A Simple,Quick, and Precise Procedure for the Determination of Water in Organic Solvents

Abstract

A procedure for the UV/VIS-spectroscopic determination of water by the use of a solvatochromic pyridiniumphenolate betaine is given. The water content of organic solvents is calculated by a two parameter equation from λ_max of the dye. A typical, detection limit is of the order of 1 mg in 1 ml solvent for routine spectrometers. The parameters for the determination of water are given for a number of commonly used solvents.     

Quantification of Glucose Using Extended Colorimetry

Abstract

The use of extended colorimetry to increase the range over which colorimetric measurments can be made without loss of sensitivity is described. Its potential for use with dehydrogenase and oxidase enzymes is demonstrated. Construction of a device for the quantification of glucose based on this technique is described. The results of assays on undiluted solutions containing glucose in the range 1 - 20mM were assesed using reflectance spectrophotometry.     

New Immobilized Enzyme Membranes for Tailor-Made Biosensors

Abstract

Commercially available polyamide preactivated membranes for immunodiagnostic use were found suitable for the preparation of immobilized enzyme membranes adaptable to biosensors. Membranes with immobilized glucose oxidese as model enzyme, tested with a microprocessor-based device involving an enzymatic electrode, gave excellent results. The extremely simple and fast procedure allows anyone to prepare such bioactive membranes easily, possibly from his own enzyme preparation and within a few minutes set up a specific probe from commercially available sensors.     

New Device for Adding Polar Modifiers to Carbon Dioxide Mobile Phase for Supercritical Fluid Chromatography

Abstract

Adding additional components to supercritical carbon dioxide in supercritical fluid chromatography can extend or significantly alter the fluid solvating properties. Polar samples which are difficult to be analyzed with pure supercritical CO₂ because of their high polarity can be separated by adding polar modifiers to supercritical CO₂. In this paper, a new mixing device using a teflon high capacity filter for adding polar modifiers to carbon dioxide mobile phase is introduced. This new mixing device could keep the amount of modifier in the mobile phase constant for a much longer time than a saturator column. The amount of water or methanol dissolved in supercritical CO₂ was measured by amperometric microsensor which is made of thin film of perfluorosulfonate ionomer(PFSI).     

Isolation and Determination of Volatile Organic Compounds from Water by Dynamic Purge-and-Trap Technique Coupled with Capillary Gas Chromatography

The preconcentration technique of purge-and-trap has been investigated in the present work for quantitative adsorption of volatile organic pollutants purged from water samples. A dynamic purging device with variable volume size has been constructed and tested to purge different concentrations of organic compounds. With Tenax GR as the adsorbent, a dynamic purge-and-trap technique was developed combining on-column preconcentration procedures using ambient trapping/thermal desorption/cryogenic focusing/back-flash injection prior to separation and determination using capillary gas chromatography. Various aromatic compounds in water were determined, giving linear working ranges over five orders of magnitude from 0.02 to 5000 µg/L. The analytical procedures were optimized under the assistance of ultrasonication with results validated for the determination of organic contaminants in underground water and tap water, giving over 93% recoveries and a detection limit of 0.01 µg/L, two orders of magnitude lower than those obtained using commercial available instruments with on-line configuration to minimize cross-contamination. The technique provides a potential automated method for in situ monitoring of volatile organic compounds in water.     

A Simple,Portable and Low Cost Device for a Colorimetric Spot-Test Quantitative Analysis

ABSTRACT

This paper describes a very simple device that can be used for colorimetric quantitative determinations, including spot-test analysis. The sensor is a light detector resistor (LDR) placed into a black PTFE cell and coupled to a low cost multimeter (Ohmmeter). The device has been tested and is easy and fast to use. Quantitative studies were performed with KMnO4 solutions and with the vanadium (V)/PAR/H₂O₂ system. Calibration curves were obtained by plotting the electric resistance of the LDR against the concentration of the colored species from 0 (blank) to 4.0 × 10^-3 mol L^-1 for permanganate and from 0 (blank) to 5.0 × 10^-5 mol L^-1 for vanadium. The detection limit (3σ) was found to be about 5.0 × 10^-5 mol L^-1 for permanganate and 4.0 × 10^-6 mol L^-1 for vanadium. The device was used to analyze total vanadium, as vanadium (V), in wastes from an adipic acid plant. The results obtained clearly show that the device can be used for accurate, precise, fast, in situ and low cost colorimetric analysis including quantitative spot-test procedures.     

Field Determination of Cr(VI) in Water At Low PPB Level

Abstract

Methods for determining chromium (VI) at the ppb level, in tap water and ground water, were developed. These make use of anion exchange resin beads or anion exchange membrane filters to preconcentrate the Cr(VI) and separate it from interfering cations. The color is developed by reaction with diphenylcarbazide and the quantitation is carried out using a portable UV/Vis spectrometer, in the liquid or solid phase, or by visual color matching. These methods are suitable for use in the field.     

Sensitive Solid Reagent For Formaldehyde,And A New Formaldehyde Generator

Abstract

A solid reagent of Purpald®-acetone aminal on sodium or potassium bicarbonate responds to formaldehyde in the sub-ppm concentration range. A purple color (λ=560 nm) is developed proportional to concentration of formaldehyde and time of exposure after wetting with a 90% acetone-10% water solution. The reagent should be of value as a semi-quantitative warning device for the presence of formaldehyde. A device is described which generates formaldehyde in air in the sub-ppm concentration range at room temperature with desired relative humidity. This generator could be used in the same manner to generate low concentrations of other substances of low volatility.     

Comparison of Different Assay Methods for Determination of Elastase Activity

Abstract

Four different methods of pancreatic elastase (E. C. 3.4.21.11) assay have been compared: one use N-succinyl-(Ala)₃-paranitroanilide as a substrate; the three others use elastin, modified or not.

The former has been monitored either with a spectrophotometric or a conductimetric device.

All methods give a linear relationship with amounts of pancreatic elastase in the range 0–5 μg.

The conductimetric method is the only one using unmodified elastin which measures elastolysis in initial rate conditions, avoiding artificial amplification of hydrolysis if other proteases are present.     

On a New Enzyme Transducer Combination: The Enzyme Transistor

Abstract

The application of a hydrogen- and ammonia-sensitive, palladium-coated semiconductor device (Pd-MOSFET) in enzymic analysis has been studied. The response of the device to NH₃ liberated both non-enzymically as well as by the enzymes urease from urea and creatinine deiminase from creatinine was investigated. In the latter case, a flow-cell was used and the analysis was continuous. The device described, a kind of enzyme-transistor, is of relatively simple design.     

Electrochemical Techniques for Study of Phenolic Natural Products and Drugs in Microliter Volumes

Abstract

A simple semimicro carbon paste electrode is described for use in several electrochemical cells designed to accommodate between 1 and 300 μ1 of sample solution. Using this apparatus it is possible to study the electrochemical properties of phenolic compounds when the total sample available is on the microgram level or below. Quantitative work is possible for samples eluted from paper or thin-layer chromatograms. A semiautomatic device for serial assay of over 60 samples/hour is described.     

Evaluation of a Continuous Composite Sampler for Volatile Organic Compounds in Water

Abstract

The high volatility and low water solubility of volatile organic compounds (VOCs), make the collection of representative samples difficult. The standard grab sampling method only gives information of that moment in time when the sample is taken. When the composition of VOCs is varying, continuous composite sampling will give a more representative sample. However, no thorough evaluation of its use for VOCs has been reported.

The use of an automatic continuous composite sampler for the analysis of VOCs in water was studied. The causes and magnitude of the VOCs losses during the sampling process were determined.

Adsorbent cartridges were used to trap the VOCs escaping from solution during the sampling process. Sorption phenomena occurring on the containers and/or tubings were also evaluated. Sorption losses were much more significant than volatilization losses.

The results indicate that a modified version of this sampler can be an alternative for the long term sampling of water for VOC analysis.     

Flow Injection Determination of Chloride Ions with Spectrophotometric Detection

Abstract

A single-line FIA system with a stream-sample splitting device for chloride determination is presented. The analytical method is based on the Fe^3+/Hg(SCN)₂/Cl^? system and the absorbance of the red Fe(SCN)²⁺ species monitored spectrophotometrically at 480 nm. Using a stream-sample splitting device, the recorded signal is composed of two merged peaks. Three calibration curves were obtained, once injecting the standard solution series, two using the maximum heights of P₁ and P₂ peaks and one using the height of T trough. The FIA system showed three linear responses to the concentration of chloride in the ranges 10-100 ppm (P₁); 10-500 ppm (P₂) and 20-1000 ppm (T), respectively. Also, it was capable of detecting chloride ions in different types of water with a throughput of 15 samples h^?1 and the RSD for 240 ppm of Cl^? (n=10) were 1.67% (P₁); 2.38% (P₂) and 1.23% (T), respectively. The interference of several ions (commonly found in water) on the FIA outputs was investigated.     

An improved Sampling Strategy for the Measurement of VOCs in Air,Based on Cooled Sampling and Analysis by Thermodesorption-GC-MS/FID

Abstract

Reliable and comprehensive sampling methods are required to obtain accurate data for VOC concentrations in air samples. The major drawback of the adsorption tube sampling method, widely employed in environmental studies, is the fact that C₂ compounds are usually not trapped quantitatively.

The focus of this work was thus to improve sampling based on adsorption tubes packed with Molsieve and Carbosieve. To improve the sampling efficiency for the C₂ compounds, a cooling device, based on Peltier cooling was constructed, which could be operated at a temperature down to ?30°C.

Experiments under laboratory and field conditions were carried out to study the influence of the sampling temperatuie on the recovery of ethane and ethene as the most volatile VOCs. The results clearly demonstrate the need for a cooled sampling device for the analysis of C₂ compounds in air. Under the investigated conditions, the recoveries with ambient temperature sampling were only in the range of 38–46% for ethane and 33–59% for ethene respectively, in comparison to the cooled sampling device. These findings are only valid for the described conditions and can change significantly with temperature and concentration. A generalisation of the recovery is thus very difficult to give.

The use of the sampling device for a field study is reported, where samples were collected simultaneously at three different altitudes in a diurnal profile on the slope of the Schulterberg mountain in Tyrol (Austria).     

A conductometric device for monitoring of enzyme-catalyzed reactions

A new conductometric device is described for measurement of conductance changes during enzyme-catalyzed reactions. The use of platinum resistances inside the cell allows temperature regulation to be obtained without circulating water. Solutions are introduced and removed from the cell with a peristaltic pump. The device is evaluated by assaying serum urea concentrations down to 40 nM. The results correlate well with a spectrophotometric method based on biacetylmonoxime (r=0.997).     

Enzyme Electrode with Collagen-Immobilized Cholesterol Oxidase for the Microdetermination of Free Cholesterol

Abstract

Cholesterol oxidase has been immobililzed on collagen films associated to an electrochemical sensor to form a “cholesterol electrode”. The electrode poised at a potential of + 650 my vs Ag/AgCl detects the hydrogen peroxide produced in the enzymatic reaction. This device presents a very high sensitivity and a wide range of linearity (10^?7 M - 0.8.10^?4 M). The use of a non enzymatic electrode associated with the enzymatic one allowed the detection and correction of electrochemical interferences when applied to human sera for free cholesterol determination.     

Analysis of Planar Chromatograms by Fast Atom Bombardment and Laser Desorption Mass Spectrometry

Abstract

The applications of fast atom bombardment mass spectrometry coupled with thin-layer chromatography in a study of phospholipids, alkaloids derived from bloodroot rhizomes, and diuretics are summarized. Use of the mass spectrometric data to trace compounds via characteristic fragment ions increases the effective resolution of the chromatographic resolution. Quantitative values derived in TLC/FAB experiments for the diuretic amiloride hydrochloride is linear over two orders of magnitude encompassing the clinically useful range. The use of a laser desorption ionization method and Fourier transform mass analysis for TLC plate detection is also described; matrix and concentration effects are significant in this case, but several successful applications are described. An interface device for the linkage     

Separation of Substances in Rotating Coiled Columns: From Trace Elements to Microparticles

The potentialities of rotating coiled columns in countercurrent chromatography (CCC) and centrifugal field-flow fractionation (CFFF) are demonstrated. A rotating coiled column is a fluoroplastic or steel coil wound around a rigid cylindrical drum, which revolves about its axis and, at the same time, revolves around the central axis of the device called planet centrifuge. The stationary (liquid, solid, or heterogeneous) phase is retained in the column because of the centrifugal force field, and the mobile liquid phase is continuously pumped through the column. The methods for recovery, separation, and preconcentration of various trace elements in geological samples and high-purity substances with the use of two-phase liquid systems (CCC) are developed. Procedures are proposed for the continuous sequential extraction of various element species from soil and for the recovery of polycyclic aromatic hydrocarbons from sewage sludge with the use of natural suspensions or solid particulates as stationary phases. It is also shown that rotating coiled columns can be used in a new field, microparticle fractionation by CFFF.     

Membrane Extraction of Volatile Organic Compounds in Combination with Mobile Gas Chromatographic Analysis

Abstract

The field of application of a mobile gas chromatographic device (Airmobtx monitor HC 1000 manufactured by Airmotec GmbH) originally conceived for the analysis of BTEX in air was extended to water analysis by using it in conjunction with membrane extraction. Volatile organic compounds diffuse out of water through a hollow fibre or flat membrane, are enriched onto sorption tubes integrated in the device, and then thermally desorbed and analysed by the gas chromatograph/flame ionisation detector. The suitability of various flat membranes and hollow fibres was investigated. Maximum extraction efficiency was obtained with a silicone hollow fibre measuring 0.3 m long, and with an inner diameter of 0.7 mm and a wall thickness of 100 μm. The extraction parameters were optimised. The linear dynamic range of the optimised method spans two orders of magnitude and the detection limits were found to be 0.1 μg/L for all BTEX compounds. By way of environmental applications, highly contaminated groundwater samples were analysed. The results correspond well to those achieved using conventional headspace/gas chromatography/flame ionisation detection.     

Preparation of biocarbon micro coils

ABSTRACT

A novel synthetic polymer-plant-precursor carbonization technique was developed. Carbon micro coils were prepared by the carbonization of plant helical vessels coated with polyaniline or poly(acrylonitrile-co-acrylic acid). The helical vessels served as a helical guide, while the synthetic polymers coated on the vessel surface, which consisted of cellulose, were transformed into carbon material while retaining the helical form. The helical carbon material was prepared without the use of an organic gas or solvents through a relatively simple and convenient process. This technique involved the application of natural resources, the synthesis of a conducting polymer, and carbon science. The biocarbon micro coils thus prepared in this study were characterized by infrared absorption, optical microscopy, and scanning electron microscopy. Moreover, the magnetic properties of the helical carbon were examined by electron spin resonance and a superconducting quantum interference device that proved its paramagnetic features. Additionally, the water transport function in the helical vessels was discussed.