On-line collection/concentration of trace amounts of formaldehyde in air with chromatomembrane cell and its sensitive determination by flow injection technique coupled with spectrophotometric and fluorometric detection

A simple, rapid and highly sensitive method for the determination of trace amounts of formaldehyde in air by using flow injection analysis (FIA) system coupled with a three-hole chromatomembrane cell (CMC) was investigated by using a spectrophotometer and a fluorometer. The CMC was applied to on-line collection/concentration of trace amounts of formaldehyde in air into water as an absorbing solution; formaldehyde in the air was found to be quantitatively transferred into the absorbing solution in CMC. The solution, containing absorbed formaldehyde, was introduced into the carrier stream of the FIA system. The amount of formaldehyde in an absorbing solution was measured spectrophotometrically and fluorometrically after the reaction with a mixed reagent of acetylacetone and ammonium acetate at pH 5.6–5.8. The amount of formaldehyde in the absorbing solution, measured by the proposed system, could be converted to the concentration of formaldehyde in the air sample. A calibration graph prepared by a series of standard formaldehyde aqueous solutions was adopted. The formaldehyde in indoor air, determined as exampled by the proposed spectrophotometric FIA, was found to be 5.14 ± 0.08 ppbv for 20 ml of the air sample at the air flow rate of 6 ml min⁻¹, and the relative standard deviation (R.S.D.) was 1.56%. The limit of detections (LODs) of HCHO in an absorbing solution was 2 × 10⁻⁸ M (0.6 ppb) and 8 × 10⁻⁹ M (0.2 ppb), respectively, by the spectrophotometric and the fluorometric FIA, and the LODs of HCHO in air sample of 40 ml were 0.05 and 0.03 ppbv, respectively. The interferences from foreign species were examined; tolerable concentrations of other aldehydes were more than 50-fold of formaldehyde (1 × 10⁻⁶ M).     

Absorption, concentration and determination of trace amounts of air pollutants by flow injection method coupled with a chromatomembrane cell system: application to nitrogen dioxide determination

The concentration distribution of an analyte in a chromatomembrane cell (CMC) was examined by using various air samples of different air pollutant (NO₂) concentrations and volumes, and the results obtained could be explained by a proposed principle of the concentration distribution of the analyte in the CMC. This principle was for the first time proved experimentally in the present study. On-line preconcentration and continuous determination of the air pollutant (NO₂) in air samples were realized by coupling a three-hole CMC with a flow injection analysis (FIA) system, where a triethanolamine (TEA) aqueous solution (2 g l⁻¹) was used as an absorbing solution for NO₂ in the air samples. A calibration method with standard nitrite aqueous solutions was developed for the determination of NO₂ in the air samples. Concentrations of NO₂ in indoor air and its diluted air samples were determined by the proposed CMC/FIA method. The volume of air sample necessary for the measurement was decreased to only 5 ml. The measuring time for one sample was about 5–6 min even when a 20 ml air sample was used.     

The application of the chromatomembrane cell for the absorptive sampling of nitrogen dioxide followed by continuous determination of nitrite using a micro-flow injection system

A simple and rapid procedure for NO(2) determination in air was developed by coupling the chromatomembrane method with a micro-FIA system. A three-hole chromatomembrane cell was successfully applied to on-line preconcentration of atmospheric NO(2) in a solution of 2 g l(-1) triethanolamine (TEA) as an aqueous absorbing solution. The lowest volume of an air sample necessary for the measurement was 5, and 0.02 ml portions of the solution containing the absorbed NO(2) (NO(2)(-) and NO(3)(-)) were supplied to a micro-FIA system being the succeeding component of the proposed analyzer. The amounts of NO(2)(-) in the absorbing solution were measured by a diazotization-coupling reaction with sulfanilamide and N-(1-naphthyl) ethylenediamine, and referred to the concentration of NO(2) in the air sample. The NO(2) content of indoor air was determined to be 43+/-1 ppb using 20 ml of air, and the R.S.D. was +/-1.89%.     

Determination of volatile carbonyl compounds in clean air

Summary An improved analytical procedure has been developed for the detection of formaldehyde, acetaldehyde, acetone and other volatile carbonyls in clean air. For sampling, 2,4-dinitrophenyl-hydrazine (DNPH) coated silica gel cartridges were used. DNPH reacts with carbonyls and forms carbonyl hydrazones which are extracted with acetonitrile and subsequently separated by reversed phase HPLC. Sampling flow rates up to 3.5 l/min were tested. The quantification limit of the complete sampling and analytical procedure is 60 ng carbonyl which corresponds to a mixing ratio of 1 ppbv HCHO in a 45 l air sample taken during a sampling time of 13 min. Carbonyl mixing ratios down to 0.1 ppbv can be determined. The collection efficiency and the elution recovery range between 96 and 100%; the precision is ±5% for HCHO and ±4% for CH₃CHO at mixing ratios of 1 ppbv. This technique can also be applied for the determination of aldehydes and ketones in the aqueous phase, e.g. cloud and fog water. In this case, carbonyls were converted to hydrazones simply by mixing the aqueous sample with an acidified DNPH solution. After 40 min reaction time, the hydrazones were analysed by HPLC. The detection limit was 0.2 mol HCHO/l. Possible interference caused by ozone and NO₂ was eliminated by using KI filters connected in series with the DNPH-coated cartridges. The analytical procedure was tested at a mountain measuring station and proved to be a suitable method for monitoring carbonyl compounds in clean air.     

Determination of copper at ng levels by in-line preconcentration and flow-injection analysis coupled with flame atomic-absorption spectrometry

Oxine/formaldehyde/resorcinol and oxine/formaldehyde/hydroquinone resins have been synthesized and their physicochemical properties studied. Conditions were optimized for the preconcentration of copper by batch extraction and column chromatography with the resins. A flow-injection analysis (FIA) manifold was constructed for the determination of copper at ng levels by preconcentration on microcolumns containing the resins, stripping, and atomic-absorption spectrometry. For batch preconcentration a pH of about 2.5-3 was optimal whereas in the FIA system a broader pH range (approximately 2-3.5) could be used. Separations of binary mixtures of Cu(II) with Ni(II) or PB(II) at microg/ml level did not show any cross-contamination. In the FIA, a 2 cm long column and 2 ml/min flow-rate were adequate for quantitative uptake of copper; 50 micro1 of 0.1M hydrochloric acid quantitatively eluted the copper.     

BSA和SDBS在水溶液与空气界面的相互作用

表面活性剂与蛋白质在界面处的相互作用在许多应用里都会遇到．如去污、药品或生物制剂的制备和提纯、某些开科手术等等[1]这常常涉及到表面活性剂与蛋白质在界面的吸附，蛋白质大分子在界面吸附层的取向和构象．对于这两种物质在界面处可能发生的相互作用的性质，是表面活性剂     

反离子对离子液体氯化1-(2-羟乙基)-3-十二烷基咪唑在水溶液中自组装的影响

用表面张力法和荧光探针技术分别测定了阳离子型离子液体表面活性剂氯化1-(2-羟乙基)-3-十二烷基咪唑([C2OHC12im]Cl)在无机盐(NaX,X=Cl-,Br-,I-和Na2SO4)水溶液中的自组装参数。 结果表明,反离子通过结合[C2OHC12im]+并中和其表面电荷,使[C2OHC12im]+的临界胶束浓度(CMC)和胶束平均聚集数(Nm)等自组装参数明显改变;改变幅度按照Cl-＜Br-＜I-＜SO2-4次序递增;但是反离子(Cl-、Br-和SO2-4)种类对临界胶束平均聚集数(Nm,c)和胶束微极性([I1/I3]m)的影响不甚明显;随着Br-浓度增加,lg CMC线性减小,而Nm则以幂函数形式递增。     

A new method for the determination of the critical micelle concentration of Triton X-100 in the absence and presence of beta-cyclodextrin by resonance Rayleigh scattering technology

A new method for the determination of the critical micelle concentration (CMC) of Triton X-100 in aqueous solution and beta-cyclodextrin solution by resonance Rayleigh scattering (RRS) has been developed. The method is based on the measurement of the RRS intensity of different concentration of Triton X-100 in aqueous solution and beta-cyclodextrin solution (6.0 x 10(-4) mol l(-1)). When the RRS intensities were plotted against the concentration of Triton X-100, an inflection point appeared at the Triton X-100 concentration of 5.0 x 10(-4) mol l(-1) in aqueous solution and 1.1 x 10(-3) mol l(-1) in beta-cyclodextrin solution, respectively. These values of concentration corresponded to the CMC of Triton X-100 in aqueous solution and beta-cyclodextrin solution, which also agreed closely with the results reported by surface tension and UV-Vis absorption spectrophotometry. Therefore, the present RRS method is very convenient, rapid and accurate and can be used as a new technology for the determination of CMC values of surfactants without any probe. The relationship between the RRS intensity and the concentration, aggregate state and the aggregate molecular size of Triton X-100 has been primarily discussed.     

Flow-injection systems for determination of trace manganese in various salts by catalytic photometric detection

Two flow-injection analysis (FIA) systems for the determination of trace manganese in salts are presented using highly sensitive catalytic detection based on the oxidation of 3,4-dihydroxybenzoic acid by hydrogen peroxide. Two different approaches, the use of a large sample volume injection in a usual FIA mode (system A) and on-line coupling of a cation-exchange separation column with detection in a continuous flow system (system B), have proved very effective for eliminating the blank peak problem and thus affording direct injection of a sample solution containing a large concentration of salt. The limits of determinations are 0.04 ppm and 0.01 ppm for systems A and B respectively, when a 5 g sample is used for preparing the 100 ml sample solution. The proposed FIA systems were satisfactorily applied to the determination of manganese at 0.03-1.59 ppm in solar salts (salts made by exposing brine to the sun) with good precision.     

分光光度法测定空气中甲醛不确定度评定

采用分光光度法测定空气中甲醛,对测定结果的不确定度进行评定。采用酚试剂分光光度法测定空气中甲醛,分析测定过程中的各项不确定度来源,包括样品采集、标准工作溶液配制、标准工作曲线拟合、测定仪器以及重复测定等引入的不确定度,计算合成不确定度,最后获得相对扩展不确定度。当空气中甲醛质量浓度为0.0244~0.2218 mg/m^3时,测定结果在95%置信区间时的相对扩展不确定度为0.1172(k=2)。不确定度主要来源于A类不确定度和系列标准工作溶液制备、标准工作曲线拟合、水中甲醛溶液标准物质的稀释引入的不确定度。     

Extraction mechanism of Cr(VI) on the aqueous two-phase system of tetrabutylammonium bromide and (NH(4))(2)SO(4) mixture

An aqueous two-phase system of tetrabutylammonium bromide (TBAB) and (NH(4))(2)SO(4) mixture has been developed for the extractive preconcentration and separation of certain compounds. TBAB concentration in upper phase is much higher than that of bottom solution. This new aqueous two-phase system is proposed for the highly selective extraction of Cr(VI) from large amounts of Cr(3+). The Cr(VI) is found to be extracted into the TBAB-rich upper phase due to ion pair formation such as HCrO(4)(-) . TBAB(+). The Cr(VI) was sufficiently extracted into the upper phase in the pH range from 1 to 5. The proposed method has been applied to the determination of trace of Cr(VI) in wastewater samples with a coefficient of variation less than 3.2%. The recovery obtained was not lower than 90%. The determination limit for the Cr(VI) was found to be 60 mug l(-1) in 10 ml of sample solution.     

Flow injection/atomic absorption spectrometric determination of zineb in commercial formulations of pesticide based on slurry sampling.

This paper reports on a new strategy for the slurry sampling determination of dithiocarbamate pesticide zineb [[ethylenebis(dithiocarbamato)]zinc] employing a FIA system with a flame atomic absorption spectrometry detector. In the flow system, an on-line alkaline hydrolysis of the pesticide is performed, allowing the release of Zn(II) ions to the solution, which are easily detected by a flame AAS technique. Several parameters that could affect the performance of the analytical methodology were studied, such as the concentration of NH3(aq) used in the hydrolysis step, the effect of the presence of Triton X-100 on the sensitivity and precision, and the FIA parameters (carrier flow rate and mixing coil volume). Under optimized conditions, aqueous slurries containing 2.5 to 25 microg ml(-1) zineb provided good linear calibration fits. From the obtained data, a detection limit (3sigma) of 1.0 microg ml(-1) zineb was found and a repeatability of 2.7% was obtained from 12 measurements of a slurry containing 2.5 microg m(-1) zineb. On the other hand, a precision (reproducibility) of 7.8% was achieved from three determinations of a sample containing 128 mg g(-1) of the pesticide. Also, the developed system provides a sampling frequency of 72 h(-1).     

Determination of formaldehyde based on the enhancement of the chemiluminescence produced by CdTe quantum dots and hydrogen peroxide

Water-soluble cadmium telluride quantum dots (CdTe QDs) capped with glutathione (GSH) display chemiluminescence (CL) emission on reaction with hydrogen peroxide (H₂O₂) in strongly alkaline medium. It is found that the CL is strongly enhanced on addition of formaldehyde in aqueous solution. A flow injection system was developed, and it is shown that there is good linearity between CL intensity and the concentration of formaldehyde in the 0.06–3.0 μg L^?1 range. The limit of detection is as low as 10 ng L^?1. The method was successfully applied to the determination of formaldehyde in indoor air after adsorption into an aqueous phase. The recoveries for the real samples range from 97 % to 102.5 %, and the relative standard deviation is <3.8 % for intra- and inter-assay precision.

Determination of chromium(III) in water by solid-phase microextraction with a polyimide-coated fiber and gas chromatography-flame photometric detection

A method for the determination of trace Cr(III) in aqueous solution by solid-phase microextraction (SPME) coupled with gas chromatography (GC)-flame photometric detection (FPD) was developed. Aqueous Cr(III) was first converted to the volatile chromium trifluoroacetylacetonate (Cr(tfa)3) by derivatization with 1,1,1-trifluoroacetylacetone (Htfa), followed by SPME extraction using a polyimide-coated silica fiber. The distribution constants (K) of derivatized cis- and trans-Cr(tfa)3 between the polyimide phase and aqueous phase were 2012 and 2214, respectively. The two Cr(tfa)3 isomers extracted can be efficiently separated by a DB-210 GC column within 9 min. Selective detection of Cr was performed by a FPD equipped with a 385-nm long-pass filter. Linearity (r> 0.99) over the concentration range 5-300 ng ml(-1) Cr was obtained and the limit of detection was 2 ng ml(-1) Cr. The relative standard deviation was 7% at 10 ng ml(-1) Cr (n = 5). Applicability of this method to water analysis was tested by analyzing the chromium content in a reference standard water sample and an industrial effluent.     

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).     

Near-Infrared Hydrophobic Probes as Molecular Light Switch for CMC Determination of Triton X-100 Solution

The fluorescence behavior of two near-infrared (NIR) chromophores with linear alkyl chains of different lengths, 2-[4′chloro-7′(3″ethyl-2″benzothiaolinylidene)-3′,5′-(1″′3′″-propanediyl)-1′3′,5′-heptantriene-1′-yL]-3-ethylbenzothiazolium iodide (Probe Ⅰ) and 2-[4′chloro-7′(3″hexadecyl-2″benzothiazolinylidene)-3′,5′-(1′″,3′″-propanediyl)-1′,3′,5′-heptantriene-1′-yl]-3-ethylbenzothiazolium iodide (Probe Ⅱ), in aqueous solution containing different concentrations of surfactants was studied. The fluorescence of the probe with a short chain (probe Ⅰ) was completely quenched in water and aqueous solution containing a low concentration (below the critical micelle concentration,CMC) of surfactant Triton X-100. However, the fluorescence reappeared and reached maximum rapidly once the concentration of the surfactant approached the CMC. The probe with a long chain (probe II) displayed a similar fluorescence behavior but more dramatically fluorescent recovery in Triton X-100 system, which gave a direct in- dication for the micelle forming process and provided a simple method for the determination of the critical micelle concentration of the surfactant. The CMC values determined by this method were in good agreement with those obtained by other techniques. The fluorescence behavior of the two probes in other surfactant systems was also investigated.     

交联CMC控制释放除草剂的研究

本文报道以交联羧甲基纤维素囊化除草剂2，4，5－T、2，4－D和麦草畏二甲基胺盐所制成的控制释放体系的释放性能。研究了交联方法。制品形态、CMC取代度、交联剂用量和载药量等制备工艺条件对控释性能的影响。结果表明，以低取代度的CMC，经较大量甲醛交联制得的粒状制品，具有较好的控制释放性能。     

Improving continuous chemiluminescence determination method of formaldehyde in the atmosphere: reducing interference of acetaldehyde and others by using iodoform reaction

ABSTRACT

The continuous and selective determination method of formaldehyde (HCHO) in ambient air using chemiluminescence method has been developed. The counter current flow tube was used to collect gaseous formaldehyde. The major interferences of HCHO determination from acetaldehyde, ethanol, and ferrous ion were removed by applying iodoform reaction. Effect of acetaldehyde on chemiluminescence signal of formaldehyde at the same concentration was reduced from 19 to 0.3% by applying iodoform reaction. Subsequently, HCHO was online detected by measuring chemiluminescence produced from the reaction of HCHO, gallic acid, H₂O_2, and KOH. The limit of detection (S/N = 3) was 4.5 ppbv in air. The calibration graph was linear up to 6.25 ppmv. HCHO concentration measured by the present method showed good agreement with that obtained by the 2–4 DNPH-HPLC method.     

Sampling and analysing mixtures of sulphate, sulphite, thiosulphate and polythionate

Interpreting the redox chemistry of sulphur in aqueous systems requires the analysis of mixtures of various sulphoxy anions. Previous methods have been too involved to permit high sample throughout if good quality control is to be maintained. Methods based on ion chromatography have been developed for the direct determination of SO(2-)(4), SO(2-)(3), S(2)O(2-)(3), and SCN(-). The determination of thiocyanate permits the indirect determination of polythionates by treatment with cyanide. Formate, acetate, F(-), Cl(-), CO(2-)(3), and PO(3-)(4), do not interfere, but NO(-)(2) and NO(-)(3) interfere with determination of SO(2-)(3),. The sample preservation treatment includes addition of formaldehyde, cation-exchange and cold storage, to retard oxidation of S(2)O(2-)(3), and SO(2-)(3), and inhibits the rearrangement of SO(2-)(3),/S(2)O(2-)(3),/S(n)O(2-)(6), mixtures caused by bimolecular nucleophilic displacement (S(N)2) reactions. Treated samples may be stored for up to 6 weeks with only minor loss of thiosulphate.     

Determination of passive-sampled sulphur dioxide in ambient air as sulphate ion by flow injection analysis with an in-line reaction column

A modified FIA method was developed for the determination of sulphur dioxide (SO(2)) in ambient air collected by a passive sampler. SO(2) was oxidized by hydrogen peroxide and determined as sulphate ion in solution. Barium-dimethylsulfoazo-III complex was used as spectrophotometric reagent. A BaSO(4)-immobilized in-line reaction column was introduced into the flow system to increase the sensitivity and reproducibility. An in-line cation exchange column was used to eliminate triethanolamine, which was used as the absorbent reagent in the passive sampler. Sulphate ions can be analyzed in the range of 0.08-10.00 mg l(-1) with the R.S.D. less than 1.6% at the rate of 15 samples h(-1). It was satisfactory to apply this method to the analysis of sulphur dioxide in ambient air and the results agreed with those obtained by ion chromatography.