Ammonia Electrode Performance in Deuterium Oxide Solutions

Abstract

Response characteristics of the ammonia gassensing membrane electrode have been evaluated in deuterium oxide solutions. Results indicate no significant differences in electrode slope, recovery time, and standard deviation of the fit for the calibration line. Only slight differences in response times, limit of detection, baseline potential and position of the calibration line have been found. Overall, steady-state and dynamic measurements in deuterium oxide solutions are possible with this electrode.     

Detection of Nitrite Using Electrodes Modified with an Electrodeposited Ruthenium-Containing Polymer

Abstract

The electrochemical detection of nitrite in flowing solutions using a polymer modified electrode with electrocatalytic properties is described. The modifier was an electrodeposited polymer film of the [Ru(bpy)₂(vpy)₂+²⁺ complex, where bpy is 2,2′ bypyridyl and vpy is 4-vinylpyridine. The modified electrodes showed the ability to enhance the nitrite response and avoid surface fouling. The electrodeposited films exhibited higher mechanical stability than similar chemisorbed coatings.     

Separation of Sulfur Species in Water by Co-Electroosmotic Capillary Electrophoresis with Direct and Indirect UV Detection

Co-electroosmotic capillary electrophoresis (co-CZE) with both direct and indirect UV detection was investigated for the separation of sulfur species. With direct UV detection, the separation of S₂O^2? ₃, S₂O^2? ₄ was possible using 20 mM phosphate electrolyte containing 0.75 mM tetradecyltrimethylammonium bromide (TTAB) and 15% acetonitrile. To obtain optimal peak shape and sensitivity using indirect UV detection, a range of background electrolytes (BGEs), including benzoate, phthalate, 2,6-pyridinedicarboxylate (2,6-PDCA) and trimellitate, were examined as the BGEs. Of all the BGEs, 2,6-PDCA gave high selectivity and indirect UV response due to its mobility matching to that of sulfur species and its high absorptivity. Detection limits in range of 3-6 μM were obtained using either direct UV or indirect UV detection. The proposed CZE methods were used for the determination of sulfur species in water samples, and provided fast separation of sulfur species in less than 5 min.     

On-Plate Electrochemical Detection for Thin-Layer Chromatography

Abstract

Voltammetric electrochemical detection (ECD) coupled with thin-layer chromatography (TLC) was demonstrated for the quantification of trace organic compounds directly on a TLC plate. the electrochemical detection solvent was a thin layer of aqueous potassium chloride. For undeveloped plates, detection limits for p-anisidine and p-phenetidine were 10 ng and 13 ng, respectively. Linearity was demonstrated over nearly 2 orders of magnitude. After development, detection limits increased by approximately a factor of ten. Advantages of this method over other quantitative TLC methods include sensitivity, speed, simplicity, and cost. in addition, this method is selective for electrochemically active compounds. Major sources of experimental error include spot size reproducibility, working electrode placement, and supporting electrolyte film thickness.     

Potentiometric Flow-Injection Determination of Sugars Using a Metallic Copper Electrode

Abstract

The determination of reducing sugars is shown to be possible by use of potentiometric detection with a metallic copper indicator electrode by either flow-injection analysis (FIA) or high-performance liquid chromatography. Various sugars including arabinose, maltose, sorbose, glucose, fructose, sucrose, lactose and xylose, give an electrode response when injected into different carrier streams composed of cupric ions in weakly complexing ligand solutions comprised of either ammonia or tartrate. Optimization of response depends on flow-rate, temperature, pH, and concentrations of carrier components. Chromatography using a cation-exchange column and post-column addition of carrier reagents similar to those used for FIA is demonstrated to give detectable separation of four sugar components with umole injection quantities.     

The Reliability of Detection Limits in Analytical Chemistry

Abstract

Five guidelines were elucidated to be of importance in improving the reliability of detection limits in analytical chemistry. The necessity of following rigid statistical rules and documentation of the experimental system, the experimental parameters and the entire analytical procedure, is stressed, in order for the detection limits to have any reliability.     

An off-on fluorescent sensor with high selectivity and sensitivity for Fe(III)

A new fluorescent derivative (1) containing coumarin exhibits Fe(III)-selective strong yellow-green fluorescence in ethanol. This compound could be used as an “off-on” chemosensor and allow the detection of Fe³⁺ by monitoring changes in absorption and fluorescence spectra. Upon addition of Fe³⁺, an overall emission change of 125-fold was observed. High selectivity and sensitivity were observed over other metal ions, mainly due to the spirolactam ring-opening power of Fe³⁺. The detection limit was as low as 5.6?ppb. Photo-induced electron transfer, coupled with intramolecular charge transfer are proposed to account for the observed spectral response.     

Elemental Analysis by Gas Chromatography-Atomic Emission Detection for the Control of a Deuterated Derivatization Reagent

Abstract

Methyl iodide is a derivatization reagent often used to methylate molecules with amine, hydroxyl or carboxylic groups before a gas chromatographic analysis. In order to improve the analytical qualities of quantitative determination by gas chromatography mass spectrometry, derivatization with reagents labelled with stable isotopes can be used. Deuteromethyliodide can be used instead of methyliodide to obtain labelled compounds easily detected, as far as the reagent is pure enough.

This paper illustrates the use of the gas chromatography atomic emission detection coupling (GC-AED) for the study of the purity of a reagent labelled with deuterium (IC²H3) used for the derivatization of a new immunoenhancer (sodium ditiocarb - lmuthiol^R) before the GC-MS determination of the parent drug and its methylated metabolite. The elements monitored simultaneously are: carbon (193.03 nm), hydrogen (656.3 nm), deuterium (656.04 nm), iodine (183.1 nm) and sulfur (180.7 nm). The chromatograms corresponding to these various elements obviously show the presence of compounds containing deuterium and I or hydrogen associated with iodine and make easier and faster the determination of the chemical pollution of the IC²H3 batch. The monitoring of the specific wavelength associated to the atomic emission of sulfur (180.7 nm) allows easy detection o f ditiocarb and its metabolite from the chromatogram made very complex by the reagent pollution.     

A Piezoelectric Crystal Detector for Acetoin

Abstract

A piezoelectric quartz crystal coated with tetrabutyphosphoniun chloride was found to be a good detector for acetoin. The coating is sensitive in the ppb range and completely reversible. The response curve is linear over a concentration range of 8-120 ppb. The detector can be tuned to give a satisfactory response in 30 seconds.     

Glass Electrode Measurements in Deuterium Oxide

Abstract

When hydrogen selective glass electrodes are transferred between acid solutions in ordinary water and deuterium oxide their potentials drift systematically by 1–2 mV over several hours, and hence electrodes standardised in H₂O cannot be readily used for the precise measurement of deuterium ion activity a_D+ in D₂O.     

Catalytic Kinetic Determination of Trace Amounts of Iron(III) With Polarographic Detection

Abstract

This method is based on the catalytic effect of Fe³⁺ on the oxidation reaction between Acid Chrome Blue K and potassium bromate in sulfuric acid medium at 100deg;C, and in 0.08 mol/L NH₄OH - 0.01 mol/L (NH₄)₂ SO₄ supporting electrolyte, Acid Chrome Blue K exhibits a sensitive polarographic wave at -0.55V vs. SCE, and change of concentration is traced by a polarographic detection technique. The linear range of Fe³⁺ is 10–100ng/mL. This new catalytic method has been applied to the determination of iron in natural water and food with satisfactory results.     

Detection of Galactose and Lactose by a Poly(Amphiphilic Pyrrole)-Galactose Oxidase Electrode

Abstract

The entrapment of galactose oxidase (GAO) on an electrode surface by coadsorption with a cationic amphiphilic pyrrole and electropolymerization of this pyrrole monomer is described. This simple and rapid procedure for biosensor construction provides very fast responsive and sensitive GAO-based sensors to galactose and lactose. The electrode response is based on the electrochemical detection of enzymically generated hydrogen peroxide. The stability, optimum pH and selectivity of the bioelectrode as well as the characteristics of the immobilized galactose oxidase have been determined. Poly(amphiphilic pyrrole) films have been electrogenerated on the surface of the bioelectrode and the effect of such additional coatings on the biosensor selectivity have also been examined.     

Piezoelectric Detection of Ricin and Affinity-Purified Goat Anti-ricin Antibody

Abstract

Detection of ricin, in a piezoelectric quartz crystal microbalance format, can be accomplished with the use of capture antibody techniques. These techniques allow for the specific attachment of ricin to immobilized capture antibodies on the quartz crystal transducer area. A reversed format can also be used to detect antibody in solution. In this case, the antigen is immobilized and antibody attaches specifically, thus increasing the overall mass and decreasing the resonant frequency. In this report we describe detection of both ricin and anti-ricin antibody using immunological piezoelectric quartz crystal microbalance techniques.

     

Deuterium N.M.R. of liquid crystal solutions with proton–proton dipolar decoupling

Abstract

Deuterium N.M.R. of solute molecules in liquid crystal solutions with the removal of proton–proton dipolar coupling has been explored. The deuterium N.M.R. spectrum of a partially deuterated compound dissolved in a liquid crystal solvent is usually complex or unresolved because of proton–deuterium coupling and extensive proton–proton dipolar coupling. When the latter is removed by a special dipolar decoupling sequence, the deuterium N.M.R. spectrum becomes first order, and deuterium–proton dipolar coupling constants can be readily obtained from the spectrum. Results of monodeuterated hexanes and heptanes dissolved in ZLI 2142 are reported.     

Determination of Reserpine in Plasma Using High-Performance Liquid Chromatography with Fluorescence Detection

Abstract

A high-performance liquid chromatographic method for determining reserpine in plasma has been developed. The procedure involves extraction of reserpine from buffered plasma into benzene, oxidation of reserpine to a fluorophor by treatment with vanadium pentoxide in phosphoric acid, and chromatographic separation of the reserpine fluorophor on an octadecylsilane column by ion-pairing with heptanesulfonate ions. Fluorescence monitoring of the column effluent provides high sensitivity of detection and increases the specificity of the procedure. A detection limit of approximately 100 pg of reserpine per ml of plasma was obtained following analysis of 2 ml samples. Analysis of a number of samples demonstrated the applicability of this method in confirming the presence of reserpine in equine plasma specimens collected at various horse shows and in evaluating the pharmacokinetic behavior of reserpine following intramuscular administration to horses.     

Persistence of Diflubenzuron on Conifer Forest Foliage in a Mediterranean-Climate Ecosystem Following Aerial Application

Dimilin 45 ODC (diflubenzuron) was applied in a Mediterranean-climate conifer forest, near Vitoria, Basque Country, Spain. Pine needles were collected at post-treatment 5-day intervals for analysis of the diflubenzuron residues. A liquid chromatography method with on-line diode-array and electrochemical detection was developed for the determination of the pesticide diflubenzuron and its main metabolites: 2,6-diflurobenzamide, 4-chlorophenylurea, 4-chloroacetanilide, 4-chloroaniline and N-methyl-4-chloroaniline in forestry matrices. Aerial application at 56.3 g AI ha^?1 resulted in deposition levels of the insecticide of 1080 ng g^?1. Within 40-65 days following treatment, 51-73% of the insecticide had been removed from the foliage. During this period, the concentration of diflubenzuron was higher than 295 ng g^?1. The only metabolite detected was 2,6-difluorobenzamide and this persisted on foliage until the first rainfalls occurred. An empirical mathematical correlation was found to express the influence of rainfall, solar radiation and temperature on the persistence of the insecticide.     

A Simple Electrochemical Method for the Quantitative Determination of Acetaminophen in Serum

Abstract

A simple electrochemical method for the determination of acetaminophen in serum is described. The eleotrode and associated electronics are simple, reliable, and inexpensive to build. The apparatus can be operated at a rate of 2–3 determinations per minute using only 10 μl serum per determination. The procedure includes extraction of acetaminophen in ethyl acetate and subsequent oxidative amperometric detection of the drug by a form of flow-injection analysis. The system parameters of buffer, pH, and redox potential have been optimized to permit measurement of less than 10 μg/ml of acetaminophen. The determination is linear over the range of 10–300 μg/ml with a C.V. of less than 3% for replicate analysis of the same sample.     

A Study on Effective Derivatization for Ultra-Micro Detection of Dopamine by Gas Chromatography / Electron Capture Negative Ion Chemical Ionization Mass Spectrometry

Abstract

N-Pentafluorobenzenesulfonyl-O-bis (trimethylsilyl) dopamine was prepared and its properties were discussed for ultra-micro detection of dopamine by gas chromatography / electron capture negative ion chemical ionization mass spectrometry (GC/ECNICIMS). Detection of this derivative was at least 100 times as sensitive by GC/ECNICIMS as by gas chromatography / positive ion chemical ionization mass spectrometry. Deuterium labelled dopamine, dopamine analog phenethylamine and deuterium labelled phenethylamine were also derivatized, respectively, to reveal the fragmentation mechanism of the dopamine derivative. the high sensitivity and speculated fragment ion composition of the derivative by GC/ECNICIMS showed a possibility for highly sensitive detect ion of dopamine.     

Determination OP Picogram Concentrations of Sodium in Flame by Stepwise Photoionization of Atoms

Abstract

The first experiment in which stepwise photoionization of atoms is used for analytical purposes is reported. A detection limit of 12 pg/ml has been achieved for sodium in aqueous solutions. The results are compared with atomic fluorescence measurements. The potentialities of the new method are discussed.     

Determination of Hydrazine Compounds by Capillary Electrophoresis with a Poly(Glutamic Acid) Modified Microdisk Carbon Fiber Electrode

ABSTRACT

Hydrazine compounds, including hydrazine (HZ), phenylhydrazine (PHZ), semicarbazide (SCZ) and isoniazid (INZ) were separated and determined by capillary electrophoresis (CE) with a poly(glutamic acid) modified microdisk carbon fiber electrode. The modified electrode exhibited highly catalytic activity for hydrazines and has good stability. Linear responses for hydrazines over 2~3 orders of magnitude were obtained. The detection limits for HZ, PHZ, SCE and INZ were 7.8, 8.0, 14.0 and 11.0 fmol, respectively.