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.

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.

A coupling system of capillary gel electrophoresis with inductively coupled plasma-mass spectrometry for the determination of double stranded DNA fragments.

The coupling system of capillary gel electrophoresis (CGE) and inductively coupled plasma-mass spectrometry (ICP-MS) was newly developed and successfully applied to the double-stranded (ds) DNA quantification. The developed system combines the separation technique for large biomolecules and element selective detection of ICP-MS. This coupling was achieved by using the modified high performance concentric nebulizer (HPCN) with the PTFE tube (HPCN-PT), which can produce the liquid jet by the flow focusing effect. The HPCN-PT effectively nebulizes the highly viscous solution containing gel buffer even at a low flow rate. At a liquid flow rate of 0.010 mL min(-1) and a nebulizer gas flow rate of 1 L min(-1), the Sauter mean diameter (D3,2) of primary aerosols generated by the HPCN-PT was 3.4 µm, and over 90% (v/v) of the aerosol droplets were less than 10 µm in diameter. The electrophoresis capillary filled with gel buffer was connected to the HPCN-PT via the interface. This interface has two connectors and an electrode that can connect CE and ICP-MS. After the electrophoretic separation at atmospheric pressure, the samples were transferred to the ICP-MS through the interface by applying additional pressure. Fragments of dsDNA, which were commercially available as a ladder marker solution, were successfully separated and analyzed by measuring (31)P(+) with CGE-ICP-MS, and a linear calibration curve of the phosphorus standard solution (R(2) = 0.999) was obtained from 2.7 to 27 mg kg(-1). The detection limit (LOD) and absolute detection limit of P were 3.7 µg kg(-1) and 0.6 pg (equivalent to 6 pg of DNA), respectively. This absolute detection limit value was equal to the conventional fluorescence determination of DNA.

Development of salt-tolerance interface for an high performance liquid chromatography/inductively coupled plasma mass spectrometry system and its application to accurate quantification of DNA samples.

Accurate quantification of DNA is highly important in various fields. Determination of phosphorus by ICP-MS is one of the most effective methods for accurate quantification of DNA due to the fixed stoichiometry of phosphate to this molecule. In this paper, a smart and reliable method for accurate quantification of DNA fragments and oligodeoxythymidilic acids by hyphenated HPLC/ICP-MS equipped with a highly efficient interface device is presented. The interface was constructed of a home-made capillary-attached micronebulizer and temperature-controllable cyclonic spray chamber (IsoMist). As a separation column for DNA samples, home-made methacrylate-based weak anion-exchange monolith was employed. Some parameters, which include composition of mobile phase, gradient program, inner and outer diameters of capillary, temperature of spray chamber etc., were optimized to find the best performance for separation and accurate quantification of DNA samples. The proposed system could achieve many advantages, such as total consumption for small amount sample analysis, salt-tolerance for hyphenated analysis, high accuracy and precision for quantitative analysis. Using this proposed system, the samples of 20 bp DNA ladder (20, 40, 60, 80, 100, 120, 140, 160, 180, 200, 300, 400, 500 base pairs) and oligodeoxythymidilic acids (dT(12-18)) were rapidly separated and accurately quantified.

Development of a certified reference material (NMIJ CRM 7505-a) for the determination of trace elements in tea leaves.

A certified reference material (CRM) for trace elements in tea leaves has been developed in National Metrology Institute of Japan (NMIJ). The CRM was provided as a dry powder (<90 µm) after frozen pulverization of washed and dried fresh tea leaves from a tea plant farm in Shizuoka Prefecture, Japan. Characterization of the property value for each element was carried out exclusively by NMIJ with at least two independent analytical methods, including inductively coupled plasma mass spectrometry (ICP-MS), high-resolution (HR-) ICP-MS, isotope-dilution (ID-) ICP-MS, inductively coupled plasma optical emission spectrometry (ICP-OES), graphite-furnace atomic-absorption spectrometry (GF-AAS) and flame atomic-absorption spectrometry (FAAS). Property values were provided for 19 elements (Ca, K, Mg, P, Al, B, Ba, Cd, Cu, Fe, Li, Mn, Na, Ni, Pb, Rb, Sr, Zn and Co) and informative values for 18 elements (Ti, V, Cr, Y, and all of the lanthanides, except for Pm whose isotopes are exclusively radioactive). The concentration ranges of property values and informative values were from 1.59% (mass) of K to 0.0139 mg kg(-1) of Cd and from 0.6 mg kg(-1) of Ti to 0.0014 mg kg(-1) of Lu, respectively. Combined relatively standard uncertainties of the property values were estimated by considering the uncertainties of the homogeneity, analytical methods, characterization, calibration standard, and dry-mass correction factor. The range of the relative combined standard uncertainties was from 1.5% of Mg and K to 4.1% of Cd.

Quantification of phosphorus in DNA using capillary electrophoresis hyphenated with inductively coupled plasma mass spectrometry.

We have analyzed phosphorus in an enzymatically digested DNA molecule using capillary electrophoresis (CE) hyphenated with inductively coupled plasma mass spectrometry (ICP-MS). The DNA concentration was quantified by the phosphorus value obtained in the CE-ICP-MS analysis. The CE-ICP-MS measurement, for which the interface device AIF-01 equipped three layered nebulizer was adopted, was achieved with limited µL/min nebulizing without loss of sample in the vaporizing chamber. The samples of nucleotides and free phosphate were separated well in the CE-ICP-MS measurement, and the calibration curve (0.1-10µg/mL) of the phosphorus showed a linear (R(2)=0.999) increase in intensity. After digestion of the 100-bp double-strand DNA sample to deoxyribonucleotide-5'-monophosphates (dNMPs) by phosphodiesterase-I, phosphorus was detected by CE-ICP-MS without further purification steps. In this study, we applied two calculation schemes of DNA analysis using a dNMP concentration obtained from CE-ICP-MS. Comparative CE-ICP-MS analysis with DNA digested to dNMPs showed that the assay gave an equal value obtained from the total DNA quantification using fluorescence detection. The detection limits of the DNA sample obtained from these species and phosphorus in nucleotides using CE-ICP-MS were 3.1-26ng/mL. These LOD values were equal to the conventional fluorescence determination of DNA.

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 and size-fractional distribution of the elements in garlic.

Thirty elements in garlic sample were determined by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) after microwave digestion. The concentrations of K, Ca,Na, Sr, and Hg in the present garlic sample were higher than those in rice and wheat, but the concentration of Se in the garlic sample was relatively lower. The extractability of the elements in the garlic sample was also examined; the results showed that most of the elements could be easily extracted by pure water and/or a 0.1 M HNO(3) solution, except for Hg. Furthermore, the size-fractional distribution of the elements in garlic was investigated by pure water extraction and centrifugal ultrafiltration.

Determination of selenium in sediment by isotope-dilution inductively coupled plasma mass spectrometry with an octapole reaction cell.

A method is described for determination of selenium in sediment by isotope-dilution inductively coupled plasma mass spectrometry with an octapole reaction cell (ID-ICP-ORCMS). Sediment samples were digested with HNO3, HClO4, and HF, and the digestion included an elaborate evaporation process to remove bromine from the digested solution. Simple strong cation-exchange disk filtration was used to remove rare earth elements (REE) from the digested solution, because REE2+ seriously interfere with Se isotopes (i.e. 156Gd2+ with 78Se+, 160Gd2+ with 80Se+). Addition of acetic acid to the filtrate was examined to improve the sensitivity of ICP-ORCMS measurement of Se+ by means of a carbon-enhancement effect. The interfering Ar2+ for selenium isotopes were almost eliminated by use of H2 as reaction gas. Interference from BrH+ formed in the reaction cell was negligible because the Br was removed in the evaporation process. Approximately 99.5% of REE were removed by cation-exchange disk filtration yet more than 99% of Se remained in the filtrate solution. The intensity for Se+ was enhanced approximately fourfold by addition of 5% (v/v) of acetic acid whereas that for Ar2+ was barely enhanced. Measured 80Se/78Se ratios in unspiked digested solutions of the sample were in good agreement with that for an Se standard solution. The analytical results for Se in the certified reference materials MESS-3 and PACS-1 were in good agreement with their certified values, with small uncertainties.