Kazumi Inagaki

The extraction and speciation of arsenic in rice flour by HPLC–ICP-MS

Several solvent mixtures and techniques for the extraction of arsenic (As) species from rice flour samples prior to their analysis by HPLC-ICP-MS were investigated. Microwave-assisted extraction using water at 80 degrees C for 30 min provided the highest extraction efficiency. Total recoveries of extracted As species were in good agreement with the total As concentrations determined by ICP-MS after microwave-assisted acid digestion of the samples. Arsenite [As(III)], arsenate [As(V)] and dimethylarsinic acid (DMAA) were the main species detected in rice flour samples.

Possible chemical forms of cadmium and varietal differences in cadmium concentrations in the phloem sap of rice plants (Oryza sativa L.)

Abstract In rice (Oryza sativa L.), cadmium (Cd), a toxic heavy metal, is found in phloem sap and eventually accumulates in the grains. To further characterize phloem-transported Cd, the chemical forms of Cd and other metals and varietal differences in phloem sap Cd concentrations were investigated in young rice plants. The size-exclusion chromatography elution times for Cd-bound compounds indicated that phloem Cd in cv. Nipponbare exists mainly as an approximately 13 kDa complex. Protease digestion of rice phloem sap reduced the bound Cd content from 92 to 19%. The remaining Cd may bind to low-molecule SH compounds. An experiment examining in vitro addition of Cd2+ to phloem sap from non-Cd-treated plants revealed that rice phloem sap constitutively contains Cd chelators. The major Cd peak is distinguishable from those of Fe, Zn, Cu, Mn, Ni and Co, which probably bind to nicotianamine, 2′-deoxymugineic acid, citrate and histidine. The Cd concentrations of the phloem saps in three varieties (Milyang 23, LAC 23 and Koshihikari) grown under the same soil conditions were correlated with their grain Cd concentrations, which had been reported previously, whereas the concentrations of the xylem saps were not. In conclusion, rice phloem sap Cd differs from other metals as it may bind to a novel approximately 13 kDa protein and SH compounds, and the concentration of Cd in rice phloem sap may be a key determinant of its grain content.

Determination of REEs in seawater by ICP-MS after on-line preconcentration using a syringe-driven chelating column

A syringe-driven chelating column (SDCC) was applied to develop an on-line preconcentration/inductively coupled plasma mass spectrometry (ICP-MS) method for preconcentration and determination of rare earth elements (REEs) in seawater samples. The present on-line preconcentration system consists of only one pump, two valves, an SDCC, an ICP-MS, several connectors, and Teflon tubes. Optimizations of adsorption pH condition, sample loading flow rate, and integration range were carried out to achieve optimum measurement conditions for REEs in seawater sample. Six minutes was enough for a preconcentration and measurement cycle using 10 mL of seawater sample, where the detection limits for different REEs were in the range of 0.005 pg mL(-1) to 0.09 pg mL(-1). Analytical results of REEs in a seawater certified reference material (CRM), NASS-5, confirmed the usefulness of the present method. Furthermore, concentrations of REEs in Nikkawa Beach coastal seawater were determined and discussed with shale normalized REE distribution pattern.

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.

Determination of phosphorus using capillary electrophoresis and micro-high-performance liquid chromatography hyphenated with inductively coupled plasma mass spectrometry for the quantification of nucleotides

We performed the quantification of phosphorus in deoxynucleotides using capillary electrophoresis (CE) and micro-HPLC (microHPLC) hyphenated with inductively coupled plasma mass spectrometry (ICP-MS). DNA and its component units have conventionally been determined by photometry; however, more selective and sensitive methods are needed for small biological samples. CE and microHPLC offer the advantages of good separation and small consumption of samples, and ICP-MS is a highly sensitive technique for the determination of a chemical element. Therefore, we have developed an interface device for combining CE and microHPLC with ICP-MS for quantifying nucleotides based on phosphorus content. The interface utilizes 4.5 microL/min for nebulizing and effective introduction of the sample into ICP. The samples of nucleotides and free phosphoric acid were well separated in the CE-ICP-MS measurement, and the calibration curves (1-100 microg/mL) of the nucleotides showed a linear (R2>0.999) increase in intensity. Similarly, the samples of nucleotides were baseline separated using microHPLC-ICP-MS, and the calibration curves of the nucleotides were linear (R2>0.998). The detection limits of these species and phosphorus in nucleotides using CE-ICP-MS and microHPLC-ICP-MS were 0.77-6.5 ng/mL and 4.0-6.5 ng/mL, respectively. These values were about one or two orders lower than those in a previous report. The sample volumes of these experiments were calculated to be about 10 nL and 50 nL per analysis. Therefore, these analytical methods have the potential to be useful for the determination of biological samples, such as DNA and RNA molecules.

Determination of Fe, Cu, Ni, and Zn in seawater by ID-ICP-MS after preconcentration using a syringe-driven chelating column

A hybrid method was suggested for preconcentration of trace metals and removal of matrix elements in seawater samples. In this method, seawater samples were loaded off-line into the syringe-driven chelating columns (SDCCs), which were then connected to a valve-switching system for on-line elution and on-line determination of Fe, Cu, Ni, and Zn by ID-ICP-MS. Optimizations of operating conditions were carried out for sample loading flow rate and pH. The removal of matrix elements was not carried out, because the concentrations of Mg, Ca, Na, and K were sufficiently low when 5 mL or less of the seawater sample was used for analysis. The usefulness of the present method was confirmed by analysis of NASS-5. Detection limits for Fe, Ni, Cu, and Zn were 0.03, 0.012, 0.018, and 0.009 ng mL−1, respectively.

Direct injection determination of theophylline and caffeine in blood serum by high-performance liquid chromatography using an ODS column coated with a zwitterionic bile acid derivative.

An ODS column dynamically coated with zwitterionic bile acid derivative, 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate (CHAPS), was evaluated for direct injection determination of drugs in blood serum by HPLC. Polar functional groups such as sulfonate, ammonium and the three hydroxyl groups in CHAPS protruding towards an aqueous mobile phase formed a hydrophilic layer over the ODS reversed-phase surface, which resulted in high molecular mass compounds such as proteins being prevented from penetrating into the internal hydrophobic region. The bulk of the proteins were eluted as an unretained or nearly unretained band by using 0.2 mM sodium hydrogenphosphate solution (pH 7.4) as the mobile phase. In contrast, small molecules such as some inorganic anions and aromatic compounds were retained and thereby separated from one another. It was confirmed that the ODS column modified with CHAPS acts as a restricted access-type column with a hydrophobic interior and a hydrophilic exterior. Hence biological fluids could be directly injected into the CHAPS-coated ODS column. The present HPLC system using the CHAPS-coated ODS column was applied to the determination of theophylline and caffeine in human blood serum. The detection limits for the two drugs with UV absorption at 273 nm were 0.2 and 0.5 mg l-1 (injection volume 20 microliters) and the relative standard deviations of peak area measurements were < 1.4% and 2.2%, respectively, for 10 replicate measurements of serum spiked with 5 mg l-1 of each of the drugs.

Species-specific isotope dilution analysis of mono-, di, and tri-butyltin compounds in sediment using gas chromatography-inductively coupled plasma mass spectrometry with synthesized 118Sn-enriched butyltins

A species-specific isotope dilution (ID) method is described for the determination of mono-, di, and tri-butyltin compounds in sediment by gas chromatography-inductively coupled plasma mass spectrometry (GC-ICP-MS), where the mixture of 118Sn-enriched butyltin compounds synthesized in our laboratory was used as a spike. A correction method for the mass bias, a quantitative extraction of the butyltins from sediment, and an assay for the concentration of the standard solution for the reverse ID procedure were investigated to achieve a reliable ID analysis. The spike solution was added with tri-propyltin (TPrT), and the butyltins were extracted by mechanical shaking into acetic acid-tropolone-toluene. The extracted butyltins were ethylated with sodium tetraethylborate and measured by GC-ICP-MS. The mass bias correction factor for the butyltins was calculated with the measured area ratio of 120Sn/118Sn of TPrT in each chromatographic run, and the correction was carried out. The mass bias was well corrected with this in-run correction (the standard uncertainties of the corrected 120Sn/118Sn for the butyltins were in the range 0.03-0.45%, typically 0.25%, with triplicate measurement corresponding to 0.02-0.37% mass bias). The extraction efficiency of mono-butyltin (MBT) from sediment was improved by using tropolone-toluene as the solvent. Well-defined standard solutions for the reverse-ID procedure could be obtained by an assay for the purities of the natural abundance butyltin chloride reagents used for preparing the standard solutions. Overall uncertainties associated with the present method were estimated, where the sediment certified reference materials, PACS-2 and BCR 646, were analyzed. The uncertainty arising from the extraction was the main contributor to the overall uncertainties for MBT and di-butyltin (DBT) determinations, while with the case of tri-butyltin (TBT) determination the uncertainties arising from the purity of TBT chloride reagent used for preparing the standard solution was a large contributor to the overall uncertainties although the uncertainty arising from the extraction was also a main contributor. The analytical results of MBT, DBT, and TBT in both reference materials, except for MBT results in PACS-2, were in good agreement with the certified values in each. The result of MBT in PACS-2 (0.677 +/- 0.049 microg g(-1) as tin, mean +/- expanded uncertainty) was significantly higher than the certified value (0.45 +/- 0.05 microg g(-1)), but closely matched with the lately reported values (Rajendran, Tao, Nakazato and Miyazaki, Analyst, 2000, 125, 1757: 0.62 +/- 0.02 microg g(-1); Chiron, Roy, Cottier and Jeannot, J. Chromatogr. A, 2000, 879, 137: 0.634 +/- 0.082 microg g(-1); Alonso, Encinar, Gonzalez and Sanz-Medal, Anal. Bioanal. Chem., 2002, 373, 432: 0.64 +/- 0.04 microg g(-1). The present method is concluded to be reliable for the determination of MBT, DBT, and TBT in sediment.

High performance concentric nebulizer for low-flow rate liquid sample introduction to ICP-MS

A high performance concentric nebulizer (HPCN) was developed for sample introduction to inductively coupled plasma mass spectrometer (ICP-MS) at liquid flow rates of less than 10 µL min−1. The HPCN has a triple tube concentric structure and consists of a concentric type nebulizer body and a fused silica glass capillary (i.d./o.d.: 50 µm/150 µm) mounted in the center of the nebulizer body as a sample introduction capillary. The nebulizing performance was greatly improved by tapering the liquid capillary (tip orifice i.d.: 20 µm, tip wall thickness: <8 µm) and by setting the liquid capillary tip at a proper position. When the set position was recessed by 25 µm to 50 µm with respect to the nebulizer nozzle tip, a liquid jet was produced inside the nozzle by a flow focusing effect. This phenomenon gives a fine aerosol generation. At a liquid flow rate of 5 µL min−1 and a nebulizer gas flow rate of 1 L min−1, the Sauter mean diameter D3,2 of the primary drops generated by the HPCN (2.4 µm) was almost the same as that generated by the HEN-120-A.01 (2.6 µm) and was smaller than those generated by the HEN-90-A.01 (4.6 µm), CEI-100 (5.9 µm), and AriMist-HP (6.3 µm). The sensitivity in ICP-MS with the HPCN was over two-fold higher than those with the other microflow nebulizers, except for the HEN-120-A.01. The HEN-120-A.01 provides almost the same sensitivity as the HPCN, but it requires two-fold higher gas pressure than the HPCN. The HPCN can continuously and stably nebulize 1% NaCl solution for over 8 h without clogging. The HPCN combined with an on-axis cylinder chamber was applied to capillary liquid chromatography-ICP-MS, by which the speciation of eight arsenic compounds was demonstrated. We concluded the HPCN is a useful nebulizer for less than 10 µL min−1 sample introduction to ICP-MS.

Estimation of the distribution of intravenously injected adipose tissue-derived stem cells labeled with quantum dots in mice organs through the determination of their metallic components by ICPMS.

Adipose tissue-derived stem cells (ASCs) have shown promise in cell therapy because of their ability to self-renew damaged or diseased organs and easy harvest. To ensure the distribution and quantification of the ASCs injected from tail vein, several whole-body imaging techniques including fluorescence optical imaging with quantum dots (QDs) have been employed, but they may suffer from insufficient sensitivity and accuracy. Here, we report quantitative distribution of ASCs in various organs (heart, lung, liver, spleen, and kidney) of mice, which were intravenously injected with QDs-labeled ASCs (QDs-ASCs), through the detection of QDs-derived metallic components by inductively coupled plasma mass spectrometry (ICPMS). For accurate and precise determination, each organ was harvested and completely digested with a mixture of HNO(3) and H(2)O(2) in a microwave oven prior to ICPMS measurement, which was equipped with a microflow injection system and a laboratory-made capillary-attached micronebulizer. After optimization, 16 elements including major components (Cd, Se, and Te) of QDs and essential elements (Na, K, Mg, Ca, P, S, Mn, Fe, Co, Cu, Zn, Se, Sr, and Mo) were successfully determined in the organs. As compared to untreated mice, QDs-ASCs-treated mice showed significantly higher levels of Cd and Te in all organs, and as expected, the molar ratio of Cd to Te in each organ was in good agreement with the molar composition ratio in the QDs. This result indicates that the increment of Cd (or Te) can be used as a tracer for calculating the distribution of ASCs in mice organs. As a result of the calculation, 36.8%, 19.1%, 0.59%, 0.49%, and 0.25% of the total ASCs injected were estimated to be distributed in the liver, lung, heart, spleen, and kidney, respectively.