Sample Introduction Technique Research Articles

Internal standardization with yttrium spectral lines using axial-viewing inductively coupled plasma atomic emission spectrometry for plant certified reference materials analysis

The performance of yttrium as internal standard was investigated when aspirating digested samples or alternatively slurries of certified plant reference materials. The stability of the yttrium signal used for analyte signal normalization was examined for three ionic emission lines of yttrium. The results showed that the use of yttrium was beneficial; however for the slurry sample introduction technique it was not equivalently efficient in terms of overall recovery. In this case, the employment of a cyclonic instead of a double-pass spray chamber in combination with yttrium internal standardization leads to quantitative recoveries of the analytes.

Determination of organophosphorus pesticides by capillary electrophoresis‐inductively coupled plasma mass spectrometry with collective sample‐introduction technique

A new method for the determination of organophosphorus pesticides using CE-ICP-MS with collective sample-introduction technique has been developed in this study. The method has been successfully used to separate and determine dimethoate, trichlorfon and glyphosate with an RSD of < 5% for migration times (n = 6) and < 4% for peak areas (n = 6). The experimental results showed that the collective sample-introduction considerably reduced the makeup volume and the dilution of analyte, and eventually resulted in a much lower detection limit and a much better electrophoretic resolution. The peak widths and the detection limits of dimethoate, trichlorfon and glyphosate obtained with this method are 15-17 s and 0.05-0.07 microg/mL (as compound), respectively. Using this method, we have successfully separated and determined dimethoate, trichlorfon and glyphosate in vegetable sample with a recovery of 90-96%.

Determination of ammonium and organic bound nitrogen by inductively coupled plasma emission spectroscopy

The continuous flow sample introduction technique with a hydride generator system in conjunction with an inductively coupled plasma emission spectrometer (ICP-AES-HG), is used in this study for quantitative determination of ammonium and organic bound nitrogen in aqueous and solid samples. Ammonia vapor released from ammonium salt after treatment with concentrated NaOH is transferred by argon to plasma for detection at 174.273 nm using axial argon plasma mode. The calibration curves were linear within a range of 25–1000 mg L −1 N as ammonium molybdate with correlation coefficients of better than 0.99 and limits of detection of about 10–25 mg L −1 N. The percent recovery of N (25–500 mg L −1 N) in soft (distilled) water and high salt content (1.7 mol L −1 NaCl) matrices was found to be in the range of about 97–102% with %RSD in the range of 4.6–0.62. The sensitivity, limit of detection, and blank contribution from the atmospheric nitrogen, were tremendously improved in this method compared with the available ICP-AES spray chamber counterpart. Furthermore, the ICP-AES-HG method gave results for real samples (soil, fertilizer, waste water) containing about 50–1800 mg L −1 N in good agreement with those obtained by the standard Kjeldahl method. No statistical differences at the 95% confidence level on applying the t-test were observed between the values obtained by the two methods. Thus, the ICP-AES-HG method is reliable and faster than the conventional tedious Kjeldahl method, superior to the ICP-AES spray chamber method, and almost free from matrix interference which is usually a critical factor in atomic emission spectroscopic techniques.

Atomic Spectrometry Update. Elemental speciation

This is the fourth Atomic Spectrometry Update (ASU) to focus specifically on developments in elemental speciation and covers a period of approximately 12 months from January 2011. The International Union for Pure and Applied Chemistry (IUPAC) has evaluated speciation and provided a definition as follows: “speciation analysis is the analytical activity of identifying and/or measuring the quantities of one or more individual chemical species in a sample; the chemical species are specific forms of an element defined as to isotopic composition, electronic or oxidation state, and/or complex or molecular structure; the speciation of an element is the distribution of an element amongst defined chemical species in a system.” This review therefore deals with all aspects of the analytical speciation methods developed for: the determination of oxidation states; organometallic compounds; coordination compounds; metal and heteroatom-containing biomolecules, including metalloproteins, proteins, peptides and amino acids; and the use of metal-tagging to facilitate detection via atomic spectrometry. The review does not cover operationally defined ‘speciation’, which is correctly termed fractionation. As with all ASU reviews1–6 the coverage of the topic is confined to those methods that incorporate atomic spectrometry as the measurement technique. However, in the spirit of meeting the needs of the subject, material is incorporated that is not strictly “atomic spectrometry” but the separation or sample introduction technique used could also be coupled with an atomic spectrometry detector. For the most part, such procedures are those in which some form of molecular MS is used for speciation measurements. As the content of this Update shows, the field is now maturing as evidenced by the extent to which the speciation of particular elements or technique combinations have been the subject of review articles. However, it is becoming increasingly difficult to ascertain the analytical details of the methodologies applied in speciation analysis, particularly where the paper is published in an ‘application’ based journal.

Speciation analysis of arsenic in Mya arenaria Linnaeus and Shrimp with capillary electrophoresis-inductively coupled plasma mass spectrometry

An improved sheath-flow interface used to couple capillary electrophoresis (CE) with inductively coupled plasma mass spectrometry (ICP-MS) and a microwave-assisted extraction used to extract each arsenic species in seafood were developed in this work. The improved sheath-flow interface completely avoids laminar flow in CE capillary caused by the suction from ICP-MS, makes electric supply more stable in CE, and transports analyte solution to ICP-MS easily and more efficiently. CE-ICP-MS coupled with our interface have two quantitative analysis modes: continuous sample-introduction mode and collective sample-introduction mode. The collective sample-introduction technique greatly reduced the dead volume of interface to approximately zero, obviously avoided the excessive dilution of analyte, and eventually led to a much lower detection limit and a much better electrophoretic resolution. This was demonstrated by the better symmetry and narrow peak widths (10–12 s) and much lower detection limits (0.030–0.042 μg/L) of four species of arsenic determined with collective sample-introduction mode. With the help of this improved sheath-flow interface and the microwave-assisted extraction, we have successfully separated and determined four arsenic species, As(III), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in dried Mya arenaria Linnaeus and Shrimp samples using CE-ICP-MS within 10 min with a relative standard deviation of 2–4% (peak areas, n = 6) and a recovery of 96–105%.

Chemiluminescence determination of gossypol at trace levels using flow injection as sample introduction techniques

A simple and sensitive flow injection method with chemiluminescence (CL) detection is developed for the determination of gossypol at trace levels. The method is based on the reaction of luminol with ferricyanid in a sodium hydroxide medium sensitized by gossypol. Under the optimum conditions, the CL intensity is proportional to the concentration of gossypol over the range of 1.11 × 10−17 − 2.78 × 10−16 M in an acidic solution and 8.00 × 10−11 − 7.39 × 10−8 M in a neutral solution with correlation coefficients of 0.9983 and 0.9905, respectively. The detection limit is 1.48 × 10−18 M (3σ). The proposed method has been applied to the determination of gossypol in cottonseeds and pharmaceutical preparations with satisfactory results. The CL mechanism is discussed by examining the CL emission spectrum and the effect of various free radical scavengers on the CL emission intensity.

Evaluation of automated direct sample introduction with comprehensive two-dimensional gas chromatography/time-of-flight mass spectrometry for the screening analysis of dioxins in fish oil

An automated direct sample introduction technique coupled to comprehensive two-dimensional gas chromatography-time of flight mass spectrometry (DSI-GC × GC/TOF-MS) was applied for the development of a relatively fast and easy analytical screening method for 17 polychlorinated dibenzo- p-dioxins/dibenzofurans (PCDD/Fs) and 4 non-ortho polychlorinated biphenyls (PCBs) in fish oil. Comparison of instrumental performance between DSI-GC × GC/TOF-MS and the traditional gas chromatographic high resolution mass spectrometric (GC-HRMS) method showed good agreement of results for standard solutions analyzed in blind fashion. Relatively high tolerance of the DSI technique for lipids in the final extracts enabled a streamlined sample preparation procedure that only required gel permeation chromatography (GPC) and solid-phase extraction (SPE) cleanup with graphitized carbon black. The sample size for the method was 2 g of cod liver oil, which achieved limits of quantitation (LOQs) of 0.019–7.8 pg/g toxic equivalent quotients for the individual PCDD/Fs. Lower detection limits can be achieved by using larger sample size and scaling up the sample preparation procedure, but this adds to the labor, time, solvent consumption, and expense of the approach. However, the streamlined method yielded 0.94 pg/g and 2.3 pg/g LOQs for 2,3,7,8-tetrachloro dibenzofuran (TCDF) and 3,3′,4,4′,5-pentachloro biphenyl (CB126), which were sufficiently low for regulatory monitoring of 2 g samples. Therefore, instead of congener specific analysis, this streamlined analytical screening method for TCDF and CB126 has the potential to monitor fish oil contaminated with dioxin and dioxin-like PCBs at or above current food safety limits. Acceptable recoveries for nearly all analytes at three different spiking levels in fish oil samples were achieved with good repeatability.

High-throughput microfluidic sample-introduction systems

We give an overview on recent developments in high-throughput microfluidic sample-introduction techniques based on a capillary sampling probe and a slotted-vial array (SVA). We discuss the advantages and the potential of SVA-based sample-introduction systems as well as their applications in miniaturized flow-injection analysis, sequential-injection analysis, capillary electrophoresis and liquid-liquid extraction. We illustrate the advantages and the potential of SVA-based sample-introduction systems using results obtained recently.

Use of slurry suspension sample introduction technique in fast multielement analysis of multimineral and multivitamin formulations by inductively coupled plasma atomic emission spectrometry

A slurry suspension sampling technique has been developed and optimized for rapid multielemental analysis of multivitamin/multimineral preparations using inductively coupled plasma atomic emission spectrometry (ICP-AES). The following macro-, micro- and trace-elements: Ca, Mg, Mn, Fe, Cr, Al, Ag, B, Ba, Bi, Cd, Co, Cu, Ga, In, Ni, Pb, Zn, As and Se were determined by the proposed method. The lower detection limits were obtained for Mn, Mg, Cu and Ca whereas the highest for Bi, Pb, As and Se. Consequently the method can be used as a fast screening method. A wet-acid mineralization method was applied as total recovery method for comparative purposes. Samples were prepared as slurries at a concentration of 5% (m/v) in aqueous acidic media (0.8 M HNO 3). Various factors affecting the sensitivity of the method were optimized. The obtained results were subjected to two-way analysis of variance to examine any significant difference between the developed slurry procedure and the wet-acid complete decomposition. Finally, the slurry suspension technique was found to be applicable in routine quality control and contamination monitoring of multimineral preparations. For the analyzed commercial preparations, the found elemental concentrations are compared to those appearing in the label of the products.

Detection of counterfeit tablets of an antiviral drug using δ34S measurements by MC-ICP-MS and confirmation by LA-MC-ICP-MS and HPLC-MC-ICP-MS

A new approach for pharmaceutical counterfeit detection using laser ablation multicollector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) and high performance liquid chromatography multicollector inductively coupled plasma mass spectrometry (HPLC-MC-ICP-MS) has been developed. Laser ablation and chromatographic separation parameters have been previously optimised and helium has been used as the carrier gas for better sensitivity. A homogeneity study of 288 pharmaceutical tablets from different batches of the genuine drug has been performed by MC-ICP-MS and characteristic sulfur isotopic signature has been obtained for the genuine product. δ34S measurements by MC-ICP-MS using silicon internal standardisation for the correction of instrumental mass bias effects led to a δ34S of 3.6‰ and an associated combined expanded uncertainty of 1‰ (k = 2). The active pharmaceutical ingredient (API) of the tablets, a S-containing compound, has been separated by HPLC and sulfur isotope amount ratios have been measured by MC-ICP-MS. δ34S values obtained by HPLC-MC-ICP-MS for the genuine tablets agreed with those obtained by laser ablation MC-ICP-MS, thus confirming that the sulfur isotopic signature is inherent to the S-containing API. Following the initial development work, a blind exercise was performed for four hundred tablets. The discriminating power of the technique was assessed and uncertainties associated to δ34S values for counterfeit and genuine tablets varied depending on the sample introduction technique utilised. The three approaches were able to differentiate genuine from counterfeit tablets. During the exercise, four distinct groups of counterfeit tablets were detected. The MC-ICP-MS method therefore has potential as a rapid screening tool for pharmaceutical counterfeit detection and classification.

Direct multielement trace analyses of silicon carbide powders by spark ablation simultaneous inductively coupled plasma optical emission spectrometry

A procedure for the direct analysis of silicon carbide powders (SiC) by simultaneous detection inductively coupled plasma optical emission spectrometry using a Spectro-CIROS™ spectrometer (CCD-ICP-OES) and a novel spark ablation system Spectro-SASSy (SA) as sample introduction technique is described. The sample preparation procedure for SA of non-conducting material is based on mixing the sample powders with a conducting matrix, in this case copper and briquetting pellets. Pressing time, pressure and mixing ratio are shown to be important parameters of the pelleting technique with respect to their mechanical stability for the reliability of the analysis results. A mixing ratio of 0.2 g +0.6 g for SiC and Cu, a pressure of 10 t cm − 2 and a pressing time of 8 min have been found optimum. It has also been shown that the spark parameters selected are crucial for uniform volatilization. Electron probe micrographs of the burning spots and the analytical signal magnitude showed that a rather hard spark at 100 Hz was optimum. The determination of trace elements in silicon carbide powders is demonstrated using a calibration based on the addition of standard solutions. For Al, Ti, V, Mn and Fe detection limits in the lower µg g − 1 range can be achieved. Internal standardization with Y in combination with the addition of standard solutions allows relative standard deviations in the range of 4 to 24% for concentration levels of the order of 3 to 350 µg g − 1 .

Comparative performance study of different sample introduction techniques for rapid and precise selenium isotope ratio determination using multi-collector inductively coupled plasma mass spectrometry (MC-ICP/MS)

The analytical performance of five sample introduction systems, a cross flow nebulizer spray chamber, two different solvent desolvation systems, a multi-mode sample introduction system (MSIS), and a hydride generation (LI2) system were compared for the determination of Se isotope ratio measurements using multi-collector inductively coupled plasma mass spectrometry (MC-ICP/MS). The optimal operating parameters for obtaining the highest Se signal-to-noise (S/N) ratios and isotope ratio precision for each sample introduction were determined. The hydride generation (LI2) system was identified as the most suitable sample introduction method yielding maximum sensitivity and precision for Se isotope ratio measurement. It provided five times higher S/N ratios for all Se isotopes compared to the MSIS, 20 times the S/N ratios of both desolvation units, and 100 times the S/N ratios produced by the conventional spray chamber sample introduction method. The internal precision achieved for the (78)Se/(82)Se ratio at 100 ng mL(-1) Se with the spray chamber, two desolvation, MSIS, and the LI2 systems coupled to MC-ICP/MS was 150, 125, 114, 13, and 7 ppm, respectively. Instrument mass bias factors (K) were calculated using an exponential law correction function. Among the five studied sample introduction systems the LI2 showed the lowest mass bias of -0.0265 and the desolvation system showed the largest bias with -0.0321.

Electrothermal vaporization dynamic reaction cell inductively coupled plasma mass spectrometry for the determination of Fe, Co, Ni, Cu, and Zn in biological samples

Slurry sampling electrothermal vaporization dynamic reaction cell inductively coupled plasma mass spectrometry (ETV-DRC-ICP-MS) has been applied to determine Fe, Co, Ni, Cu, and Zn in biological samples. The influences of instrument operating conditions and slurry preparation on the ion signals were reported. Pd was used as the modifier. The effectiveness of the ETV sample introduction technique and dynamic reaction cell in alleviating various spectral interferences in ICP-MS analysis has been demonstrated. This method has been applied to determine Fe, Co, Ni, Cu, and Zn in NIST SRM 1573a tomato leaves reference material and NRCC DORM-2 dogfish muscle reference material and also real samples such as a tea and a swordfish sample purchased locally. Since the sensitivities of the elements studied in slurry and aqueous solution were different, an analyte addition technique was used for the determinations. The analytical results of the reference materials agreed with the certified values. The precision between sample replicates was better than 6% for all determinations. The method detection limit estimated from analyte addition curves was 0.01, 0.006, 0.007, 0.004, and 0.006 microg g(-1) for Fe, Co, Ni, Cu, and Zn, respectively, in the original biological samples.

Slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of As and Se in soil and sludge

Slurry sampling electrothermal vaporization (ETV) inductively coupled plasma mass spectrometry (ICP-MS) has been applied to determine As and Se in soil and sludge samples. The influences of instrument operating conditions and slurry preparation on the ion signals were reported. Pd and ascorbic acid were used as mixed modifiers to enhance the ion signals. The effectiveness of ETV sample introduction technique for alleviating various spectral interferences in ICP-MS analysis has been demonstrated. This method has been applied to determine As and Se in NIST SRM 2709 San Joaquin soil reference material and NIST SRM 2781 domestic sludge reference material and a farmland soil sample collected locally. Since the sensitivities of As and Se in slurry solution and aqueous solution were different, analyte addition technique was used to determine As and Se in these samples. The As and Se analysis results of the reference materials agreed with the certified values. The precision between sample replicates was better than 5% for all determinations. The method detection limit estimated from analyte addition curves was about 0.03 and 0.02 μg g −1 for As and Se, respectively, in original soil and sludge samples.

Electrochemical hydride generation as a sample-introduction technique in atomic spectrometry: fundamentals, interferences, and applications

Electrochemical hydride generation (EC-HG) has been proposed as a valid alternative to chemical generation as a sample-introduction technique in atomic spectrometry. In this review fundamental aspects of the technique are revised, including designs of electrolytic cells, mechanisms of the generation process, and interferences caused by the presence of different species. Special attention is paid to the role of the configuration of the cathodes and their materials on the efficiency of hydride generation and on interferences from concomitant species. An overview of the application of EC-HG to the analysis of real samples is also given.

The efficiency of chemical vapour generation of transition and noble metals

The efficiency data from individual reports on chemical vapour generation (CVG) of transition and noble metals are overviewed with respect to the ways that they were obtained. The values derived from direct measurement of analyte in the gaseous phase or obtained from comparison with other sample introduction techniques reflect well the true chemical vapour generation efficiency. The efficiencies reported this way do not exceed 30%. On the other hand, the percentage efficiency values derived from determination of analyte remaining in the waste liquid, usually in the high tens, can substantially overestimate the efficiency by neglecting the analyte retained within the system.

Rapid Sample Preparation Method for LC−MS/MS or GC−MS Analysis of Acrylamide in Various Food Matrices

A fast and easy sample preparation procedure for analysis of acrylamide in various food matrices was developed and optimized. In its first step, deuterated acrylamide internal standard is added to 1 g of homogenized sample together with 5 mL of hexane, 10 mL of water, 10 mL of acetonitrile, 4 g of MgSO4, and 0.5 g of NaCl. Water facilitates the extraction of acrylamide; hexane serves for sample defatting; and the salt combination induces separation of water and acetonitrile layers and forces the majority of acrylamide into the acetonitrile layer. After vigorous shaking of the extraction mixture for 1 min and centrifugation, the upper hexane layer is discarded and a 1 mL aliquot of the acetonitrile extract is cleaned up by dispersive solid-phase extraction using 50 mg of primary secondary amine sorbent and 150 mg of anhydrous MgSO4. The final extract is analyzed either by liquid chromatography-tandem mass spectrometry or by gas chromatography-mass spectrometry (in positive chemical ionization mode) using the direct sample introduction technique for rugged large-volume injection.

Influence of binders on infrared laser ablation of powdered tungsten carbide pressed pellets in comparison with sintered tungsten carbide hardmetals studied by inductively coupled plasma atomic emission spectrometry

Laser ablation (LA) was studied as a sample introduction technique for the analysis of powdered and sintered tungsten carbides (WC/Co) by inductively coupled plasma optical emission spectrometry (ICP–OES). The possibility to work with powdered and compact materials with close chemical composition provided the opportunity to compare LA sampling of similar substances in different forms that require different preparation procedures. Powdered WC/Co precursors of sintered hardmetals were prepared for the ablation as pressed pellets with and without powdered silver as a binder, while sintered hardmetal blocks were embedded into a resin to obtain discs, which were then smoothed and polished. A Q-switched Nd:YAG laser operated at its fundamental wavelength of 1064 nm with a pulse frequency of 10 Hz and maximum pulse energy of 220 mJ was used. A single lens was used for the laser beam focusing. An ablation cell (14 cm 3) mounted on a PC-controlled XY-translator was connected to an ICP spectrometer Jobin Yvon 170 Ultrace (laterally viewed ICP, mono- and polychromator) using a 1.5-m tubing (4 mm i.d.). Ablation was performed in a circular motion (2 mm diameter). Close attention was paid to the study of the crater parametres depending on hardness, cohesion and Ag binder presence in WC/Co samples. The influence of the Co content on the depth and structure of the ablation craters of the binderless pellets was also studied. Linear calibration plots of Nb, Ta and Ti were obtained for cemented WC/Co samples, binderless and binder-containing pellets. Relative widths of uncertainty intervals about the centroids vary between ± 3% and ± 7%, and exceptionally reach a value above 10%. The lowest determinable quantities (LDQ) of Nb, Ta and Ti calculated from the calibration lines were less than 0.5% (m/m). To evaluate the possibility of quantitative elemental analysis by LA–ICP–OES, two real sintered WC/Co samples and two real samples of powdered WC/Co materials were analysed. The results of LA–ICP–OES real sample analysis correlated well with the results obtained by X-ray fluorescence (sintered samples) and pneumatic nebulization inductively coupled plasma optimal emmission spectrometry (powdered samples) with a bias not exceeding 6.5%.

Selenium speciation by high-performance anion-exchange chromatography–post-column UV irradiation coupled with atomic fluorescence spectrometry

A technique for the speciation of selenomethylcysteine (SeMeCys), selenocystine (SeCys), selenite [Se(IV)] and selenomethionine (SeMet) was established in this paper using high-performance anion-exchange chromatography coupled with atomic fluorescence spectrometry (HPAEC–AFS). Analytes were separated on an AminoPac PA10 column and then digested by on-line ultraviolet (UV) irradiation, which destroyed organic compound structure. Hydride generation was used as an available sample introduction technique for atomic fluorescence detection. The detection limits of four compounds were 1–5 μg/L (250 μL injection, 10 times of the baseline noise). The relative standard deviations (RSDs), calculated from seven consecutive injections of 100 μg/L standard mixtures, were from 2 to 4%. Selenious yeast tablet, which had been proposed as selenium supplement, and human urine collected from a volunteer were analyzed. Good spiked recoveries from 86 to 103% were obtained.

Multiplicity and contiguity of ablation mechanisms in laser-assisted analytical micro-sampling

Laser ablation is implemented in several scientific and technological fields, as well as a rapid sample introduction technique in elemental and trace analysis. At high laser fluence, the ejection of micro-sized droplets causes the enhancement of the surface recession speed and depth resolution degradation as well as the alteration of the sampling stoichiometry. The origin of such large particles seems to be due to at least two different processes, phase explosion and melt splashing. Experimental evidence for both was found in metallic matrices, whereas non-metallic samples showed more complex phenomena like cracking. The spatial distribution of the beam energy profile is responsible for significant differences in the ablation mechanism across the irradiated region and for heterogeneous sampling. Under Gaussian irradiance distribution, the center of the crater, where the irradiance is the highest, experienced a fast heating with rapid ejection of a mixture of particles and vapor (spinodal breakdown). The crater periphery was subjected to more modest irradiation, with melt mobilization and walls formation. The overall resulting particle size distribution was composed of an abundant nano-sized fraction, produced by vapor condensation, and a micro-sized fraction during melt expulsion.