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.

Evaluation of the long-term stability of arsenic species in certified reference materials: certification of arsenobetaine, As(V), and dimethylarsinic acid in NMIJ CRMs 7901-a, 7912-a, and 7913-a.

The long-term stabilities of arsenobetaine (AsB), arsenate (As(V)), and dimethylarsinic acid (DMA), which are arsenic (As) compounds in certified reference materials (CRMs), namely, NMIJ CRMs 7901-a, 7912-a, and 7913-a, were monitored. The CRMs were developed and certified by the National Metrology Institute of Japan (NMIJ) and the National Institute of Advanced Industrial Science and Technology (AIST) in 2009 to prepare a calibrant for the speciation analysis of As species. The CRMs were prepared from high-purity reagent powders as raw materials, and each reagent was dissolved in water or diluted acid. The certification of the CRMs for AsB, As(V), and DMA was conducted by NMIJ. The concentration of total As was determined by more than three independent analytical techniques. Then, the obtained As concentrations were converted into the concentration of each chemical species, and the mass fractions of each certified value were certificated. The long-term stability of As species in the CRMs under storage was performed by liquid chromatography-inductively coupled plasma-mass spectrometry, and this report presents data on long-term stability that occurred approximately 13 years. The obtained monitoring results were evaluated using both measurement results with uncertainty and a statistical parameter method, complying with ISO Guide 35. According to the results, the long-term stability of all mass fractions was confirmed.

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.

Dietary intake and urinary excretion of methylated arsenicals of Japanese adults consuming marine foods and rice.

Dietary intake and urinary excretion of monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) and arsenobetaine (AsB) were measured in 150 adult Japanese subjects. Duplicate diet (DD) samples and first void of urine on the next morning of DD sampling day were collected and analysed for arsenic species with liquid chromatography-ICP mass spectrometry. Median (min-max) intakes of MMA, DMA and AsB were <2.3 (<2.3-<2.3), 4.57 (<2.3-24.3), and 13.6 (<2.4-231) µg As/day, respectively, and median urinary concentrations were 1.90 (<0.37-26.), 21.9 (<0.27-141) and 19.6 (<0.37-1063) ng As/mg creatinine, respectively. Interrelationships between intake levels and urinary concentrations were mostly significant with positive coefficients indicating mutual association due to co-exposure, metabolism and/or dietary habit. Urinary concentrations and intake levels of AsB were also positively correlated confirming the applicability of urine analysis as biomarker of exposure. The present descriptive results provide with essential piece of information in assessing health risk of methylated arsenicals for population who consume marine products and rice.

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.

A Simplified Questionnaire for the Assessment of Inorganic Arsenic Intake in a Japanese Population.

A simplified questionnaire was developed to assess inorganic arsenic (iAs) intake level in a Japanese population. The two page questionnaire included photographs of single serving sizes of rice and cooked hijiki (Hizikia fusiforme: brown algae), and asked subjects about the number of servings of rice and cooked hijiki, two predominant dietary sources of iAs in Japan, they consume in a day. Daily intake of iAs was estimated for 72 Japanese subjects using the questionnaire together with data of iAs content in rice and hijiki seaweed, and the estimated intakes were compared with actual iAs intakes of the subjects as measured for a duplicate diet using liquid chromatography-inductively coupled plasma mass spectrometry. A highly significant correlation was found between the estimated and measured intakes (r = 0.65, p < 0.001); however, the slope of regression indicated a systematic error in the intake estimation. Possible sources of error are discussed herein. It was concluded that this approach is promising if minor improvements are made to the questionnaire.

Association of dietary intake and urinary excretion of inorganic arsenic in the Japanese subjects.

Quantitative relationship between intake of inorganic arsenic (iAs) and urinary excretion of iAs and its metabolite, methylarsonic acid (MMA), was investigated for 150 adult Japanese subjects. Duplicate diet was used for the determination of intake and first void of urine on the next day of duplicate diet sampling was used for urinary iAs + MMA determination. Speciation analysis of arsenic in diet and urine was carried out with liquid chromatography-inductively coupled plasma mass spectrometry. Geometric mean iAs intake of the subjects was 0.349 µg/kg/day and that of urinary iAs + MMA concentration was 5.20 ng As/mL (specific gravity (SG) corrected) or 4.05 ng As/mg creatinine (Cre). There was a significant positive correlation between iAs intake and urinary iAs + MMA concentration: the correlation coefficient between intake and Cre-corrected urinary concentration (r = 0.544) was greater than that between intake and SG-corrected concentration (r = 0.458). The regression equation of intake-excretion was: log10[dailyintake]=0.451×log10[creatininecorrectedurinaryiAs+MMA]+0.814. This equation has a practical value for converting urinary As levels, measured as a biomarker of exposure in epidemiologic study, to dietary intake levels in the future risk assessment.

A New Candidate Reference Material for Inorganic Arsenic and Arsenosugars in Hijiki Seaweed: First Results from an Inter-laboratory Study.

An inter-laboratory study was carried out to characterize a candidate hijiki seaweed for its concentrations of total arsenic and water-soluble arsenic compounds, particularly arsenosugar compounds. The candidate material, a dried hijiki seaweed powder, was analyzed by individual techniques in two laboratories. The water-soluble arsenic compounds were separated by anion exchange, and reversed-phase columns, and As(V), DMA and four kinds of arsenosugars, namely glycerol (-OH), phosphate (-PO4), sulfonate (-SO3), and sulfate (-SO4) types were detected by HPLC-ICP-MS. The methods applied were validated by analyzing a second sample, the NMIJ CRM 7405-a hijiki seaweed, which is certified for both total arsenic and As(V). Techniques for the inter-laboratory study, extraction efficiencies under different extraction conditions, some chromatographic techniques and sequential extraction were investigated. The results from the two laboratories for the candidate hijiki material showed good agreement within the measurement uncertainties for total and water-soluble arsenic compounds.

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.

Speciation and isotopic characterization of mercury detected at high concentration in Pakistani hair samples.

Speciation and isotopic analyses of mercury (Hg) detected at high concentration (11-107 mg total Hg/kg) in the hair samples of Pakistani subjects were carried out to analyze whether the source of Hg was the skin cream or the soap they used. Liquid chromatography-ICP mass spectrometric speciation analysis revealed that the Hg in the hair was primarily inorganic. This result supported our assumption that skin care products were the source of the high concentration of Hg in hair, which was based on the statistical association found in our previous study because it is known that inorganic Hg compounds are added to some skin care products sold in some countries. Stable isotope ratios of the Hg in the hair samples of 6 subjects and 3 skin cream samples, which were reported to be used by the subjects, were measured by multi-collector ICP mass spectrometry after acid digestion. A comparison of the isotopic compositions of Hg in hair and skin cream in two subjects revealed that the composition in both samples matched in one subject, hence confirming that the products were the source of high Hg concentration in hair. However, the isotopic compositions of Hg in hair and skin cream did not match in the other subject demonstrating the presence of other exposure source(s).

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.

Development of a Certified Reference Material (NMIJ CRM 7203-a) for Elemental Analysis of Tap Water.

A certified reference material (CRM), NMIJ CRM 7203-a, was developed for the elemental analysis of tap water. At least two independent analytical methods were applied to characterize the certified value of each element. The elements certified in the present CRM were as follows: Al, As, B, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Rb, Sb, Se, Sr, and Zn. The certified value for each element was given as the (property value ± expanded uncertainty), with a coverage factor of 2 for the expanded uncertainty. The expanded uncertainties were estimated while considering the contribution of the analytical methods, the method-to-method variance, the sample homogeneity, the long-term stability, and the concentrations of the standard solutions for calibration. The concentration of Hg (0.39 µg kg-1) was given as the information value, since loss of Hg was observed when the sample was stored at room temperature and exposed to light. The certified values of selected elements were confirmed by a co-analysis carried out independently by the NMIJ (Japan) and the KRISS (Korea).

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.

Reversed Phase Column HPLC-ICP-MS Conditions for Arsenic Speciation Analysis of Rice Flour.

New measurement conditions for arsenic speciation analysis of rice flour were developed using HPLC-ICP-MS equipped with a reversed phase ODS column. Eight arsenic species, namely, arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid (MMAA), dimethylarsinic acid (DMAA), trimethylarsine oxide (TMAO), tetramethylarsonium (TeMA), arsenobetaine (AsB) and arsenocholine (AsC), were separated and determined under the proposed conditions. In particular, As(III) and MMAA and DMAA and AsB were completely separated using a newly proposed eluent containing ammonium dihydrogen phosphate. Importantly, the sensitivity changes, in particular those of As(V) and As(III) caused by coexisting elements and by complex matrix composition, which had been problematical in previously reported methods, were eliminated. The new eluent can be applied to C8, C18 and C30 ODS columns with the same effectiveness and with excellent repeatability. The proposed analytical method was successfully applied to extracts of rice flour certified reference materials.

Extraction techniques for arsenic species in rice flour and their speciation by HPLC-ICP-MS.

The extraction of arsenic (As) species present in rice flour samples was investigated using different extracting solvents, and the concentration of each species was determined by HPLC-ICP-MS after heat-assisted extraction. The extraction efficiencies for total arsenic species and especially for arsenite [As(III)] and arsenate [As(V)] were investigated. As(III), As(V) and dimethylarsinic acid (DMAA) were found in the samples, and the concentration of DMAA did not vary with treatment conditions. However, the concentrations of extracted total arsenic and those of As(III) and As(V) depended on the extracting solvents. When an extracting solvent was highly acidic, the concentrations of extracted total arsenic were in good agreement with the total arsenic concentration determined by ICP-MS after microwave-assisted digestion, though a part of the As(V) was reduced to As(III) during the highly acidic extraction process. Extraction under neutral conditions increased the extracted As(V), but extracted total arsenic was decreased because a part of the As(III) could not be extracted. Optimum conditions for the extraction of As(III) and As(V) from rice flour samples are discussed to allow the accurate determinations of As(III), As(V) and DMAA in the rice flour samples. Heat block extraction techniques using 0.05 mol L(-1) HClO4 and silver-containing 0.15 mol L(-1) HNO3 were also developed.

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).

Determination of sixteen elements and arsenic species in brown, polished and milled rice.

The concentrations of 16 elements in 10 rice flour samples and the distribution of the elements in the rice grains from which the flour were made were determined by ICP-MS and ICP-OES after microwave-assisted digestion of the samples. Arsenic speciation analysis was carried out by HPLC-ICP-MS following heat-assisted extraction of the sample. The concentrations of inorganic As (As(III) and As(V)), monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA) and their distribution in the rice grains were determined. Portions of the brown rice were polished/milled to different degrees to yield milled off samples and polished rice samples. All samples were powdered and analyzed for 16 elements and for As species. The recoveries and mass balances for all elements in all samples showed good agreements with the starting materials. As(III), As(V), MMAA and DMAA were detected, and the sums of the concentrations of all species in the extract were 86-105% of the total As concentration in each case.