Thin-layer hydrodynamic biamperometric end-point detection: application to the coulometric titration of arsenic(III) with bromine

A sandwich-type thin-layer cell has been applied to hydrodynamic biamperometric end-point detection in coulometric titrations. The detector cell, constructed from two pieces of teflon, has platinum indicator electrodes and is placed in a flow loop attached to the coulometric titration cell. The thin-layer cavity has a volume of 6.5 μl and a thickness of 51μm, which are obtained using teflon tape as a spacer. A peristaltic pump maintains a continual flow through the loop. The titration cell is a closed vessel completely filled with the solution to be titrated. Operational amplifier circuits control the potential difference applied across the two thin-layer electrodes, and to measure the current developed in the thin-layer cell. Noise arising from the pulsed nature of the flow is reduced by a factor of 25 by using an electronic filter. The titration of arsenic(III) with electrogenerated bromine was used to study the performance of the system. Concentrations from 24 ppb to 1.6 ppm can be determined with relative inaccuracies of +4 and +0.1%, respectively.     

Determination of arsenic at the picogram level by atomic absorption spectrometry with miniaturized suction-flow hydride generation

A continuous-flow hydride generator is modified and miniaturized for the determination of picogram amounts of arsenic by atomic absorption spectrometry. A 300-μl sample is dropped into a teflon cup and pumped into an alkaline sodium tetrahydroborate stream, which is acidified in a reaction coil. The evolved hydride is swept with argon through a phase separator into an electrically-heated quartz absorption cell and the absorbance is recorded. To eliminate differences in sensitivity between arsenic(III) and arsenic(V) without prereduction by potassium iodide, it is important that arsenic(V) be mixed with tetrahydroborate prior to mixing with hydrochloric acid. The method has a detection limit of 0.08 ng As ml^?1 (24 pg) and the calibrations is linear up to 50 ng As ml^?1. The relative standard deviation for 10 replicate measurements is 5.4% for 0.5 ng As ml^?1. The addition of potassium iodide and hydroxylamine is confirmed to be effective in minimizing some interferences. The sampling rate is 90 h^?1. Results for NBS biological and steel reference materials demonstrate applicability of the technique.     

Determination of minor and trace elements in silicate rocks by inductively-coupled plasma emission spectrometry

Samples (0.5 g) are decomposed with mixed acids in a sealed teflon vessel. After suitable treatment, barium, cobalt, chromium, copper, lithium, nickel, scandium. strontium, vanadium and zirconium are determined sequentially. The method is satisfactory for a variety of standard silicate materials.     

Improved dynamic response of potentiometric ammonia sensors using pure teflon membranes

Several microporous membrane parameters are investigated in an attempt to improve the dynamic response of ammonia gas-sensing electrodes. Parameters of interest include hydrophobic and support membrane porosities as well as support polymer composition. Results show that the electrode recovery process represents the major component of the total dynamic response and that, of the teflon membranes currently available, the 0.02-μm pure teflon membrane is the membrane of choice for these electrodes.     

微波消解样品-电感耦合等离子体原子发射光谱法测定竹叶中9种必需微量元素

竹叶样品置于聚四氟乙烯罐中,加入硝酸及过氧化氢后在微波消解仪中按设定程序加热消解。所得样品溶液定容至25mL后用电感耦合等离子体原子发射光谱法测定其中铬、锌、镍、钴、铁、硼、锰、铜和锶等9种元素的含量。9种元素的质量浓度在0.05～2.00mg.L-1范围内与其发射强度呈线性关系,方法的检出限(3s)在0.04～0.50μg.g-1之间。方法应用于分析了一种杨树叶标准物质(GBW 07604),所得9种元素的测定结果与证书值相符。方法的回收率在87.0%～107.6%之间。     

Unusual transformations of difluorosilanone F<Subscript>2</Subscript>Si=O

The structure and properties of fluorosilicon polymer (fluorosil) formed by the reaction of phenyltrifluorosilane with aliphatic alcohols have been studied by the methods of IR, ¹⁹F, ²⁹Si NMR spectroscopy, high temperature mass-spectrometry, derivatography and atom emission analysis. Due to its high reactivity, this polymer readily reacts with glass of the reaction vessel extracting the ions of all metals entering into its composition. Fluorosil formed in a quartz, teflon or polypropylene reactors is characterized by low stability and is slowly decomposed to SiF₄ and SiO₂. Apparently, fluorosil is the product of incorporation of SiF⁴ into the SiO₂ matrix.     

Atomic absorption spectrometric determination of aluminium in whole blood

Two methods are described for atomic absorption spectrometric determinations of aluminium m heparinized and haemolyzed samples of undiluted whole human blood. In the direct method 2μl of blood are pipetted into a graphite cup atomizer; after a drying and two ashing steps aluminium is determined by atomization at 2500°C. In the second method, 15μl of blood are decomposed by nitric acid in polytetrafluoroethylene tubes; 2-μl portions of the solution are then analyzed with the graphite tube atomizer. The direct method was applied to the determination of aluminium in whole blood from 48 Norwegian workers occupationally unexposed to the element; the concentrations of aluminium ranged from 0.05—0.59 p.p.m. (mean value, 0.20 p.p.m.). For 0.35 p.p.m. aluminium, the relative standard deviation of both methods was 8%. The detection limit of the direct method is 0.05 p.p.m. aluminium.     

The “On Line” Determination of Cefsulodin by High Performance Liquid Chromatography in CSF and Plasma of Rats

Abstract

After an intraveinous injection of 20 mg.kg^?1 of cefsulodin in anaesthetized rats, the cerebrospinal fluid (CSF) and plasma drug levels were determined on line by HPLC. The CSF was withdrawn from the IIIe venticle at a flow rate of I μl. minute and pushed with a peristaltic pump, via a teflon tube into a “micro vial” inside the WISP vial. At the end of fiveteen minutes, about 15 μ1 of CSF was collected and a small volume (7 μl) was injected by the WISP into the column, the excess of CSF was discarded by another teflon tube inside the “micro-vial”. After the injection, the continous flow of CSF filled the “micro vial”, an injection was running at fiveteen minutes and so on during three hours. Plasma samples were collected every thirty minutes, and after methanol extraction cefsulodin levels were determined by HPLC. Given the low drug levels found in the CSF, this method appeared very sensitive; it was a direct, rapid, automatic technique. Other biological molecules can be determined by this automatic dosage.     

Determination of morphine in poppy straw by highperformance liquid chromatography

A simple high-performance liquid Chromatographie method for determining morphine in poppy straw is reported. The sample (ca. 2g) is ground and extracted with 0.02 M HCl; after suitable treatment, the morphine is extracted into chloroform—propan-2-ol (3:1), the acidified extract is evaporated, the residue is dissolved in dilute acid, and after further extraction, 100-μl aliquots are injected into the Chromatograph. The method is specific and gives a precision of ±2% relative.     

Speciation of n-butyltin compounds by atomic absorption spectrometry with an electrothermal quartz furnace after hydride generation

A method is described for the speciation of n-butyltin compounds. The compounds are volatilized from aqueous solution, trapped on a chromatographic packing material contained in a teflon column, and separated on the basis of differing boiling points. The column is attached directly to an electrothermal quartz furnace of an atomic absorption spectrometer for detection at 224.61 nm. Absolute detection limits (3σ) are 11–45 pg as tin, calibration curves are linear to 13 ng, and reproducibility at the 2-ng level ranges from 5% for mono-n-butyltin to 18% for tri(n-butyl)tin.     

Determination of trace amounts of vanadium in air samples with 2-(8-quinolylazo)-5-N,N-diethylaminophenol by reversed-phase liquid chromatography

A reversed-phase liquid chromatographic method for the determination of trace amounts of vanadium is described. Metal ions are converted into 2-(8-quinolylazo)-5-N,N-diethylaminophenol chelates in an off-line system. The chelates are injected onto a Zorbax CN column and separated with an aqueous acetonitrile mobile phase containing no chromogenic reagent. Unter these conditions, only vanadium(V) is spectrophotometrically detected at 540 nm among the metal ions Al(III), Ba(II), Ca(II), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Ga(III), Hg(II), Mg(II), Mn(II), Ni(II), Pb(II), V(V) and Zn(II). Amounts of 8.0–200 pg of vanadium(V) in 100-μl injections can be determined without interference from 10-fold molar excesses of many cations. At 0.001 a.u.f.s., the detection limit (twice the peak-to-peak noise) for vanadium(V) is 8.0 pg in 100 μl of injected solution and the relative standard deviation at 120 pg of vanadium(V) in a 100-μl injection is 3.5%. The proposed method is applied to the determination of vanadium in rain water and airborne particulates.     

Storage and stability of inorganic and methylmercury solutions

Summary The storage behaviour of mercurychloride and methylmercury chloride solutions in deionized water and in seawater stored in polyethylene (PE), pyrex glass and teflon (PTFE) containers at various concentration levels (4 ppb, 50 ppt, natural seawater concentrations) was studied using various preservatives and container pretreament procedures. For PE bottles, the best results are obtained, after pretreatment of the bottles with an acidified KMnO₄ solution, with a 0.05% (v/v) H₂SO₄+0.02% (w/v) KMnO₄ preservative. However, the solution becomes heterogeneous rather fast, due to the formation of a MnO₂ precipitate. Acidified (pH 1 with HNO₃) deionized or seawater samples stored in pyrex glass BOD-bottles (analyses are carried out in these bottles too) or teflon containers are stable with respect to inorganic mercury for at least 1 month. Instead of acidification an oxidant such as BrCl can also be used to stabilize the solution. Methylmercury solutions (80 ppt) in deionized water (pH 6) and stored in teflon containers are stable for at least 1 month. In glass bottles, the solution should be acidified to pH 1. Methylmercury seems to be unstable in acidified seawater samples (pH 1 with HNO₃); after 2 weeks about 60% of the methylmercury is converted into inorganic mercury.     

Liquid-phase microextraction and GC for the determination of primary, secondary and tertiary aromatic amines as their iodo-derivatives

Presence of iodine in aromatic amines, introduced by their reaction with iodine, and other electron withdrawing substituents such as chlorine and nitro, has been found to afford excellent liquid-phase microextraction (LPME) in toluene and separation by gas chromatography in the determination of primary, secondary and tertiary aromatic amines. The effect is due to decreased basic nature of amines when electronegative substituents are present. Single drop microextraction (SDME) of the amines in 2 μl of toluene and injection of the whole extract into GC, or LPME into 50 μl of toluene and injection of 2 μl of extract, were used. LPME has been found more robust and to give better extraction in shorter period than SDME. In SDME-GC-FID, the average correlation coefficient was 0.9939 and average limit of detection 25 μg l⁻¹ (range 12-61 μg l⁻¹) whereas the corresponding values in LPME-GC-MS were, respectively, 0.9953 and 33 ng l⁻¹ (range 18-60 ng l⁻¹). The method has been applied to determine aromatic amines in river water, dye factory effluents and food dye stuffs. The LPME was found as robust, rugged and simple extraction method.     

Spectrophotometric determination of boron in plants after separation as trimethyl borate by microdiffusion

A sensitive and precise method based on microdiffusion is proposed for the determination of traces of boron in plants. A sealed digestion bomb is used; the powdered sample is dissolved in ZnCl₂/AlCl₃ solution containing methanol in the teflon vessel and the trimethyl borate formed is collected in sodium hydroxide pellets. The boron, as an ion-associate of the 2,6-dihydroxybenzoic acid complex and malachite green, is extracted into chlorobenzene. At 629 nm, Beer's law is obeyed for the range 0.05–0.5 μg of boron. The accuracy of the proposed method was confirmed by analyzing the Orchard Leaves and Pepperbush standards.     

Determination of nickel in biological samples by ETA-AAS and ICP-AES after acidic dissolution (with microwave heating and preconcentration by liquid-liquid extraction)

The determination of nickel by ETA-AAS and ICP-AES in biological samples with prior extraction into methyl isobutyl ketone with 1,5-bis(di-2-pyridylmethylene) thiocarbonohydrazide as extracting reagent is described. Microwave dissolution in closed teflon vessels has been used for the dissolution of biological materials. At least three samples can be decomposed simultaneously with a preset heating programme. Results of analyses of some certified biological reference materials are given.     

An inhibition type amperometric biosensor based on tyrosinase enzyme for fluoride determination

In this study, a new biosensor based on the inhibition of tyrosinase for the determination of fluoride is described. To construct the biosensor tyrosinase was immobilized by using gelatine and cross-linking agent glutaraldehyde on a Clark type dissolved oxygen (DO) probe covered with a teflon membrane which is sensitive for oxygen. The phosphate buffer (50 mM, pH 7.0) at 30 °C were established as providing the optimum working conditions. The method is based on the measurement of the decreasing of dissolved oxygen level of the interval surface that related to fluoride concentration added into reaction medium in the presence of catechol. Inhibitor effect of fluoride results in decrease in dissolved oxygen concentration. The biosensor response depends linearly on fluoride concentration between 1.0 and 20 μM with a response time of 3 min.In the characterization studies of the biosensor some parameters such as reproducibility, substrate specificity and storage stability were carried out. From the experiments, the average value (x), Standard deviation (S.D) and coefficient of variation (C.V %) were found as 10.5 μM, ± 0.57 μM, 5.43%, respectively for 10 μM fluoride standard.     

Determination of 7-aminoflunitrazepam in urine by dispersive liquid-liquid microextraction with liquid chromatography-electrospray-tandem mass spectrometry

Dispersive liquid-liquid microextraction (DLLME) and liquid chromatography-electrospray-tandem mass spectrometry (LC-ES-MS/MS) procedure was presented for the extraction and determination of 7-aminoflunitrazepam (7-aminoFM2), a biomarker of the hypnotic flunitrazepam (FM2) in urine sample. The method was based on the formation of tiny droplets of an organic extractant in the sample solution using water-immiscible organic solvent [dichloromethane (DCM), an extractant] dissolved in water-miscible organic dispersive solvent [isopropyl alcohol (IPA)]. First, 7-aminoFM2 from basified urine sample was extracted into the dispersed DCM droplets. The extracting organic phase was separated by centrifuging and the sedimented phase was transferred into a 300 μl vial insert and evaporated to dryness. The residue was reconstituted in 30 μl mobile phase (20:80, acetonitrile:water). An aliquot of 20 μl as injected into LC-ES-MS/MS. Various parameters affecting the extraction efficiency (type and volume of extraction and dispersive solvent, effect of alkali and salt) were evaluated. Under optimum conditions, precision, linearity (correlation coefficient, r² = 0.988 over the concentration range of 0.05-2.5 ng/ml), detection limit (0.025 ng/ml) and enrichment factor (20) had been obtained. To our knowledge, DLLME was applied to urine sample for the first time.     

On-line preconcentration and speciation of arsenic by flow injection hydride generation atomic absorption spectrophotometry

A flow injection-column preconcentration-hydride generation atomic absorption spectrophotometric (FI-column-HGAAS) method was developed for determining μg/l levels of As(III) and As(V) in water samples, with simultaneous preconcentration and speciation. The speciation scheme involved determining As(V) at neutral pH and As(III + V) at pH 12, with As(III) obtained by difference. The enrichment factor (EF) increased with increase in sample loading volume from 2.5 to 10 ml, and for preconcentration using the chloride-form anion exchange column, EFs ranged from 5 to 48 for As(V) and 4 to 24 for As(III + V), with corresponding detection limits of 0.03-0.3 and 0.07-0.3 μg/l. Linear concentration range (LCR) also varied with sample loading volume, and for a 5-ml sample was 0.3-5 and 0.2-8 μg/l for As(V) and As(III + V), respectively. Sample throughput, which decreased with increase in sample volume, was 8-17 samples/h. For the hydroxide-form column, the EFS for 2.5-10 ml samples were 3-23 for As(V) and 2-15 for As(III + V), with corresponding detection limits of 0.07-0.4 and 0.1-0.5 μg/l. The LCR for a 5-ml sample was 0.3-10 μg/l for As(V) and 0.2-20 μg/l for As(III + V). Sample throughput was 10-20 samples/h. The developed method has been effectively applied to tap water and mineral water samples, with recoveries ranging from 90 to 102% for 5-ml samples passed through the two columns.     

微波溶解光度法测定茶叶中痕量锗

采用微波加热和双层聚四氟乙烯密闭容器，以HNO3－HClO4为消解试剂、MgO为外层吸收剂，用CCl4萃取，光度法快速测定茶叶中痕量锗。研究了消化茶叶的最佳条件。萃取锗的最佳酸度及其它影响因素。该方法具有选择性高，成本低等特点，其精密度和准确度令人满意。     

An automated system for liquid-liquid extraction based on a new micro-batch extraction chamber with on-line detection: Preconcentration and determination of copper(II)

An automated system to perform liquid-liquid extraction is proposed, in which the effective mixture (the intimate contact) between the aqueous phase and the organic phase, as well as the separation of the phases, are carried out in a micro-batch glass extraction chamber. Sample, reagents and organic solvent are introduced into the glass extraction chamber by a peristaltic pump using air as carrier. The detection of the extracted species from the aqueous phase is made in a small volume (120-150 μl) of isobutyl methyl ketone (MIBK). The system allows enrichment factors of 2-10-fold. The proposed automatic system was evaluated for Cu(II) extraction based on complex formation between copper(II) and 1-(2′-pyridylazo)naphthol (PAN) in MIBK. When a volumetric ration of 2:1 (aqueous:organic) was implemented, copper was detected in the concentration range of 100-1600 μg l⁻¹ (r = 0.9995) with a relative standard deviation of 2% (200 μg l⁻¹, n = 5) and a detection limit of 20 μg l⁻¹. The analytical curve was linear over the concentration range 25-500 μg l⁻¹ (r = 0.9994) when a volumetric ratio of 10:1 was employed. With this ratio, the detection limit was 5.0 μg l⁻¹ and the relative standard deviation was 6% (50 μg l⁻¹, n = 5).