Separation and determination of tellurium(IV) and tellurium(VI) using reversed-phase high-performance liquid chromatography-inductively coupled plasma mass spectrometry.

A new method for speciation analysis of tellurium(IV) and Te(VI) using high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) has been developed. Tellurium(IV) and Te(VI) were completely separated using a reversed-phase column with an L-cysteine eluent under an isocratic elution condition. The detection limits (3σ) of Te(IV) and Te(VI) monitored by HPLC-ICP-MS at m/z 125 were 1.4 and 0.5 ng g-1, respectively. The proposed determination method was precisely applied to assessing total concentrations and chemical species of Te in several standard solutions. The recovery rates of Te(IV) and Te(VI) were almost 100% from the results of the addition-recovery examinations, even when a high matrix sample such as seawater was measured. The method was applied to seawater samples and electronic products, and was proved quite effective for environmental risk assessment.

Migration of trace elements and radioisotopes to various fractions of solid wastes generated as a result of the sewage sludge incineration process.

The research was aimed at providing new knowledge in the field of chemical characteristics of solid waste generated in the process of combustion of sewage sludge in fluidized bed furnaces. The research material consisted of disposed fluidized beds (DFB), sewage sludge ash (SSA) and air pollution control residues (APC) from three Polish installations for the thermal treatment of sewage sludge. Natural radionuclides as well as anthropogenic isotope 137Cs were determined in the tested materials and the migration of a wide spectrum of trace elements to various waste fractions generated in the process of sewage sludge combustion was examined. It was observed that both radioisotopes and most of the trace elements determined accumulate in SSA and DFB, while the APC fraction contains a much smaller amount of them. The exceptions are mercury and selenium, whose volatile compounds migrate to the exhaust gas dedusting system and accumulate in the APC fraction (up to 40 mg/kg and 13 mg/kg, respectively). A potential threat from the 226Ra isotope in SSA is identified in the context of the management of this waste in the production of building materials because the typical activity of 226Ra in SSA collected from areas with very low Ra content in natural environment exceeds 1.5-6 times the activity of this isotope in conventional cement mixtures. When managing SSA and DFB, special attention should be paid to the content of metalloids such as As, B and Se, due to the high content of mobile forms of these elements in the mentioned materials.

Combination of isotope dilution with liquid chromatography-inductively coupled plasma mass spectrometry for the simultaneous monitoring and evaluation of cadmium and inorganic arsenic in polished rice.

A new monitoring and evaluation technique for cadmium (Cd) and inorganic arsenic (i-As) in rice was developed, where the isotope dilution (ID) method was applied in combination with high performance liquid chromatography-inductively coupled plasma mass spectrometry (LC-ICP-MS), following heat-assisted extraction. Cadmium and i-As in a rice sample were extracted using the HNO3-H2O2 extractant, and an appropriate amount of enriched 111Cd was spiked into it. Cadmium and As species were measured simultaneously by LC-ICP-MS. The cadmium concentration was calculated from the isotope dilution analysis, and i-As was determined by the comparison (1 point calibration) method using additional 111Cd as an internal standard. The proposed method provides accurate and precise determination of Cd based on the isotope dilution analysis. Moreover, it can be applied to a rapid screening test to find contaminated rice samples, by means of monitoring the intensity ratios of natural 111Cd and i-As to the additional 111Cd. The developed technique was applied to analyzing multiple rice reference materials, and the measurement results of Cd and i-As agreed with the certified values within the uncertainty range. It is noted that the grain size of rice samples does not affect the extraction data, when the rice sample is crushed into powder less than 850 µm. The proposed method was very useful for the monitoring and evaluation of Cd and i-As in rice as a precise analytical method as well as a screening method.

Elimination of spectral interference of 87Rb with 87Sr during ICP-MS measurements using a chromatographic technique.

A new chromatographic separation technique was developed for the measurement of the strontium (Sr) isotope abundance ratio using inductively coupled plasma mass spectrometry (ICP-MS). This technique, LC-ICP-MS, utilizes the addition of 18-crown-the eluent and an ODS column. The technique completely eliminates the spectral interference of 87Rb (an isobar of 87Sr) with 87Sr during the ICP-MS measurement. 18-Crown-6 selectively forms a clathrate compound with some metals. When the Sr isotope abundances are measured using LC-ICP-MS with an ODS column, the addition of a specific amount of 18-crown-6 to the HNO3/0.1% methanol eluent elongates the retention time of Rb. Therefore, Rb can be completely separated from Sr using LC because Rb is captured into the 18-crown-6 molecule and forms a clathrate compound. The technique enables the measurement of Sr isotope abundance ratios easily, even in the presence of a large amount of Rb. The proposed technique was applied to the measurement of Sr isotope abundance ratios in rice samples. To validate the LC-ICP-MS technique, a fraction containing Sr was collected, and the 87Sr/86Sr isotope ratio was precisely measured using ICP-MS.

An online internal standard technique for high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS).

An online internal standard correction technique for high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) was designed using an autosampler system equipped with HPLC to improve the analytical precision. The autosampler was programed to operate in the following sequence: it first takes up a portion of sample solution, rinses the nozzle, sucks air as a spacer, takes an internal standard solution and finally injects all of them into a sampling loop through an injection valve. The repeatability of the sampling (amount 20 µL) was improved from 2.5 to 1.2% using the online internal standard technique. This technique was applied to As speciation in food samples, since food safety monitoring requires high precision and high sample throughput. Rhenium was very suitable as an internal standard element due to its retention time, peak shape and water solubility. This technique effectively improved the analytical precision of the As speciation and got rid of the operation of adding an internal standard solution into samples.

Speciation analysis of Gadolinium-based contrast agents using aqueous eluent-hydrophilic interaction liquid chromatography hyphenated with inductively coupled plasma-mass spectrometry.

Gadolinium chelates are widely used as contrast agents for magnetic resonance imaging (MRI). In recent decades, the amount of Gd in river water has been increasing owing to the input of Gd-based contrast agents. To identify and quantify the Gd-based contrast agents in river water, the novel technique of hydrophilic interaction liquid chromatography (HILIC) hyphenated with inductively coupled plasma-mass spectrometry (ICP-MS) was developed. To avoid deposition of carbon on the ICP-MS interface, a mobile phase consisting of an ammonium acetate buffer diluted with pure water was applied to separate Gd-based contrast agents. Despite the absence of an organic solvent in the mobile phase, six Gd-based contrast agents, Gd-DTPA, Gd-EOB-DTPA, Gd-DOTA, Gd-DTPA-BMA, Gd-BT-DO3A, and Gd-HP-DO3A, were successfully separated. This technique was applied for river water samples. As a result, Gd-DOTA, Gd-BT-DO3A, and Gd-HP-DO3A were observed from the sample near the outfall of a wastewater treatment plant (WWTP), indicating that at least some of the Gd-based contrast agents are passed through treatment in a WWTP. In addition to Gd-based contrast agents, unidentified Gd compounds were found to be present in river water. These results infer that transformation and/or dissociation of Gd chelates may be caused during the treatment procedure in a WWTP.

Simultaneous speciation analysis of inorganic arsenic and methylmercury in edible oil by high-performance liquid chromatography-inductively coupled plasma mass spectrometry.

A simultaneous speciation method of arsenic and mercury species by inductively coupled plasma mass spectrometry with a reversed-phase C18 ODS column was developed. The separation of inorganic arsenic (iAs) from As species and inorganic mercury (iHg) from methylmercury (MeHg) were achieved by HPLC with a single mobile phase containing ion-pair reagent and l-cysteine. The limits of detection of iAs and MeHg were 0.05 ng g-1 as As and 0.09 ng g-1 as Hg, respectively. The simultaneous extraction, i-As and MeHg from in edible oil were achieved using 2% (w/w) tetramethylammonium hydroxide (TMAH) solution. The proposed method was successfully applied to the food matrix type CRMs. When the simultaneous speciation was applied to several kinds of edible oil, iAs and MeHg were founded in the concentration range of 0.001 mg kg-1 to 0.010 mg kg-1 and 1.21 ng g-1 to 10.18 ng g-1, respectively.

A Method for Methylmercury and Inorganic Mercury in Biological Samples Using High Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry.

A new determination method was developed for the measurement of methylmercury (Me-Hg) and inorganic mercury (i-Hg) in biological samples using high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) following alkaline extraction. Mercury species in biological samples were extracted with 10% (w/w) tetramethylammonium hydroxide (TMAH) solution at 80°C for 2 h. Methylmercury was completely separated from i-Hg by adamantyl type and octadecylsilyl type columns within 6 and 4 min using isocratic elution, respectively. The detection limits (3σ) of adamantyl and octadecylsilyl columns using the proposed system were 0.08 and 0.13 ng g-1 (as Hg), respectively. Inorganic Hg completely separates from Me-Hg without tailing. The proposed determination methods were applied to several biological certified reference materials (CRMs). The measurement results of Me-Hg obtained by the present method were in good agreement within the expanded uncertainties (k = 2) with the certified values. The analytical precision (n = 3) of Me-Hg was less than 2%, and the recoveries of Me-Hg and i-Hg were 101 ± 1 and 103 ± 3%, respectively. In addition, this method enables the determination of Me-Hg and i-Hg for 20 samples in 1 h.

Determination of Inorganic Arsenic in Grape Products Using HPLC-ICP-MS.

The inorganic arsenic (i-As) in grape products, in particular juice, wine and raisins, collected from the Japanese market was investigated. The concentrations of total As in nine grape concentrated juices ranged from 3 to 20 ng g-1, and more than 80% of the As was inorganic according to the results of speciation by HPLC-ICP-MS. Among them, four samples contained more than 10 ng g-1 of i-As, although 10 ng g-1 of i-As is the limit for apple juice recommended by the U.S. Food and Drug Administration. Moreover, more than 10 ng g-1 of i-As was found in some of the wine and raisin samples, with the total As concentrations ranging from 17 to 37 ng g-1. When fresh grapes were analyzed, As was mainly concentrated in the pericarp and a small amount was found in the fruit, although no As was observed in the branches and the juice. When grapes, including the pericarp, are processed, the As concentration in the products may increase during production processes such as drying, concentration, and ripening.

Applications and Uncertainty Estimation of Single Level Standard Addition Method ICP-MS for Elemental Analysis in Various Matrix.

The standard addition method (SAM) based on gravimetric sample preparation was investigated as an approach for the removal or cancelling of matrix effects in measurements by inductively coupled plasma mass spectrometry (ICP-MS). Deduction of the equations and experimental confirmation of the method are both given in the present work. After measuring both spiked and non-spiked samples by ICP-MS, the concentration of an element could be calculated based on the signal intensity ratio to an internal standard. A practical example was provided for the measurement of Fe in a certified reference material (CRM), i.e. NMIJ CRM 7512-a (milk powder). The validity of the method had been confirmed by the results of international comparisons with various kinds of matrix, including bioethanol, human serum, biodiesel fuel, drinking water, infant formula milk power, and seafood. The suggested method had been applied to measurements of multiple elements in three CRMs, including tap water, milk powder, and tea leave powder, respectively.

A rapid monitoring method for inorganic arsenic in rice flour using reversed phase-high performance liquid chromatography-inductively coupled plasma mass spectrometry.

A new rapid monitoring method by means of high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS) following the heat-assisted extraction was developed for measurement of total inorganic arsenic species in rice flour. As(III) and As(V) eluted at the same retention time and completely separated from organoarsenic species by an isocratic elution program on a reversed phase column. Therefore, neither ambiguous oxidation of arsenite to arsenate nor the integration of two peaks were necessary to determine directly the target analyte inorganic arsenic. Rapid injection allowed measuring 3 replicates within 6min and this combined with a quantitative extraction of all arsenic species from rice flour by a 15min HNO3-H2O2 extraction makes this the fastest laboratory based method for inorganic arsenic in rice flour.

Arsenic Speciation and Cadmium Determination in Tobacco Leaves, Ash and Smoke.

The concentrations of arsenic (As) and cadmium (Cd) in the tobacco leaves, ash and smoke of 10 kinds of cigarettes collected from different countries worldwide were determined by ICP-MS after microwave-assisted digestion. Total As and Cd concentrations in the tobacco leaves ranged from 0.20 to 0.63 and 1.8 to 9.9 mg kg(-1), respectively. By the speciation analysis of As in tobacco leaves and ash by HPLC-ICP-MS following acid extraction, arsenite [As(III)] and arsenate [As(V)] were determined and trace amounts of monomethylarsonic acid (MMAA), dimethylarsinic acid (DMAA), trimethylarsine oxide (TMAO), tetramethylarsonium (TeMA) and some unidentified As species were also found. Arsenic speciation for smoke absorbed in an aqueous solution was carried out. The sum of the As species in tobacco leaves, ash and smoke was in good agreement with the result of total As determination in each sample, and the recoveries of speciation were 100 ± 10%. The distributions and the behaviors of As species were clarified.

Effect of the detector dead-time uncertainty on the analytical result of minor elements in low-alloy steel by isotope dilution/ICP sector field mass spectrometry.

In the present study the effects of the detector dead-time and its uncertainties on the accuracy and uncertainty of isotope dilution mass spectrometry (IDMS) were considered through an interlaboratory study on the analysis of low-alloy steel by using an ICP-sector field mass spectrometer. Also, an optimized mixing ratio of the sample and the spike to obtain highly precise results was theoretically and experimentally investigated. The detector dead-time used in the interlaboratory study showed a negative value. However, it less affected the trueness of the analytical result if the dead-time correction for the measured isotope ratio was done properly. As many researchers have pointed out, the detector dead-time showed a clear mass dependence. Therefore, it is desirable to check the dead-time in every target element by using assay standards or isotopic standards, which would lead to an accurate result even if the detector dead-time is a negative value. On the other hand, the effect of the uncertainty of the detector dead-time can be minimized when both isotope ratios and ICP-MS signals of the [sample + spike] blend in IDMS are equal to those of [spike + assay standard] in reverse IDMS. From standpoints of error magnification theory and the precision of the isotope ratio measurement, an optimized isotope ratio of the sample-spike blend would be 1.0 for an element with a large difference in ten times and more between the atomic fractions of two isotopes used for IDMS. In the case of an element with no significant difference between the atomic fractions of two isotopes, an optimized isotope ratio can be calculated by a formula expressed as a function of the atomic fractions of the sample and the spike as well as the signal of ICP-MS.

Suppression of the incoherent molecular formation effect by oxygen gas in arsenic analysis by ICP-MS.

The Incoherent Molecular Formation (IMF) effect, which involves the molecular formation of arsenic (As) atoms depends, on its oxidation state in the inductively coupled plasma. This leads to determination errors, when As is measured by inductively coupled plasma mass spectrometry (ICP-MS). The sensitivity of As(V) is 4-7% higher than that of As(III) at m/z 75, since the final ionization rates of As(V) and As(III) are different from each other due to the IMF effect. A precise measurement of As by ICP-MS is generally very difficult. Recently, the collision/reaction cell is widely used for ICP-MS to eliminate spectral interferences caused by polyatomic molecules. Especially, oxygen gas (O2) is one of the most useful reaction cell gases for As analysis, because As(+) is oxygenated into AsO(+), which is free from the such interferences as ArCl(+). In addition, the use of O2 as a reaction gas is extremely effective for reducing the IMF effect and eliminating the sensitivity difference between As(III) and As(V).

Time-resolved ICP-MS measurement: a new method for elemental and multiparametric analysis of single cells.

Time-resolved inductively coupled plasma mass spectrometry (ICP-MS) has attracted much attention for elemental and multiparametric analysis of single cells, instead of a classical bulk analysis of large amount of cells after a dissolution. In the time-resolved measurement, cells are directly introduced into the plasma via nebulizing or micro drop dispensing, and then ion plumes corresponding to single cells are individually detected with a high time resolution. The sensitivity and cell throughput in the measurement strongly depend on the time resolution. A high cell introduction efficiency into the plasma supports for a reduction of cell consumption. Biomolecules can also be measured through the attachment of elemental tags, and then the amount distribution of elements and biomolecules in single cells can be evaluated, while providing information concerning cell-to-cell variations. By applying ICP time-of-flight mass spectrometry (ICP-TOFMS), multiparametric analysis of elements and biomolecules can be achieved similar to that by a flow cytometer. This article highlights the technical aspects of the time-resolved ICP-MS measurement technique for elemental and multiparametric analysis of single cells.

Measurement of strontium isotope ratio in nitric acid extract of peanut testa by ICP-Q-MS after removal of Rb by extraction with pure water.

The difference in the distributions of Sr and Rb in peanut seeds was utilized to develop a precise method for Sr isotope ratio measurement by inductively coupled plasma quadruple mass spectrometry (ICP-Q-MS). The testa instead of the whole peanut seed was selected as the sample because apparent enrichment of Sr in comparison to Rb was found in the testa. Furthermore, Rb in the testa was removed by pure water extraction with the aid of sonication to remove the isobaric interference in Sr isotope ratio measurement. The testa taken from one peanut seed was treated as one sample for the analysis. After optimization of the operating conditions, pure water (10 mL for each sample) extraction in 30 min with sonication was able to remove over 95% of Rb in the testa, while after the Rb removal Sr could be completely extracted using 10 mL of 0.3 mol L(-1) HNO3 for each sample. The integration time in ICP-Q-MS measurement was optimized to achieve a lower measurement uncertainty in a shorter time; the results showed that 1s was required and enough for the precise measurement of Sr isotope ratios giving a relative standard uncertainty (n=10) of ca. 0.1%. The present method was applied to peanut seeds grown in Japan, China, USA, India, and South Africa.

The effect of plasma reactions on arsenic measurement by ICP spectrometry.

Inductively coupled plasma mass spectrometry (ICP-MS) is of great value to researchers concerned with inorganic analytical chemistry as well as to engineers performing elemental analysis. However, the effects of the plasma reactions on ICP spectrometry are still incompletely understood and they sometimes introduce severe problems for measurements, such as spectral interferences. When we determine arsenic (As) by ICP-MS or ICP-AES, we observe two interesting plasma phenomena; one is the incoherent molecular formation (IMF) effect in the plasma, and the other the selective and partial oxygenation of ions with O2 gas in a dynamic reaction cell. The mechanisms of the IMF effect and selective oxygenation of As with a reaction gas were investigated and the techniques to remove their influence on As determination are discussed.

Separation and quantification of RNA molecules using size-exclusion chromatography hyphenated with inductively coupled plasma-mass spectrometry.

The hyphenation of SEC with ICP-MS was successfully applied to RNA quantification. The developed method combines the separation technique for large biomolecules and element selective detection of ICP-MS. The separation of RNA molecules was performed under the SEC condition without additive reagents such as salts to prevent the adhesion of RNA molecules on the column resin. Fragments of RNA, which were commercially available as a ladder marker solution and certified reference materials, were successfully separated and analyzed by measuring ³¹P⁺ with this method. RNA was quantified with good repeatability (RSD of peak area; 2.7%, n = 3) and linearity (R² = 0.999) using a P standard solution as a calibrant. LOD and absolute detection limit of RNA were 6.7 µg/kg and 67 pg, respectively, which were equal to the values obtained by the analysis of a P standard solution. The accuracy of the proposed measurement was evaluated by measuring certified reference materials of RNA solutions for quantitative analysis (NMIJ CRM 6204-a). The results obtained by this method agreed with the certified values within uncertainty. The proposed analysis method, which demonstrates good accuracy and high precision and is free from interference by nucleotide analogues, qualifies as a method of quality control for the RNA synthesis and extraction process.

Distribution of the elements in cotyledon, embryonic axis, and testa of peanut seeds obtained by ICP-MS with microwave acid digestion.

Eighteen elements in the cotyledon, the embryonic axis, and the testa of peanut seeds were determined by inductively coupled plasma mass spectrometry (ICP-MS) after microwave acid digestion, while the gravimetric standard addition with internal standard was applied for the calibration of the elemental concentrations. The detection limit and the procedure blank value for each element were low enough to ensure the precise analysis of the elements, with a relative expanded uncertainty of less than 5%. The concentrations of the elements in peanut seed samples covered 6 orders of magnitude from approximately 0.01 mg kg(-1) of Co to approximately 7000 mg kg(-1) of K. The correlation coefficient factor was around 0.98 for the elemental concentrations in peanut seeds grown in Japan and those grown in China, indicating a good correlation. Most of the elements distributed in the cotyledon in large amounts because of the cotyledon's relatively high mass fraction. By contrast, Na, Ca, Fe, Co, Ni, Cu, Ga, Sr, Cd, and Ba were apparently enriched in the testa and the relative enrichment factor (REF) values of the elements were over 4. The relative enrichment of Mo, Fe, Zn and other elements was observed in the embryonic axis samples with REF values over 2. The relative enrichment of Cd in the testa of peanut seed indicates that about 15 to 25% of the Cd intake through peanut seeds could be effectively lowered by removal of the testa (roughly 2.5 to 3.5% of the peanut seed).

Identification of possible technical problems in determination of the major inorganic constituents of brown-rice flour by evaluating proficiency test results.

To support skill upgrading in analysis of inorganic constituents of environmental and food samples, the National Metrology Institute of Japan (NMIJ) and the National Food Research Institute (NFRI) have organized a proficiency test (PT) of determination of Mn, Fe, Cu, Zn, As, and Cd in brown-rice flour based on the international standard (ISO/IEC 17043:2010). One hundred and thirty-three sets of reports were assessed by use of the E(n)-number and z-score approaches in accordance with ISO/IEC 17043 and the international harmonized protocol for PT. The PT results and analytical procedures, reported in detail, were reviewed, and possible technical reasons for questionable or unsatisfactory results are discussed.