Shin Ichi Ohira

A Capacitance Sensor for Water: Trace Moisture Measurement in Gases and Organic Solvents

The determination of water in various matrices is one of the most important analytical measurements. We report on a high-resolution capacitance-based moisture sensor utilizing a thin film of a perfluorosulfonate ionomer (PFSI)-H(3)PO(4) composite in a flow-through configuration, for both gas and liquid samples. Incorporation of H(3)PO(4) into a PFSI sensing film improved the limit of detection (LOD) (signal-to-noise ratio, S/N = 3) by a factor of 16 in the gas phase to 0.075% relative humidity (RH) (dew point = -56 °C). The response time was dependent on the sensing film thickness and composition and was as low as ∼60 ms. The temperature dependence of the sensor response, and its relative selectivity over alcohol and various other solvents, are reported. Measurement of water in organic solvents was carried out in two different ways. In one procedure, the sample was vaporized and swept into the detector (e.g., in a gas chromatograph (GC) without a column); it permitted a throughput of 80 samples/h. This is well-suited for higher (%) levels of water. In the other method, a flow injection analysis system integrated to a tubular dialysis membrane pervaporizer (PV-FIA) was used; the LOD for water in ethanol was 0.019% (w/w). We demonstrated the temporal course of drying of ethanol by Drierite; the PV-FIA results showed excellent correspondence (r(2) > 0.99) with results from GC-thermal conductivity detection. The system can measure trace water in many types of organic solvents; no reagent consumption is involved.

Perchlorate, iodine supplements, iodized salt and breast milk iodine content

This study was undertaken to determine if increasing maternal iodine intake through single dose tablets will decrease breast milk concentrations of the iodine-uptake inhibitor, perchlorate, through competitive inhibition. We also sought to determine if the timing of supplementation influences the fraction of iodine excreted in milk versus urine and to compare the effectiveness of iodized salt as a means of providing iodine to breastfed infants. Thirteen women who did not use supplements, seven of whom used iodized salt and six of whom used non-iodized salt, submitted four milk samples and a 24-h urine collection daily for three days. Women repeated the sampling protocol for three more days during which ~150μg of iodine were taken in the evening and again for three days with morning supplementation. Samples were analyzed using isotope-dilution inductively-coupled plasma-mass spectrometry for iodine and isotope-dilution ion chromatography-tandem mass spectrometry for perchlorate. No statistically significant differences were observed in milk iodine or perchlorate concentrations during the two treatment periods. Estimated perchlorate intake was above the U.S. National Academy of Sciences suggested reference dose for most infants. Single daily dose iodine supplementation was not effective in decreasing milk perchlorate concentrations. Users of iodized salt had significantly higher iodine levels in milk than non-users. Iodized salt may be a more effective means of iodine supplementation than tablets.

Electrodialytic ion isolation for matrix removal

We report a fully automated online sample pretreatment system for ionic analytes that extracts the ionic analytes from the sample and largely removes the nonionic sample matrix and can preconcentrate the analyte. Sample pretreatment is a key analytical process; conventional pretreatment is conducted in a difficult to automate batchwise manner. The present system relies on the transport of ions induced by an electric field to a water acceptor. Cations and anions are simultaneously and separately collected into individual acceptor streams which can be directly introduced to a chemical analyzer. Common inorganic ions (≤10 meq/L) are quantitatively transferred from samples within a few seconds. Small nonionic molecules are transferred by 0.5-10%, and proteins are not transferred at all. The method has been successfully applied to drinking water, urine, and cows milk with 3.7 ± 2.5, 3.8 ± 2.6, and 4.6 ± 2.6%, respectively, in variance (n = 10). Present results agreed well with those from conventional pretreatment methods. Interestingly, when calcium in milk is measured by the present method, the results correspond to the total calcium by conventional methods; i.e., it can extract calcium from its protein-bound form in milk.

On-line electrodialytic matrix isolation for chromatographic determination of organic acids in wine

Chromatographic determination of organic acids is widely performed, but the matrix often calls for lengthy and elaborate sample preparation prior to actual analysis. Matrix components, e.g., proteins, non-ionics, lipids etc. are typically removed by a combination of centrifugation/filtration and solid phase extraction (SPE) that may include the use of ion-exchange media. Here we report the quantitative electrodialytic transfer of organic acids from complex samples to ultrapure water in seconds using cellulose membranes modified with N,N-dimethylaminoethyl methacrylate, which essentially eliminates the negative ζ-potential of a regenerated cellulose membrane surface. The transfer characteristics of the ion transfer device (ITD) were evaluated with linear carboxylic acids. While the ion transfer efficiencies may be affected by the acid dissociation constants, in most cases it is possible to achieve quantitative transfer under optimized device residence time (solution flow rate) and the applied voltage. In addition, the transfer efficiency was unaffected by the wide natural variation of pH represented in real samples. The approach was applied to organic acids in various samples, including red wine, considered to represent an especially difficult matrix. While quantitative transfer of the organic acids (as judged by agreement with standard pretreatment procedures involving SPE) was achieved, transfer of other matrix components was <5%. The processed samples could then be chromatographically analyzed in a straightforward manner. We used ion exclusion chromatography with direct UV detection; in treated samples; there was a dramatic reduction of the large early peaks observed compared to only 0.45μm membrane filtered samples.

Simultaneous Electrodialytic Preconcentration and Speciation of Chromium(III) and Chromium(VI)

Large amounts of chromium (Cr) compounds are used for manufacturing of various products and various chemical processes. Some inevitably find their way into the environment. Environmental Cr is dominantly inorganic and is either in the cationic +3 oxidation state or in the anionic oxochromium +6 oxidation state. The two differ dramatically in their implications; Cr(III) is essential to human nutrition and even sold as a supplement, while Cr(VI) is a potent carcinogen. Drinking water standards for chromium may be based on total Cr or Cr(VI) only. Thus, Cr speciation analysis is very important. Despite their high sensitivity, atomic spectrometric techniques or induction coupled plasma-mass spectrometry (ICP-MS) cannot directly differentiate the oxidation states. We present here a new electrodialytic separation concept. Sample analyte ions are quantitatively transferred via appropriately ionically functionalized dialysis membranes into individual receptors that are introduced into the ICP-MS. There was no significant conversion of Cr(VI) to Cr(III) or vice versa during the very short (6 s) separation process. Effects of salinity (up to ∼20 mM NaCl) can be eliminated with proper membrane functionalization and receptor optimization. With the ICP-MS detector we used, the limits of detection for either form of Cr was 0.1 μg/L without preconcentration. Up to 10-fold preconcentration was readily possible by increasing the donor solution flow rate relative to the acceptor solution flow rates. The proposed approach permits simultaneous matrix isolation, preconcentration, and chromium speciation.

A fiber optic sensor with a metal organic framework as a sensing material for trace levels of water in industrial gases

Industrial gases such as nitrogen, oxygen, argon, and helium are easily contaminated with water during production, transfer and use, because there is a high volume fraction of water in the atmosphere (approximately 1.2% estimated with the average annual atmospheric temperature and relative humidity). Even trace water (<1 parts per million by volume (ppmv) of H2O, dew point < -76 °C) in the industrial gases can cause quality problems in the process such as production of semiconductors. Therefore, it is important to monitor and to control trace water levels in industrial gases at each supplying step, and especially during their use. In the present study, a fiber optic gas sensor was investigated for monitoring trace water levels in industrial gases. The sensor consists of a film containing a metal organic framework (MOF). MOFs are made of metals coordinated to organic ligands, and have mesoscale pores that adsorb gas molecules. When the MOF, copper benzene-1,3,5-tricarboxylate (Cu-BTC), was used as a sensing material, we investigated the color of Cu-BTC with water adsorption changed both in depth and tone. Cu-BTC crystals appeared deep blue in dry gases, and then changed to light blue in wet gases. An optical gas sensor with the Cu-BTC film was developed using a light emitting diode as the light source and a photodiode as the light intensity detector. The sensor showed a reversible response to trace water, did not require heating to remove the adsorbed water molecules. The sample gas flow rate did not affect the sensitivity. The obtained limit of detection was 40 parts per billion by volume (ppbv). The response time for sample gas containing 2.5 ppmvH2O was 23 s. The standard deviation obtained for daily analysis of 1.0 ppmvH2O standard gas over 20 days was 9%. Furthermore, the type of industrial gas did not affect the sensitivity. These properties mean the sensor will be applicable to trace water detection in various industrial gases.

Electrodialytic matrix isolation for metal cations

Electrodialytic ion transfer was studied as a matrix isolation tool for heavy metal determinations. An ion transfer device (ITD) was used for the transfer of heavy metal cations. Under optimized flow rates applied voltage and receptor composition, heavy metal ions were quantitatively transferred at concentrations spanning µg L(-1) to mg L(-1). As long as the sample pH was acidic, there was no significant sample pH effect on the transfer efficiencies. Significant salt concentrations (>1 mM NaCl), however, decreased the transfer efficiency. This could be ameliorated (up to 5 mM NaCl) by transient instead of continuous sample introduction. The device was applied to the determination of Fe, Cu and Zn in equine and bovine serum; the reproducibility was better than conventional digestion method.

Flow-based ammonia gas analyzer with an open channel scrubber for indoor environments

A robust and fully automated indoor ammonia gas monitoring system with an open channel scrubber (OCS) was developed. The sample gas channel dimensions, hydrophilic surface treatment to produce a thin absorbing solution layer, and solution flow rate of the OCS were optimized to connect the OCS as in-line gas collector and avoid sample humidity effects. The OCS effluent containing absorbed ammonia in sample gas was injected into a derivatization solution flow. Derivatization was achieved with o-phthalaldehyde and sulfite in pH 11 buffer solution. The product, 1-sulfonateisoindole, is detected with a home-made fluorescence detector. The limit of detection of the analyzer based on three times the standard deviation of baseline noise was 0.9 ppbv. Sample gas could be analyzed 40 times per hour. Furthermore, relative humidity of up to 90% did not interfere considerably with the analyzer. Interference from amines was not observed. The developed gas analysis system was calibrated using a solution-based method. The system was used to analyze ammonia in an indoor environment along with an off-site method, traditional impinger gas collection followed by ion chromatographic analysis, for comparison. The results obtained using both methods agreed well. Therefore, the developed system can perform on-site monitoring of ammonia in indoor environments with improved time resolution compared with that of other methods.

Matrix isolation with an ion transfer device for interference-free simultaneous spectrophotometric determinations of hexavalent and trivalent chromium in a flow-based system

Chromium speciation by spectrophotometric determination of hexavalent chromium (Cr(VI)) with diphenylcarbazide (DPC) has several problems. These include: (1) the inability to directly detect trivalent chromium (Cr(III)) with DPC, (2) positive interference in Cr(VI) determination by other metal cations and (3) negative interference by any reducing agent present in the sample. These are addressed with an ion transfer device (ITD) in a flow injection analysis system. We previously developed the ITD for electrodialytic separations. Here we separate oppositely charged Cr(III) and Cr(VI) species by the ITD into two different acceptor solutions within ~5 s. The acceptor solutions consist of buffered H2O2 to oxidize the Cr(III) to Cr(VI). Then DPC is added to either acceptor to measure Cr(III) and Cr(VI) spectrophotometrically. The system was optimized to provide the same response for Cr(VI) and Cr(III) with limits of detection (LODs, S/N=3) of 0.5 μg L-1 for each and a throughput rate of 30 samples h-1. The ITD separation was also effective for matrix isolation and reduction of interferences. Potential cationic interferences were not transferred into the anionic Cr(VI) acceptor stream. Much of the organic compounds in soil extracts were also eliminated as evidenced from standard addition and recovery studies.

Simultaneous analysis of silicon and boron dissolved in water by combination of electrodialytic salt removal and ion-exclusion chromatography with corona charged aerosol detection

Selective separation and sensitive detection of dissolved silicon and boron (DSi and DB) in aqueous solution was achieved by combining an electrodialytic ion isolation device (EID) as a salt remover, an ion-exclusion chromatography (IEC) column, and a corona charged aerosol detector (CCAD) in sequence. DSi and DB were separated by IEC on the H(+)-form of a cation exchange resin column using pure water eluent. DSi and DB were detected after IEC separation by the CCAD with much greater sensitivity than by conductimetric detection. The five-channel EID, which consisted of anion and cation acceptors, cathode and anode isolators, and a sample channel, removed salt from the sample prior to the IEC-CCAD. DSi and DB were scarcely attracted to the anion accepter in the EID and passed almost quantitatively through the sample channel. Thus, the coupled EID-IEC-CCAD device can isolate DSi and DB from artificial seawater and hot spring water by efficiently removing high concentrations of Cl(-) and SO4(2-) (e.g., 98% and 80% at 0.10molL(-1) each, respectively). The detection limits at a signal-to-noise ratio of 3 were 0.52μmolL(-1) for DSi and 7.1μmolL(-1) for DB. The relative standard deviations (RSD, n=5) of peak areas were 0.12% for DSi and 4.3% for DB.