加碘食盐中微量碘的离子选择性电极测定

在加碘食盐中加入还原剂将KIO3中的IO3^-还原为I^-,使用碘离子选择性电极技术,采用标准曲线法直接测定了溶液中的I-量.并引入表面活性剂作为增敏剂,降低了检测下限,提高了检测的灵敏度.实际测定3种食盐样品,取得了较好的效果.     

Recovery of fortified (2 ppb) EPA method 525.1 analytes from Chesapeake Bay water via solid phase deposition followed by supercritical fluid elution

Application of solid phase deposition/supercitical fluid (SPD/SF) elution to real, brackish water samples, obtained from the Chesapeake Bay, has been investigated. The fortified (2ppb) brackish water samples contained suspended sediment, dissolved organic matter and salt. The sediment made post-deposition drying of the SPE disk difficult and the residual water interfered with analyte recovery. Attempts to dry the disk included increasing the vacuum drying time, use of a higher percent of modifier, and desiccation. The best results were obtained by first drying the disk for 10 min under a stream of nitrogen, followed by overnight desiccation, and finally, SF elution. The SF method required a 3 step, 42 min extraction which reduced organic solvent use by 60% compared to traditional elution. All but five analytes met EPA criteria when fresh desiccant was used to dry the disk; four of the unacceptable recoveries were presumably due to plasticizer contamination.     

Simple and rapid determination of iodide in table salt by stripping potentiometry at a carbon-paste electrode

A simple and rapid procedure, utilising constant-current stripping analysis (CCSA) at a carbon-paste electrode containing tricresyl phosphate as a pasting liquid (TCP-CPE), has been developed for the determination of iodide in table salt. Because of a synergistic accumulation mechanism based on ion-pairing and extraction of iodide in combination with electrolytic pretreatment of the TCP-CPE, the method is selective for iodide and enables direct determination of iodide in samples of table salt containing anti-caking agents such as K(4)[Fe(CN)(6)] (food additive "E 536") or MgO. The iodide content (calculated as KI) can be determined in a concentration range of 2 to 100 mg kg(-1) salt, with a detection limit (S/N=3) of 1 mg kg(-1), and a recovery from 90 to 115%. The proposed method has been used to determine iodide in several types of artificially iodised table salt and in one sample of natural sea salt. The results obtained agreed well with those obtained by use of three independent reference methods (titration, spectrophotometry, and ICP-MS) used to validate the CCSA method, indicating that the developed method is applicable as a routine procedure for rapid testing in salt production process control and in the analysis of marketed table salts.     

Determination of cadmium and lead in table salt by sequential multi-element flame atomic absorption spectrometry

In the present paper, a simultaneous pre-concentration procedure for the sequential determination of cadmium and lead in table salt samples using flame atomic absorption spectrometry is proposed. This method is based on the liquid-liquid extraction of cadmium(II) and lead(II) ions as dithizone complexes and direct aspiration of the organic phase for the spectrometer. The sequential determination of cadmium and lead is possible using a computer program. The optimization step was performed by a two-level fractional factorial design involving the variables: pH, dithizone mass, shaking time after addition of dithizone and shaking time after addition of solvent. In the studied levels these variables are not significant. The experimental conditions established propose a sample volume of 250 mL and the extraction process using 4.0 mL of methyl isobutyl ketone. This way, the procedure allows determination of cadmium and lead in table salt samples with a pre-concentration factor higher than 80, and detection limits of 0.3 ng g⁻¹ for cadmium and 4.2 ng g⁻¹ for lead. The precision expressed as relative standard deviation (n = 10) were 5.6 and 2.6% for cadmium concentration of 2 and 20 ng g⁻¹, respectively, and of 3.2 and 1.1% for lead concentration of 20 and 200 ng g⁻¹, respectively. Recoveries of cadmium and lead in several samples, measured by standard addition technique, proved also that this procedure is not affected by the matrix and can be applied satisfactorily for the determination of cadmium and lead in saline samples. The method was applied for the evaluation of the concentration of cadmium and lead in table salt samples consumed in Salvador City, Bahia, Brazil.     

一种新的FIA导数光谱技术测定食盐中碘含量

提出一种新的流动注射导数光谱检测技术,即双光束同时扫描法。将自行研制的流动池比色装置分别安置在双光束检测器中样品光束和参比光束的光路中,实现同时扫描,获得响应曲线为一阶导数光谱。对该方法的原理和实验技术进行了讨论,基于碘酸根与碘化钾生成碘,并与淀粉生成蓝色络合物(λmax=574 nm)原理,确定了最佳实验条件,建立了一种导数光谱法测定加碘食盐中的碘含量。该法分析速度为130次/h,方法灵敏度比普通FIA法提高了1.8倍,测定结果的相对标准偏差为0.97%(n=9),方法可直接用于实际样品中碘含量的检测。     

Assessment of iodine content in Brazilian duplicate portion diets and in table salt

Excess dietary intake may increase the risk for the hyperthyroidism in the elderly. This study investigated iodine dietary intake by epithermal neutron activation analysis (ENAA) analyzing duplicate portion diet and fortified table salt samples. Duplicate diet samples were obtained from a group of twenty-five steel mill workers from the city of São Paulo, over a 3-day period. The samples were freeze dried, mixed and homogenized. Fortified table salt brands were collected from the market and were analyzed with no pre-treatment. Assays for the iodine concentration in the table salt samples revealed values between 24 to 65 mg/kg. The average iodine daily intake for the worker’s diets was 813 μg/day, ranging from 402 to 1363 μg/day. In some cases daily intakes were around 10 times higher than the recommended dietary allowance (RDA) value (150 μg/day).     

Catalytic determination of iodide by continuous addition of catalyst to a reference solution with photometric probe monitoring

Probe photometry is proposed as a simple monitoring technique for catalytic determinations by continuous addition of catalyst to a reference solution. The approach has been tested on the catalytic determination of iodide which in the concentration range of 10-100 ng/ml, can be determined with a relative error usually lower than 4-5% and relative standard deviations of 4.6 and 4.0% for 9.98 and 79.92 ng/ml, respectively. Two alternative techniques of measuring the analytical signal (the intersection time) are suggested to improve the reproducibility: the "initial signal preadjustment" and the "two-intersection point" techniques. The method has been applied to determination of iodide in table salt samples.     

Effect of solvents on the selectivity of terbutylazine imprinted polymer sorbents used in solid-phase extraction

A solid-phase extraction sample preparation method using a molecularly imprinted polymer (MIP) selective for the triazine type pesticide terbutylazine has been developed. The method involves preconcentration from large volumes of water samples on a C18 disk coupled to selective clean-up on the MIP. The method has been optimised by studying the recovery and retention of terbutylazine and some other structurally related triazine derivates as a function of the selective washing solvent used. The effect of the water content of the selective washing solvent was also investigated on the recovery of the MIP. River water samples were analysed with the coupled technique, and efficient clean-up of the samples was observed.     

Determination of Total Iron in Environmental Samples by Solid Phase Extraction with Dimethyl(E)‐2‐(2‐Methoxyphenoxy)‐2‐Butenedioate

A novel solid phase extraction technique for determination of total iron in environmental water samples was developed. The method is based on sorption of Fe(III) ions on octadecyl silica membrane disk modified with a new synthetic ligand dimethyl(E)‐2‐(2‐methoxyphenoxy)‐2‐butenedioate (I). Iron(III) is quantitatively retained on the disk in the pH range of 3–7 at a flow rate of 1–7 mL min⁻¹. The Fe(III) eluted with 10 mL of 0.01 M EDTA and than was measured by flame atomic absorption spectrometry (FAAS) at 248.3 nm. The maximum capacity disk modified by 7 mg of ligand was found to be 197 ± 2 μg of iron(III). The breakthrough volume was greater than 2000 mL. The iron(III) was completely recovered (> 99%) from water with a preconcentration factor of more than 200. The limit of detection of the proposed method was 1.00 ng mL⁻¹. The various cationic and anionic interferences had no effect on the recovery of iron(III) from the binary mixtures. The proposed method was successfully applied to determination of total iron from three different water samples.     

Inductively coupled plasma atomic emission spectrometric determination of 27 trace elements in table salts after coprecipitation with indium phosphate

The coprecipitation method using indium phosphate as a new coprecipitant has been developed for the separation of trace elements in table salts prior to their determination using inductively coupled plasma atomic emission spectrometry (ICP-AES). Indium phosphate could quantitatively coprecipitate 27 trace elements, namely, Be, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, in a table salt solution at pH 10. The rapid coprecipitation technique, in which complete recovery of the precipitate was not required in the precipitate-separation process, was completely applicable, and, therefore, the operation for the coprecipitation was quite simple. The coprecipitated elements could be determined accurately and precisely by ICP-AES using indium as an internal standard element after dissolution of the precipitate with 5 mL of 1 mol L⁻¹ nitric acid. The detection limits (three times the standard deviation of the blank values, n = 10) ranged from 0.001 μg (Lu) to 0.11 μg (Zn) in 300 mL of a 10% (w/v) table salt solution. The method proposed here could be applied to the analyses of commercially available table salts.     

Preconcentration of trace amounts of silver ion in aqueous samples on octadecyl silica membrane disks modified with hexathia-18-crown-6 and its determination by atomic absorption spectrometry

A simple and reliable method has been developed to selectively separate and concentrate trace amounts of silver ion from aqueous samples for the subsequent measurement by atomic absorption spectrometry. Ag+ ions are absorbed quantitatively during passage of aqueous samples through an octadecyl-bonded silica membrane disk modified by hexathia-18-crown-6. Almost all matrix elements will pass through the disk to drain. The retained Ag+ ions are then stripped from the disk with a minimal amount of thiosulfate solution as eluent. The proposed method permitted large enrichment factors of about 200 and higher. The limit of detection of the proposed method is 50 ng Ag+ per 1,000 mL. The effects of various cationic interferences on the recovery of silver in binary mixtures were studied. The method was applied to the recovery of Ag+ ions from different synthetic and water samples.     

Solid phase extraction and determination of lead in soil and water samples using octadecyl silica membrane disks modified by bis[1-hydroxy-9,10-anthraquinone-2-methyl]sulfide and flame atomic absorption spectrometry

A simple, reliable and relatively fast method has been developed to selectively separate and concentrate trace amounts of lead from aqueous samples for the measurement by flame atomic absorption spectrometry. By the passage of aqueous samples through an octadecyl-bonded silica membrane disk modified by a recently synthesized bis(anthraquinone)sulfide, Pb(2+) ions adsorb quantitatively and almost all matrix elements will pass through the disk to drain. The retained lead ions are then stripped from the disk by minimal amount of acetic acid as eluent. The proposed method permitted large enrichment factors of about 300 and higher. The limit of detection of the proposed method is 50 ng Pb(2+) per 1000 ml. The effects of various cationic interferences on the recovery of lead in binary mixtures were studied. The method was successfully applied to the determination of lead in soil and water samples.     

Elimination of suction effect in interfacing microchip electrophoresis with inductively coupled plasma mass spectrometry using porous monolithic plugs

A suction-free interfacing method was developed for microchip electrophoresis hyphenated with inductively coupled plasma mass spectrometry (MCE-ICP-MS). The hyphenated system was composed of a microchip, a demountable capillary microflow nebulizer (d-CMN) combined with a heated single pass spray chamber, a negative pressure sampling device, a high voltage power supply, a syringe pump and an ICP-MS. To eliminate the nebulizer suction generated by the pneumatic nebulizer and to ensure that the makeup solution flowed into the nebulizer, two porous polymer plugs were fabricated in the microchip. As a result, reasonably true electropherograms were obtained when compared to the CE separation performed in the traditional MCE-ICP-MS mode without porous polymer plugs. Electrophoretic separation of I(-) and IO(3)(-) was achieved within 25 s in a microchip with an effective separation length of only 15 mm at an electric field of 857 V cm(-1) using 10 mmol L(-1) borate (pH 9.2) as the running buffer. A resolution of 1.3 was obtained and the absolute detection limits for I(-) and IO(3)(-) were 0.12 and 0.13 fg, respectively. The precisions (RSD, n = 10) of the migration time and peak height for I(-) and IO(3)(-) were in the range of 1.1-1.6% and 2.5-2.8%, respectively. Two table salt samples were analyzed by an external calibration method. The iodate contents were in accordance with their labeled values. The recoveries of I(-) and IO(3)(-) in the table salt samples were in the range of 92-105%.     

High performance liquid chromatography - Quantitative nuclear magnetic resonance - High performance liquid chromatography for purity measurement of human insulin

Quantitative Nuclear Magnetic Resonance (qNMR) is a reliable quantitative spectroscopic technique, wherein the intensity of a resonance line is directly proportional to the number of resonant nucleus, and the absolute content of the compound can be determined, this means the inorganic stabilizer in the sample would not affect the result of qNMR. High performance liquid chromatography (HPLC) is a common analytical method with a high separation capacity. This study combined HPLC and qNMR, to measure the purity of Human Insulin (HI). It started from an original HI. The first step is purifying the original HI by HPLC to get a purified HI, with organic purity of 99.78%. The second step is assessing the absolute content of the purified HI by qNMR, and got 40.25%. The third step is measuring the purity of original HI by HPLC again, using the purified HI as the reference material. This method, called HPLC-qNMR-HPLC, is more accurate (84.12%?±?1.14%) than the traditional IDMS (isotope dilution mass spectrometry) method (86.6%?±?3.4%). This study expanded the application of qNMR to proteins with molecular weight of about 5800, and showed that this method can be widely used in measuring the purity of macromolecular proteins.     

Comparison of the dehalogenation of polyhalomethanes and production of strong acids in aqueous and salt (NaCl) water environments: Ultraviolet photolysis of CH(2)I(2)

The ultraviolet photolysis of CH(2)I(2) was studied in water and salt water solutions using photochemistry and picosecond time-resolved resonance Raman spectroscopy. Photolysis in both types of environments produces mainly CH(2)(OH)(2) and HI products. However, photolysis of CH(2)I(2) in salt water leads to the formation of different products/intermediates (CH(2)ICl and Cl(2) (-)) not observed in the absence of salt in aqueous solutions. The amount of CH(2)(OH)(2) and HI products appears to decrease after photolysis of CH(2)I(2) in salt water compared to pure water. We briefly discuss possible implications of these results for photolysis of CH(2)I(2) and other polyhalomethanes in sea water and other salt aqueous environments compared to nonsalt water solvated environments.     

Preconcentration of trace amounts of silver ion in aqueous samples on octadecyl silica membrane disks modified with hexathia-18-crown-6 and its determination by atomic absorption spectrometry

A simple and reliable method has been developed to selectively separate and concentrate trace amounts of silver ion from aqueous samples for the subsequent measurement by atomic absorption spectrometry. Ag⁺ ions are absorbed quantitatively during passage of aqueous samples through an octadecyl-bonded silica membrane disk modified by hexathia-18-crown-6. Almost all matrix elements will pass through the disk to drain. The retained Ag⁺ ions are then stripped from the disk with a minimal amount of thiosulfate solution as eluent. The proposed method permitted large enrichment factors of about 200 and higher. The limit of detection of the proposed method is 50 ng Ag⁺ per 1000 mL. The effects of various cationic interferences on the recovery of silver in binary mixtures were studied. The method was applied to the recovery of Ag⁺ ions from different synthetic and water samples. Received: 28 September 1999 / Revised: 2 December 1999 / Accepted: 8 December 1999     

Comparison of the dehalogenation of dihalomethanes (CH2XI, where X = Cl, Br, I) following ultraviolet photolysis in aqueous and NaCl saltwater environments

The ultraviolet photolysis of low concentrations of CH(2)XI (X = Cl, Br, I) were investigated in water and saltwater solutions by photochemistry and picosecond time-resolved resonance Raman spectroscopy. Photolysis in both kinds of solutions formed mostly CH(2)(OH)(2) and HI and HX products. However, photolysis of the CH(2)XI molecules in saltwater resulted in production of some CH(2)XCl products not observed in aqueous solutions without salt present. The appearance of these new products in saltwater solutions is accompanied by a decrease in the amount of CH(2)(OH)(2), HI, and HX products compared to photolysis in aqueous solutions without salt present. The possible implications for photolysis of CH(2)XI and other polyhalomethanes in seawater and other salt aqueous environments compared to nonsaltwater solvated environments is briefly discussed.     

Determination of Airborne Nicotine by Automatic Two-Stage Thermal Desorption Gas Chromatography

Abstract

An automated two-stage thermal desorption technique has been developed for the determination of airborne nicotine. Pumped samples are collected on adsorbent tubes and analysed by capillary gas chromatography using flame ionisation detection. The preconcentration effect of the adsorbent compared to solvent trapping or solvent desorption methods permits shorter sampling times and precludes the need for a selective detector.

By use of a basic program all exposure volumes and component details are entered into a method run table and after analysis exposure levels are automatically calculated and printed in report form by the data handling system. Consequently a large throughput samples may be analysed automatically and efficiently with minimal analyst involvement or sample preparation.

The technique described was originally developed to sample airborne nicotine in workplace environments where tobacco is processed. Comparison between this technique and the standard NIOSH method for airborne nicotine is discussed.     

基于四环素荧光熄灭测定碘的研究

基于碘对荧光试剂四环素的荧光熄灭,建立了测定微量碘的荧光分析方法。在pH10的碱性介质中,最大激发/发射波长分别为400.0nm/509.0nm,四环素的荧光强度与碘浓度的对数呈良好的线性关系,测定碘浓度的线性范围为3.20×10^-7～1.00×10^-4mol/L,检出限为1.30×10^-8mol/L,常见的共存离子不干扰测定。该方法适用于食盐中微量碘含量的测定。     

Potentiometric stripping analysis (PSA) for monitoring of antimony in samples of vegetation from a mining area

A potentiometric stripping analysis (PSA) method has been developed and checked for the fast and reliable determination of antimony in vegetation samples of Cistus ladanifer from a mining area in Badajoz, Southwest Spain. The method, modified from previous PSA methods for Sb in environmental samples, is based on dry ashing of the homogenized leaves, dissolution in hydrochloric acid, and PSA analysis on a mercury film plated on to a glassy carbon disk electrode. The influence of experimental variables such as the deposition potential, the deposition time, the signal stability and the calibration parameters, has been investigated. The method has been compared with an independent technique (instrumental neutron activation analysis) by analysis of standards and reference materials and comparison of the results. As a result of automation of the PSA equipment, the proposed method enables unattended analysis of 20 digested samples in a total time of 2 h, thus providing a useful tool for Sb monitoring of a large number of samples.