Highly sensitive determination method for total carbonate in water samples by flow injection analysis coupled with gas-diffusion separation.

A spectrophotometric method for the determination of total carbonate in water samples was developed. The method is based on the color change of an acid-base indicator in relation to the concentration of permeable gas substances through a membrane. By using a new portable FIA system equipped with a gas-diffusion unit, a highly sensitive and on-site determination of total carbonate in aqueous solutions was investigated. A new color-change system with 4-(2',4'-dinitrophenylazo)-1-naphthol-5-sulfonic acid (DNN5S) was developed. Absorbance changes of the reagent solution were measured at 450 nm with a light-emitting diode (LED) as a light source. A new type of gas-diffusion unit was used, and was constructed with double tubing: the inner tubing was a micro porous PTFE (polytetrafluoroethylene) tubing (1.0 mm inner diameter and 1.8 mm outer diameter, pore size 2 microns, porosity 50%); the outer tubing was made of glass with 2.0 mm inner diameter. The optimized system conditions were as follows: the sample size was 200 microliters, the temperature of the air bath for the gas-diffusion unit was 25 degrees C, and the length of the gas-diffusion unit was 15 cm; each flow rate was 0.3 ml min-1. For measuring carbonate at low concentrations, a method for preparing water with less carbonate was proposed: the carbonate content of the water was decreased down to 5 x 10(-7) M. The calibration graph was rectilinear from 1 x 10(-6) M to 10(-3) M, and the detection limit (corresponding to a signal-to-noise ratio of 3) was 1 x 10(-6) M of carbonate. The relative standard deviation (RSD) of ten measurements of 2.3 x 10(-5) M Na2CO3 solution was 1.9%. The total carbonate in various kinds of water (such as river, sea, rain, distilled and ultra purified) was determined.     

Pulsed reagent introduction through a membrane reactor for flow-injection systems

A method of intermittent reagent introduction, functionally equivalent to stop-go pumping, is described. A pneumatically pressurized reagent reservoir is used to deliver liquid through a high-speed on/off valve to the outer channel of an annular tube assembly. Except for this single entry point, the outer channel is otherwise sealed. The inner flow channel bearing the principal flow stream contains a short microporous membrane tube. When the reagent delivery valve is activated, reagent flows radially inward through the membrane into the principal flow stream.     

Determination of Henry''s law coefficients by combination of the equilibrium partitioning in closed systems and solid-phase microextraction techniques

This paper describes the determination of Henry's law coefficients by means of the EPICS (equilibrium partitioning in closed systems) technique in combination with SPME (solid-phase microextraction). The use of solid-phase microextraction-sampling allowed us to extend the possibilities of the equilibrium partitioning in closed systems technique with respect to the range of Henry's law coefficients which can be measured. Whereas the equilibrium partitioning in closed systems technique is limited to determine air–water equilibrium partitioning of volatile compounds with Henry's law coefficients of at least 0.06 (dimensionless), the current method allowed to measure coefficients between 0.0023 and 13.5. In this way Henry's law coefficients of 20 compounds, being in a range covering five orders of magnitude, were measured with relative standard deviations between 1.0 and 19.8% (mean standard deviation: 5.7%; median of standard deviations: 4.8%, n=99). Several types of compounds were examined i.e. aliphatic hydrocarbons, monocyclic and polycyclic aromatic hydrocarbons, chlorinated and fluorinated compounds, ethers and esters, biphenyl and N-containing compounds, including compounds for which availability of experimental Henry's law coefficients is limited. Measurement of the equilibrium partitioning in the 2 to 25°C range allowed to establish relations of Henry's law coefficient as a function of temperature.     

Deactivation,coating and performance of nickel capillary columns for GLC

Electroformed nickel tubing was deactivated by chemical vapor deposition of silicon from silane gas and subsequent treatment with cyclooctamethyltetrasiloxane (D4). Standard activity tests performed on the uncoated tube and also on columns coated with crosslinked and uncrosslinked, nonpolar stationary phase, show that good quality flexible columns can be prepared from nickel tubing. The inner surface of the silicon coated tube was characterized by Auger depth profile analysis.     

Tropospheric multiphase chemistry of 2,5- and 2,6-dimethylphenols: determination of the mass accommodation coefficients and the Henry's law constants

The uptake of 2,5-dimethylphenol and 2,6-dimethylphenol on aqueous surfaces was measured between 279 and 293 K, using the wetted-wall flow tube technique coupled with UV absorption spectroscopic detection. For both compounds, the uptake coefficients gamma were found to be independent of the KOH scavenger concentration in the range of 0.01 to 1 M (pH > pK(a)) and of the liquid-gas contact times. In addition, the uptake coefficients and the derived mass accommodation coefficients alpha show a negative temperature dependence in the investigated temperature range. The mass accommodation coefficients decrease from 1.1 x 10(-3) to 1.1 x 10(-4), and from 5.4 x 10(-4) to 6.4 x 10(-5) for 2,5-dimethylphenol and 2,6-dimethylphenol, respectively. These results are used to discuss the incorporation of these species into the liquid using the nucleation theory. Henry's law constants (HLC) of both compounds were directly measured using a dynamic equilibrium system based on the water/air equilibrium at the interface within the length of a microporous tube. The measurements were conducted over the range 278-293 K in both deionized water and 35 g L(-1) solution of NaCl. At 293 K and in pure water, HLC were found to be equal to (in units of M atm(-1)): 2,5-dimethylphenol, HLC = (1270 +/- 240); 2,6-dimethylphenol, HLC = (250 +/- 80). All of the values for HLC in 35 g L(-1) salt solution were 5-55% lower than the corresponding values in deionized water, depending on the compound and the temperature. These data (mass accommodation coefficients and Henry's law constants) were then used to estimate the partitioning of these phenolic compounds between gaseous and aqueous phases and the corresponding atmospheric lifetimes under clear sky (tau(gas)) and cloudy conditions (tau(multiphase)) have then been derived. The calculated multiphase lifetimes (in units of hours) are lower than those in gas phase at a cumulus temperature of 283 K (in parentheses): 2,5-dimethylphenol, 2.2 (3.5); 2,6-dimethylphenol, 3.8 (4.2).     

A method for measuring enthalpy of volatilization of a compound, Delta(vol)H, from dilute aqueous solution

This study has developed a method for measuring the enthalpy of volatilization (Delta(vol)H) of a compound in a dilute solution via ion-molecule reactions and gas-phase analysis using selected ion flow tube mass spectrometry (SIFT-MS). The Delta(vol)H/R value was obtained using an equation with three variant forms either from the headspace concentration of the solution or from individual product ion(s). Under certain experimental conditions, the equation has the simplest form [formula: see text], where R is the gas constant (8.314 J . mol(-1) . K(-1)), i(n) and I are the respective product and precursor ion count rates, and T is the temperature of the solution. As an example, a series of 27.0 micromol/L aqueous solutions of acetone was analyzed over a temperature range of 25-50 degrees C at 5 degrees C intervals using H3O+, NO+ and O2+* precursor ions, producing a mean Delta(vol)H/R value of 4700 +/- 200 K. This corresponds with current literature values and supports the consistency of the new method. Notably, using this method, as long as the concentration of the solution falls into the range of Henry's law, the exact concentration does not have to be known and it can require only one sample at each temperature. Compared with previous methods which involve the measurement of Henry's law constant at each temperature, this method significantly reduces the number of samples required and avoids the labour and difficulties in preparing standard solutions at very low concentrations. Further to this, if the contents of a solution were unknown the measured Delta(vol)H/R from individual product ion(s) can help to identify the origin of the ion(s).     

Chemically modified teflon wall-coated open tubular columns for gas chromatography

Summary Wall-coated open tubular columns prepared from chemically modified teflon tubing have been developed for gas chromatography. Chemical reaction of the inner walls of teflon tubing allows bonding of an adhesive layer on which a variety of stationary phaes can be coated. Test mixtures of alkanes and alcohols were used to investigate the chromatographic properties of these columns and the stability and mixing of the adhesive and stationary phae layers. the results in dicate that mixing of the layers is negligible and that the column is stable for a long period of time.Principle author     

Separation of ammonia with a gas-permeable tubular membrane

Ammonia concentrations in reaction mixtures at pH ? 7.1 are measured by diffusion of the ammonia through a hydrophobic microporous poly (tetrafluoroethylene) tubular membrane placed in the solution. The ammonia is absorbed in an acidic (pH 5) carrier flowing the bore of the tubing, and measured in portions of the effluent with an ammonia electrode. The slopes of the linear responses are influenced by pH, flow rate and tubing dimensions.     

Preparation of stable gas mixtures with microconcentrations of volatile substances in vapor-phase sources at elevated pressures

Tools are proposed for the preparation of stable vapor-gas mixtures with microconcentrations of volatile components (vapor-phase sources of gas mixtures). These work at elevated pressures and ensure the generation of gas flows with component concentrations differing within an order of magnitude from one and the same source.     

A One-pot-synthesized Double-layered Anticoagulant Hydrogel Tube

Extracorporeal membrane oxygenation(ECMO) has emerged as a viable treatment in severe cases of acute respiratory distress syndrome, acute respiratory failure, and adult respiratory distress syndrome. However, thromboembolic events stemming from the use of ECMO devices results in significant morbidity and mortality rates; the inner surface of the ECMO tubing comes into contact with the blood and can readily initiate coagulation. In addition, the tubing needs to be continually replaced due to thromboses on the inner tube wall, which not only increases the risk of infection but also the economic burden. Despite considerable effort, a surface modification strategy that effectively addresses these challenges has not yet been realized. In this study, we developed an integrated hollow core-shell-shell hydrogel tube of gelatin/alginate/acrylamide-bacterial nanocellulose(GAA) that meets the anticoagulant requirements for the inner tubing layer as well as the highly elastic soft material needed for the outer layer. Using static blood from healthy volunteers, we confirmed that the platelets or coagulation is not stimulated by the GAA tubing. Importantly, experiments with dynamic blood also demonstrated that the inner layer of the tubing does not elicit blood clotting. The one-pot-synthesized process may provide guidance for the design of anticoagulation tubes used clinically.     

The Henry's law constants of water in the binary mixtures of benzene,carbon tetrachloride,and cyclohexane at 25°C

The solubilities of water in each of the three binary mixtures benzene-carbon tetrachloride, benzene-cyclohexane, and carbon tetrachloride-cyclohexane were determined as a function of solvent composition at 25°C. It was found that, as with the pure solvents, water in the 0.50 mole fraction binary mixtures of these solvents obeyed Henry's law up to saturation. The experimentally determined solubilities were converted to Henry's law constants of water for the entire range of solvent compositions. These values for the Henry's law constants were compared with theoretically calculated values. The comparisons indicated that water in the benzene-cyclohexane and in the benzene-carbon tetrachloride mixtures was preferentially solvated by benzene. Preferential solvation of water was not indicated for the carbon tetrachloride-cyclohexane mixtures.     

Determination of arsenic by continuous hydride generation with direct introduction into an O2-argon microwave plasma torch atomic emission spectrometer

The determination of arsenic was studied with a simple and economic method. A continuous hydride generation system is interfaced to a microwave plasma torch atomic emission spectrometer (MPT-AES). Arsenic hydride is transferred directly and continuously by the carrier gas into the plasma torch without separation of hydrogen. When oxygen is introduced into the outer tube of the plasma torch, the plasma is more stable and has a higher tolerance to hydrogen. The detection limit (3σ) is 5.2 μg/L when the forward power is 100 W with argon as support gas. Application to the standard sample coal fly ash showed a comparable result to the certified quantity.     

Dielectric barrier discharge-plasma induced vaporization and its application to the determination of mercury by atomic fluorescence spectrometry

This paper describes a low-temperature dielectric barrier discharge (DBD)-plasma induced vaporization technique using mercury as a model analyte. The evaporation and atomization of dissolved mercury species in the sample solution can be achieved rapidly in one step, allowing mercury to be directly detected by atomic fluorescence spectrometry. The DBD plasma was generated concentrically in-between two quartz tube (outer tube: i.d. 5 mm and o.d. 6 mm, inner tube: i.d. 2 mm and o.d. 3 mm). A copper electrode was embedded inside the inner quartz tube and sample solution was applied onto the outer surface of the inner tube. The effects of operating parameters such as plasma power, plasma gas identity, plasma gas flow rate and interferences from concomitant elements have been investigated. The difference in the sensitivities of Hg(2+), methylmercury (MeHg) and ethylmercury (EtHg) was found to be negligible in the presence of formic acid (≥1% v/v). The analytical performance of the present technique was evaluated under optimized conditions. The limits of detection were calculated to be 0.02 ng mL(-1) for Hg(2+), MeHg and EtHg, and repeatability was 6.2%, 4.9% and 4.3% RSD (n = 11) for 1 ng mL(-1) of Hg(2+), MeHg and EtHg, respectively. This provides a simple mercury detection method for small-volume samples with an absolute limit of detection at femtogram level. The accuracy of the system was verified by the determination of mercury in reference materials including freeze-dried urine ZK020-2, simulated water matrix reference material GBW(E) 080392 and tuna fish GBW10029, and the concentration of mercury determined by the present method agreed well with the reference values.     

Plasticizers,antioxidants, and other contaminants found in air delivered by PVC tubing used in respiratory therapy

Of the many compounds that leach from respiratory therapy tubing into air passing through it, we selected five compounds to analyze. The five compounds are known to be potentially carcinogenic, toxic or known to induce estrogenic activity. Parts-per-million and parts-per-billion concentrations of these species were found in the air passing through the tubing: the plasticizers di-(2-ethylhexyl) phthalate (DEHP) and di-ethyl phthalate (DEP), the antioxidants butylated hydroxy toluene (BHT) and p-nonylphenol (p-NP), and the contaminant (from commercial preparation of DEHP) 2-ethylhexanol (2-EH). These levels are high enough to cause some concern about exposure for patients who use oxygen on a long-term basis, those sensitive or allergic to these species, or those with asthma. A method was developed for analysis of solid tubing samples, showing great variability in concentrations of small, volatile molecules from sample to sample. A method was also developed for pre-concentration of small molecules onto Tenax adsorbants from air passing through the tubing. Both solid samples and adsorbant loaded with analyte were analyzed by direct dynamic thermal desorption gas chromatography mass spectrometry (GCMS). This study does not imply that adverse reactions by patients to chemical compounds leaching from respiratory medical tubing will occur but that further investigation is warranted.     

Permeation devices for the preparation of standard gaseous mixtures

Summary Two new permeation devices for generation of standard gaseous mixtures in wide concentration range have been designer. Teflon membranes and tubing have been utilized as the permeation barriers. The devices enable generation of multi-component mixtures.     

Metrological performances of mass flow controllers for dynamic gas dilution

The method of dynamically generating reference mixtures of volatile organic compounds at trace levels requires the uninterrupted blending of the component flows during the generation time. The target flow rate uncertainty depends on the application and the range of the concentration generated. Accurate air flow rates used for dilution can be realized by mass flow controllers (MFCs). The short-term stability of MFCs has been measured in order to assess their usefulness in dynamic gas dilutors. As shown here, MFCs are appropriate for the dynamic preparation of diluted gas mixtures provided they are calibrated prior to each use, because their calibration is not stable over longer time periods. The calibration results of the low pressure drop MFC proved its applicability in a wide range of pressure drop. The uncertainty of the dilution flow rate resulted mainly from the limited short-term stability of the MFC at low dilution flow rate or at short generation time. Consequently, MFCs can provide highly accurate dilution air flow rates with a relative uncertainty of 0.2 %, for flow rates larger than 70 % of the MFC’s maximum flow rate and generation times longer than 5 min.     

Continuous dynamic-gravimetric preparation of calibration gas mixtures for air pollution measurements

 The preparation of calibration gas mixtures for air pollution measurements by the dynamic-gravimetric method was investigated using sulphur dioxide in nitrogen as a model. The target mole fraction was 200×10^–9 mol/mol, with the option of also getting smaller mole fractions. Thermal mass flow meters calibrated with reference mass flows were used to measure the dilution gas flow (nitrogen). The relative standard uncertainty of the dilution gas flows between 10 mg/s (approx. 500 ml/min) and 40 mg/s (approx. 2000 ml/min) was 0.15%. The mass flow of the target component measured as the permeation rate was determined via the quasi-continuous observation of the loss in the permeation tube mass during the measuring time. A magnetic coupling system and an adapted microbalance were used for this purpose. The results presented show permeation rates measured over the lifetime of a tubular permeation source. The measurement cycles took between 3 days and 7 h at least. The relative standard uncertainty of the mixture composition did not exceed 2%. First comparisons with gas mixtures prepared by the static-gravimetric method show compatibility. The applicability of the system is not restricted to the SO₂/N₂ mixture. It can also be used for preparing other gas mixtures in this field of application. Received: 26 April 2000 / Accepted: 12 September 2000     

一种经氟化和热处理在双壁碳纳米管上生成缺陷的方法(英文)

Nanoscale defects in the outer tube to preserve the electrical and optical features of the inner tube can be engineered to exploit the intrinsic properties of double walled carbon nanotubes (DWCNTs) for various promising applications. We demonstrated a selective way to make defects in the outer tube by the fluorination of DWCNTs followed by the thermal detachment of the F atoms at 1000 °C in argon. Fluorinated DWCNTs with different amounts of F atoms were prepared by reacting with fluorine gas at 25, 200, and 400 °C that gave the stoichiometry of CF0.20, CF0.30, and CF0.43, respectively. At the three different temperatures used, we observed preservation of the coaxial morphology in the fluorinated DWCNTs. For the DWCNTs fluorinated at 25 and 200 °C, the strong radial breathing modes (RBMs) of the inner tube and weakened RBMs of the outer tube indicated selective fluorine attachment onto the outer tube. However, the disappearance of the RBMs in the Raman spectrum of the DWCNTs fluorinated at 400 °C showed the introduction of F atoms onto both inner and outer tubes. There was no significant change in the morphology and optical properties when the DWCNTs fluorinated at 25 and 200 °C were thermally treated at 1000 °C in argon. However, in the case of the DWCNTs fluorinated at 400 °C, the recovery of strong RBMs from the inner tube and weakened RBMs from the outer tube indicated the selective introduction of substantial defects on the outer tube while preserving the original tubular shape. The thermal detachment of F atoms from fluorinated DWCNTs is an efficient way to make highly defective outer tubes for preserving the electrical conduction and optical activity of the inner tubes.     

Theoretical aspects of quantitative mass spectrometry of gas mixtures

The problem of calibration of mass spectrometers with standard gas mixtures is studied theoretically. The results obtained can be used in deciding the number and optimum composition of standard mixtures. An analogy is drawn between this calibration problem and the mathematical theory of experimental design when mixtures are considered. It is shown that calibration based on a number of standard mixtures is more accurate than calibration with pure gases. A procedure for correction of calibration coefficients is described; it can be applied during measurements on the composition of gas mixtures or gas flows. Application to gas mixtures containing CO, N₂ and CO₂ is discussed.     

Adsorption separation performance of H2/CH4 on ETS-4 by concentration pulse chromatography

To exploit an effective adsorbent to separate hydrogen and methane, microporous titanium silicate molecular sieve NaETS-4 was synthesized and modified by strontium. The adsorption characteristics and diffusion behaviors of the prepared titanosilicate molecular sieve were studied by concentration pulse chromatography. And the effects of ion-exchange and dehydration temperature on adsorbent structure and gas diffusion were also discussed. The results showed that the thermal stability and Henry＇s Law constants were enhanced and micropore diffusivity decreased after exchanging Na＋ with Sr2＋. With the increase of dehydration temperature, Henry＇s Law constant and micropore diffusivity of CI-I4 decreased in both NaETS-4 and SrETS-4. While for 1-12 in SrETS-4, the increase of Henry＇s Law constant and the decrease of diffusion rate can be attributed to the shrinks of pore diameter resulting from the relocation of Sr2＋. Correspondingly, the kinetic selectivity of H2/CH4 reached 8.91 indicating its potentiality in separating H2 and CH4.