Sample Introduction Technique Research Articles

気相試料導入-誘導結合プラズマ発光分光分析による鉄鋼中の銅の定量

気相試料導入-誘導結合プラズマ発光分光分析による鉄鋼中の銅の定量

At-column dilution for improved loading in preparative chromatography

Maximizing column loadability is an important part of preparative chromatography, since both the cost of the equipment and the cost of the operation increase with the size of the column. We have studied the parameters that determine column loadability. In this publication, we describe the influence that the choice of the sample solvent and the nature of the sample have on loadability. If the sample is injected onto the column in the classical way, overload effects result from the choice of conditions that favor a high solubility of the sample. We then demonstrate how a sample introduction technique called at-column dilution circumvents the difficulties associated with the limited solubility of samples under the preferred conditions of preparative chromatography. The technique is discussed in detail.

Determination of perfume oil in household products by headspace solid-phase microextraction and fast capillary gas chromatography

Headspace solid-phase microextraction (HS-SPME) has been successfully applied to the determination of perfume components in scented candle wax, liquid laundry detergent, and fabric softener. Different fiber coatings (100 μm polydimethylsiloxane, 50/30 μm divinylbenzene/Carboxen/polydimethylsiloxane, 70 μm Carbowax/divinylbenzene, and 85 μm polyacrylate) were tested and the extraction conditions were optimized. For most compounds extraction efficiency, reproducibility, and long-term stability were highest for polydimethylsiloxane. The compatibility of SPME with fast gas chromatographic separation was investigated. The speed of conventional gas chromatography was increased by a factor of 2.5, without loss of separation efficiency, simply by reducing the column length and inner diameter and adjusting the separation conditions by use of method translation software. It was demonstrated that SPME is a suitable sample-introduction technique for fast GC if split injection is used.

Estimation of the homogeneity of reference materials by SS-ETAAS and use of the "tape-sandwich" sample-introduction technique.

The so called "tape sandwich", a novel sample-introduction technique developed for SS-ETAAS, has been employed in a study of the microheterogeneity of some biological CRM. Pb, Cd, and Cr were measured by use of a laboratory-assembled instrument with graphite-cup atomizer. Aqueous standards were found satisfactory for calibration. The average mass of sub-samples atomised was in the range 0.250-0.660 mg+/-30%. The relative sampling error found for the CRM investigated varied from 15-34%. Calculated relative homogeneity constants of the order of 4-21 mg(1/2) were obtained, and were reduced considerably by reduction of the particle size. The minimum sample sizes representative of the CRM were, with one exception, much lower (11-75 mg) than those recommended in the documentation accompanying the standards (100-200 mg). In a Chinese hair reference sample Cr data were normally distributed but the presence of nuggets was observed for Cd and Pb; this was associated with severe radial and longitudinal gradients of these elements in hair.

Osmium isotopic compositions by vapor phase sample introduction using a multi-collector ICP-MS

Osmium isotopic compositions have been measured using a vapor phase sample introduction technique in which volatile OsO4 is sparged directly into a multi-collector ICP-MS for analysis. Replicate analyses of an in-house solution standard yield an average 188Os/192Os value that is within 10 ppm of the accepted natural value when corrected for mass discrimination using 189Os/192Os, with a reproducibility of ±0.5 permil (2 SE, n = 9) for samples containing 10 ng of Os. The average 187Os/192Os measured for this solution agrees with the value determined by negative thermal ionization mass spectrometry to <1 permil, with a precision of ±1.5 permil (2 SE). Vapour phase analysis of Os isotopic compositions by MC-ICP-MS is applicable to a variety of geological and environmental studies.

Rb isotope dilution analyses by MC-ICPMS using Zr to correct for mass fractionation: towards improved Rb–Sr geochronology?

A new technique is presented where mass fractionation during Rb isotope dilution analyses by multi-collector inductively coupled plasma mass spectrometry is corrected for by measuring the amount of fractionation on admixed Zr. Replicate analyses of natural Rb interspersed with analyses of 87Rb tracer enriched samples yield a mean 87Rb/ 85Rb=0.38540±19 (0.05%, 2 s.d.), assuming a natural 90Zr/ 91Zr of 4.588. Each Rb analysis takes 1 min, consumes 20 ng of Rb and has an internal precision of ∼0.02% (2 s.e.). Washouts between samples take 5 min. Persistent but small stable Rb backgrounds are overcome by an on-peak-zeroes (OPZ) measurement prior to data acquisition. Close examination of measured 87Rb/ 85Rb and 90Zr/ 91Zr ratios indicate small changes in relative fractionation of Rb and Zr during plasma ionisation occur when different sample introduction techniques are used (e.g., ‘wet’ vs. ‘dry’ nebulisation), although the differences are insignificant compared to the level of precision required for isotope dilution measurements. Replicate analyses of whole rock samples suggest a reproducibility for Rb concentration measurements of ≤0.5% and 87Rb/ 86Sr measurements of 0.2% when interfering Sr is reduced to satisfactory levels. However, it is difficult to ascertain to what extent this reproducibility reflects the limit of the technique or powder heterogeneity. Much of the error involved in the Rb isotope dilution and Sr isotope ratio measurements by multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS) is derived from uncertainties as to which 87Sr/ 86Sr (and 87Rb/ 85Rb) ratios to use when correcting for isobaric interferences due to the presence of spike Sr and Rb at mass 87. If isobaric interferences are minimised by efficient separation of Rb from Sr during cation exchange chemistry, the use of natural ratios for isobaric interference corrections yields the most reproducible data, indicating that the interferences are derived from environmental blank. Larger isobaric interferences at mass 87 are indicative of inefficient chemical separations, and the measured ratio from the complementary analysis provide more reproducible data. Burning off of Rb during conventional thermal ionisation mass spectrometry (TIMS) Sr isotope analysis nullifies this isobaric interference, and therefore, TIMS remains the method of choice for reliable and precise 87Sr/ 86Sr determinations on spiked samples. Application of our technique to minerals separated from Tertiary to Palaeozoic plutons yields age data consistent with previous determinations. Where different two-point isochron ages can be calculated for individual plutons, the ages reproduce to ≤±0.3%. The method represents an initial improvement in Rb isotope dilution measurements over TIMS by allowing a quantifiable correction to be made for mass fractionation, confirmed by duplicate analyses of standards and samples by both TIMS and MC-ICPMS. Mass fractionation corrected Rb isotope dilution analyses should result in: (1) improved Rb–Sr geochronology in examples where the Rb–Sr ratio provides the largest source of error; (2) application of this improved method to Rb–Sr geochronology on smaller samples such as single mica-flakes and micro-drill samples and; (3) by comparison with other geochronological techniques, more detailed cooling and crystallisation histories of igneous and metamorphic rocks. Taking advantage of these improvements requires a reevaluation of the Rb decay constant, which this technique should also permit.

Continuous flow chemical vapour generation of silver for atomic absorption spectrometry using tetrahydroborate(iii) reduction—system performance and assessment of the efficiency using instrumental neutron activation analysis

The chemical vapour generation (CVG) of silver by tetrahydroborate(III) reduction as a sample introduction technique for atomic absorption spectrometry was studied. 7% of the analyte was volatilized in a miniature batch arrangement, as determined by instrumental neutron activation analysis. The continuous flow silver CVG system was designed to be interfaced with a diffusion flame or multiple microflame quartz tube atomizer, and peak area characteristic masses of 7 and 0.6 ng, respectively, were achieved. The chemical vapour generation efficiency of the described continuous flow system was in the same range as that of the batch system.

Calibration graphs for Ti, Ta and Nb in sintered tungsten carbide by infrared laser ablation inductively coupled plasma atomic emission spectrometry.

Infrared laser ablation (IR-LA) has been studied as a sample introduction technique for the analysis of sintered cobalt-cemented tungsten carbide materials by inductively coupled plasma atomic emission spectrometry (ICP-AES). Fractionation of cobalt was observed. Linearity of calibration plots was verified at least up to 15% Ti, 8% Ta, and 3% Nb. Above 1% (m/m) Ti, Ta, and Nb, the repeatability of results was better than 3% R.S.D. The relative uncertainty at the centroid of the calibration line was in the range from +/- 3% to +/- 4% for Ti, Ta, and Nb with internal standardization by tungsten and up to +/- 5% without internal standardization. The limits of detection were 0.004% Ti, 0.001% Ta, and 0.004% Nb. Elimination of the cemented hardmetal dissolution procedure is the main advantage of this method.

A retrospective view of mass spectrometry and natural products—sixty years of progress, with a focus on contributions by R. Graham Cooks

Modern mass spectrometry as used by chemists has prospered for the past sixty years. During the first decade of this period, the primary compounds studied were from petroleum, although other organic compounds soon attracted interest. By the mid nineteen fifties, mass spectra were being recorded on thousands of compounds each year. Most of this activity was in industrial laboratories, although by 1960 the academic world had realized the potential of the technique. This retrospective, reviewing the past sixty years, is divided into four quarters. The first two quarters cover the thirty-year period to 1970, by the end of which R. Graham Cooks had begun to plant firm roots into mass spectrometry. The major feature of the third quarter is the development by Cooks and his students of tandem mass spectrometry using isobutane or ammonia chemical ionization mass spectrometry coupled to the mass-analyzed ion kinetic energy spectroscopy (MIKES) technique for the direct, rapid, and efficient analysis of complex biological matrices. A milestone in the work was the direct introduction of plant material into the mass spectrometry (MS) source. The fourth quarter of the review covers an explosive growth in the breadth of mass spectrometry. Work in the Cooks laboratory was focused on the application of a series of ion generation and sample introduction techniques, such as desorption chemical ionization, surface-induced dissociation, secondary ion mass spectrometry, and membrane introduction mass spectrometry, to analyze increasingly complex biological matrices. In contrast to the earlier MIKES technique on a sector spectrometer, tandem MS became more common using a triple quadrupole spectrometer, with the natural products being studied ranging in complexity from ethanol to proteins and DNA.

Factors influencing the determination of analyte ion surface partitioning coefficients in electrosprayed droplets

The observed response in mass spectrometry utilizing electrospray as a sample introduction technique can be affected by a number of factors. In this study a series of two-electrolyte systems was investigated and the mass spectrometric responses were modeled by the use of droplet surface partitioning coefficients and instrumental response factors according to a recently reported method (Sjöberg et al., Anal. Chem. 2001, 73, 23–28). The partitioning coefficient and the instrumental response factor were found to be affected by the chosen experimental conditions. Experimental parameters that were investigated include spray position relative to the orifice, spray potential, nebulizer and curtain gas flow rates, ionic strength, and organic content of the sprayed solution. The time history of the generated droplets turned out to be of importance to both the partitioning coefficients and the instrumental response factor. For example, a general increase in the surface partitioning coefficients for the tetrapentylammonium ion was initially observed when the spray was aiming closer to the sampling orifice. Furthermore, it was shown with a small amount of deuterium labeled electrolyte that the total ionic strength and not just the electrolyte concentration influence the instrumental response factor.

Determination of mercury compounds in fish by microwave-assisted extraction and liquid chromatography-vapor generation-inductively coupled plasma mass spectrometry

A method employing a vapor generation system and LC combined with inductively coupled plasma mass spectrometry (LC-ICP-MS) is presented for the determination of mercury in biological tissues. An open vessel microwave digestion system was used to extract the mercury compounds from the sample matrix. The efficiency of the mobile phase, a mixture of l-cysteine and 2-mercaptoethanol, was evaluated for LC separation of inorganic mercury [Hg(II)], methylmercury (methyl-Hg) and ethylmercury (ethyl-Hg). The sensitivity, detection limits and repeatability of the liquid chromatography (LC) ICP-MS system with a vapor generator were comparable to, or better than, that of an LC-ICP-MS system with conventional pneumatic nebulization, or other sample introduction techniques. The experimental detection limits for various mercury species were in the range of 0.05–0.09 ng ml −1 Hg, based on peak height. The proposed method was successfully applied to the determination of mercury compounds in a swordfish sample purchased from the local market. The accuracy of the method was evaluated by analyzing a marine biological certified reference material (DORM-2, NRCC).

Calibration graphs for steels by IR laser ablation inductively coupled plasma atomic emission spectrometry.

Infrared laser ablation (IRLA) was studied as a sample-introduction technique for the analysis of steels by inductively coupled plasma atomic emission spectrometry (ICP-AES). A comparison of two IRLA-ICP-AES systems based on Q-switched nanosecond Nd: YAG lasers was performed. The beam of the LINA-Spark atomizer (LSA Sarl, Cully, Switzerland) based on the Surelite 1-20 laser (Continuum, USA) was moved along a circle. A Perkin-Elmer Optima 3000 DV ICP system was used both with lateral and axial viewing modes. A laboratory-made ablation system based on the Brilliant laser (Quantel) was coupled to a Jobin-Yvon 170 Ultrace ICP (lateral viewing, polychromator part employed). A sample was rotated along a circle during ablation. Linearity of calibration plots was verified at least up to 19% Cr and 12% Ni without internal standardization for both LA-ICP-AES systems. Other elements examined were Mo up to 3%, Mn up 1.5%, Si up to 1.7%, and Cu up to 0.15%. The reproducibility was in the range 5-1 %RSD for a mass percentage 0.5-20% of steel constituents. The relative uncertainty of the centroids of the calibration lines was in the range from +/- 4% to +/- 12% for Cr, Ni, Mn, Mo, and Si, and from +/- 8% to +/- 19% for Cu. The lowest determinable quantities were calculated for calibration dependencies. Performances of both the IR-LA-ICP-AES were comparable.

Investigation of matrix effects in inductively coupled plasma-atomic emission spectroscopy using laser ablation and solution nebulization — effect of second ionization potential

Plasma-related non-spectroscopic matrix effects of 31 elements in inductively coupled plasma (ICP)-atomic emission spectrometry were investigated using both laser ablation and solution nebulization as sample introduction techniques. Matrix effects were studied by monitoring the excitation conditions of the plasma using the ionic to atomic spectral line intensity ratios of zinc and magnesium. A new kind of matrix interference was found in the ICP that appears to be related to matrices with elements of low second ionization potential. The matrix effects do not correlate with the first ionization potential of the element. Only those matrix elements with low second ionization potential showed severe matrix effects. Increasing the forward power of the ICP or replacing the carrier gas with a 50%/50% argon–helium mixture did not significantly reduce this matrix effect. However, using 100% helium as the carrier gas greatly reduced the extent of this matrix effect, suggesting that argon is involved in the interference mechanism. The interference mechanism may involve interactions between doubly-charged matrix ions and argon species.

Mass spectrometry with laser sampling: A new tool to characterize archaeological materials

Interest in mass spectrometry with an inductively coupled plasma as an ion source and its association with laser ablation as a sample introduction technique (LA-ICP-MS) has steadily increased during the past few years. After a description of the analytical procedure and the calculation method, we show the potential of this technique to characterize non destructively archaeological artefacts. A comparison is made between the results obtained with LA-ICP-MS and those obtained on the same objects with other analytical methods. A large variety of archaeological materials such as obsidians, glasses, glazes and flints are studied.

A comparison of continuous flow hydride generation laser-induced fluorescence and laser-enhanced ionization spectrometry approaches for parts per trillion level measurements of arsenic, selenium and antimony

Hydride generation (HG) is a sample introduction technique that provides enhanced sensitivity for metalloids and allows chemical speciation between selected arsenic (As) and selenium (Se) anion species. The present studies have demonstrated high sensitivity for As, Se, and antimony (Sb) using continuous flow HG-laser induced fluorescence (LIF) and HG-laser enhanced ionization (LEI) spectrometric techniques. The limits of detection (LODs) are 200, 90 and 300 fg ml−1 for As, Se and Sb, respectively, using HG-LIF and 50 and 2 pg ml−1 for As and Se, respectively, using HG-LEI approaches. Measurements performed using HG combined with LIF detection in an electrothermal atomizer resulted in LODs of 3 pg ml−1 (6 pg absolute mass) and 20 pg ml−1 (40 pg) for As and Se, respectively. All of the techniques are linear in their responses to at least 10 ng ml−1 for the corresponding elements. Reliable chemical speciation of As(III/V) and Se(IV/VI) species has been obtained using the flame HG-LIF approaches. Selective determinations of Se(IV) and Se(VI) have been carried out using an on-line pre-reduction procedure, where selective HG of Se(IV) is performed in 31% HBr at room temperature, while HG of [Se(IV) + Se(VI)] is performed following pre-reduction in 31% HBr at 100°C. Selective HG of As species is accomplished by control of the solution pH, where selective HG of As(III) is performed at pH 6 and HG of [As(III) + As(V)] is performed at pH 0. The results obtained demonstrate that the HG approaches are selective and provide quantitative recoveries of the individual Se and As species at sub-ppb levels.

In-situ isotopic ratio analysis of iron using laser ablation-multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICP-MS)

In-situ 54Fe/56Fe and 57Fe/56Fe ratio measurements for solid samples have been carried out using laser ablation-multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICP-MS). Using a dry plasma condition achieved by laser sample introduction technique, mass spectrometric interferences such as 54ArN+, 56ArO+ or 57ArOH+ could be successfully reduced. Although these argide interference signals were not completely eliminated, the contribution of the remnant signals could be effectively corrected by an “on-peak” baseline subtraction technique. Resultant repeatability or external precision of the measurement over the four month period was almost 0.5–1%, which was insufficient to detect the isotopic variations of Fe in natural samples (typically smaller than 0.3%). We found that the poor repeatability in Fe isotopic ratio measurements was mainly due to instability or poor reproducibility of the high voltage power supply, especially for ion acceleration voltage, of our instrument. The mass discrimination effect on Fe isotopic ratios was strongly correlated with accelerating energy (ion energy) of analyte ions. To overcome this, Fe isotopic ratios of NIST Standard Reference Material (SRM) 665 metallic standard were measured between the sample measurements. This sample–standard bracketing method successfully results in internal precisions of the 54Fe/56Fe and 57Fe/56Fe ratios of better than 0.1% at the 95% confidence level. The analysis time for one sample was about 50 s, and the total amount of Fe used for an analysis was about 30 ng. The 54Fe/56Fe and 57Fe/56Fe ratios measured for NIST SRM 661 steel, three Fe-bearing minerals, and six iron meteorites, show no significant variations within the analytical uncertainties achieved in this study. The good agreement between samples suggests that our approach successfully compensates for both the instrumental drift and the background correction. The data presented here demonstrate clearly that the Fe isotopic ratios obtained by the LA-MC-ICP-MS technique can give strong clues to elucidate the Fe isotopic fractionation occurring in biochemical reactions, which may cause a larger isotopic fractionation effect in nature.

The use of radiofrequency glow discharge-mass spectrometry (rf-GD-MS) coupled to gas chromatography for the determination of selenoaminoacids in biological samples

A radiofrequency glow discharge (rf-GD) has been used as an ion source for mass spectrometry using gas chromatography as the sample introduction technique for the speciation of seleno amino acids. The use of helium as the plasma gas allowed the monitoring of selenium's major isotope (80Se), interfered by polyatomic species when using Ar as the plasma gas. Optimization of the power and pressure of the source was undertaken to achieve the best sensitivity for selenium determination and detection limits of about 100 pg (as Se) have been obtained for the derivatized Se-methionine. Studying the cell pressure and power on the fragmentation patterns obtained for Se-methionine and Se-ethionine has also been undertaken to characterize the source. No significant variations were observed on the mass spectra under different operating conditions, although noticeable variation of the fragment intensities was observed. The system has been applied to the determination of Se-methionine in selenium-enriched yeast after enzymatic extraction of the corresponding species using Proteinase K to cleave the peptide bonds. The results obtained showed a Se-methionine content of about 78% in the enriched yeast.

Determination of arsenic by inductively coupled plasma mass spectrometry--comparison of sample introduction techniques.

A comparison is made of four sample introduction techniques for the determination of As by inductively coupled plasma mass spectrometry. The techniques studied were 1) flow injection with pneumatic nebulization (FIA-PN), 2) direct electrothermal vaporization (ETV), 3) continuous hydride generation (HG) and 4) hydride generation with in situ trapping followed by electrothermal vaporization (HG-ETV). It was found that FIA-PN and ETV gave similar detection limits in concentration units (about 20 pg mL(-1)), although ETV had a much lower absolute detection limit (0.2 pg). Sample introduction by hydride generation gave an inferior detection limit (100-200 pg mL(-1)), also in combination with in situ trapping and ETV, owing to the blank signal from traces of As in NaBH4 which is difficult to eliminate. The results indicate that the more elaborate sample introduction techniques based on ETV and HG may not offer significant advantages compared to normal solution nebulization for the determination of As in simple sample matrices such as natural fresh waters, where matrix removal is not required.

Direct analysis of titanium dioxide solid powder by fluorination assisted electrothermal vaporization inductively coupled plasma atomic emission spectrometry

Fluorination assisted electrothermal vaporization (ETV) was employed as sample introduction technique for the direct determination of trace amounts of impurities in titanium dioxide solid powder by inductively coupled plasma atomic emission spectrometry (ICP-AES). A polytetrafluoroethylene (PTFE) emulsion is used as a fluorination reagent to promote the vaporization of impurity elements in TiO 2 powder from the graphite tube; the vaporization behavior of matrix element (Ti) and analyte (Cr, Cu, Fe and V) were studied. Under the selected conditions, about 100 μg solid sample (10 μl of 1% m/v TiO 2 slurry) was pipetted into furnace, a pre-volatilization of the matrix could be performed by an ashing time of 70 s at 800°C to eliminate the matrix effect, and then the analytes were vaporized into plasma at the vaporizing temperature of 2600°C. Calibration was performed using the standard addition method. The accuracy was checked by comparison of the results with solution fluorination assisted ETV-ICP-AES and pneumatic nebulization (PN)-ICP-AES based on the wet-chemical decomposition. Limits of detection between 0.07 μg g −1 (Cr) and 0.2 μg g −1 (V) were achieved.

Analysis of Interlaboratory Performance in the Determination of Total Selenium in Water

This study explored the performance of experienced laboratories in the analysis for total selenium in water by a variety of analytical methods. The goal of the study was to examine intra- and interlaboratory variability. Replicates (n = 7) of 7 sample types that included a reference material of known Se concentration, natural waters, and treated wastewaters were submitted to 7 laboratories with prequalified Se analytical experience. Results of the study indicated wide ranges in minimum and maximum results, distinct differences in laboratory precision, and routine reporting of numerical results below statistical limits of quantitation. Hydride generation as a sample introduction technique demonstrated superior performance. In general, the study supports a caution advisory about using low-level Se data, especially results lower than about 10 micrograms Se/L, without quantitating the statistical uncertainty of the data. Because this study used data from samples that were submitted in bulk to participating laboratories prequalified for Se analytical expertise and experience, it can be considered a best-case demonstration of performance.