The development of an automated continuous measurement system for the monitoring of HCHO and CH3CHO in the atmosphere by using an annular diffusion scrubber coupled to HPLC

An automated continuous measurement system for the monitoring of formaldehyde (HCHO) and acetaldehyde (CH₃CHO) in the urban atmosphere was developed by using an annular diffusion scrubber in conjunction with a high-performance liquid chromatograph (HPLC). With this technique, atmospheric HCHO and CH₃CHO were effectively collected by the annular diffusion scrubber which consists of a porous polytetrafluoroethylene (PTFE) tube disposed concentrically within a Pyrex-glass tube and a scrubbing solution. 2,4-Dinitrophenylhydrazine (DNPH) was selected as the scrubbing solution for collecting HCHO and CH₃CHO, which are derivatized to 2,4-dinitrophenylhydrazone-formaldehyde (DNPH-HCHO) and 2,4-dinitrophenylhydrazone-acetaldehyde (DNPH-CH₃CHO), respectively. An aliquot of the sample solution was automatically injected into an HPLC equipped with a semi-micro ODS column and a UV-VIS detector for separating and determining DNPH-HCHO and DNPH-CH₃CHO. All the operations are sequenced by a programmable controller, and automated continuous measurements are performed with a typical temporal resolution of 1 h. The collection efficiencies of HCHO and CH₃CHO were about 97% and 93%, respectively, at an air flow rate of 0.2 L/min. The lower detection limits (3σ of the blank hydrazones) of HCHO and CH₃CHO were 0.05 ppbv and 0.10 ppbv, respectively, in the case of 12-L air sample volume. Analytical response of a standard solution of DNPH-HCHO and DNPH-CH₃CHO by the HPLC during a 10-day continuous measurement was unchanged and the relative standard deviation (RSD) was < 1.0%. Interferences from O₃ and NO₂ were insignificant in this annular diffusion scrubber method. Both for HCHO and CH₃CHO measurements, concentrations from this developed system well agreed with those measured by a DNPH Silica cartridge method.     

Development of an automated measurement system using a diffusion scrubber and high-performance liquid chromatography for the monitoring of formaldehyde and acetaldehyde in automotive exhaust gas.

An automated measurement system for monitoring formaldehyde (HCHO) and acetaldehyde (CH3CHO) in automotive exhaust gas by using a diffusion scrubber in combination with high-performance liquid chromatography (HPLC) was developed. HCHO and CH3CHO are effectively collected by the diffusion scrubber, which consists of a hydrophobic porous PTFE tube disposed concentrically within a Pyrex-glass tube and a scrubbing solution. 2,4-Dinitrophenylhydrazine is used as the scrubbing solution for trapping HCHO and CH3CHO, which are derivatized to formaldehyde 2,4-dinitrophenylhydrazone (DNPH-HCHO) and acetaldehyde 2,4-dinitrophenylhydrazone (DNPH-CH3CHO), respectively, with phosphoric acid as an acid catalyst. After the collection of the gas sample, the sample solution in the diffusion scrubber is injected into the HPLC system and DNPH-HCHO and DNPH-CH3CHO are separated and determined. All measurement operations are sequenced by a programmable controller and an automated continuous measurement can be performed at 10 min intervals. The collection efficiencies of HCHO and CH3CHO were higher than 97% at a gas flow rate of 0.21 min-1. The detection limit (3 sigma of the blank value) was 0.001 ppm v/v for HCHO and CH3CHO for a 1.61 gas sample volume. No interference of co-existing nitrogen dioxide (NO2) in the collection of HCHO and CH3CHO was observed. The average concentration of HCHO in the exhaust gas from methanol-fueled vehicles was 77.3 ppm v/v (n = 5) in the cold-phase mode when engines were first started. In the hot-phase mode, the average concentration of HCHO was 3.3 ppm v/v (n = 15). The concentrations of HCHO measured by this automated measurement system were in good agreement with those obtained using the impinger-HPLC method.     

Enzyme-based online monitoring and measurement of antioxidant activity using an optical oxygen sensor coupled to an HPLC system

It is estimated that up to 50 % of the adult population take antioxidant products on a daily basis to promote their health status. Strangely, despite the well-recognized importance of antioxidants, currently there is no international standard index for labeling owing to the lack of standardized methods for antioxidant measurement in complex products. Here, an online high-performance liquid chromatography (HPLC)-based method to detect and measure the total antioxidant capacity of antioxidant samples is presented. In this approach, complex samples containing antioxidants are separated by the HPLC system, which is further coupled to an antioxidant measuring system consisting of an optical oxygen sensor, laccase, and tetramethoxy azobismethylene quinone (TMAMQ). The antioxidants, separated via HPLC, reduce TMAMQ to syringaldazine, which is then reoxidized by laccase while simultaneously consuming O₂. The amount of consumed oxygen is directly proportional to the concentration of antioxidants and is measured by the optical oxygen sensor. The sensor is fabricated by coating a glass capillary with an oxygen-sensitive thin layer made of platinum(II) meso-tetra(4-fluorophenyl)tetrabenzoporphyrin and polystyrene, which makes real-time analysis possible (t ₉₀?=?1.1 s in solution). Four selected antioxidants (3 mM), namely, catechin, ferulic acid, naringenin (used as a control), and Trolox, representing flavonol, hydrocinnamic acid, flavanone, and vitamin E, respectively, were injected into the online antioxidant monitoring system, separated, and then mixed with the TMAMQ/laccase solution, which resulted in oxygen consumption. This study shows that, with the use of such a system, the antioxidant activity of individual antioxidant molecules in a sample and their contribution to the total antioxidant activity of the sample can be correctly assigned.     

The development of an automated HPLC system for the determination of trace-metals in concentrated brines and its application to process monitoring

Methodology based on high performance liquid chromatography (HPLC) has been developed for the determination of trace-metals in concentrated brines. Metal ions, (Al, Ba, Ca, Mg, Sr and Zn) were concentrated quantitatively and isolated from the sodium chloride matrix using a chelating ion-exchange column dynamically coated with the chelating dye xylenol orange. The pH dependence of the uptake of the metals was studied. Using the chelating ion-exchange preconcentration column followed by ion chromatography all the metals studied were determined at the low ng ml^–1 level in concentrated brines and linear/workable calibrations were obtained in the concentration range of interest (<100 ng ml^–1). The methodology developed was successfully transferred to an automated on-line monitoring system for the determination of Ba, Ca, Mg and Sr in concentrated feed brines used in the chlor-alkali industry.     

Automated measurement system for H2O2 in the atmosphere by diffusion scrubber sampling and HPLC analysis of Ti(IV)-PAR-H2O2 complex

An automated selective measurement system for monitoring hydrogen peroxide (H2O2) in the atmosphere was developed (using a diffusion scrubber coupled to a high performance liquid chromatography) due to the importance of H2O2 in understanding tropospheric chemistry and its harmful effects on vegetation. H2O2 in the atmosphere was effectively collected by a diffusion scrubber, which consisted of a hydrophobic porous polytetrafluorethylene (PTFE) tube positioned concentrically within a Pyrex glass tube. Titanium(IV)-4-(2-pyridylazo)resorcinol (Ti(IV)-PAR) solution acidified at pH 2.2 was used as the scrubbing solution for the diffusion scrubber. After the collection of the air sample by the diffusion scrubber, the pH value of the Ti(IV)-PAR scrubbing solution was adjusted to pH 11.9 to form a stable complex of Ti(IV)-PAR-H2O2. An aliquot of the sample solution was injected into a high performance liquid chromatograph equipped with a semi-micro-reversed-phase column and a spectrophotometric detector set at 508 nm for separating and determining the Ti(IV)-PAR-H2O2 complex. The automated measurement could be performed at 60 min intervals. The collection efficiency of H2O2 was higher than 98% at an air flow rate of 1.0 l min-1. The detection limit (3 sigma of the blank value) of H2O2 was 9 parts per trillion by volume (pptv) for an air sampling volume of 55.1. The interference from coexisting O3 or SO2 in the atmosphere was negligible during the collection of H2O2 by the diffusion scrubber. The developed automated measurement system was suitable for monitoring H2O2 in the atmosphere.     

Simultaneous determination of HCHO,CH3CHO and O(x) in ambient air by hydrazine reagent and hplc

Formaldehyde, acetaldehyde, ozone and nitrogen dioxide in ambient air are simultaneously collected on silica gel cartridges coated with 1-methyl-1-(2,4-dinitrophenyl)hydrazine (MDNPH), where the two aldehydes are derivatized to their respective hydrazones, while the two oxidants are converted into N-methyl-2,4-dinitroaniline (MDNA). The three products are then separated and quantified by HPLC with UV detection at 360 nm. The stoichiometric factors of the MDNPH reactions with O3 and NO2 in laboratory tests correspond to 2.0 +/- 0.1 moles of MDNA per mole of O(x) (O3 + NO2). The limits of detection (LOD) are 0.7 ppbv HCHO, 0.8 ppbv CH3CHO and 1.6 ppbv O(x) for 30 L (1 h) air sampled. The sampling performance is insensitive to relative humidities encountered in real atmospheres. When compared with Sep-Pak DNPH silica cartridges as well as with ozone photometric and nitrogen dioxide chemiluminescent analyzers, the proposed chromatographic method demonstrates a very good accuracy (12% for HCHO, 14% for CH3CHO and 7% for O(x), on the average) under field sampling conditions at concentrations lower than 3 and 1 ppbv, for HCHO and CH3CHO, respectively and ranging from 28 to 62 ppbv for O(x).     

Post-column on-line HPLC measurement of reaction rates by using an open-closed derivatizing system

An open-closed high-performance liquid chromatography (HPLC) assembly that enables post-column derivatization of the eluates and kinetic measurements (reaction-rate methods) with enhanced sensitivity and selectivity is constructed and tested by applying it to the separation and determination of the three main creatine kinase (CK) isoenzymes in serum samples with excellent results (consistent with those provided by the standard method) and recoveries between 95 and 105%.     

Performance of a 2,4-DNPH coated annular denuder/HPLC system for formaldehyde monitoring in air

Summary The performance of annular denuders coated with 2,4-dinitrophenylhydrazine for collection of atmospheric HCHO has been evaluated by HPLC/UV analysis of samples coming from laboratory tests and field experiments. A number of parameters, such as collection efficiency at varying air humidity, detection limit, operative capacity and temporal self-consistency have been investigated to optimize the denuder behaviour under different weather conditions and to obtain short-term concentration profiles of HCHO. Deviations between measurements made simultaneously by the DNPH denuder method and differential optical absorption spectrometry (DOAS) have been found to average approximately 30% in the 0–5 ppb HCHO concentration range.     

The use of a chloride-selective combination electrode in an automated continuous potentiometric system

The use of a combination chloride-selective electrode is proposed for potentiometric automated measurements. With this type of electrode, potential oscillations can be completely eliminated by earthing the flow-through cell, even at high flow rates. With the chloride electrode, sample rates up to 50 samples/h can be reached. The system has been tested for carry-over at high and low concentration ranges. Accuracy and precision of the system are determined by chloride measurements in mineral water samples.     

High-precision isotopic ratio measurement system for methane (12CH3D/12CH4,13CH4/12CH4) by using near-infrared diode laser absorption spectroscopy

We demonstrate that the absorption spectroscopic method can be applied to a precise deltaD (an index of 12CH3D/12CH4) and delta13C (an index of 13CH4/12CH4) analysis for methane samples of natural isotopic abundance. We chose an appropriate absorption line pair whose absorption coefficients have nearly the same temperature dependences so as to minimize the temperature effect in absorbance ratio measurements. We measured 12CH3D/12CH4 ratio by using near-infrared external cavity diode lasers and a new type multi-pass cell. The deltaD value can be determined from the 12CH3D/12CH4 signal-intensity ratio with a fine correction by taking account of the interference of 13CH4 lines. Similarly, the delta13C value is determined from the 13CH4/12CH4 signal-intensity ratio, which is measured by using distributed-feedback laser and a modified Herriot-type cell and corrected for the abundance of 12CH3D. The precision was +/-0.7 and +/-0.027/1000 for deltaD and delta13C, respectively.     

Development of an automated monitoring system for various gas-phase organic carbonyls in ambient air

An automated monitoring system for various C₁ to C₅ gas-phase organic carbonyls in ambient air is described. The system consists of a parallel plate diffusion scrubber (PPDS), which is coupled with a high-performance liquid chromatography–ultraviolet (HPLC–UV) system using an automated injection valve. Compared with an annular diffusion scrubber (DS) employed so far for gas-phase carbonyl monitoring, PPDS shows an improved collection efficiency for formaldehyde, acetaldehyde, propionaldehyde, and acetone with >97% at an airflow rate of 0.5?L/min. High gas–liquid concentration ratios of PPDS and an optimised HPLC–UV system allow limits of detection (LOD) in a range of 80–500?pptv. A low liquid hold-up volume of the PPDS results in a short response time of about 10?min. Additionally, the optimised analysis time for 13 carbonyl compounds containing calibration standard enables brief measurement intervals of 25?min. The developed PPDS–HPLC system shows its reliability from urban site monitoring in Seoul, South Korea.     

An automated system for track measurement for the employment of CR-39 as alpha spectrometer in radon and its daughters monitoring

In this work we studied an automated analysis of alpha particle tracks in CR-39, by employing a MITAKA photo-microdensitometer with a C1522 HAMAMATSU Image Analysis System. This system can be used to measure track diameters (with a nominal precision of 0.8 m), superficial track density, and track darkness. This information can be used to determine the alpha particle energies and also their incidence angles (azimuthal and zenithal). The performance of such an automated system, to analyze CR-39 samples which were exposed to alpha particles of known energies, was studied, comparing its response with measurements performed manually by experienced microscopists. The experimental results indicate that the MITAKA/HAMAMATSU system is very reliable for alpha track analysis in CR-39, making possible its use to perform time-consuming measurements in microscopy, as in the case of radon and its daughters surveys.     

A description of an automatic continuous equilibrium system for the measurement of dissolved gaseous mercury

A novel continuous equilibrium system with high time resolution, i.e. every ten minutes, was developed to sample and determine dissolved gaseous mercury (DGM) in natural surface waters. The system is based on the opposite flow principle, can be connected to a ship’s bow water system, and can be applied under most ambient conditions, such as high wind speeds and onboard a moving ship. For the DGM determination the system uses the measured equilibrium concentration of mercury established between the aqueous and gaseous phases, i.e. DGM = Hg_extr / k _H′, where Hg_extr is the measured mercury concentration in the outgoing gas phase and k_H′ is the dimensionless Henry’s Law constant at the desired temperature and salinity. The efficiency of the system was investigated via theoretical calculations and by comparing the continuous equilibrium system with discrete samples. The measurements obtained by the continuous equilibrium system agree within 13% at the 95% confidence level with the measurements of discrete samples obtained by the traditional technique. The theoretical calculations estimated that the continuous equilibrium system described here had an efficiency of 99% for determining the DGM concentration.     

HPLC micro-fractionation coupled to a cell-based assay for automated on-line primary screening of calcium antagonistic components in plant extracts

High performance liquid chromatography (HPLC) micro-fractionation was successfully coupled to an automated ⁴⁵Ca²⁺ uptake assay using GH₄C₁ cells for the separation of natural product extracts and for the primary detection of their calcium antagonistic components. The reliability of the procedure was first established with a reference solution consisting of pure compounds with a known effect on the Ca²⁺ uptake. No loss of activity was observed to occur after HPLC micro-fractionation. Extracts of Peucedanum palustre and Pinus sylvestris, showing high and no inhibition of Ca²⁺ uptake as total extracts, respectively, were analysed and the inhibitory activity of the P. palustre extract could be traced to two components, identified as columbianadin and isoimperatorin. As expected, no significant inhibition was observed with the micro-fractionated P. sylvestris samples. In summary, the procedure was found to be applicable for primary detection of calcium antagonistic components in complex matrices and to significantly reduce the time previously needed for bioactivity-guided isolation.     

Development of a monitoring system for vinyl chloride gas in air by using an HCl monitoring tape and pyrolyzer

A continuous monitoring system for vinyl chloride gas in air has been developed using an HCl monitoring tape and pyrolyzer consisting of a heater around a quartz tube. It is based on the color change of the tape by reaction with HCl gas produced by decomposition of vinyl chloride gas in the heated quartz tube. The conversion efficiency of vinyl chloride into HCl depends on the temperature of the pyrolyzer. The tape impregnated with a coloring solution that includes Metanil Yellow (pH indicator; pH 1.2-2.3, red-yellow), glycerin and methanol is a highly sensitive means of detecting HCl gas. When vinyl chloride gas was passed through the heated quartz tube (910 degrees C) and the HCl gas produced was passed through the tape, the color of the tape changed from yellow to red. The degree of color change was proportional to the concentration of vinyl chloride gas with a constant sampling time and flow rate. The degree of color change could be recorded by measuring the intensity of reflecting light (555 nm). This method is scarcely affected by other gases with the exception of chlorinated hydrocarbons such as trichloroethylene and chloroform or strong acids such as HCl gas. Reproducibility tests showed that the relative standard deviation of the relative intensity (n = 10) was 4.5 for 5 ppm vinyl chloride. The detection limit was 0.4 ppm for vinyl chloride with a sampling time of 40 s and a flow rate of 300 ml min (-1).     

Amperometric determination of cyanides at the low ppb level by automated preconcentration based on gas diffusion coupled to sequential injection analysis

A simple, sensitive method for determining free cyanides is described. The assay is based on automated gas diffusion of the analyte using sequential injection analysis (SIA) coupled to amperometric detection on a silver working electrode. The effects of varying several parameters affecting the analytical procedure (including the flow rates of the donor and acceptor streams, the concentrations of the reagents and the sample volumes) were studied. The validity and quality of the method were also assessed, by examining its linearity, limits of detection and quantitation, precision, selectivity to potentially interfering substances. Its sensitivity can be enhanced by applying a simple preconcentration step, following which limits of detection were found to be 0.05-0.12 μg L⁻¹. Application of the proposed assay to the analysis of tap, mineral and table water samples spiked at concentrations ranging from 1 to 10 μg L⁻¹ CN⁻, yielded satisfactory recoveries (88-112%).     

Enhancement of the detection sensitivity for volatile organic compounds by using an annular type photoionization detector and a pre-concentration system

Photoionization detector (PID) was developed for a sensitive on-site detection of trace amounts of volatile organic compounds (VOCs) based on an annular type ion collection electrode assembly. An ion collector with an annular geometry could detect more stable ion signals in the PID system when compared to the other types of ion collectors when an UV lamp of 10.6 eV was used as an ionization source. In order to enhance the detection sensitivity, a pre-concentration system, which was developed by adopting a ceramic heater packed with rod shaped molecular sieves, was adopted for a detection of VOCs. The adopted ceramic heaters had a resistance of 10-20 Ohm, and the temperature of the heater was optimized by controlling the heating time of the resistor. The enhancement of the detection sensitivity was found to be 8-10 times with the PID system when compared to the signals measured without a pre-concentrator. The overall detection sensitivity of the developed PID system was estimated as 10 ppb or better.     

Online measurement of denitrification rates in aquifer samples by an approach coupling an automated sampling and calibration unit to a membrane inlet mass spectrometry system

Aquifers within agricultural catchments are characterised by high spatial heterogeneity of their denitrification potential. Therefore, simple but sophisticated methods for measuring denitrification rates within the groundwater are crucial for predicting and managing N-fluxes within these anthropogenic ecosystems. Here, a newly developed automated online (15)N-tracer system is presented for measuring (N(2)+N(2)O) production due to denitrification in aquifer samples. The system consists of a self-developed sampler which automatically supplies sample aliquots to a membrane-inlet mass spectrometer. The developed system has been evaluated by a (15)N-nitrate tracer incubation experiment using samples (sulphidic and non-sulphidic) from the aquifer of the Fuhrberger Feld in northern Germany. It is shown that the membrane-inlet mass spectrometry (MIMS) system successfully enabled nearly unattended measurement of (N(2)+N(2)O) production within a range of 10 to 3300 μg N L(-1) over 7 days of incubation. The automated online approach provided results in good agreement with simultaneous measurements obtained with the well-established offline approach using isotope ratio mass spectrometry (IRMS). In addition, three different (15)N-aided mathematical approaches have been evaluated for their suitability to analyse the MIMS raw data under the given experimental conditions. Two approaches, which rely on the measurement of (28)N(2), (29)N(2) and (30)N(2), exhibit the best reliability in the case of a clear (15) N enrichment of evolved denitrification gases. The third approach, which uses only the ratio of (29)N(2)/(28)N(2), overestimates the concentration of labelled denitrification products under these conditions. By contrast, at low (15)N enrichments and low fractions of denitrified gas, the latter approach is on a par with the other two approaches. Finally, it can be concluded that the newly developed system represents a comprehensive and simply applicable tool for the determination of denitrification in aquifers.