Investigation of the contact charge transfer absorption of organic solvents with oxygen for use in oxygen determination

The contact charge transfer (CCT) absorption spectra of dimethylsulphoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), ethanol, methanol, water, benzene (Bz), N,N'-diethylaniline (DEA), N,N'-dimethyl-p-toluidine (DMT) and N,N'-diethyl-p-toluidine with molecular oxygen have been investigated. These solvents form strong ultraviolet/visible CCT absorption spectra with intensities that are related to the partial pressure of the applied oxygen. DMSO, DMF, DMA, Bz, DEA and DMT are shown to form 1:1 molecular contact complexes with molecular oxygen. A simple oxygen sensing system is described using CCT absorption spectroscopy of DMT at a wavelength of 400 nm, with a gas flow rate of 60 cm(3) min(-1) through the solvent in a cuvette with a pathlength of 1 cm. Inexpensive plastic fibres are used to relay the light from a xenon lamp source to the cuvette and back to a photo-detector. The response of the sensing system to changes in oxygen concentration is reversible, non-linear and in good agreement with the Beer-Lambert law. The most sensitive response region is from 0 to 20% O(2) with a change in signal level of about 35%. The solvent used shows no deterioration in performance over a long period and can be used to determine gaseous oxygen concentrations from 0 to 100%. It does not respond to carbon dioxide.     

Distillation and detection of SO2 using a microfluidic chip

A miniaturized distillation system is presented for separating sulfurous acid (H(2)SO(3)) into sulfur dioxide (SO(2)) and water (H(2)O). The major components of the proposed system include a microfluidic distillation chip, a power control module, and a carrier gas pressure control module. The microfluidic chip is patterned using a commercial CO(2) laser and comprises a serpentine channel, a heating zone, a buffer zone, a cooling zone, and a collection tank. In the proposed device, the H(2)SO(3) solution is injected into the microfluidic chip and is separated into SO(2) and H(2)O via an appropriate control of the distillation time and temperature. The gaseous SO(2) is then transported into the collection chamber by the carrier gas and is mixed with DI water. Finally, the SO(2) concentration is deduced from the absorbance measurements obtained using a spectrophotometer. The experimental results show that a correlation coefficient of R(2) = 0.9981 and a distillation efficiency as high as 94.6% are obtained for H(2)SO(3) solutions with SO(2) concentrations in the range of 100-500 ppm. The SO(2) concentrations of two commercial red wines are successfully detected using the developed device. Overall, the results presented in this study show that the proposed system provides a compact and reliable tool for SO(2) concentration measurement purposes.     

A long pathlength spectrophotometric pCO(2) sensor using a gas-permeable liquid-core waveguide

The first long pathlength fiber optic-based sensor system to measure pCO(2) in natural waters and the atmosphere is described. The sensor is based on a liquid-core (an indicator-HCO(3)(-)/CO(3)(2-) buffer solution) waveguide made of a low refractive index amorphous fluoropolymer tubing, the wall of which serves as a gas-permeable membrane to sense pCO(2) changes. The system detects the indicator absorbance changes when the liquid-core reaches CO(2) equilibrium with the surrounding sample. Theoretical calculations demonstrate that due to indicator buffer effects, increasing the optical pathlength is a more efficient way to obtain higher sensitivity than increasing the indicator concentration. Using an 18-cm cell with low indicator concentrations (10 muM), this system achieves a precision and an accuracy of +/-2-3 muatm in the pCO(2) range of 200-500 muatm. The sensor also features a response time (99%) of only 2 min for low-level (<1000 muatm) pCO(2) measurements as a result of high CO(2) permeability of the amorphous fluoropolymer membrane. Field tests indicate that this new sensor is capable of handling both atmospheric and aquatic pCO(2) monitoring.     

Flow injection analysis of nitrite by gas phase molecular absorption UV spectrophotometry

A flow injection method on the basis of gas phase molecular absorption is described for the determination of nitrite in the aqueous solution. 200 mul of nitrite solution is introduced into a carrier stream of distilled water. The carrier stream containing nitrite zone is reacted with a stream of hydrochloric acid (2 M). The stream is then segmented by O(2) gas. The produced gaseous products are purged into the O(2) segments, react with O(2) and are carried toward the gas-liquid separator. The gaseous phase is separated from the liquid stream by the use of home-made gas-liquid separator and then is swept into a home-made flow cell. The absorbance of gaseous phase is measured at 205 nm using a UV/VIS spectrophotometer. Under selected conditions, two linear ranges, up to 1000 mug ml(-1) and 1000-2000 mug ml(-1) of nitrite were obtained. The limit of detection was 7.5 mug ml(-1) NO(2)(-). The relative standard deviations of repeated measurements of 100 and 500 mug ml(-1) NO(2)(-) were 3.7 and 1.0%, respectively. Up to 30 samples h(-1) can be analyzed. Interferences in the proposed method were few and were readily overcome. The proposed method was successfully applied to the determination of nitrite in the spiked water samples, a number of meat products and urine.     

Acceleration of the reaction OH + CO → H + CO2 by vibrational excitation of OH

The collision complex formed from a vibrationally excited reactant undergoes redissociation to the reactant, intramolecular vibrational relaxation (randomization of vibrational energy), or chemical reaction to the products. If attractive interaction between the reactants is large, efficient vibrational relaxation in the complex prevents redissociation to the reactants with the initial vibrational energy, and the complex decomposes to the reactants with low vibrational energy or converts to the products. In this paper, we have studied the branching ratios between the intramolecular vibrational relaxation and chemical reaction of an adduct HO(v)-CO formed from OH(X(2)Π(i)) in different vibrational levels v = 0-4 and CO. OH(v = 0-4) generated in a gaseous mixture of O(3)/H(2)/CO/He irradiated at 266 nm was detected with laser-induced fluorescence (LIF) via the A(2)Σ(+)-X(2)Π(i) transition, and H atoms were probed by the two-photon excited LIF technique. From the kinetic analysis of the time-resolved LIF intensities of OH(v) and H, we have found that the intramolecular vibrational relaxation is mainly governed by a single quantum change, HO(v)-CO → HO(v-1)-CO, followed by redissociation to OH(v-1) and CO. With the vibrational quantum number v, chemical process from the adduct to H + CO(2) is accelerated, and vibrational relaxation is decelerated. The countertrend is elucidated by the competition between chemical reaction and vibrational relaxation in the adduct HOCO.     

Determination of total gaseous lead in the atmosphere by honeycomb denuder/electrothermal atomic absorption spectrometry.

A technique is described for the determination of total gaseous lead in the atmosphere by honeycomb denuder collection, followed by an electrothermal atomic absorption spectrometry (ETAAS) measurement. The collection efficiency of the honeycomb denuder in which a solution containing 2% HNO3/2% glycerine/1% ammonium dihydrogenphosphate was coated for trapping the gaseous lead in the atmosphere was 98.8%. The linear absorbance response was obtained for a concentration range of 0-1.39 microg m(-3) of lead in the atmosphere. A precision of 4.8% RSD (peak-height absorbance, n = 11) for an aqueous solution of 1 ng of lead standard, characteristic masses (CM) of 23 pg and detection limit (3sigma) of 54 pg for an aqueous solution of 0.01 ng lead standard was achieved with 100 microg ammonium dihydrogenphosphate as a chemical modifier. The average recovery of lead in three standard samples prepared by the independent digestion of NIST SRM 1648 (Urban Particulate Matter) using our analytical system was 97.8%. The total content of the gaseous lead in the atmosphere of our laboratories was 0.35-0.38 microg m(-3).     

Magnesium aminoethyl phosphonate (Mg(AEP)(H2O)): an inorganic-organic hybrid nanomaterial with high CO2:N2 sorption selectivity

The inorganic-organic hybrid magnesium aminoethyl phosphonate (Mg(AEP)(H(2)O), particle diameter: 20 nm; specific surface area: 322(10) m(2) g(-1); pore volume: 0.9(1) cm(3) g(-1)) shows reversible CO(2) sorption (152(5) mg g(-1)) at high pressure (≤110 bar). In contrast, N(2) uptake remains below 1.0(1) mg g(-1). Based on this selectivity (～100%) Mg(AEP)(H(2)O) expands the range of materials available for CO(2) capture.     

Piezoelectric crystal sensor for the determination of formaldehyde in air

Formaldehyde in air was detected and assayed with a piezoelectric quartz crystal coated with a 7,10-dioxa-3,4-diaza-1,5,12,16-hexadecatetrol/chromotropic acid solution. Water vapor and several gaseous interferents were removed by passing the sampling stream through a column of anhydrous magnesium perchlorate. The response curves were linear in the concentration ranges 0.4-4.5 and 0.4-3.6 ppm v/v CH(2)O with and without the scrubber column, respectively. A single coating was used for 12 days (500 assays) without significant loss in sensitivity. With a single-point daily recalibration, the useful lifetime of the coating is about 2 months.     

Surface abundance change in vacuum ultraviolet photodissociation of CO2 and H2O mixture ices

Photodissociation of amorphous ice films of carbon dioxide and water co-adsorbed at 90 K was carried out at 157 nm using oxygen-16 and -18 isotopomers with a time-of-flight photofragment mass spectrometer. O((3)P(J)) atoms, OH (v = 0) radicals, and CO (v = 0,1) molecules were detected as photofragments. CO is produced directly from the photodissociation of CO(2). Two different adsorption states of CO(2), i.e., physisorbed CO(2) on the surface of amorphous solid water and trapped CO(2) in the pores of the film, are clearly distinguished by the translational and internal energy distributions of the CO molecules. The O atom and OH radical are produced from the photodissociation of H(2)O. Since the absorption cross section of CO(2) is smaller than that of H(2)O at 157 nm, the CO(2) surface abundance is relatively increased after prolonged photoirradiation of the mixed ice film, resulting in the formation of a heterogeneously layered structure in the mixed ice at low temperatures. Astrophysical implications are discussed.     

Vapour phase Fourier transform infrared spectrometric determination of thiourea

A novel and precise procedure for the determination of thiourea based on vapour-generation Fourier transform infrared spectrometry is described. A 4 ml volume of 1.4% m/v iodine solution was injected into a glass vessel containing 5 ml of thiourea and 0.2 ml of 1 M sodium hydrogencarbonate solution. The CO2 evolved under these conditions was swept by a stream of nitrogen to an infrared gas cell. At 200 s after injection of the iodine solution, the vapour phase FTIR spectra were continously recorded, as a function of time, between 2500 and 2200 cm(-1), which includes the CO2 absorption band at 2350 cm(-1). From the absorbance data in the 2399-2284 cm(-1) range, integrated absorbance measurements were obtained providing transient recordings which correspond to the absorbance of CO2 in the selected wavenumber range. The method provided a limit of detection of 10 ppm of thiourea, a throughput of 14 samples h(-1) and an RSD of 1.1% for three independent analyses of a 500 ppm thiourea solution. Results obtained for a series of real samples compared well with those obtained using potentiometric titration as a reference method.     

In Process Citation

Carbonate as impurity often interferes in acid-base titrations. To take into account the liquid-gas equilibrium [H(2)CO(3) right harpoon over left harpoon CO(2(g)) H(2)O)] a new method is proposed: neutratizations are performed in a closed system with a known volume of gaseous phase. The corresponding equations, processed by multiparametric refinement, are successfully applied in the extreme case, viz. neutralization of a strong acid by sodium carbonate solution.     

First identification and thermodynamic characterization of the ternary U(VI) species, UO2(O2)(CO3)2(4-), in UO2-H2O2-K2CO3 solutions

In alkaline carbonate solutions, hydrogen peroxide can selectively replace one of the carbonate ligands in UO2(CO3)3(4-) to form the ternary mixed U(VI) peroxo-carbonato species UO2(O2)(CO3)2(4-). Orange rectangular plates of K4[UO2(CO3)2(O2)].H2O were isolated and characterized by single crystal X-ray diffraction studies. Crystallographic data: monoclinic, space group P2(1)/ n, a = 6.9670(14) A, b = 9.2158(10) A, c = 18.052(4) A, Z = 4. Spectrophotometric titrations with H 2O 2 were performed in 0.5 M K 2CO 3, with UO2(O2)(CO3)2(4-) concentrations ranging from 0.1 to 0.55 mM. The molar absorptivities (M(-1) cm(-1)) for UO2(CO3)3(4-) and UO2(O2)(CO3)2(4-) were determined to be 23.3 +/- 0.3 at 448.5 nm and 1022.7 +/- 19.0 at 347.5 nm, respectively. Stoichiometric analyses coupled with spectroscopic comparisons between solution and solid state indicate that the stable solution species is UO2(O2)(CO3)2(4-), which has an apparent formation constant of log K' = 4.70 +/- 0.02 relative to the tris-carbonato complex.     

Simultaneous kinetic determination of phenols by use of the kalman filter

A multicomponent analysis method based on the Kalman filter algorithm is proposed for the determination of phenolic compounds. The method relies on the oxidative coupling of phenols (phenol, 2-chlorophenol and 3-chlorophenol) to N,N-diethyl-p-phenylenediamine in the presence of hexacyanoferrate(III), the reaction being monitored via changes in the absorbance at 660 nm of the dye formed. Phenols can be determined individually over the concentration range 1.25-25 muM with a relative standard deviation of ca 0.6-0.8%. Differences in the kinetic behaviour of the three species were exploited by using the linear Kalman filter to resolve mixtures of the phenols at the muM level in a widely variable concentration ratios with errors less than 10%.     

Physical organic chemistry of transition metal carbene complexes. 25. Kinetic and thermodynamic acidities of substituted (methylthiophenylcarbene)pentacarbonyl tungsten(0) and (Benzoxymethylcarbene)pentacarbonyl tungsten(0) in aqueous acetonitrile. Evidence for transition state imbalances

A kinetic study of the reversible deprotonation of substituted (methylthiophenylcarbene)pentacarbonyltungsten(0) ((CO)(5)W=C(SC(6)H(4)Z)CH(3)) and of substituted (benzoxymethylcarbene)pentacarbonyltungsten(0) ((CO)(5)W=C(OCH(2)C(6)H(4)Z)CH(3)) by primary aliphatic and secondary alicyclic amines in 50% MeCN-50% water (v/v) at 25 degrees C is reported. From the dependence of the deprotonation rate constants on amine basicity and on carbene complex acidity (variation of Z), Br?nsted beta(B) and alpha(CH) values, respectively, were obtained. The alpha(CH) values were found to be smaller than the beta(B) values. These results indicate a transition state imbalance in which the loss of the carbene complex stabilizing pi-donor effect of the OCH(2)Ar and SAr groups lags behind the proton transfer. These findings confirm a previously formulated hypothesis as to how pi-donor groups attached to the carbene carbon of carbene complexes can affect transition state imbalances and mask the experimental manifestation of such imbalances. It is also shown that the transition state structure of the reactions examined in this work is subject to changes with changing amine basicity and carbene complex acidity; these changes can be expressed by p(xy)() cross correlation coefficients, which are positive.     

Stopped-flow spectrophotometric study of the kinetics and mechanism of CO₂ uptake by cis-[Cr(C₂O₄)(BaraNH₂)(OH₂)₂]+ cation and the acid-catalyzed decomposition of cis-[Cr(C₂O₄)(BaraNH₂)OCO₂]- anion in aqueous solution

The kinetics of CO(2) uptake by the cis-[Cr(C(2)O(4))(BaraNH(2))(OH(2))(2)]+ complex cation and the acid hydrolysis of the cis-[Cr(C(2)O(4))(BaraNH(2))OCO(2)]- complex anion (where BaraNH(2) denotes methyl 3-amino-2,3-dideoxy-b-D-arabino-hexopyranoside) were studied using the stopped-flow technique. The reactions under study were investigated in aqueous solution in the 288-308 K temperature range. In the case of the reaction between CO(2) and cis-[Cr(C(2)O(4))(BaraNH(2))(OH(2))(2)]+ cation variable pH values (6.82-8.91) and the constant ionic strength of solution (H+, Na+, ClO(4)- = 1.0) were used. Carbon dioxide was generated by the reaction between sodium pyruvate and hydrogen peroxide. The acid hydrolysis of cis-[Cr(C(2)O(4))(BaraNH(2))OCO(2)]- was investigated for varying concentrations of H+ ions (0.01-2.7 M). The obtained results enabled the determination of the number of steps of the studied reactions. Based on the kinetic equations, rate constants were determined for each step. Finally, mechanisms for both reactions were proposed and discussed. Based on the obtained results it was concluded that the carboxylation (CO(2) uptake) reactions of cis-[Cr(C(2)O(4))(BaraNH(2))(OH(2))(2)]+ and the decarboxylation (acid hydrolysis) of the cis-[Cr(C(2)O(4))(BaraNH(2))OCO(2)]- are the opposite of each other.     

模拟合成盐卤与盐酸反应的热化学研究

青藏高原新类型盐湖卤水日晒蒸发过程中硼酸盐在浓缩卤水中富集L‘。，我们在前又问中曾报道天然浓缩盐卤中硼酸盐是以“四硼酸盐”的综合统计形式存在，当盐卤浓缩到氯化镁共饱和时，可视为MgO－BZO3－MgC12－HZO四元体系中的一个特定的膺三元体系MgO·2B2O3－MgC12－H。O．该四元体系20oC热力学非平衡态液固相图问与25oC热力学平衡态相图＊存在较大差别．由于聚合翻氧配阴离子的存在，使得对含棚浓缩盐卤的研究变得复杂而困难＊．李积才等“～SJ对合成盐卤的稀释热和表观摩尔热径进行过测定，李军间在对多种水合硼酸盐在盐酸中…     

Pulse radiolysis studies on galactose oxidase

Single-Cu-containing galactose oxidase in the GOase(semi) state (Cu(II), no Tyr(*) radical) reacts with pulse radiolysis generated formate radicals CO(2)(*-) to give an intermediate UV-vis spectrum assigned as RSSR(*-), peak at 450 nm (epsilon = 8100 M(-1) cm(-1)). From a detailed kinetic analysis at 450 nm, pH 7.0, the following steps have been identified. First the strongly reducing CO(2)(*-) (-1.9V) reduces GOase(semi) (k(0) > or = 6.5 x 10(8) M(-1) s(-1)) to a species GOase(semi)(*-). This is followed by biphasic reactions (i) GOase(semi)(*-) + GOase(semi) (k(1) = 1.6 x 10(7) M(-1) s(-1)) to give GOase(semi) + P(*-) and (ii) P(*-) + GOase(semi) (k(2) = 6.7 x 10(6) M(-1) s(-1)) to give GOase(semi)RSSR(*-). There are no significant absorbance changes for the formation of GOase(semi)(*-) and P(*-), which are Cu(I) (or related) species. However, GOase(semi)RSSR(*-) has an absorption spectrum which differs significantly from that of GOase(semi). The 450 nm peak is characteristic of an RSSR(*-) radical with two cysteines in close sequence proximity and is here assigned to Cys515-Cys518, which is at the GOase surface and 10.2 A from the Cu. On chemical modification of the RSSR group with HSPO(3)(2-) to give RSSPO(3)H(-) and RS(-), absorbance changes are approximately 50% of those previously observed. The decay of RSSR(*-) (0.17 s(-1)) results in the formation of GOase(red). No RSSR(*-) formation is observed in the reaction of GOase(semi) Tyr495Phe with CO(2)(*-), and a single process giving GOase(red)Tyr495Phe occurs. Similarly in the reaction of GOase(ox) with CO(2)(*-), a single-stage reaction gives GOase(semi).     

Effect of complexones and tensides on selectivity of nitrogen dioxide determination in air with a chemiluminescence aerosol detector

Modification of the luminol solution by means of addition of various complexones and surfactants has been investigated to eliminate interferences from gaseous co-pollutants in the determination of ambient nitrogen dioxide using a chemiluminescence aerosol detector. The simultaneous presence of EDTA and triton X-100 or X-405 together with sulphite and iodide in the luminol solution suppressed interferences from ozone and peroxyacetyl nitrate to a negligible level and no scrubbers or corrections of the NO₂ measurements were needed.

In general, the best composition of the reagent solution included luminol, KOH, Na₂SO₃, KI, Na₂EDTA and triton X-100. From the point of view of selectivity of NO₂ determination, an optimum reagent solution consisted of luminol (0.002 M), KOH (0.5 M), Na₂SO₃ (0.2 M), KI (0.1 M), Na₂EDTA (0.05 M) and triton X-100 (0.5 vol.%). Interferences from ozone (170 ppb (v/v)) and peroxyacetyl nitrate (81 ppb (v/v)) were 0.2 and 1.2%, respectively, for nitrogen dioxide at a concentration of 50 ppb (v/v) and 0.25 and 1.7%, respectively, for 0.5 ppb (v/v) NO₂. The calibration graph was linear for NO₂ concentrations ranging from 3 to 665 ppb (v/v). Below 3 ppb (v/v) NO₂ the detector response to nitrogen dioxide can be fitted with a linear equation of the third order.     

Quantitative trace-level speciation of arsenite and arsenate in drinking water by ion chromatography

We describe an improved method for the determination of inorganic arsenic in drinking water. The method is based on comprehensive optimization of the anion-exchange ion chromatographic (IC) separation of arsenite and arsenate with post-column generation and detection of the arsenate-molybdate heteropoly acid (AMHPA) complex ion. The arsenite capacity factor was improved from 0.081 to 0.13 by using a mobile phase (2.0 mL min(-1)) composed of 2.5 mM Na2CO3 and 0.91 mM NaHCO3 (pH 10.5). A post-column photo-oxidation reactor (2.5 m x 0.7 mm) was optimized (0.37 microM potassium persulfate at 0.50 mL min(-1)) such that arsenite was converted to arsenate with 99.8 +/- 4.2% efficiency. Multi-variate optimization of the complexation reaction conditions yielded the following levels: 1.3 mM ammonium molybdate, 7.7 mM ascorbic acid, 0.48 M nitric acid, 0.17 mM potassium antimony tartrate, and 1.0% (v/v) glycerol. A long-path length flow cell (Teflon AF, 100-cm) was used to measure the absorption of the AMHPA complex (818 +/- 2 nm). Figures of merit for arsenite/arsenate include: limit of detection (1.6/0.40 microg L(-1)): standard error in absorbance (5.1 x 10(-3)/3.5 x 10(-3)); and sensitivity (2.9 x 10(-3)/2.2 x 10(-3) absorbance units per ppb). Successful application of the method to fortified surface and ground waters (100 microL samples) is also described.     

Distribution of internal states of CO from O (1D) + CO determined with time-resolved fourier transform spectroscopy

Following collisions of O (1D) with CO, rotationally resolved emission spectra of CO (1 < or = v < or = 6) in the spectral region 1800-2350 cm(-1) were detected with a step-scan Fourier transform spectrometer. O (1D) was produced by photolysis of O3 with light from a KrF excimer laser at 248 nm. Upon irradiation of a flowing mixture of O3 (0.016 Torr) and CO (0.058 Torr), emission of CO (v < or = 6) increases with time, reaches a maximum approximately 10 micros. At the earliest applicable period (2-3 micros), the rotational distribution of CO is not Boltzmann; it may be approximately described with a bimodal distribution corresponding to temperatures approximately 8000 and approximately 500 K, with the proportion of these two components varying with the vibrational level. A short extrapolation from data in the period 2-6 micros leads to a nascent rotational temperature of approximately 10170 +/- 600 K for v = 1 and approximately 1400 +/- 40 K for v = 6, with an average rotational energy of 33 +/- 6 kJ mol(-1). Absorption by CO (v = 0) in the system interfered with population of low J levels of CO (v = 1). The observed vibrational distribution of (v = 2):(v = 3):(v = 4):(v = 5):(v = 6) = 1.00:0.64:0.51:0.32:0.16 corresponds to a vibrational temperature of 6850 +/- 750 K. An average vibrational energy of 40 +/- 4 kJ mol(-1) is derived based on the observed population of CO (2 < or = v < or = 6) and estimates of the population of CO (v = 0, 1, and 7) by extrapolation. The observed rotational distributions of CO (1 < or = v < or = 3) are consistent with results of previous experiments and trajectory calculations; data for CO (4 < or = v < or = 6) are new.