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).     

On-line collection/concentration and detection of sulfur dioxide in air by flow-injection spectrophotometry coupled with a chromatomembrane cell.

A simple and rapid procedure for SO2 determination in air was developed by using a flow injection analysis (FIA) system coupled with a 3-hole chromatomembrane cell (CMC). The CMC was applied for the on-line collection/concentration of SO2 from air into a solution of 2 g l(-1) triethanolamine (TEA) solution as an absorbing solution: SO2 was converted to SO3(2-) in the alkaline absorbing solution. The solution containing absorbed SO2 was introduced into the carrier stream of the FIA system. The amount of SO3(2-) in the absorbing solution was measured by spectrophotometry with a mixed reagent of pararosaniline and formaldehyde, and was converted to the concentration of SO2 in the air sample. A calibration graph prepared by using standard sodium sulfite aqueous solutions was adopted for the determination of SO3(2-) in the absorbing solution. The SO2 concentration in indoor air examined was found to be 22.7 +/- 0.2 ppbv using 20 ml of air sample with the air flow rate of 5 ml min(-1), where the relative standard deviation was 1.7%. The detection limit for aqueous solutions and air samples were 6.9 x 10(-8) M and 0.48 ppbv, respectively. The measuring time for one sample was about 10 min when a 20 ml air sample was used. The interferences from common anionic species, formaldehyde and acetaldehyde, were also examined.     

Evaluation of ammonia as diluent for serum sample preparation and determination of selenium by graphite furnace atomic absorption spectrometry

A method for the determination of total selenium in serum samples by graphite furnace atomic absorption spectrometry was evaluated. The method involved direct introduction of 1:5 diluted serum samples (1% v/v NH₄OH+0.05% w/v Triton X-100^®) into transversely heated graphite tubes, and the use of 10 μg Pd+3 μg Mg(NO₃)₂ as chemical modifier. Optimization of the modifier mass and the atomization temperature was conducted by simultaneously varying such parameters and evaluating both the integrated absorbance and the peak height/peak area ratio. The latter allowed the selection of compromise conditions rendering good sensitivity and adequate analyte peak profiles. A characteristic mass of 49 pg and a detection limit (3s) of 6 μg 1⁻¹ Se, corresponding to 30 μg l⁻¹ Se in the serum sample, were obtained. The analyte addition technique was used for calibration. The accuracy was assessed by the determination of total selenium in Seronorm™ Trace Elements Serum Batch 116 (Nycomed Pharma AS). The method was applied for the determination of total selenium in ten serum samples taken from individuals with no known physical affection. The selenium concentration ranged between 79 and 147 μg l⁻¹, with a mean value of 114±22 μg l⁻¹.     

A novel method for the spectrophotometric determination of nitrite in water

A rapid, simple, selective and sensitive method for the spectrophotometric determination of nitrite in water has been developed and optimum reaction conditions along with other analytical parameters have been evaluated. Nitrite reacts with barbituric acid in acidic solution to give the nitroso derivative, violuric acid. At analytical wavelength of 310 nm, Beer's law is obeyed over the concentration range 0.00–3.22 ppm of nitrite. The molar absorptivity is 15330 ± 259.7 (95%) with pooled standard deviation of 355.57 and R.S.D. of 2.32%. As well as the method is sensitive (2.99 × 10⁻³ μg NO₂ cm⁻²) and selective, it tolerates most of the potential interferents. It has been successfully applied to nitrite determination in natural waters by use of a calibration graph with determination limit of 1.66 μg NO₂ in 100 mL working solution corresponding to minimum 9.5 ppb NO₂–N in water samples. Lower concentrations of nitrite (3.0 μg NO₂/L sample) is precisely analyzed by using the method of dilution with sample, with R.S.D. of lower than 0.5%. The results were compared with standard N-(1-naphtyl)ethylenediamine dihydrochloride method and very good agreement between the data was observed. The method can easily be applied in the field.     

Simple flow-injection system for the simultaneous determination of nitrite and nitrate in water samples

A novel spectrophotometric reaction system was developed for the determination of nitrite as well as nitrate in water samples, and was applied to a flow-injection analysis (FIA). The spectrophotometric flow-injection system coupled with a copperised cadmium reductor column was proposed. The detection was based on the nitrosation reaction between nitrite ion and phloroglucinol (1,3,5-trihydroxybenzene), a commercially available phenolic compound. Sample injected into a carrier stream was split into two streams at the Y-shaped connector. One of the streams merged directly and reacted with the reagent stream: nitrite ion in the samples was detected. The other stream was passed through the copperised cadmium reductor column, where the reduction of nitrate to nitrite occurred, and the sample zone was then mixed with the reagent stream and passed through the detector: the sum of nitrate and nitrite was detected. The optimised conditions allow a linear calibration range of 0.03–0.30 μg NO₂⁻-N ml⁻¹ and 0.10–1.00 μg NO₃⁻-N ml⁻¹. The detection limits for nitrite and nitrate, defined as three times the standard deviation of measured blanks are 2.9 ng NO₂⁻-N ml⁻¹ and 2.3 ng NO₃⁻-N ml⁻¹, respectively. Up to 20 samples can be analyzed per hour with a relative standard deviation of less than 1.5%. The proposed method could be applied successfully to the simultaneous determination of nitrite and nitrate in water samples.     

Titanium as a chemical modifier for the determination of cobalt in marine sediments

The determination of cobalt in marine sediments by electrothermal atomic absorption spectrometry was studied using no modifier and magnesium and titanium as modifiers. Titanium is one of the major sediment constituents, which widely affects the cobalt determination and it was studied as a chemical modifier since it was the only concomitant that increased the cobalt signal in the concentration range usually found in sediments. The performance of Mg and Ti as chemical modifiers was compared relative to maximum pyrolysis and atomization temperatures, linear calibration range, sensitivity and matrix effects. The pyrolysis curves showed that the analyte could be stabilized up to 1400 °C when either Ti or Mg(NO₃)₂ was present, while only 1000 °C could be used in the absence of a modifier. The optimum atomization temperature was 2500 °C in all cases. Analytical curves were compared using no modifier, 5 μg Ti and 100 μg Mg(NO₃)₂ as modifiers, and the linear range found was up to approximately 4 ng Co whether a modifier was used or not. With Ti as a chemical modifier, analytical curves for cobalt in aqueous solution and in a synthetic matrix resulted in the same sensitivity (m₀=55 pg), whereas the use of Mg led to characteristic mass values of 59 and 72 pg in aqueous solution and in a synthetic matrix, respectively, showing some matrix effect. The detection limits (3σ, n=10) were 0.4 μg g⁻¹ using no modifier and 0.3 μg g⁻¹ with Ti as a modifier in the original matrix. A reference estuarine sediment NIST 1646 with a non-certified content of 10.5 μg g⁻¹ Co was analyzed and the found value of 10.9±2.4 μg g⁻¹, (n=3), using Ti as chemical modifier and calibration against aqueous standards, was in good agreement with the recommended value.     

Molecular iodine preconcentration and determination in aqueous samples using poly(vinylpyrrolidone) containing membranes

Membranes for preconcentration of molecular iodine were developed by two different routes: (i) UV-grafting of 1-vinyl-2-pyrrolidone in the pores of microporous poly(propylene) host membrane (grafted membrane), and (ii) physical immobilization of preformed poly(vinylpyrrolidone) (PVP) in a plasticized cellulose triacetate matrix to form the polymer inclusion membrane (PVP-PIM). The UV-grafted PVP-membrane was found to be hydrophilic (water uptake capacity = 166 wt.%), while the PVP-PIM was found to be highly hydrophobic (≈2 wt.%). PVP-PIM was found to uptake only I₂ from aqueous sample whereas I₂ and I₃⁻ were sorbed in the grafted membrane. This selectivity of PVP-PIM towards I₂ was attributed to its hydrophobicity that allows only neutral I₂ to interact with PVP in the membrane matrix. Thus, the selective preconcentration and quantitative determination of I₂ in aqueous sample was carried out using PVP-PIM. As PVP-PIM was optically transparent, the characteristic absorbance of PVP–I₂ complex (λ_max = 361 nm) could be used for quantitative determination of I₂ in the membrane. The instrumental neutron activation analysis (INAA) of the I₂-loaded PIM samples indicated that 82% could be sorbed into the PIM samples from the solution within 10 min of equilibration time. This membrane was applied to I₂ determinations in the samples of ¹³¹I radiotracer. The concentration level of iodine species in these samples were in sub-ppb level. Therefore, these samples were ideal for testing the preconcentration efficiency of the membrane towards I₂ by monitoring the radioactivity of ¹³¹I. The amounts of I₂ in the aqueous samples were standardized by conventional solvent extraction of I₂ with the chloroform for validating the preconcentration efficiency of PVP-PIM. The detection limit of I₂ in aqueous samples by INAA hyphenated with PVP-PIM was found to be 0.3 ppb for a sample size of 25 mL.     

An automatic falling drop system based on multicommutation process for photometric chlorine determination in bleach

In this work an automatic photometric procedure for the determination of chlorine in bleach samples employing N,N′-diethyl-p-phenylenediamine (DPD) as chromogenic reagent is described. The procedure was based on a falling drop system where the analyte (Cl₂) was collected by a DPD solution drop (50 μL) after its delivery from the sample bulk that was previously acidified. The flow system was designed based on the multicommutation process assembling a set of three-way solenoid valves, which under microcomputer control afforded facilities to handle sample and reagent solution in order to control analyte delivering and solution drop generation. The analyte volatilization was improved by coupling online a little heating device. The detection system comprised a green LED (515 nm) and a phototransistor. Aiming to prove the usefulness of the proposed procedure a set of bleach samples was analyzed. Comparing the results with those obtained with reference method no significant difference at 95% confidence level was observed. Other profitable features such as a linear response ranging from 15 up to 100 mg L⁻¹ Cl₂ (R = 0.999); a detection limit of 4.5 mg L⁻¹ Cl₂ estimated based on the 3σ criterion; a relative standard deviation of 2.5% (n = 10) using a typical bleach sample containing 25.0 mg L⁻¹ Cl₂; a consumption of 55 μg of DPD per determination; and a analytical frequency of 20 determinations per hour were also achieved.     

Spectrophotometric determination of nitrate and nitrite in soil and water samples with a diazotizable aromatic amine and coupling agent using column preconcentration on naphthalene supported with ion-pair of tetradecyldimethylbenzylammonium and iodide

Composite diazotization-coupling reagents containing sulfanilamide (SAM), sulfapyridine (SP) or sulfathiazole (ST) as the diazotizable aromatic amines and sodium 1-naphthol-4-sulfonate (NS) as the coupling agent using column preconcentration on naphthalene-tetradecyldimethylbenzylammonium(TDBA)-iodide adsorbent have been used for the spectrometric determination of trace nitrate and nitrite in soil and water samples. Nitrite ion reacts with SAM in the pH range 2.0–5.0, SP in the pH range 2.0–2.5 and ST in the pH range 2.0–3.3 in HCl medium to form water-soluble colourless diazonium cations. These cations were coupled with NS in the pH range 9.0–12.0 for the SAM system, 9.6–12.0 for the SP system and 8.5–12.0 for the ST system to be retained on naphthalene-TDBA-I material packed in a column. The solid mass is dissolved from the column with 5 ml of dimethylformamide and the absorbance is measured spectrometerically at 543 nm for SAM-NS, 533 nm for SP-NS and 535 nm for ST-NS. Nitrate is reduced to nitrite by a copper-coated cadmium reductor column and the nitrite is then treated with the diazotization-coupling reagent by column preconcentration. The absorbance due to the sum of nitrate and nitrite is measured and nitrate is determined by difference. The calibration graph was linear over the range 2–40 ng NO₂⁻-N ml⁻¹ and 1.5–30 ng NO₃⁻-N ml⁻¹ in aqueous samples for the SAM and ST systems and 2–48 ng NO₂⁻-N ml⁻¹ and 1.5–36 ng NO₃⁻-N ml⁻¹ in aqueous samples for the SP system, respectively. The sensitivity, accuracy and precision of the systems decreased in the order STSAMSP. The detection limits were 1.4 ng NO₂⁻-N ml⁻¹ and 1.1 ng NO₃⁻-N ml⁻¹ for SAM, 1.6 ng NO₂⁻-N ml⁻¹ and 1.2 ng NO₃⁻-N ml⁻¹ for SP, and 1.0 ng NO₂⁻-N ml⁻¹ and 0.75 ng NO₃⁻-N ml⁻¹ for ST, respectively. The preconcentration factors are 8, 5 and 6 for SAM-NS, SP-NS and ST-NS, respectively. Interferences from various foreign ions have been studied and the methods have been applied to the determination of ng ml⁻¹ levels of nitrite and nitrate in soil and water samples. The mean recovery was 95–102% for all three systems.     

Binary modifiers for the determination of zinc in pure copper and nickel-based alloy by longitudinal Zeeman electrothermal atomic absorption spectrometry

The determination of zinc in pure copper and nickel-based alloy was successfully accomplished with a longitudinal Zeeman-effect correction and end-capped transversely heated graphite atomizer. Since aqua regia (an acid mixture of nitric acid and hydrochloric acid, 1:3, v/v) was used as the dissolving reagent, volatile ZnCl₂ was formed. Consequently, less Zn was found in the sample. EDTA could improve the atomic absorption profiles. Binary modifiers, EDTA + Pd(NO₃)₂ and EDTA + Mg(NO₃)₂, were effective for eliminating the chloride interference and the spectral interference from Cu I 213.853 nm. The experimental results obtained with and without the modifiers were compared. Increase of 200 °C in the pyrolysis temperature resulted from the addition of binary modifiers for both pure copper and nickel-based alloys. For pure copper, the atomization temperature increased from 1400 to 1600 °C whereas the atomization temperature increased from 1100 to 1600 °C for nickel-based alloys. The analytical performance of the proposed method was evaluated. Zinc contents in the pure copper and nickel-based alloy standards determined with both binary modifiers agreed closely with the certified values. The recovery ranged from 93 ± 2 to 104 ± 6% at 95% confidence level. The detection limits obtained by the binary modifiers of EDTA + Pd(NO₃)₂ and EDTA + Mg(NO₃)₂ were 0.77 and 0.31 pg, respectively.     

Supported liquid membranes for the determination of vanillin in food samples with amperometric detection

A supported liquid membrane system has been developed for the extraction of vanillin from food samples. A porous PTFE membrane is impregnated with an organic solvent, which forms a barrier between two aqueous phases. The analyte is extracted from a donor phase into the hydrophobic membrane and then back extracted into a second aqueous solution, the acceptor. The determination (100–1400 μg ml⁻¹ vanillin) was performed using a PVC-graphite composite electrode versus Ag/AgCl/3MKCl at +0.850 V placed in a wall-jet flow cell as amperometric detector. The solid sample is directly placed in the membrane unit without any treatment, and the analyte was extracted from the sample, passes through the membrane and conduced to the flow cell by the acceptor stream. The limit of detection (3σ) was 44 μg ml⁻¹. The method was applied to the determination of vanillin (9–606 μg g⁻¹) in food samples.     

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.     

THE ACTION MODE OF CISPLATIN ON DNA-SYNTHESIS AND CHARACTERIZATION OF N7 N1 CROSS-LINKAGE MODEL COMPOUND OF PLATINUM AND GUANOSINE

The title Pt-Guo compound was synthesized and isolated by the reaction between cis-[Pt(NH3)2(H2O)2](NO3)2 and guanosine of mol ratio1:1 in a neutral aqueous solution followed by careful purification with partial crystalization and recrystallizatlon from water at 0℃.The compound was characterized by elemental analysis,molecular weight determination,DTA,and C NMR spectroscopy and its formulawas found to be [8(GuoH-1)7 (OH)2] (NO3)7 8H2O.The isolation of the compound provides direct evidence for the intrastrand cross-linkage between cisplatin and DNA through N7,N1 atoms of two adjacent guanines.     

ICP-AES determination of silver after chemical separation from uranium matrix

The separation of silver from a uranium matrix has been carried out using Cyanex-471X (triisobutylphosphine sulphide) in xylene. The effects of various parameters such as the Cyanex-471X concentration, the nitric acid molarity, the contact time and the nitrate ion concentration on the extraction of silver have been studied. The silver metal ion species extracted into the organic phase was found to be Ag(NO₃)·2S (where S is Cyanex-471X). The stripping of silver into an aqueous medium was carried out with 5% NaHSO₃, followed by its determination using ICP-AES.     

Spectrophotometric determination of tungsten(VI) enriched by nanometer-size titanium dioxide in water and sediment

The adsorption of W (VI) on different metal oxides (TiO₂, ZrO₂), different crystal form of TiO₂ (rutile, anatase) with high surface areas was studied and compared under different pH. A novel method for preconcentration of W (VI) with nanometer size titanium dioxide (rutile) and determination by spectrophotometry has been developed. W (VI) was selective adsorbed on 100 mg TiO₂ from 250 ml solution at pH 3.0, then eluted by 2 ml 9 mol l⁻¹ sodium hydroxide solution. The eluent was adjusted to 5 ml pH 0 solution, added 0.5 ml 12 mol l⁻¹ HCl, 0.3 ml 3% TiCl₃, 0.3 ml 50% NH₄SCN, stirred for 20 min, used for the analysis of W (VI) by measuring the absorbance at 402 nm with spectrophotometry, based on the chromogenic reaction between the W (VI) and the mixture of TiCl₃ and NH₄SCN. This method gave a concentration enhancement of 50 for 250 ml sample, eliminated the sizable interferences on direct determination with spectrophotometry. Detection limits (3σ, n=11) of 1.2 ng ml⁻¹, relative standard deviation of 2.3% at 10 ng ml⁻¹ level were obtained. The method was applied to determine the W (VI) in hot spring water, river water, tap water and stream sediment. Analytical recoveries of W (VI) added to samples were 98–101%.     

CuCrO2的合成及其复合催化剂的光催化性能

以硝酸铬和硝酸铜为原料,通过半湿法经两种不同路径合成了CuCrO₂半导体物质。分别采用热重-差示扫描（TG-DSC）、X射线衍射（XRD）、紫外-可见漫反射（UV-vis DR）、扫描电镜（SEM）及X射线光电子能谱（XPS）对样品进行了表征分析。确立了以氨水为Cr³⁺沉淀剂制得的氢氧化铬沉淀中加入硝酸铜溶液是合成CuCrO₂较适宜的路径。借助TG-DSC和XRD的分析结果确立前驱体在热处理的过程中,含Cr物相的变化历程为Cr（OH）₃ → CuCrO₄ → CuCr₂O₄ → CuCrO₂。通过机械研磨的方法合成了CuCrO₂-WO₃和CuCrO₂-ZnO复合型催化剂,对其进行了XRD、SEM和XPS表征分析,并测试了复合催化剂的光催化活性。结果表明,与单独使用CuCrO₂相比,无论是以高压汞灯,还是以氙灯为光源,CuCrO₂-WO₃和CuCrO₂-ZnO的光催化产氢活性都有显著提高。     

三丁基氧化膦-离子液体体系萃取UO2(NO3)2的机理和选择性

研究了三辛基氧化膦(TOPO)和三丁基氧化膦(TBPO)在离子液体(ILs) 1-烷基-3-甲基咪唑双三氟甲基磺酰亚胺盐(C_nmimNTf₂, n=2, 4, 6, 8)中萃取分离UO₂(NO₃)₂. TOPO-C₂mimNTf₂和TOPO-C₄mimNTf₂体系萃取UO₂(NO₃)₂时会出现三相, 而TBPO萃取UO₂(NO₃)₂的萃合物可以很好地溶解在所有离子液体中. 论文也考察了萃取过程中的萃取剂浓度效应、酸效应、盐效应. 水相加入HNO₃会降低萃取效率. 盐效应证明了萃取是一种阳离子交换机理. 水相中加入NO₃^-能够提高U的萃取, 这说明NO₃^-参与萃取. 选择性研究表明: 除了在高酸度下对Zr 的显著萃取, TBPO-C₄mimNTf₂萃取体系在低酸度下对U呈现较好的选择性; 去除U后, 在低酸度下该体系对三价Nd 仍保持较好的选择性. 通过定量比较离子液体中NO₃^-进入量, 电喷雾质谱(ESI-MS)和紫外光谱表征确定了TBPO-C_nmimNTf₂中萃取机理的差异性. 萃取中存在两种萃合物, 即UO₂(TBPO)₃(NO₃)⁺和UO₂(TBPO)₃²⁺, 其中UO₂(TBPO)₃(NO₃)⁺的比例从C₂mimNTf₂体系到C₈mimNTf₂体系逐渐增加.     

On-line aluminium preconcentration on chelating resin and its FIA-spectrofluorimetric determination in foods and dialysis concentrates

A new, sensitive and rapid spectrofluorimetric flow-injection method, is presented for the determination of trace levels of aluminium based on the formation of a fluorescent complex between aluminium and 5,7-dibromo-8-quinolinol (DBQ) and its extraction into diethylether (λ_exc = 400 nm, λ_em = 525 nm). Experimental conditions such as pH, reagent concentration, flow-rates, sample volume, extraction coil length, etc., have been optimized for on-line and batch procedures. The detection limits are 1 ppb and 0.3 ppb for batch and on-line systems respectively. The coeflicient of variation is 3.0% at the 4 ppb level for the FIA system. To remove interferences and to preconcentrate aluminium, a chelating resin microcolumn which was able to selectively complex A1(III) and was obtained by immobilizing Chromotrope 2B on AG1-X8 ion-exchange resin, was incorporated into the FIA system. The proposed method was successfully applied to determine aluminium in tap water, food samples and dialysis solutions.     

The use of microemulsion for determination of sodium and potassium in biodiesel by flame atomic absorption spectrometry

A new method for F AAS determination of sodium and potassium in biodiesel using water-in-oil microemulsion as sample preparation is proposed. The method was investigated for biodiesel produced from different sources, as soybean, castor and sunflower oil and animal fat and was also applied for vegetable oils. The optimized condition for microemulsion formation was 57.6% (w/w) of n-pentanol, 20% (w/w) of biodiesel or vegetable oil, 14.4% (w/w) of Triton X-100 and 8% (w/w) of water (aqueous standard of KCl or NaCl in/or diluted HNO₃). The optimized instrumental parameters were: aspiration rate of 2 mL min⁻¹ and the flame composition of 0.131 of C₂H₂/air ratio. For comparison purpose, the determination of sodium and potassium were also carried out according to European norms (EN 14108 and EN 14109, respectively). These norms are applied for determination of sodium and potassium in fatty acid methylic ester samples and consist in the sample dilution using organic solvent and determination by F AAS. The stability of microemulsified aqueous standards and samples was investigated and it was found to be stable for at least 3 days while the organic standard diluted with xylene showed a decrease around of 15% in the analytical signal in 1 h. The limits of detection were 0.1 μg g⁻¹ and 0.06 μg g⁻¹ and the obtained characteristic concentrations were 25 μg L⁻¹ and 28 μg L⁻¹ for sodium and potassium, respectively. The proposed method presented two times better limits of detection and better precision (0.4–1.0%) when compared with the dilution technique (1.5–4.5%). The accuracy of the method was evaluated through recovery tests and comparison with the results obtained by dilution technique. The recoveries ranged from 95% to 115% for biodiesel and 90% to 115% for vegetable oil samples. Comparison between the results obtained for biodiesel by both methods showed no significant differences at the 95% confidence level according to a Student's t-test. This study shows that the proposed method based on microemulsion as sample preparation can be applied as an efficient alternative for sodium and potassium determination in biodiesel samples.     

氮铋共掺杂TiO2的合成及其可见光催化性能研究

以纳米管钛酸为钛的前驱体,Bi(NO₃)₃·5H₂O为N源和Bi源,采用水热法制备了N、Bi共掺杂的TiO₂;并以甲基橙为目标降解物考察了所制备样品的可见光催化性能(λ≥420 nm).利用XRD、XPS、UV-Vis DRS、TEM等技术对不同条件下制备的产物进行了表征.结果表明,所得样品主要为锐钛矿型,粒径20 nm左右,掺杂的Bi主要以Bi₂O₃和BiONO₃两种形式存在.N元素除了以NO₃^-的形式存在于BiONO₃中,还有少量N以间隙氮掺杂于TiO₂中形成Ti-O-N键.N、Bi共掺杂的TiO₂在可见光下表现出了优越的光催化性能,其中水热温度为130 ℃,Bi/Ti摩尔比为1%时,催化活性最高.催化活性的提高源于N和Bi的掺杂增加了样品对可见光的利用效率,降低了光生电子空穴的复合速率.