Ion-exclusion/cation-exchange chromatography with an eluent containing the bile salt-type zwitter... more Ion-exclusion/cation-exchange chromatography with an eluent containing the bile salt-type zwitterionic surfactant CHAPS was performed in order to evaluate variations in anion (SO 4 2− , NO 3 − , and SCN − ) and cation (Na + , K + , NH 4 + , Mg 2+ , and Ca 2+ ) concentrations in human saliva. CHAPS prevents the adsorption of proteins to the stationary phase, i.e., weakly acidic cation-exchange resin, since it aggregates proteins without denaturing them. Addition of 1 mM CHAPS to the eluent comprising 6 mM tartaric acid and 7 mM 18-crown-6 yielded reproducible separations of anions and cations in protein-containing saliva. The resolutions of anions and cations were not significantly affected by the addition of CHAPS to the eluent. The concentrations of Na + and K + varied before and after meals; or that of SCN − , upon smoking. The relative standard deviations of peak areas ranged from 0.3 to 5.1% in 1 day (n = 20) and from 1.4 to 5.8% over 6 days (n = 6).
A micro-gas analysis system, μGAS, is proposed here for the continuous and highly sensitive on-si... more A micro-gas analysis system, μGAS, is proposed here for the continuous and highly sensitive on-site measurement of atmospheric trace gases. The μGAS presented here is comprised of a microchannel scrubber and a high-sensitivity small fluorescence detector. The key to the μGAS is the fabrication of a good gas permeable membrane on a shallow channel to allow for the efficient accumulation of the analyte into the absorbing solution. The channel is formed by micromachining, and a gas permeable membrane of any desired thickness is formed by spin-coating on a fluorosilane-treated substrate. In this work, polydimethylsiloxane was used for both the channel block and the gas permeable membrane, and were easily tightly bonded. The microchannel structure ensures a high sensitivity, and the sensitivity is inversely proportional to the membrane thickness. The device, including the air supply function, is set in only 30-mm-cube. The performance of the μGAS has been demonstrated as a H2S gas sensor. The μGAS consumes only 1ml of the reagent solution in 8h of operation with a detection limit of 1ppbv.
Sequential injection analysis (SIA) was applied to multi-gas monitoring for atmospheric analysis.... more Sequential injection analysis (SIA) was applied to multi-gas monitoring for atmospheric analysis. HONO, NO 2 or NO was collected in an individual diffusion scrubber in which the channel array was filled with either HCl or triethanolamine solution. All analytes were collected in the form of nitrite ions in the scrubber, and were transferred via a 12-port selection valve into a 2.5-ml syringe. The reagent, 3-amino-1,5naphthalenedisulfonic acid (C-acid) solution was subsequently introduced into the syringe, and inter-mixed with the nitrite sample, whereafter the mixed solution was transferred to a heated reactor and held for 3 min at 100 • C. After that, the sample/reagent solution was returned to the syringe and alkalinized. Then, the final solution was analyzed using a homemade fluorescence detector. Atmospheric HONO, NO 2 and NO were successfully monitored 3 or 4 times/h. The limits of detection were 0.22, 0.28 and 0.35 ppbv for HONO, NO 2 and NO, respectively. It was demonstrated for the first time that SIA is a good tool for multi-gas atmospheric analysis. These nitrogen-oxygen compounds are interconvertible, and the simultaneous measurement of these gases is important. Especially, HONO is a source of OH radicals which contribute greatly to atmospheric pollution, and indeed atmospheric chemistry. This method allows the three gases to be measured using one system. The NO 2 and NO data obtained by SIA was compared with those obtained using chemiluminescence instrument. SIA has been successfully applied to atmospheric measurements. Interestingly, it was observed that HONO levels rose toward the end of periods of rain.
A miniaturized planar-membrane-based gas collector of 800 nL internal liquid volume was integrate... more A miniaturized planar-membrane-based gas collector of 800 nL internal liquid volume was integrated with a microfabricated conductivity detector to measure atmospheric SO2. This device is operated with a dilute H2SO4/ H202/2-propanol absorber for a finite integration period (typically, 1.5 min) without liquid flow. During this period, sulfuric acid is formed from SO2 that diffuses into the liquid and accumulates therein. The increase in conductivity with ongoing sampling is measured. The absorber is then replaced with fresh solution, and the process starts anew. The most important factors that govern sensitivity and the detection limit are the choice of the membrane, the nature of the internal collector solution, and the thickness of the solution layer. A porous polypropylene membrane with some 2-propanol (IPA) incorporated in the internal solution was found to be the best combination. The sensitivity was inversely proportional to the solution layer thickness, and a layer thickness of 100 microm resulted in a practical device with good performance characteristics. Greater applied pressure on the gas phase relative to the liquid side also can improve device performance. The system is operated with 12 V DC and does not require a liquid pump. Under optimized conditions, the LOD is 0.7-1.0 ppbv for a sampling period of 1.5 min. The device was field-tested around Mt. Aso in Japan. Changes in ambient SO2 concentrations could be followed with good time resolution. The results are compared with data obtained by a collocated macroscale instrument.
A gas phase chemiluminescence (GPCL)-based method for trace measurement of arsenic has been recen... more A gas phase chemiluminescence (GPCL)-based method for trace measurement of arsenic has been recently described for the measurement of arsenic in water. The principle is based on the reduction of inorganic As to AsH 3 at a controlled pH (the choice of pH governs whether only As(III) or all inorganic As is converted) and the reaction of AsH 3 with O 3 to produce chemiluminescence (Idowu et al., Anal. Chem. 78 (2006) 7088-7097). The same general principle has also been used in postcolumn reaction detection of As, where As species are separated chromatographically, then converted into inorganic As by passing through a UV photochemical reactor followed by AsH 3 generation and CL reaction with ozone (Idowu and Dasgupta, Anal. Chem. 79 ). In the present paper we describe the measurement of As in different soil and dust samples by serial extraction with water, citric acid, sulfuric acid and nitric acid. We also compare parallel measurements for total As by induction coupled plasma mass spectrometry (ICP-MS). As(V) was the only species found in our samples. Because of chloride interference of isobaric ArCl + ICP-MS analyses could only be carried out by standard addition; these results were highly correlated with direct GPCL and LC-GPCL results (r 2 = 0.9935 and 1.0000, respectively). The limit of detection (LOD) in the extracts was 0.36 g/L by direct GPCL compared to 0.1 g/L by ICP-MS. In sulfuric acid-based extracts, the LC-GPCL method provided LODs inferior to those previously observed for water-based standards and were 2.6, 1.3, 6.7, and 6.4 g/L for As(III), As(V), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA), respectively.
Environmental and medical applications Atmospheric analysis Breath and skin gas Microchannel scru... more Environmental and medical applications Atmospheric analysis Breath and skin gas Microchannel scrubbers Micro gas chromatograph Microfluidic devices a b s t r a c t
An open channel scrubber is proposed as a miniature fieldable gas collector. The device is 100 mm... more An open channel scrubber is proposed as a miniature fieldable gas collector. The device is 100 mm in length, 26 mm in width and 22 mm in thickness. The channel bottom is rendered hydrophilic and liquid flows as a thin layer on the bottom. Air sample flows atop the appropriately chosen flowing liquid film and analyte molecules are absorbed into the liquid.
In this paper, novel microsystems for gas analysis and gas generation are described. The same mic... more In this paper, novel microsystems for gas analysis and gas generation are described. The same microchannel devices covered with a gas permeable membrane were used for both the gas collection and the gas generation. For the first time, a dual liquid flow system was utilized in a micro-gas analysis system. Even though micropumps are utilized in the dual line microsystem, a good baseline was obtained in the NO2 measurement with Griess-Saltzman chemistry. The system was developed for on-site measurements in medical treatment; the treatment is of respiratory disease syndrome by NO inhalation and the monitoring is of the product NO and the harmful byproduct NO2. The system was also applied to mobile atmospheric monitoring. Chemical NO generation using the microchannel device was investigated for safe NO inhalation as an alternative to a NO generator based on pulsed arc discharge.
An automated atmospheric elemental mercury analyzer based on the dielectric barrier discharge (DB... more An automated atmospheric elemental mercury analyzer based on the dielectric barrier discharge (DBD) atomic emission technique was developed. The instrument is based on a gold-on tungsten coiled filament preconcentrator fashioned from commercial quartz-halogen lamps, a DBD excitation source and a radiation detector. An in-house program provided system control and data collection. Several types of radiation detectors, e.g., charge coupled device (CCD) array spectrometers, photomultiplier tubes (PMTs) and phototube (PT) are investigated. An argon plasma provided better performance than a nitrogen plasma. With approximately 0.88 standard liters per min sampling rate and preconcentration for 2min, the estimated (S/N=3) detection limit was 0.12ng/L (Hg(0)), the linear range extended at least to 6.6ngHg/L. Typical RSD values for determination at the single digit ng/L level ranged from 2.8 to 4.9%. In 19 separate calibrations conducted over 7 days, the calibration slope had a standard error of 1%. The system was applied to the determination of atmospheric mercury in two different locations.
We describe a novel optical sensor for the simultaneous measurement of atmospheric nitrogen dioxi... more We describe a novel optical sensor for the simultaneous measurement of atmospheric nitrogen dioxide (NO(2)), ozone (O(3)), and relative humidity (RH). A transparent backing thin layer silica gel chromatographic plate impregnated with 8-amino-1-naphthol-5-sulfonic acid (ANS) is used as the collection/sensor element. The plate transmittance is probed by three discrete light emitting diodes (LEDs) centered, respectively, at 442, 525, and 850 nm. The transmission of the plate changes reversibly across visible to NIR wavelengths as the RH around the plate changes; this is the basis for a limited-resolution RH sensor. The ANS on the plate reacts to form brown and pink colored products, respectively, when it reacts with NO(2) and O(3). The sample air impinges on the plate via an entrance nozzle. The LEDs are alternately turned on in a preprogrammed manner and the light is brought to the impregnated face of the plate by a three-legged fiber optic. The transmitted light is detected on the obverse side of the plate. The 850 nm signal provides the RH value and optionally serves as the reference measurement for the other two wavelengths; the NO(2) and O(3) reaction products do not absorb at this wavelength. The absorbance at 442 and 525 nm, thus referenced against 850 nm, are used to obtain NO(2) and O(3) concentrations from a pair of simultaneous equations. For a sampling period of 5 min, the limits of detection (LOD) based on 3 times the standard deviation of blank responses were 0.64 and 0.42 ppbv for NO(2) and O(3), respectively. Data obtained with collocated commercial instruments (O(3) induced chemiluminescence analyzer for NO(2) and UV-absorption for O(3)) show good agreement. Overall, this provides a viable affordable approach for inexpensive measurement of atmospheric NO(2) and O(3).
Emission variability of hydrogen sulfide and sulfur dioxide from tidal flat sediments to atmosphe... more Emission variability of hydrogen sulfide and sulfur dioxide from tidal flat sediments to atmosphere in Ariake Sea, Japan was studied using a diffusion scrubber-based portable instrument. Ariake Sea is a typical closed sea consisting of a huge marsh area along the coast. Seasonal, spatial and diurnal variability in emission rates were examined. In addition, depth profiles of the gas emissions were examined with the profiles of anions, heavy metals, water and organic contents. Unexpectedly, SO 2 emission was much higher than H 2 S in all measurements, while an opposite emission trend was observed in diurnal and spatial patterns of H 2 S and SO 2 emissions. The mechanisms of these gas emissions are discussed. Total sulfur fluxes to the atmosphere as H 2 S and SO 2 during the study averaged 7.1 mg S m À2 h À1 for muddy sites and 28 mg S m À2 h À1 for sandy sites. Sulfur fluxes from tidal flats were comparable to the artificial sulfur emission from the neighboring towns. r
This manuscript describes an easy, simple and small system for gas generation. The aim of this wo... more This manuscript describes an easy, simple and small system for gas generation. The aim of this work was to establish gas generation for on-site checking or on-site calibration of a micro gas analysis system, microGAS. The new technology, microGAS, achieves real-time measurement of trace level gases in the field. To make the measurement more reliable and convenient, a small gas generation system has been developed. Source reagent solution and generator solution are made to flow by micropumps, mixed in a miniature coil, and then introduced into a microchannel gas desorber. The gas desorber is comprised of a honeycomb-shaped microchannel covered with a thin porous polytetrafluoroethylene membrane. A good generation factor is obtained due to the wide vaporization area and thin solution layer of the microchannel desorber. Generation of H(2)S, SO(2), CH(3)SH and NH(3) gases were examined. Concentrations of the gases are easily controlled by the source reagent concentration and the solution flow rates. At 100 microL min(-1) flow rates for both the source and generator solutions, 30 ppbv to 2 ppmv concentrations are formed with a gas flow rate of 200 mL min(-1). The gas concentration is proportional to the source concentration. The gas generation can be performed only when needed. The gas generation system is combined with microGAS for on-site calibration.
We describe a membrane-based collection/analysis system that differentially monitors H2S and CH3S... more We describe a membrane-based collection/analysis system that differentially monitors H2S and CH3SH, and to which a conductometric SO2 analyzer using the same collector was coupled. A diffusion scrubber (DS) comprised of a Nafion tube collects H2S selectively while a porous polytetrafluoroethylene (pPTFE) DS collects both H2S and CH3SH. Both gases are measured via their ability to react with fluorescein mercuric acetate (FMA) which results in decreased fluorescence. The limited dynamic range of a negative signal procedure was overcome by using dual DS units comprised of short and long scrubbers, placed serially in the liquid flow line. Different DS designs and membrane materials were investigated. H2S, CH3SH, and SO2 from a biogenic point source were continuously measured, and the H2S/CH3SH data compared well with a standard procedure involving Tedlar bag collection, preconcentration and thermal desorption from a Tenax trap, and measurement by gas chromatography/flame photometric detection. Walkaround portability of the instrument and very large dynamic range measurement of H2S and SO2 were demonstrated around the Mt. Aso volcano.
A simple, automated method for the measurement of methyl mercaptan (CH 3 SH) and dimethyl sulfide... more A simple, automated method for the measurement of methyl mercaptan (CH 3 SH) and dimethyl sulfide (DMS) has been investigated. These two sulfur gases have strong and unpleasant odors. The collection and separation are performed in sequence with a single short column packed with silica gel powder. CH 3 SH and DMS are separated according to their desorption temperatures and introduced into a chemiluminescence cell in this order. These two gases emit strong chemiluminescence by reaction with ozone. The calibration curves obtained are linear, which is superior to flame photometric detection of these substances. The whole system, including a small cylinder for the carrier nitrogen, can be set in a portable box. The instrument is applicable to breath odor analysis, and automated measurement of room air can also be performed. In toilet air analysis, it was observed that levels of the sulfur gases increased after dark. With this instrument, sulfur gases at a ppbv level are successfully measured by a simple procedure without much interference.
Perchlorate, thiocyanate, and iodine excretion in urine and milk of 13 breastfeeding women was in... more Perchlorate, thiocyanate, and iodine excretion in urine and milk of 13 breastfeeding women was investigated and the results were interpreted by a model of parallel/competitive transport of these species bythe sodium iodide symporter. For each species i, we assumed physiological homeostasis, where i(T,in) equals the corresponding total excretion in urine and milk (i(e,u) + i(e,m)). The fraction of the total excretion that appeared in milk f(I,m) was measured and ranged from 0.394-0.781, 0.018-0.144, and 0.086-0.464 for perchlorate,thiocyanate, and iodine, respectively. The corresponding median values were 0.541, 0.053, and 0.177, respectively. The selectivity factors of perchlorate over iodide transport, and thiocyanate over iodide transport, defined as f(PC,m)/ f(I,m), and f(SCN,m)/ f(I,m), respectively, were 3.14 +/- 1.20 and 0.27 +/- 0.26 while PC(T,in), SCN(T,in), and I(T,in) among individuals varied 4.9, 5.0, and 8.4x, respectively. These transport selectivities are an order of magnitude lower than those indicated by in vitro studies, suggesting that the impact of both these anions on inhibiting iodide transport in milk may have been overestimated in the extant literature. On the other hand, our results showed that 12 of 13 infants did not have an adequate intake of iodine as defined by the Institute of Medicine and 9 out of 13 infants were likely ingesting perchlorate at a level exceeding the reference dose suggested bythe National Academy of Science panel.
We describe a flow-through ionic charge detector in the form of a three-compartmented system. A c... more We describe a flow-through ionic charge detector in the form of a three-compartmented system. A central water channel is separated from two outer channels bearing water (or a dilute electrolyte) by a cation-exchange membrane (CEM) and an anion-exchange membrane (AEM). Independent fluid input/output ports address all channels. One platinum electrode is put in each outer channel. When the AEM-side electrode is positive with respect to the CEM-side electrode and voltage (approximately 1-10 V) is applied, the observed background current is from the transport of H(+)/OH(-) through the CEM/AEM to the negative/positive electrodes, respectively. The H(+) and OH(-) are generated by the ionization of water, in part aided by the electric field. If an electrolyte (X(+)Y(-)) is injected in to the central channel, X(+) and Y(-) migrate through the CEM and AEM to the negative and positive electrodes, respectively, and generate a current pulse. The integrated area of the current signal (coulombs) elicited by this electrolyte injection is dependent on a number of variables, the most important being the central channel residence time and the applied voltage (V(app)); these govern the transport of the injected electrolyte to/through the membranes. Other parameters include electrode placement, fluid composition, and outer channel flow rates. For strong electrolytes, depending on the operating conditions, the current peak area (hereinafter called the measured charge signal, Q(m)) can both be less or more than the charge represented by the electrolyte injected (Q(i)). Q(m) is less than Q(i) if transport to/through the membranes is subquantitative. Q(m) can be greater than Q(i) at higher V(app). At constant V(app) more voltage is dropped across the membranes as the central channel becomes more conductive and water dissociation at the membrane surface is enhanced. Effectively, the membranes experience a greater applied voltage as the central channel becomes more conductive. The resulting additional current accompanying analyte introduction to the detector can substantially augment Q(m). Thus, the device is not an absolute coulometer although V(app) can be deliberately chosen to have Q(m) = Q(i) over at least a 10-fold concentration range. Importantly, equivalent amounts of diverse strong electrolytes (with substantially different conductivities) injected into the central channel produce the same charge signals. In ion chromatography, this results in identical calibration curves for all strong acid anions, obviating individual calibrations. Whereas with a conductivity detector (CD) only the ionized portion of a weak electrolyte responds, in the present charge detector (ChD), ions are actually removed, leading to further ionization and the detection of a proportionately greater analyte amount.
A honeycomb structure microchannel scrubber was developed to achieve efficient and stable gas col... more A honeycomb structure microchannel scrubber was developed to achieve efficient and stable gas collection. A thin porous membrane was pasted on a microchannel by the adhesive force of a fresh polydimethylsiloxane surface. The microchannel scrubber achieved much more efficient gas collection than conventional impingers and diffusion scrubbers. Two sets of the microchannel scrubbers and detectors were integrated in a 10 cm x 9 cm plastic board to create a micro gas analysis system (microGAS) for simultaneous measurements of H2S and SO2. The whole system including a battery was incorporated in a carrying case 34 cm W x 16 cm D x 17 cm H for use in the field. Liquid flows at 30 microl min(-1) were obtained by bimetal micropumps. The estimated detection limits were 0.1 ppbv for H2S and 1 ppbv for SO2. The system was demonstrated for real atmospheric gas analysis, and the results agreed well with data concurrently obtained by ion chromatography coupled with a cylindrical diffusion scrubber. The system we developed allowed automated continuous analyses in the field and achieved a much higher time resolution compared to those by ion chromatographic analysis.
Accurate liquid flow control is important in most chemical analyses. In this work, the measuremen... more Accurate liquid flow control is important in most chemical analyses. In this work, the measurement of liquid flow in microliters per minute was performed, and feedback control of the flow rate was examined. The flow sensor was arranged on a channel made in a polydimethylsiloxane (PDMS) block. The center of the channel was cooled by a miniature Peltier device, and the change in temperature balance along the channel formed by the flow was measured by two temperature sensors. Using this flow sensor, feedback flow control was examined with two pumping methods. One was the electroosmotic flow method, made by applying a high voltage (HV) between the reagent and waste reservoirs; the other was the piezo valve method, in which a micro-valve-seat was fabricated in a PDMS cavity with a silicone diaphragm. The latter was adopted for a micro gas analysis system (microGAS) for measuring atmospheric H2S and SO2. The obtained baselines were stable, and better limits of detection were obtained.
Ion-exclusion/cation-exchange chromatography with an eluent containing the bile salt-type zwitter... more Ion-exclusion/cation-exchange chromatography with an eluent containing the bile salt-type zwitterionic surfactant CHAPS was performed in order to evaluate variations in anion (SO 4 2− , NO 3 − , and SCN − ) and cation (Na + , K + , NH 4 + , Mg 2+ , and Ca 2+ ) concentrations in human saliva. CHAPS prevents the adsorption of proteins to the stationary phase, i.e., weakly acidic cation-exchange resin, since it aggregates proteins without denaturing them. Addition of 1 mM CHAPS to the eluent comprising 6 mM tartaric acid and 7 mM 18-crown-6 yielded reproducible separations of anions and cations in protein-containing saliva. The resolutions of anions and cations were not significantly affected by the addition of CHAPS to the eluent. The concentrations of Na + and K + varied before and after meals; or that of SCN − , upon smoking. The relative standard deviations of peak areas ranged from 0.3 to 5.1% in 1 day (n = 20) and from 1.4 to 5.8% over 6 days (n = 6).
A micro-gas analysis system, μGAS, is proposed here for the continuous and highly sensitive on-si... more A micro-gas analysis system, μGAS, is proposed here for the continuous and highly sensitive on-site measurement of atmospheric trace gases. The μGAS presented here is comprised of a microchannel scrubber and a high-sensitivity small fluorescence detector. The key to the μGAS is the fabrication of a good gas permeable membrane on a shallow channel to allow for the efficient accumulation of the analyte into the absorbing solution. The channel is formed by micromachining, and a gas permeable membrane of any desired thickness is formed by spin-coating on a fluorosilane-treated substrate. In this work, polydimethylsiloxane was used for both the channel block and the gas permeable membrane, and were easily tightly bonded. The microchannel structure ensures a high sensitivity, and the sensitivity is inversely proportional to the membrane thickness. The device, including the air supply function, is set in only 30-mm-cube. The performance of the μGAS has been demonstrated as a H2S gas sensor. The μGAS consumes only 1ml of the reagent solution in 8h of operation with a detection limit of 1ppbv.
Sequential injection analysis (SIA) was applied to multi-gas monitoring for atmospheric analysis.... more Sequential injection analysis (SIA) was applied to multi-gas monitoring for atmospheric analysis. HONO, NO 2 or NO was collected in an individual diffusion scrubber in which the channel array was filled with either HCl or triethanolamine solution. All analytes were collected in the form of nitrite ions in the scrubber, and were transferred via a 12-port selection valve into a 2.5-ml syringe. The reagent, 3-amino-1,5naphthalenedisulfonic acid (C-acid) solution was subsequently introduced into the syringe, and inter-mixed with the nitrite sample, whereafter the mixed solution was transferred to a heated reactor and held for 3 min at 100 • C. After that, the sample/reagent solution was returned to the syringe and alkalinized. Then, the final solution was analyzed using a homemade fluorescence detector. Atmospheric HONO, NO 2 and NO were successfully monitored 3 or 4 times/h. The limits of detection were 0.22, 0.28 and 0.35 ppbv for HONO, NO 2 and NO, respectively. It was demonstrated for the first time that SIA is a good tool for multi-gas atmospheric analysis. These nitrogen-oxygen compounds are interconvertible, and the simultaneous measurement of these gases is important. Especially, HONO is a source of OH radicals which contribute greatly to atmospheric pollution, and indeed atmospheric chemistry. This method allows the three gases to be measured using one system. The NO 2 and NO data obtained by SIA was compared with those obtained using chemiluminescence instrument. SIA has been successfully applied to atmospheric measurements. Interestingly, it was observed that HONO levels rose toward the end of periods of rain.
A miniaturized planar-membrane-based gas collector of 800 nL internal liquid volume was integrate... more A miniaturized planar-membrane-based gas collector of 800 nL internal liquid volume was integrated with a microfabricated conductivity detector to measure atmospheric SO2. This device is operated with a dilute H2SO4/ H202/2-propanol absorber for a finite integration period (typically, 1.5 min) without liquid flow. During this period, sulfuric acid is formed from SO2 that diffuses into the liquid and accumulates therein. The increase in conductivity with ongoing sampling is measured. The absorber is then replaced with fresh solution, and the process starts anew. The most important factors that govern sensitivity and the detection limit are the choice of the membrane, the nature of the internal collector solution, and the thickness of the solution layer. A porous polypropylene membrane with some 2-propanol (IPA) incorporated in the internal solution was found to be the best combination. The sensitivity was inversely proportional to the solution layer thickness, and a layer thickness of 100 microm resulted in a practical device with good performance characteristics. Greater applied pressure on the gas phase relative to the liquid side also can improve device performance. The system is operated with 12 V DC and does not require a liquid pump. Under optimized conditions, the LOD is 0.7-1.0 ppbv for a sampling period of 1.5 min. The device was field-tested around Mt. Aso in Japan. Changes in ambient SO2 concentrations could be followed with good time resolution. The results are compared with data obtained by a collocated macroscale instrument.
A gas phase chemiluminescence (GPCL)-based method for trace measurement of arsenic has been recen... more A gas phase chemiluminescence (GPCL)-based method for trace measurement of arsenic has been recently described for the measurement of arsenic in water. The principle is based on the reduction of inorganic As to AsH 3 at a controlled pH (the choice of pH governs whether only As(III) or all inorganic As is converted) and the reaction of AsH 3 with O 3 to produce chemiluminescence (Idowu et al., Anal. Chem. 78 (2006) 7088-7097). The same general principle has also been used in postcolumn reaction detection of As, where As species are separated chromatographically, then converted into inorganic As by passing through a UV photochemical reactor followed by AsH 3 generation and CL reaction with ozone (Idowu and Dasgupta, Anal. Chem. 79 ). In the present paper we describe the measurement of As in different soil and dust samples by serial extraction with water, citric acid, sulfuric acid and nitric acid. We also compare parallel measurements for total As by induction coupled plasma mass spectrometry (ICP-MS). As(V) was the only species found in our samples. Because of chloride interference of isobaric ArCl + ICP-MS analyses could only be carried out by standard addition; these results were highly correlated with direct GPCL and LC-GPCL results (r 2 = 0.9935 and 1.0000, respectively). The limit of detection (LOD) in the extracts was 0.36 g/L by direct GPCL compared to 0.1 g/L by ICP-MS. In sulfuric acid-based extracts, the LC-GPCL method provided LODs inferior to those previously observed for water-based standards and were 2.6, 1.3, 6.7, and 6.4 g/L for As(III), As(V), dimethylarsinic acid (DMA) and monomethylarsonic acid (MMA), respectively.
Environmental and medical applications Atmospheric analysis Breath and skin gas Microchannel scru... more Environmental and medical applications Atmospheric analysis Breath and skin gas Microchannel scrubbers Micro gas chromatograph Microfluidic devices a b s t r a c t
An open channel scrubber is proposed as a miniature fieldable gas collector. The device is 100 mm... more An open channel scrubber is proposed as a miniature fieldable gas collector. The device is 100 mm in length, 26 mm in width and 22 mm in thickness. The channel bottom is rendered hydrophilic and liquid flows as a thin layer on the bottom. Air sample flows atop the appropriately chosen flowing liquid film and analyte molecules are absorbed into the liquid.
In this paper, novel microsystems for gas analysis and gas generation are described. The same mic... more In this paper, novel microsystems for gas analysis and gas generation are described. The same microchannel devices covered with a gas permeable membrane were used for both the gas collection and the gas generation. For the first time, a dual liquid flow system was utilized in a micro-gas analysis system. Even though micropumps are utilized in the dual line microsystem, a good baseline was obtained in the NO2 measurement with Griess-Saltzman chemistry. The system was developed for on-site measurements in medical treatment; the treatment is of respiratory disease syndrome by NO inhalation and the monitoring is of the product NO and the harmful byproduct NO2. The system was also applied to mobile atmospheric monitoring. Chemical NO generation using the microchannel device was investigated for safe NO inhalation as an alternative to a NO generator based on pulsed arc discharge.
An automated atmospheric elemental mercury analyzer based on the dielectric barrier discharge (DB... more An automated atmospheric elemental mercury analyzer based on the dielectric barrier discharge (DBD) atomic emission technique was developed. The instrument is based on a gold-on tungsten coiled filament preconcentrator fashioned from commercial quartz-halogen lamps, a DBD excitation source and a radiation detector. An in-house program provided system control and data collection. Several types of radiation detectors, e.g., charge coupled device (CCD) array spectrometers, photomultiplier tubes (PMTs) and phototube (PT) are investigated. An argon plasma provided better performance than a nitrogen plasma. With approximately 0.88 standard liters per min sampling rate and preconcentration for 2min, the estimated (S/N=3) detection limit was 0.12ng/L (Hg(0)), the linear range extended at least to 6.6ngHg/L. Typical RSD values for determination at the single digit ng/L level ranged from 2.8 to 4.9%. In 19 separate calibrations conducted over 7 days, the calibration slope had a standard error of 1%. The system was applied to the determination of atmospheric mercury in two different locations.
We describe a novel optical sensor for the simultaneous measurement of atmospheric nitrogen dioxi... more We describe a novel optical sensor for the simultaneous measurement of atmospheric nitrogen dioxide (NO(2)), ozone (O(3)), and relative humidity (RH). A transparent backing thin layer silica gel chromatographic plate impregnated with 8-amino-1-naphthol-5-sulfonic acid (ANS) is used as the collection/sensor element. The plate transmittance is probed by three discrete light emitting diodes (LEDs) centered, respectively, at 442, 525, and 850 nm. The transmission of the plate changes reversibly across visible to NIR wavelengths as the RH around the plate changes; this is the basis for a limited-resolution RH sensor. The ANS on the plate reacts to form brown and pink colored products, respectively, when it reacts with NO(2) and O(3). The sample air impinges on the plate via an entrance nozzle. The LEDs are alternately turned on in a preprogrammed manner and the light is brought to the impregnated face of the plate by a three-legged fiber optic. The transmitted light is detected on the obverse side of the plate. The 850 nm signal provides the RH value and optionally serves as the reference measurement for the other two wavelengths; the NO(2) and O(3) reaction products do not absorb at this wavelength. The absorbance at 442 and 525 nm, thus referenced against 850 nm, are used to obtain NO(2) and O(3) concentrations from a pair of simultaneous equations. For a sampling period of 5 min, the limits of detection (LOD) based on 3 times the standard deviation of blank responses were 0.64 and 0.42 ppbv for NO(2) and O(3), respectively. Data obtained with collocated commercial instruments (O(3) induced chemiluminescence analyzer for NO(2) and UV-absorption for O(3)) show good agreement. Overall, this provides a viable affordable approach for inexpensive measurement of atmospheric NO(2) and O(3).
Emission variability of hydrogen sulfide and sulfur dioxide from tidal flat sediments to atmosphe... more Emission variability of hydrogen sulfide and sulfur dioxide from tidal flat sediments to atmosphere in Ariake Sea, Japan was studied using a diffusion scrubber-based portable instrument. Ariake Sea is a typical closed sea consisting of a huge marsh area along the coast. Seasonal, spatial and diurnal variability in emission rates were examined. In addition, depth profiles of the gas emissions were examined with the profiles of anions, heavy metals, water and organic contents. Unexpectedly, SO 2 emission was much higher than H 2 S in all measurements, while an opposite emission trend was observed in diurnal and spatial patterns of H 2 S and SO 2 emissions. The mechanisms of these gas emissions are discussed. Total sulfur fluxes to the atmosphere as H 2 S and SO 2 during the study averaged 7.1 mg S m À2 h À1 for muddy sites and 28 mg S m À2 h À1 for sandy sites. Sulfur fluxes from tidal flats were comparable to the artificial sulfur emission from the neighboring towns. r
This manuscript describes an easy, simple and small system for gas generation. The aim of this wo... more This manuscript describes an easy, simple and small system for gas generation. The aim of this work was to establish gas generation for on-site checking or on-site calibration of a micro gas analysis system, microGAS. The new technology, microGAS, achieves real-time measurement of trace level gases in the field. To make the measurement more reliable and convenient, a small gas generation system has been developed. Source reagent solution and generator solution are made to flow by micropumps, mixed in a miniature coil, and then introduced into a microchannel gas desorber. The gas desorber is comprised of a honeycomb-shaped microchannel covered with a thin porous polytetrafluoroethylene membrane. A good generation factor is obtained due to the wide vaporization area and thin solution layer of the microchannel desorber. Generation of H(2)S, SO(2), CH(3)SH and NH(3) gases were examined. Concentrations of the gases are easily controlled by the source reagent concentration and the solution flow rates. At 100 microL min(-1) flow rates for both the source and generator solutions, 30 ppbv to 2 ppmv concentrations are formed with a gas flow rate of 200 mL min(-1). The gas concentration is proportional to the source concentration. The gas generation can be performed only when needed. The gas generation system is combined with microGAS for on-site calibration.
We describe a membrane-based collection/analysis system that differentially monitors H2S and CH3S... more We describe a membrane-based collection/analysis system that differentially monitors H2S and CH3SH, and to which a conductometric SO2 analyzer using the same collector was coupled. A diffusion scrubber (DS) comprised of a Nafion tube collects H2S selectively while a porous polytetrafluoroethylene (pPTFE) DS collects both H2S and CH3SH. Both gases are measured via their ability to react with fluorescein mercuric acetate (FMA) which results in decreased fluorescence. The limited dynamic range of a negative signal procedure was overcome by using dual DS units comprised of short and long scrubbers, placed serially in the liquid flow line. Different DS designs and membrane materials were investigated. H2S, CH3SH, and SO2 from a biogenic point source were continuously measured, and the H2S/CH3SH data compared well with a standard procedure involving Tedlar bag collection, preconcentration and thermal desorption from a Tenax trap, and measurement by gas chromatography/flame photometric detection. Walkaround portability of the instrument and very large dynamic range measurement of H2S and SO2 were demonstrated around the Mt. Aso volcano.
A simple, automated method for the measurement of methyl mercaptan (CH 3 SH) and dimethyl sulfide... more A simple, automated method for the measurement of methyl mercaptan (CH 3 SH) and dimethyl sulfide (DMS) has been investigated. These two sulfur gases have strong and unpleasant odors. The collection and separation are performed in sequence with a single short column packed with silica gel powder. CH 3 SH and DMS are separated according to their desorption temperatures and introduced into a chemiluminescence cell in this order. These two gases emit strong chemiluminescence by reaction with ozone. The calibration curves obtained are linear, which is superior to flame photometric detection of these substances. The whole system, including a small cylinder for the carrier nitrogen, can be set in a portable box. The instrument is applicable to breath odor analysis, and automated measurement of room air can also be performed. In toilet air analysis, it was observed that levels of the sulfur gases increased after dark. With this instrument, sulfur gases at a ppbv level are successfully measured by a simple procedure without much interference.
Perchlorate, thiocyanate, and iodine excretion in urine and milk of 13 breastfeeding women was in... more Perchlorate, thiocyanate, and iodine excretion in urine and milk of 13 breastfeeding women was investigated and the results were interpreted by a model of parallel/competitive transport of these species bythe sodium iodide symporter. For each species i, we assumed physiological homeostasis, where i(T,in) equals the corresponding total excretion in urine and milk (i(e,u) + i(e,m)). The fraction of the total excretion that appeared in milk f(I,m) was measured and ranged from 0.394-0.781, 0.018-0.144, and 0.086-0.464 for perchlorate,thiocyanate, and iodine, respectively. The corresponding median values were 0.541, 0.053, and 0.177, respectively. The selectivity factors of perchlorate over iodide transport, and thiocyanate over iodide transport, defined as f(PC,m)/ f(I,m), and f(SCN,m)/ f(I,m), respectively, were 3.14 +/- 1.20 and 0.27 +/- 0.26 while PC(T,in), SCN(T,in), and I(T,in) among individuals varied 4.9, 5.0, and 8.4x, respectively. These transport selectivities are an order of magnitude lower than those indicated by in vitro studies, suggesting that the impact of both these anions on inhibiting iodide transport in milk may have been overestimated in the extant literature. On the other hand, our results showed that 12 of 13 infants did not have an adequate intake of iodine as defined by the Institute of Medicine and 9 out of 13 infants were likely ingesting perchlorate at a level exceeding the reference dose suggested bythe National Academy of Science panel.
We describe a flow-through ionic charge detector in the form of a three-compartmented system. A c... more We describe a flow-through ionic charge detector in the form of a three-compartmented system. A central water channel is separated from two outer channels bearing water (or a dilute electrolyte) by a cation-exchange membrane (CEM) and an anion-exchange membrane (AEM). Independent fluid input/output ports address all channels. One platinum electrode is put in each outer channel. When the AEM-side electrode is positive with respect to the CEM-side electrode and voltage (approximately 1-10 V) is applied, the observed background current is from the transport of H(+)/OH(-) through the CEM/AEM to the negative/positive electrodes, respectively. The H(+) and OH(-) are generated by the ionization of water, in part aided by the electric field. If an electrolyte (X(+)Y(-)) is injected in to the central channel, X(+) and Y(-) migrate through the CEM and AEM to the negative and positive electrodes, respectively, and generate a current pulse. The integrated area of the current signal (coulombs) elicited by this electrolyte injection is dependent on a number of variables, the most important being the central channel residence time and the applied voltage (V(app)); these govern the transport of the injected electrolyte to/through the membranes. Other parameters include electrode placement, fluid composition, and outer channel flow rates. For strong electrolytes, depending on the operating conditions, the current peak area (hereinafter called the measured charge signal, Q(m)) can both be less or more than the charge represented by the electrolyte injected (Q(i)). Q(m) is less than Q(i) if transport to/through the membranes is subquantitative. Q(m) can be greater than Q(i) at higher V(app). At constant V(app) more voltage is dropped across the membranes as the central channel becomes more conductive and water dissociation at the membrane surface is enhanced. Effectively, the membranes experience a greater applied voltage as the central channel becomes more conductive. The resulting additional current accompanying analyte introduction to the detector can substantially augment Q(m). Thus, the device is not an absolute coulometer although V(app) can be deliberately chosen to have Q(m) = Q(i) over at least a 10-fold concentration range. Importantly, equivalent amounts of diverse strong electrolytes (with substantially different conductivities) injected into the central channel produce the same charge signals. In ion chromatography, this results in identical calibration curves for all strong acid anions, obviating individual calibrations. Whereas with a conductivity detector (CD) only the ionized portion of a weak electrolyte responds, in the present charge detector (ChD), ions are actually removed, leading to further ionization and the detection of a proportionately greater analyte amount.
A honeycomb structure microchannel scrubber was developed to achieve efficient and stable gas col... more A honeycomb structure microchannel scrubber was developed to achieve efficient and stable gas collection. A thin porous membrane was pasted on a microchannel by the adhesive force of a fresh polydimethylsiloxane surface. The microchannel scrubber achieved much more efficient gas collection than conventional impingers and diffusion scrubbers. Two sets of the microchannel scrubbers and detectors were integrated in a 10 cm x 9 cm plastic board to create a micro gas analysis system (microGAS) for simultaneous measurements of H2S and SO2. The whole system including a battery was incorporated in a carrying case 34 cm W x 16 cm D x 17 cm H for use in the field. Liquid flows at 30 microl min(-1) were obtained by bimetal micropumps. The estimated detection limits were 0.1 ppbv for H2S and 1 ppbv for SO2. The system was demonstrated for real atmospheric gas analysis, and the results agreed well with data concurrently obtained by ion chromatography coupled with a cylindrical diffusion scrubber. The system we developed allowed automated continuous analyses in the field and achieved a much higher time resolution compared to those by ion chromatographic analysis.
Accurate liquid flow control is important in most chemical analyses. In this work, the measuremen... more Accurate liquid flow control is important in most chemical analyses. In this work, the measurement of liquid flow in microliters per minute was performed, and feedback control of the flow rate was examined. The flow sensor was arranged on a channel made in a polydimethylsiloxane (PDMS) block. The center of the channel was cooled by a miniature Peltier device, and the change in temperature balance along the channel formed by the flow was measured by two temperature sensors. Using this flow sensor, feedback flow control was examined with two pumping methods. One was the electroosmotic flow method, made by applying a high voltage (HV) between the reagent and waste reservoirs; the other was the piezo valve method, in which a micro-valve-seat was fabricated in a PDMS cavity with a silicone diaphragm. The latter was adopted for a micro gas analysis system (microGAS) for measuring atmospheric H2S and SO2. The obtained baselines were stable, and better limits of detection were obtained.
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Papers by Shin-Ichi Ohira