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.     

Isoliquiritigenin (4,2′,4′-trihydroxychalcone): A new matrix-assisted laser desorption/ionization matrix with outstanding properties for the analysis of neutral oligosaccharides

A novel matrix of isoliquiritigenin (ISL), a flavonoid with a chalcone structure (4,2′,4′-trihydroxychalcone), was demonstrated to be advantageous in the analysis of neutral oligosaccharides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). With ISL as a matrix, adequate signal for an analyte can be obtained in much lower matrix concentrations and laser intensity compared to commonly used MALDI matrices. Four different sample preparation methods were tested, and the dried droplet method exhibited the best performance on MALDI-TOF-MS analysis of oligosaccharides with ISL as a matrix. For the analysis of carbohydrates, compared with popular matrices such as 2,5-dihydroxybenzoic acid (DHB) and 2,4,6-trihydroxyacetophenone (THAP), ISL exhibited outstanding matrix properties as follows: (1) higher homogeneity of crystallization thus allowing automatic data acquisition, (2) better spectral quality in terms of resolution and signal to noise ratio (S N⁻¹), (3) better salt tolerance, (4) higher sensitivity, and (5) enough fragmentation yield to use LIFT-TOF/TOF MS to get richer structural information. In addition, reliable quantitative analysis of oligosaccharides with a good linearity over two concentration orders (1–100 pmol μL⁻¹) and good reproducibility of the signal intensity (RSD less than 15%) were achieved using this matrix. These results give a new outlook on high-speed analysis of neutral carbohydrates by MALDI-TOF MS.     

Micelle to solvent stacking of organic cations in micellar electrokinetic chromatography with sodium dodecyl sulfate

The on-line sample concentration technique, micelle to solvent stacking (MSS), was studied for small organic cations (quaternary ammonium herbicides, β-blocker drugs, and tricyclic antidepressant drugs) in reversed migration micellar electrokinetic chromatography. Electrokinetic chromatography was carried out in fused silica capillaries with a background solution of sodium dodecyl sulfate (SDS) in a low pH phosphate buffer. MSS was performed using anionic SDS micelles in the sample solution for analyte transport and methanol or acetonitrile as organic solvent in the background solution for analyte effective electrophoretic mobility reversal. The solvent also allowed for the separation of the analyte test mixtures. A model for focusing and separation was developed and the mobility reversal that involved micelle collapse was experimentally verified. The effect of analyte retention factor was observed by changing the % organic solvent in the background solution or the concentration of SDS in the sample matrix. With an injection length of 31.9 cm (77% of effective capillary length) for the 7 test drugs, the LODs (S/N=3) of 5-14 ng/mL were 101-346-fold better when compared to typical injection. The linearity (R(2), range=0.025-0.8 μg/mL), intraday and interday repeatability (%RSD, n=10) were ≥0.988, <6.0% and <8.5%, respectively. In addition, analysis of spiked urine samples after 10-fold dilution with the sample matrix yielded LODs=0.02-0.10 μg/mL. These LODs are comparable to published electrophoretic methods that required off-line sample concentration. However, the practicality of the technique for more complex samples will rely on dedicated sample preparation schemes.     

Enhancing concentration and mass sensitivities for liquid chromatography trace analysis of clopyralid in drinking water

A theoretical treatment was developed and validated that relates analyte concentration and mass sensitivities to injection volume, retention factor, particle diameter, column length, column inner diameter and detection wavelength in liquid chromatography, and sample volume and extracted volume in solid‐phase extraction (SPE). The principles were applied to improve sensitivity for trace analysis of clopyralid in drinking water. It was demonstrated that a concentration limit of detection of 0.02 ppb (μg/L) for clopyralid could be achieved with the use of simple UV detection and 100 mL of a spiked drinking water sample. This enabled reliable quantitation of clopyralid at the targeted 0.1 ppb level. Using a buffered solution as the elution solvent (potassium acetate buffer, pH 4.5, containing 10% of methanol) in the SPE procedures was found superior to using 100% methanol, as it provided better extraction recovery (70–90%) and precision (5% for a concentration at 0.1 ppb level). In addition, the eluted sample was in a weaker solvent than the mobile phase, permitting the direct injection of the extracted sample, which enabled a faster cycle time of the overall analysis. Excluding the preparation of calibration standards, the analysis of a single sample, including acidification, extraction, elution and LC run, could be completed in 1 h. The method was used successfully for the determination of clopyralid in over 200 clopyralid monoethanolamine‐fortified drinking water samples, which were treated with various water treatment resins.     

Comparison between the use of direct current glow discharge mass spectrometry and inductively coupled plasma quadrupole mass spectrometry for the analysis of trace elements in nuclear samples

The quantitative determination of trace elements in nuclear samples by GDMS and ICP-MS is presented and compared. Spectral interferences, matrix effects, detection limits, precision and accuracy are discussed. Results for selected samples demonstrated that both techniques are complementary. The use of a multi-standard solution provides the most accurate results in ICP-MS, whereas in GDMS this is achieved by relative sensitivity factors (RSF) matrix matched. Nevertheless, the use of standard RSF allows a fast screening.     

Comparison between the use of direct current glow discharge mass spectrometry and inductively coupled plasma quadrupole mass spectrometry for the analysis of trace elements in nuclear samples

The quantitative determination of trace elements in nuclear samples by GDMS and ICP-MS is presented and compared. Spectral interferences, matrix effects, detection limits, precision and accuracy are discussed. Results for selected samples demonstrated that both techniques are complementary. The use of a multi-standard solution provides the most accurate results in ICP-MS, whereas in GDMS this is achieved by relative sensitivity factors (RSF) matrix matched. Nevertheless, the use of standard RSF allows a fast screening.     

Determination of trace phosphorus in high purity tantalum materials by inductively coupled plasma mass spectrometry subsequent to matrix separation with on-line anion exchange/coprecipitation

An on-line matrix separation/inductively coupled plasma mass spectrometry (ICP-MS) method is proposed for the determination of trace amounts of phosphorus in high purity tantalum metal, tantalum (V) oxide, and tantalum pentaethoxide. In the present method, the matrix tantalum in the sample solution was adsorbed on the anion exchange resin, and phosphorus (phosphate ion) was eluted with the carrier solution of HF and HNO3 mixture. Then, the effluent solution was subsequently mixed with bismuth solution and aqueous ammonia solution to coprecipitate phosphate together with bismuth hydroxide. The precipitate formed was collected on the in-line membrane filter to wash out nitric acid with pure water, and then dissolved with hydrochloric acid. The obtained phosphorus sample solution was introduced directly into the nebulizer of ICP-MS for the determination of phosphorus. Phosphorus was determined at the molecular ion signal of 31P16O+ (m/z 47). The detection limit (3sigma) of phosphorus in the present method was 1.3 ng mL(-1) as the sample solution basis, and the relative standard deviation for 30 ng mL(-1) of phosphorus in the standard solution was 4.3% in the replicate measurements (n=11). The present method was applied to the analysis of high purity tantalum materials. The concentrations of phosphorus in tantalum samples were in fairly good agreement with those obtained by glow discharge mass spectrometry (GDMS).     

On copper diffusion in silicon measured by glow discharge mass spectrometry

Copper contamination occurs frequently in silicon for photovoltaic applications due to its very fast diffusion coupled with a low solid solubility, especially at room temperature. The combination of these properties exerts a challenge on the direct analysis of Cu bulk concentration in Si by sputtering techniques like glow discharge mass spectrometry (GDMS). This work aims at addressing the challenges in quantitative analysis of fast diffusing elements in Si matrix by GDMS. N-type, monocrystalline (Czochralski) silicon samples were intentionally contaminated with Cu after solidification and consequently annealed at 900 °C to ensure a homogeneous distribution of Cu in the bulk. The samples were quenched after annealing to control the extent of the diffusion to the surface prior to the GDMS analyses, which were carried out at different time intervals from within few minutes after cooling onward. The Cu profiles were measured by high-resolution GDMS operating in a continuous direct current mode, where the integration step length was set to ～0.5 μm over a total sputtered depth of 8–30 μm. The temperature of the samples during the GDMS analyses was also measured in order to evaluate the diffusion. The Cu contamination of n-type Si samples was observed to be highly material dependent. The practical impact of Cu out-diffusion on the calculation of the relative sensitivity factor (RSF) of Cu in Si is discussed.     

Glow discharge mass spectrometry

Over the past twenty years or so, glow discharge mass spectrometry (GDMS) has become the industry standard for the analysis of trace elements in metals and semiconductors. A review of its history is followed by a picture of the present situation and a look to where the future may lie. Applications are summarised, including the ability of GDMS to offer depth-resolved data and non-conductor analysis, and the well-documented quantitative nature of the results is reviewed. The effects resulting from the physical properties of the analyte material are discussed at length. Finally, recent work such as fast flow sources and pulsed glow discharges is reviewed.     

Multivariate optimization of photochemical vapor generation for direct determination of arsenic in seawater by inductively coupled plasma mass spectrometry

Photochemical vapor generation (PVG) sample introduction coupled to inductively coupled plasma mass spectrometry (ICPMS) is described for the determination of As in seawater. A Plackett–Burman design (PBD) and central composite design (CCD) were employed to evaluate the significance of experimental variables relevant to the optimization of PVG-ICPMS detection. The impact of the saline matrix on the suppression of analyte signal was eliminated by use of a mixture of 20% (v/v) formic and 20% acetic acid (v/v) as the photochemical reductants. Optimized conditions yielded equivalent PVG generation efficiencies for As(III), As(V), monomethylarsonic acids (MMAs) and dimethylarsinic acids (DMAs), permitting direct and rapid determination of total arsenic in seawater without any other sample pre-treatment. Quantitation was accomplished using one point gravimetric standard addition along with a spike of ⁸²Se internal standard to compensate for signal drift and fluctuation during analysis. The resulting method detection limit of 3 pg g⁻¹ (3σ) provided a 15-fold improvement over that obtained using direct solution nebulization, and is comparable to that for conventional chemical hydride generation (HG)-ICPMS. Accuracy was demonstrated by analysis of two Certified Reference Materials (NASS-6 and CASS-5 seawater) with satisfying results characterized by precisions of 3.5% and 3.2% RSD for CASS-5 and NASS-6, respectively.     

Investigation of matrix-induced interferences in mixed-gas helium-argon inductively coupled plasma mass spectrometry

The effects of various matrix constituents, Cd, Co, Pb, and synthetic ocean water, on analyte ion signal were investigated in He-Ar plasma source mass spectrometry. Analyte ion signal suppressions and enhancements were observed in the presence of varying concomitants. The method used for optimizing analyte ion lens signal determined whether suppression or enhancement was encountered. Tuning on a nitric acid standard solution results in a suppressed signal, whereas tuning on the analyte in the presence of the matrix results in signal enhancement, relative to that obtained with no concomitant present. The heavier mass lead concomitant had the greatest effect on the ion signal. Additionally, lighter analyte elements were affected to a greater extent than heavier analytes in the presence of high concomitant concentrations.     

微量进样/ICP-MS体系中的基体效应研究

考察了自行组装的高效微量进样系统在22μL/min低提升量下电感耦合等离子体质谱的基体效应.质量数和电离电位不同的基体元素质量浓度为2g/L时,低质量数分析元素受到一定的干扰,而对于高质量数分析元素,其信号几乎不受基体元素干扰,归一化信号值接近1.对于体积分数为5%的有机基体样品溶液,此微量高效雾化系统测得的归一化信号值多接近0.5.实际样品中常见的基体元素K,Na,Ca和Mg质量浓度低于500mg/L,以及乙醇和乙酸体积分数小于1%时,微量进样系统均不产生显著干扰.     

Analysis of semiconducting materials by high-resolution radiofrequency glow discharge mass spectrometry

The analytical capabilities of a high-resolution mass spectrometer in combination with a 13.56 MHz glow discharge ion source for the analysis of semiconducting materials (silicon carbide and gallium arsenide) were studied. It was shown that single positively charged ions of sample material have about 10 eV higher average energy than the ions of the discharge and residual gas. Therefore effective energy separation of the ions of analyte from the ions of the discharge and residual gas was achieved by adjusting the ion transfer optics (breadth and position of energy slit), which improves the analytical capabilities of the developed method.Some analytical applications are presented to illustrate the performance of r.f. GDMS for the bulk analysis of semiconducting materials. The results of the trace element analysis of gallium arsenide and silicon carbide samples are compared with data of independent methods (LIMS, ICP-AES, SIMS).Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthdayOn leave from the Institute of Inorganic Chemistry, 630090 Novosibirsk, Russia     

Adsorptive stripping behaviour of mitoxantrone on carbon paste electrodes

The electrooxidation of mitoxantrone (MXT) on carbon paste electrodes was studied using voltammetric techniques in adsorption conditions. The analyte was accumulated at the working electrode (a carbon paste electrode) under precisely controlled mass-transport conditions and stripped electrochemically in the same solution. An electrode pretreatment is proposed which shows good reproducibility of the analytical signal (0.81%). The stripping step was studied with alternating current voltammetry providing a linear response in the concentration range 5 x 10(-11) to 7 x 10(-10)M in aqueous samples. Finally, a method using the medium exchange and AC phase-selective adsorptive stripping voltammetry technique was proposed for MXT analysis in urine samples.     

Use of iridium plus rhodium as permanent modifier to determine As, Cd and Pb in acids and ethanol by electrothermal atomic absorption spectrometry

The most severe interferences in atomic absorption spectrometry are caused by the presence of anions when they are in different concentrations in the samples and in the calibration solutions. The analyte addition technique or matrix matching calibration can be employed to minimize or compensate the non-spectral interferences, but they are time consuming or difficult to be carried out. The use of chemical modifiers usually allows higher pyrolysis temperatures and consequently the removal of components of the sample matrix, equalizing the analyte signal in the sample and in the calibration solution. In this work, a mixture of Ir and Rh is proposed as permanent modifier to determine As, Cd and Pb in diluted hydrochloric, sulfuric and phosphoric acids and in ethanol and methanol by electrothermal atomic absorption spectrometry (ET AAS) with calibration against 1% v/v nitric acid aqueous solutions. The performance of the proposed permanent modifier was compared to that of Pd plus Mg nitrates in solution. Better recoveries, low background levels and faster analysis were obtained with the permanent modifier. The permanent modifier was also successfully employed for the determination of As, Cd and Pb in different concentrations of sulfuric and hydrochloric acids. For the phosphoric acid, the proposed modifier was only efficient for acid concentrations up to 2% v/v for As and up to 5% v/v for Cd and Pb. The precision, expressed as the relative standard deviation (n=3), was lower than 10%, for all samples, including ethanol and methanol.     

Direct quantitative analysis of peptides using matrix assisted laser desorption ionization

The protocol and various matrices were examined for quantification of biomolecules in both the low ca. 1200 amu and mid mass 6000-12000 amu ranges using an internal standard. Comparative studies of different matrices of MALDI quantitative analysis showed that the best accuracy and standard curve linearity were obtained for two matrices: (a) 2,5-dihydroxybenzoic acid (DHB) combined with a comatrix of fucose and 5-methoxysalicylic acid (MSA) and (b) ferulic acid/fucose. In the low mass range, the quantitative limit was in the 30 fmol range and in the mid mass range the quantitative limit was in the 250 fmol range. Linear response was observed over 2-3 decades of analyte concentration. The relative error of the standard curve slope was 1.3-1.8% with correlation coefficients of 0.996-0.998.The main problem for quantitative measurement was suppression of the signal of the less concentrated component (analyte or internal standard) by the more concentrated component. The effect was identified with saturation of the matrix by the analyte. The threshold of matrix saturation was found to be in the range of 1/(3000-5000) analyte/matrix molar ratio. To avoid matrix saturation the (analyte+internal standard) to matrix molar ratio should be below this threshold. Thus the internal standard concentration should be as low as possible.DHB/MSA/fucose and ferulic acid/fucose matrices demonstrated good accuracy and linearity for standard curves even when the internal standard had chemical properties different from the analyte. However, use of an internal standard with different chemical properties requires highly stable instrumental parameters as well as constant (analyte+internal standard)/matrix molar ratio for all samples.     

Direct quantitative analysis of peptides using matrix assisted laser desorption ionization

The protocol and various matrices were examined for quantification of biomolecules in both the low ca. 1200 amu and mid mass 6000–12000 amu ranges using an internal standard. Comparative studies of different matrices of MALDI quantitative analysis showed that the best accuracy and standard curve linearity were obtained for two matrices: (a) 2,5-dihydroxybenzoic acid (DHB) combined with a comatrix of fucose and 5-methoxysalicylic acid (MSA) and (b) ferulic acid/fucose. In the low mass range, the quantitative limit was in the 30 fmol range and in the mid mass range the quantitative limit was in the 250 fmol range. Linear response was observed over 2–3 decades of analyte concentration. The relative error of the standard curve slope was 1.3–1.8% with correlation coefficients of 0.996–0.998.The main problem for quantitative measurement was suppression of the signal of the less concentrated component (analyte or internal standard) by the more concentrated component. The effect was identified with saturation of the matrix by the analyte. The threshold of matrix saturation was found to be in the range of 1/(3000–5000) analyte/matrix molar ratio. To avoid matrix saturation the (analyte+internal standard) to matrix molar ratio should be below this threshold. Thus the internal standard concentration should be as low as possible.DHB/MSA/fucose and ferulic acid/fucose matrices demonstrated good accuracy and linearity for standard curves even when the internal standard had chemical properties different from the analyte. However, use of an internal standard with different chemical properties requires highly stable instrumental parameters as well as constant (analyte+internal standard)/matrix molar ratio for all samples.     

Isotopic abundance measurements on solid nuclear-type samples by glow discharge mass spectrometry

A double-focusing Glow Discharge Mass Spectrometer (GDMS) installed in a glovebox for nuclear sample screening has been employed for isotopic measurements. Isotopic compositions of zirconium, silicon, lithium, boron, uranium and plutonium which are elements of nuclear concern have been determined. Interferences arising from the matrix sample and the discharge gas (Ar) for each of these elements are discussed. The GDMS results are compared with those from Thermal Ionization Mass Spectrometry (TIMS). For boron and lithium at g/g-ng/g levels, the two methods gave results in good agreement. In samples containing uranium the isotopic composition obtained by GDMS was in agreement with those from TIMS independently of the enrichment. Attempts for the determination of plutonium isotopic composition were also made. In this case, due to the interferences of uranium at mass 238 and americium at mass 241, the GDMS raw data are complementary with those values obtained from physical non-destructive techniques.     

Permanent length of a stain detector with nonimmobilized reagent

A length of stain detector for reproducibly performing a variety of colorimetric analysis was designed and constructed. Hydrochloric acid and sodium hydroxide solutions containing methyl red were exploited as representative reagent and analyte for evaluating the performance of the detector. Injection of a known volume of basic solution into the acidic reagent flow generates a yellow stain at the display part of the detector. The behavior of the stain area (or length) was studied during its passage through the detector for quantitative estimation of the analyte concentration. As the area of the stain strongly depends on the sample volume rather than on analyte concentration, a mathematical method for comparing the analyte concentrations at different sample volumes is suggested. The operational principles and mechanism of the detector are simple, and anyone can easily extract analytical information from the resulting stain shape and length. The system is amenable to extension to a variety of colored chemical reactions based on the lack of a need for reagent immobilization. Up to one sample per 5 min can be analyzed with an RSD of about 4%. As low as 1 × 10⁴ M of NaOH can be detected and measured. The text was submitted by the author in English.     

The Enrichment/Separation of Fe, Co, Pb, Cd, and Cr on Ambersorb 563 Prior to Their Flame Atomic Absorption Spectrometric Determinations

A sorbent extraction method for the separation/preconcentration of Fe, Co, Pb, Cd, and Cr was developed. The analyte metal ions were retained on a column of Ambersorb 563 from a buffered sample solution. The flow rates of the sample and eluent solution were controlled by a peristaltic pump. The analyte ions were quantitatively retained at pH 9 by using an ammonia/ammonium chloride buffer solution, and were then eluted with 5 mL of 0.25 M HNO₃ at 5 mL/min flow rate. The detection limits were in the range of 0.33 and 72 g/L for Cd and Pb, respectively. The relative standard deviations were less than 10%. Recoveries of spike addition to drinking water and seawater were quantitative. The method presented was applied for the determination of Fe, Co, Pb, Cd, and Cr ions in drinking and seawater samples with satisfactory results (recoveries >95%).