses with coiled systems at high linear velocities, however, appear to have a stabilizing effect at lower velocities. Desolvation significantly reduces the level of gravitational or centrifugal losses via reduction in particle sizes. Band broadening results primarily from convection within laminar flow systems. This result was established on the basis of comparison of real signals with those generated from a convolution routine which mimics the effects of convective dispersion within laminar flows. The relatively high flow rates of aerosol transport systems result in short residence times and small effects of large transport volumes on dispersion. Sample losses also appear to offset band broadening to some extent by reducing peak tailing. Conditions providing efficient analyte transport and signal recovery, as well as low dispersion, can be established.

A comparison of discrete and continuous sample introduction for flame atomic absorption spectrometry

The continuous aspiration and discrete volume sampling techniques in flame atomic absorption spectrometry were compared. Continuous sample introduction of a properly diluted sample can provide for lower absolute determination limits than the injection sampling technique for the same but pre-concentrated sample. In the analysis of a sample solution with a given absolute analyte amount there is an optimum dilution of the sample solution and an optimum sample volume to be taken for analysis, which ensures the most precise results. Theoretical assumptions were checked with the determination of iron in aqueous solutions.