UV vapor generation for determination of selenium by heated quartz tube atomic absorption spectrometry

A new vapor generation technique utilizing UV irradiation coupled with atomic absorption for the determination of selenium in aqueous solutions is described. In the presence of low molecular weight organic acid solutions, inorganic selenium(IV) is converted by UV irradiation to volatile selenium species, which are then rapidly transported to a heated quartz tube atomizer for detection by atomic absorption spectrometry. Optimum conditions for photochemical vapor generation and interferences from concomitant elements were investigated. Identification of the volatile products using cryotrapping GC/MS analysis revealed that inorganic selenium(IV) is converted to volatile selenium hydride, selenium carbonyl, dimethyl selenide, and diethyl selenide in the presence of formic, acetic, propionic, and malonic acids, respectively. In acetic acid solution, the efficiency of generation was estimated to be 50 +/- 10%. No interference from Ni(2+) and Co(2+) at concentrations of 500 and 100 mg L(-)(1), respectively, was evident. A detection limit of 2.5 microg L(-)(1) and a relative sensitivity of 1.2 microg L(-)(1) (1% absorption) with a precision of 1.2% (RSD, n = 11) at 50 microg L(-)(1) were obtained.     

A microwave-powered thermospray nebulizer for liquid sample introduction in inductively coupled plasma atomic emission spectrometry

A new thermospray nebulizer based on the absorption of microwave radiation (MWTN) by aqueous solutions of strong acids is presented for the first time. To this end, a given length of the sample capillary is placed inside the cavity of a focused microwave system. A small piece of a narrower capillary tubing is connected at the tip of the sample capillary, outside the microwave cavity, to build up pressure. Drop size distributions of primary aerosols are exhaustively measured in order to evaluate the influence of several experimental variables (microwave power, liquid flow, irradiation length, inner diameter of the outlet capillary, nature and concentration of the acid) on the characteristics of the primary aerosol that are related to the emission signal. These experiments have been performed mainly to increase our understanding of the microscopic process of this new type of aerosol generation. A standard Meinhard nebulizer was employed for comparison. Under the best conditions the entire aerosol volume is contained in droplets smaller than 20 μm compared with 45% of the volume of the aerosol generated by the Meinhard. Hence, higher analyte and aerosol transport rates are to be expected for the MWTN compared with the Meinhard nebulizer. As any highly efficient nebulizer, MWTN requires a desolvation unit. For solutions 0.75 M in strong acid, the new nebulizer improves sensitivity (1.0-2.8 times), limits of detection (1.2-3.0 times), and background equivalent concentration (0.9-2.0 times) as compared to the standard Meinhard nebulizer, features many of the advantages of the conventional thermospray nebulizer, and overcomes some of its drawbacks (MWTN does not show corrosion problems and works at lower pressure, the aerosol characteristics are not modified when the PTFE capillary is replaced).     

Determination of selenium by inductively coupled plasma mass spectrometry utilizing a new hydride generation sample introduction system.

An inductively coupled plasma mass spectrometer with a newly designed continuous flow hydride generator was used for the determination of Se in biological materials. The design of the hydride generator was important in minimizing interference from HCl and in maximizing analytical sensitivity. Two sample preparation procedures incorporating either 3.8 or 7.2 M HCl in the final sample solutions were compared. Interference from Cu was eliminated by the addition of 0.2 M NaI to the sodium borohydride solution (3.8 M method) or by maintaining a high concentration of HCl in the sample solution (7.2 M method). The 3.8 M method had the advantage of minimizing exposure of expensive equipment to corrosive HCl fumes, whereas the 7.2 M method did not contaminate equipment with I and had no measurable sample-to-sample cross-contamination. In practice, cross-contamination from sample to sample in both methods was negligible during analysis. An important factor in minimizing cross-contamination from sample to sample was the elimination of the air bubble normally entrained between samples. Determination of isotopic tracer enrichment was linear from 0 to 320% enrichment, which provided a broad range for isotope dilution analysis. A detection limit of 6.4 pg of Se was observed under optimum conditions, whereas a detection limit of 1.3 ng of Se was found for routine analysis of 1-g samples of plant material. Selenium was accurately determined by isotope dilution analysis in a variety of biological reference materials.     

浅谈用氢化物——原子吸收分光光度法测定化妆品中的砷

砷是化妆品中最常见的有害元素之一,用氢化物-原子吸收分光光度法测定微量砷,具有较高的灵敏度,而且分析方法简便、快速、准确度高,测定过程中砷损失少。     

Time-resolved inductively coupled plasma mass spectrometry measurements with individual, monodisperse drop sample introduction

Individual ion clouds, each produced in the ICP from a single drop of sample, were monitored using time-resolved mass spectrometry and optical emission spectrometry simultaneously. The widths of the ion clouds in the plasma as a function of distance from the point of initial desolvated particle vaporization in the ICP were estimated. The Li(+) cloud width (full width at halfmaximum) varied from 85 to 272 μs at 3 and 10 mm from the apparent vaporization point, respectively. The Sr(+) cloud width varied from 97 to 142 μs at 5 and 10 mm from the apparent vaporization point, respectively. The delays between optical and mass spectrometry signals were used to measure gas velocities in the ICP. The velocity data could then be used to convert ion cloud peak widths in time to cloud sizes in the ICP. Li(+) clouds varied from 2.1 to 6.6 mm (full width at half-maximum) and Sr(+) clouds varied from 2.4 to 3.5 mm at the locations specified above. Diffusion coefficients were estimated from experimental data to be 88, 44, and 24 cm(2)/s for Li(+), Mg(+), and Sr(+), respectively. The flight time of ions from the sampling orifice of the mass spectrometer to the detector were mass dependent and varied from 13 to 21 μs for Mg(+) to 93 to 115 μs for Pb(+).     

Preliminary investigation of electrothermal vaporization sample introduction for inductively coupled plasma time-of-flight mass spectrometry

The coupling of an electrothermal vaporization (ETV) apparatus to an inductively coupled plasma time-of-flight mass spectrometer (ICP-TOFMS) is described. The ability of the ICP-TOFMS to produce complete elemental mass spectra at high repetition rates is experimentally demonstrated. A signal-averaging data acquisition board is employed to rapidly record complete elemental spectra throughout the vaporization stage of the ETV temperature cycle; a solution containing 34 elements is analyzed. The reduction of both molecular and atomic isobaric interferences through the temperature program of the furnace is demonstrated. Isobaric overlaps among the isotopes of cadmium, tin, and indium are resolved by exploiting differences in the vaporization characteristics of the elements. Figures of merit for the system are defined with several different data acquisition schemes capable of operating at the high repetition rate of the TOF instrument. With the use of both ion counting and a boxcar averager, the dynamic range is shown to be linear over a range of at least 6 orders of magnitude. A pair of boxcar averagers are used to measure the isotope ratio for silver with a precision of 1.9% RSD, despite a cycle-to-cycle precision of 19% RSD. Detection limits of 10-80 fg are calculated for seven elements, based upon a 10-microL injection.     

氢化物发生-原子荧光光谱法同时测定食盐中的砷和汞

建立一种氢化物发生-原子荧光光谱法同时测定食盐中砷和汞的方法.研究样品前处理对测定结果的影响,探索同时测定砷、汞的最佳实验条件.优化条件下,砷、汞质量浓度分别在0～10.0 μμg/L和0～2.0μg/L范围内,线性关系良好.方法检出限:As为0.0043 μg/L,Hg为0.003 2 μg/L;相对标准偏差:As为0.37％,Hg为0.61％;样品加标回收率:As为97.80％ ～ 102.40％,Hg为96.78％～ 100.80％.试验表明:该方法具有操作简便、快速、准确度高等优点,可用于食盐中砷汞的同时测定.     

Nanosemiconductor-based photocatalytic vapor generation systems for subsequent selenium determination and speciation with atomic fluorescence spectrometry and inductively coupled plasma mass spectrometry

We reported novel Ag-TiO(2)- and ZrO(2)-based photocatalytic vapor generation (PCVG) systems as effective sample introduction techniques for further improving the sensitivity of the atomic spectrometric determination of selenium for the first time, in which the conduction band electron served as a "reductant" to reduce selenium species including Se(VI) and convert them directly into volatile H(2)Se, which was easily separated from the sample matrix and underwent more effectively subsequent atomization and/or ionization. These two PCVG systems helped us to overcome the problem encountered in the most conventional KBH(4)/OH(-)-H(+) system, in that Se(VI) was hardly converted into volatile selenium species without the aid of prereduction procedures. The limits of detection (LODs) (3σ) of the four most typical Se(IV), Se(VI), selenocystine ((SeCys)(2)), and selenomethionine (SeMet) species were, respectively, down to 1.2, 1.8, 7.4, and 0.9 ng mL(-1) in UV/Ag-TiO(2)-HCOOH, and 0.7, 1.0, 4.2, and 0.5 ng mL(-1) in UV/ZrO(2)-HCOOH with the relative standard deviations (RSDs) lower than 5.1% (n = 9 at 1 μg mL(-1)) when using atomic fluorescence spectrometry (AFS) under flow injection mode. They reached 10, 14, 18, and 8 pg mL(-1) in UV/Ag-TiO(2)-HCOOH, and 6, 7, 10, and 5 pg mL(-1) in UV/ZrO(2)-HCOOH with the RSDs lower than 4.4% (n = 9 at 10 ng mL(-1)) when using inductively coupled plasma mass spectrometry (ICPMS). After the two PCVG systems were validated using certified reference materials GBW(E)080395 and SELM-1, they were applied to determine the total Se in the selenium-enriched yeast sample and used as interfaces between high-performance liquid chromatography (HPLC) and AFS or ICPMS for selenium speciation in the water- and/or enzyme-extractable fractions of the selenium-enriched yeast.     

Speciation of mercury by hydrostatically modified electroosmotic flow capillary electrophoresis coupled with volatile species generation atomic fluorescence spectrometry

A novel method for speciation analysis of mercury was developed by on-line hyphenating capillary electrophoresis (CE) with atomic fluorescence spectrometry (AFS). The four mercury species of inorganic mercury Hg(II), methymercury MeHg(I), ethylmercury EtHg(I), and phenylmercury PhHg(I) were separated as mercury-cysteine complexes by CE in a 50-cm x 100-microm-i.d. fused-silica capillary at 15 kV and using a mixture of 100 mmol L(-1) of boric acid and 12% v/v methanol (pH 9.1) as electrolyte. A novel technique, hydrostatically modified electroosmotic flow (HSMEOF) in which the electroosmotic flow (EOF) was modified by applying hydrostatical pressure opposite to the direction of EOF was used to improve resolution. A volatile species generation technique was used to convert the mercury species into their respective volatile species. A newly developed CE-AFS interface was employed to provide an electrical connection for stable electrophoretic separations and to allow on-line volatile species formation. The generated volatile species were on-line detected with AFS. The precisions (RSD, n = 5) were in the range of 1.9-2.5% for migration time, 1.8-6.3% for peak area response, and 2.3-6.1% for peak height response for the four mercury species. The detection limits ranged from 6.8 to 16.5 microg L(-1) (as Hg). The recoveries of the four mercury species in the water samples were in the range of 86.6-111%. The developed technique was successfully applied to speciation analysis of mercury in a certified reference material (DORM-2, dogfish muscle).     

Highly sensitive elemental analysis for Cd and Pb by liquid electrode plasma atomic emission spectrometry with quartz glass chip and sample flow

This paper describes the development of a highly sensitive liquid-electrode plasma atomic emission spectrometry (LEP-AES) by combination of quartz glass chip and sample flow system. LEP-AES is an ultracompact elemental analysis method, in which the electroconductive sample solution is put into a microfluidic channel whose center is made narrower (～100 μm in width). When high voltage pulses (1500 V) are applied at both ends of the channel, the sample evaporates locally at the narrow part and generates plasma. By the emission from the plasma, elemental concentration is analyzed. In this paper, the limits of detection (LODs) were investigated in various conditions of accumulation time, material of the chip, and the sample flow. It was found that the long accumulation using the quartz chip with sample flow was effective to improve LOD. Authors suggested that this was because bubbles remaining after each plasma pulse were removed from the narrow channel by sample flow, resulting in highly reproducible plasma generation, to enable a high accumulation effect. Finally, LODs were calculated from a calibration curve, to be 0.52 μg/L for Cd and 19.0 μg/L for Pb at optimized condition. Sub-ppb level LOD was achieved for Cd.     

Ultrasound-promoted cold vapor generation in the presence of formic acid for determination of mercury by atomic absorption spectrometry

A new cold vapor technique within the context of green chemistry is described for determination of mercury in liquid samples following high-intensity ultrasonication. Volatile Hg evolved in a sonoreactor without the use of a chemical reducing agent is carried to a quartz cell kept at room temperature for measurement of the atomic absorption. The mechanism involved lies in the reduction of Hg(II) to Hg(0) by reducing gases formed upon sonication and subsequent volatilization of Hg(0) due to the degassing effect caused by the cavitation phenomenon. Addition of a low molecular weight organic acid such as formic acid favors the process, but vapor generation also occurs from Hg solutions in ultrapure water. The detection limit of Hg was 0.1 microg/L, and the repeatability, expressed as relative standard deviation, was 4.4% (peak height). Addition of small amounts of oxidizing substances such as the permanganate or dichromate anions completely suppressed the formation of Hg(0), which confirms the above mechanism. Effect of other factors such as ultrasound irradiation time, ultrasound amplitude, and the presence of concomitants are also investigated. Some complexing anions such as chloride favored the stabilization of Hg(II) in solution, hence causing an interference effect on the ultrasound-assisted reduction/volatilization process.     

氢化物-非色散原子荧光法快速测定饲料矿物添加剂中的砷

本文采用氢化物—非色散原子荧光光谱法详细研究了十几种饲料矿物添加剂中金属离子对砷测定的干扰,并用加入硫脲—抗坏血酸混合溶液、碘化钾分离、加热蒸干等方法消除干扰。同时本文还对砷测定的反应酸度、硼氢化钾浓度和仪器工作参数进行了研究和优化。方法相对标准偏差(RSD)0.45％,检出限(D.L)54.5ng/L,样品加标平均回收率为102.2％。实际样品测定结果与砷斑法相比具有很好的一致性。     

On-line coupling of capillary electrophoresis to hydride generation atomic fluorescence spectrometry for arsenic speciation analysis

A novel hyphenated technique, on-line coupling of capillary electrophoresis (CE) to atomic fluorescence spectrometry (AFS), was developed for speciation analysis of four environmentally significant and toxic forms of arsenic: arsenite, arsenate, monomethylarsenic acid, and dimethylarsenic acid. Baseline separation of the four arsenic species was achieved by capillary electrophoresis in a 50 cm x 100 microm i.d. fused-silica capillary at 20 kV and using a 20 mmol L(-1) phosphate buffer (pH 6.5). A hydride generation (HG) technique was employed to convert the arsenic species from the CE effluent into their respective hydrides. The CE-AFS interface was constructed on the basis of a cross design for introducing a sheath flow around the CE capillary and a Pt electrode, which provided an electrical connection for stable electrophoretic separations and allowed on-line volatile hydride formation. A laboratory-made gas-liquid separator was used to isolate the generated volatile species from the reaction mixture solution, and an argon flow was used to transport the volatile hydrides into the atomizer of AFS for on-line detection. The precision (RSD, n = 7) ranged from 2.1 to 3.1% for migration time, from 2.8 to 4.2% for peak area response, and from 2.0 to 4.1% for peak height response for the arsenic species at the 1 mg L(-1) (as As) level. The detection limits were in the range of 9-18 microg L(-1) (as As). The recoveries of the four arsenic species in locally collected water samples and urine sample ranged from 91 to 115%. The developed technique was successfully applied to the speciation of the water-methanol extractable arsenic in a sediment sample.     

Ultrasound bath-assisted enzymatic hydrolysis procedures as sample pretreatment for the multielement determination in mussels by inductively coupled plasma atomic emission spectrometry

Ultrasound energy has been applied to speed up enzymatic hydrolysis processes of mussel tissue in order to determine trace and ultratrace elements (As, Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn). The element releases, by action of three proteases (pepsin, pancreatin, trypsin), lipase, and alpha-amylase, have been evaluated by inductively coupled plasma atomic emission spectrometry. Different variables such as pH, sonication temperature, ionic strength, hydrolysis time, ultrasound frequency, extracting volume, and enzyme mass were simultaneously studied by applying an experimental design approach (Plackett-Burman design and central composite design). Results showed that the hydrolysis time was statistically nonsignificant (confidence interval of 95%) for most of the elements and enzymes, meaning that the hydrolysis procedure can be finished within a 30-60-min range. These hydrolysis times are far shorter than those obtained when using thermostatic cameras, between 12 and 24 h. Statistically significant factors were the ultrasound frequency (the highest metals releasing at high-ultrasound frequency), pH, sonication temperature, and ionic strength. All metals can be extracted using the same operating conditions (pH of 1.0 and sodium chloride at 1.0% for pepsin; pH of 7.5, temperature at 37 degrees C, and 0.4 M potassium dihydrogen phosphate/potassium hydrogen phosphate buffer for amylase; pH of 8.0 and 0.5 M potassium dihydrogen phosphate/potassium hydrogen phosphate buffer for pancreatin; pH of 5.0 and 0.5 M potassium dihydrogen phosphate/potassium hydrogen phosphate buffer for lipase; pH of 8.0 and 0.2 M potassium dihydrogen phosphate/potassium hydrogen phosphate buffer for trypsin). Analytical performances, such as limits of detection and quantification, repeatability of the overall procedure, and accuracy, by analyzing DORM-1, DORM-2, and TORT-1 certified reference materials, were finally assessed for each enzyme.     

Determination of cabergoline by electrospray ionization tandem mass spectrometry: picogram detection via column focusing sample introduction.

An electrospray ionization tandem mass spectrometric method was developed for low-picogram detection of an ergot alkaloid, cabergoline, in coyote plasma extracts. Cabergoline is under investigation as an abortifacient in canid species. Central to the successful development of this method was the ability to introduce relatively large sample volumes into the mass spectrometer. This was achieved by focusing the analyte on a conventional high-performance liquid chromatography guard column prior to elution into the spectrometer. Volumes up to at least 900 microL could be injected onto the guard column using a 100% aqueous mobile phase. Cabergoline retained on the column was eluted as a discreet band into the mass spectrometer by the rapid addition of methanol (30%) to the mobile phase. As compared to flow injection sample introduction, the ability to inject larger sample volumes led to a greatly lowered detection limit. Using this technique and a modification of a previously reported extraction procedure, cabergoline could be determined in coyote plasma at concentrations as low as 9 pg of cabergoline/mL of plasma.     

Formation of Cd particles by UV laser irradiation

Formation of the metal particles of Cd has been studied by nanosecond laser flash photolysis using an ArF excimer laser with the oscillation wavelength of 193 nm. The sample was a 10% methanol solution of CdCl₂. The solvated electron, e_aq⁻, was generated by the excitation of charge transfer bands of Cl⁻ to solvent. The e_aq⁻ efficiently reduced Cd²⁺ to Cd⁺ during a laser pulse of 30 ns (FWHM). The Cd particles were produced by the reaction between Cd⁺ and Cd⁺. In the air saturated solution, the Cd⁺ was easily oxidized by dissolved oxygen. The concentration of the Cd particles formed in the degassed solution was approximately twice of that in the air saturated solution.     

紫外辐照改性聚砜超滤膜

用紫外辐照的方法改性聚砚超滤膜，紫外辐照后膜性能的变化与辐照时间，改性剂种类，改性剂浓度等有关。聚砚超滤膜经紫外辐照改性后，通量增加，膜的亲水性增强，并讨论了此外辐照改性超滤膜的机理。     

Production of reduced graphene oxide by UV irradiation

Herein, we report on a self-photocatalytic reduction (SPCR) strategy toward the production of reduced graphene oxide (GO), carried out by UV irradiation of GO dispersion in the presence of N,N-dimethylformamide (DMF) serving as an electron donor (ED). It is found that a stable dispersion of rGO is produced by UV irradiation of GO solution in the presence of DMF. The use of natural sunlight as driving force for such SPCR reaction is also demonstrated.     

Chemical vapor generation atomic spectrometry using amineboranes and cyanotrihydroborate(III) reagents

Amineboranes of the type L-BH3 (L = NH3; tert-BuNH2; Me2NH; Me3N) and sodium cyanotrihydroborate(III) (NaBH3CN) have been tested as derivatization reagents in the generation of volatile hydrides and elemental mercury following aqueous phase reaction with ionic species of Hg(II), As(III), As(V), Sb(V), Sb(III), Bi(III), Se(IV), Se(VI), Te(IV), and Te(VI). Continuous flow generation atomic absorption spectrometry coupled with a flameless quartz tube atomizer (T = 25 degrees C) and a miniature argon-hydrogen diffusion flame atomizer were employed for the detection of mercury vapors and volatile hydrides, respectively. All of the reductants were able to reduce Hg(II) to the elemental state, giving sensitivities comparable to NaBH4 reduction. Under reaction conditions giving maximum sensitivity for hydride generation with NaBH4, only some amineboranes are able to produce volatile hydrides from all the elements. No evidence of hydride formation was observed from the Se(VI) and Te(VI). In general, the reducing power decreased in the order NaBH4 > H3N-BH3 > tert-BuNH2-BH3 > NaBH3CN > or = Me2HN-BH3 > Me3N-BH3. In comparison with THB, amineboranes and NaBH3CN allowed, in general, a better control of interference effects of Fe(III), Ni(II), Co(II), and Cu(II). Application to determination of mercury in certified reference material is reported. The most likely mechanism of reaction of borane complexes in chemical vapor generation is based on the direct action of hydrogen bound to boron.     

Background correction by wavelength modulation for pulsed-laser-excited atomic fluorescence spectrometry.

Instrumentation was constructed to modulate the dye laser wavelength for background correction in laser-excited atomic fluorescence spectrometry (LEAFS). To achieve wavelength modulation a piezoelectric pusher was used to drive the wavelength tuning mirror in a laboratory-constructed grazing incidence dye laser. The laser pulses were synchronized with the piezoelectric pusher movement so that alternate laser pulses measured the atomic fluorescence signal at the analytical atomic spectral line (on-line) and the background signal at a wavelength displaced to one side of the atomic line (off-line). The background-corrected signal was obtained by subtracting the off-line "background" from the on-line "signal plus background". The spectral line width (fwhm) of the dye laser was 0.003 nm, while the wavelength modulation interval was controllable over the range from 0 to 0.2 nm with a spectral resolution limited only by the spectral line width of the laser. This type of background correction could, in principle, be applied to other types of tunable lasers such as pulsed Ti: sapphire lasers. The performance of background correction by wavelength modulation (WM) was demonstrated by measurement of sodium resonance fluorescence in an air-acetylene flame and by thallium nonresonance fluorescence in a graphite furnace. The experimental data indicated that the wavelength modulation corrected, effectively and quantitatively, for flame background, blackbody emission from a graphite furnace, and scatter of laser radiation off aluminum chloride (1 mg/mL as AI) matrix particles in both the furnace and the flame. Analytical results were in good agreement with certified values for the determination of sodium in standard reference materials by the use of modulated LEAFS.