The Detection of Sulfur Dioxide Utilizing a Piezo-Electric Crystal Coated with Ethylenedinitrilotetraethanol

Abstract

A considerable number of compounds have been shown to be sensitive to sulfur dioxide sorption using quartz crystals. To utilize the technique for the continuous measurement of SO₂, coating loss has been shown to be a major limitation. For such a continuously flowing system a previous coating, triethanolamine, was found to evaporate at undesirable rates when used at high enough temperatures and flow rates for an adequate response time. Methods of remedying this problem have led to a new SO2 sensitive coating, ethylenedinitrilotetraethanol. This work presents the technique of coating application, the sensitivity relative to the amount of coating applied, a comparison of totally coated crystals to center coated ones, and a comparison of the new coating relative to the previously used triethanolamine.     

Active Site Titration of Horse Liver Alcohol Dehydro-Genase by Dual Wavelength Specthophotomethy

Abstract

A simple dual wavelength spectrophotometric method for determining the active site concentration of horse liver alcohol dehydrogenase is described. The method is rapid, sensitive, accurate and requires minute amounts of enzyme. A comparison between this new application of the dual wavelength technique and the conventional methods, ordinary photometry and spectrofluorometry is furthermore discussed.     

Speciation of Cr (III) and Cr (VI) via Reversed Phase HPLC with Inductively Coupled Plasma Emission Spectroscopic Detection (HPLC-ICP)24

Abstract

Chromium ions, viz., chromic (Cr^±3=III) and chromate (Cr^±6 = VI), can be reliably, conveniently, reproducibly, and quickly separated and detected by the use of conventional paired-ion, reversed phase (RP) high performance liquid chromatography (HPLC) together with refractive index (RI) and/or inductively coupled plasma emission spectroscopic (ICP) detection. A number of novel paired-ion approaches have now been developed, using PIC A (tetrabutylammonium hydroxide) or PIC B (sodium n-alkyl sulfonate) separately in the mobile phase. This allows for the retention of each Cr species depending on the particular ion pairing reagent being used, while the remaining Cr ion elutes in the solvent front. Changing the ion pairing reagent reverses the overall situation. The total time for each HPLC analysis is about 10 mins. ICP detection provides for a complete, overall method of speciation for both Cr (III) and Cr (VI) via two separate injections, together with quantitation for both species. This method of using paired-ion RP-HPLC can easily be applied to other mixtures of inorganic cations and anions, presumably with equally successful results. Minimum limits of detection are computed for chromate via direct-ICP, using at least two basic methods for such computations. It is suggested that virtually all chromatographic detection limits can be significantly improved by the application of newer, spectroscopic based methods of automated computation of detection limits.     

Pulse Enhanced Electrosorptive Detection of Ions at Silver in Ion Chromatography

Abstract

Differential double-layer capacitance measurements applied to the silver-aqueous interface may serve as the basis of detection for surface-active ions in ion chromatography. There is a caveat to this approach, though, and that is that the electrode is subject to gradual fouling due to the accumulation of adsorbed matter. We report here on the incorporation of potential pulsing sequences to counter this damaging effect. Two approaches have been taken: 1) inclusion of a periodic potential cleaning pulse in the conventional, fixed-potential double-layer capacitance measurement scheme, and 2) utilization of a potential-pulse/coulometric measurement technique. the potential-pulse/coulometric procedure entails measurement of the change in charge required to charge the electrical double layer in response to specific adsorption of analyte. Its response-concentration behavior is similar to that observed for differential capacitance detection. the use of a combined, dual-potential (sequential) capacitive/amperometric detection scheme that provides unique complementation to either amperometric or capacitance detection is also discussed.     

Use of ion exchange membranes in preparative organic electrochemistry: New processes for electrolysis

2-Amino 5-nitro pyridinc (ANP) adsorbs strongly at an electrochemically roughened silver surface and gives an intense surface-enhanced Raman (SER) spectrum which identifies the adsorbate as the [ANP]^? ion [C₅H₄N₃O₂]^?. Coulometric and spectrophotometric methods are used to provide an in situ measurement of the surface molecular concentration of this adsorbate. This is shown to be linearly dependent upon the anodic roughening charge transfer in 0.1 M KCl over the range 0–150 mC cm^?2 for double-potential-step roughening cycles. A quantitative measure of the surface Raman enhancement factor for this adsorbate is obtained, and this is shown to reach a maximum of 1.5 × 10⁴ for surface roughening involving the passage of 25 mC cm^?2. For this amount of roughening or greater, it is concluded that the surface roughness further increases the total SER intensity by a factor of 10 or more due to the resulting high effective surface concentration of the adsorbate.     

Simultaneous determination of peroxydisulfate and conventional inorganic anions by ion chromatography with the column‐switching technique

The application of ion chromatography with the column‐switching technique for the simultaneous analysis of peroxydisulfate and conventional inorganic anions in a single run is described. With this method, conventional inorganic anions were separated by consecutive elution through both the guard column and separation column, but peroxydisulfate that only passed through the guard column had a good peak shape and short retention time. A series of standard solutions consisting of target anions of various concentrations from 0.01 to 75 mg/L were analyzed, with a correlation coefficient (r) ≥ 0.9990. The limits of detection were in the range of 0.49–9.84 μg/L based on the S/N of 3 and a 25 μL injection volume. RSDs for retention time, peak area, and peak height were all <1.77%. A spiking study was performed with satisfactory recoveries between 97.6 and 103.4% for all anions. The quantitative determination of peroxydisulfate and conventional inorganic anions in surface waters was accomplished within 18 min by this column‐switching technique.     

Synthesis of polyphilic compounds Evidence for ferroelectricity in a non-chiral mesophase

Abstract

The synthesis and properties of new mesomorphic ferroelectrics composed of nonchiral polyphilic molecules are described. Polyphilic molecular units are made up of a sequence of chemical fragments differing by their chemical nature. The segregation between unlike species is used to favour a polar packing. Ferroelectricity is demonstrated by the measurement of an acoustically induced piezoelectric response and the determination of repolarization currents. It is the first time that a ferroelectric repolarizable mesophase is obtained with non-chiral molecular units. The mechanism of ferroelectricity is therefore different from that found in conventional chiral smectic C.     

Determination of Glycerol and Serum Triglycerides with Collagen-Immobilized Glycerol Dehydrogenase and Amperometric Detection

Abstract

An amperometric procedure is described for the determination of glycerol and triglycerides in aqueous samples and in serum using glycerol dehydrogenase immobilized on a collagen membrane. Glycerol is determined by measurement of the steady-state oxidation currents generated at a platinum electrode by NADH produced in the enzyme-catalyzed reaction. The triglycerides were first hydrolyzed by the enzyme lipase in solution and the resulting glycerol determined similarly. Olive oil, determined to contain 78 % triolein, was used as the source of triglycerides in this study. For both glycerol and triglycerides the calibration plots are linear in the range from 0 to 12 μM, with detection limits of 0.2 and 0.7 μM, respectively. The immobilized glycerol dehydrogenase retained high operational activity for a period longer than 30 days.     

Separation and indirect ultraviolet detection of common fluorine-containing anions by ionic liquids in reversed-phase chromatography

Abstract

A new approach for the simultaneous separation and indirect ultraviolet detection of four common fluorine-containing anions using 1-hexyl-3-methylimidazolium chloride as a mobile phase additive in reversed-phase chromatography was developed. The principle of separation and detection is that fluorine-containing anions and imidazolium cations form ion-pairs with ultraviolet absorption. Under the optimal determining conditions, the limits of detection for tetrafluoroborate, hexafluorophosphate, trifluoroacetate, and trifluoromethane sulfonate were 0.6, 0.6, 1.5, and 3.1?µmol/L, respectively. The approach has been successfully applied to the determination of these anions in ionic liquid samples, and the spiked recovery was between 98.5 and 102.6%. The detection limit, linearity, reproducibility, and accuracy of the approach are suitable for quantitative analysis. The method is simple and easy to popularize because of the use of a common C₁₈ reversed-phase column and ultraviolet detector.     

Simple UV and visible spectrophotometric methods for the determination of doxycycline hyclate in pharmaceuticals

Doxycycline hyclate (DOX), a broad spectrum antibiotic with activity against a wide range of gram-positive and gram-negative bacteria, is widely used as a pharmacological agent and as an effector molecule in inducible gene expression system. Three simple, selective, rapid, accurate, precise and cost-effective spectrophotometric methods for the determination of DOX in bulk drug and in tablets have been developed and validated. First method (method A) is based on the measurement of absorbance of DOX in 0.1 M HCl at 240 nm. The second method (method B) is based on the measurement of yellow chromogen at 375 nm which is formed in 0.1 M NaOH. The third method is based on the measurement of 2: 1 complex formed between DOX and iron(III) in H₂SO₄ medium, the complex peaking at 420 nm (method C). The optimum conditions for all the three methods are optimized. Beer’s law was obeyed over the ranges 2.5–50.0, 1.50–30.0 and 10–100 g/mL for method A, method B and method C, respectively. The apparent molar absorptivity values are calculated to be 1.03 × 10⁴, 1.73 × 10⁴, and 5.21 × 10³ L mol⁻¹ cm⁻¹ for method A, method B, and method C, respectively. The Sandell sensitivity, limit of detection (LOD) and limit quantification (LOQ) values are also reported. All the methods were validated in accordance with current ICH guidelines. The developed methods were employed with high degree of precision and accuracy for the estimation of total drug content in commercial tablet formulations of DOX.     

Simultaneous Spectrophotometric Determination of Silicate and Phosphate by Flow Injection Analysis

Abstract

A method is reported for the simultaneous determination of phosphate and silicate by flow injection analysis based on the different rate of formation of the heteromolybdic acids of the two anions. Measurements are based on the colour of the ion-pairs formed between the said molybdic acids and Rhodamine B. The method allows the determination of the two anions at a rate of 20 samples/h over the ranges 0.05–2.5 ppm (phosphate) and 0.8–15 ppm (silicate), which allows application to a variety of waters.     

Chemiluminescent Method for Flow Injection Analysis of Anions

Abstract

We present here the preliminary results on a new flow injection chemiluminescent method of analysis for anions. This technique is rapid and sensitive with detection limits on the order of 1 × 10^?6M for chloride and 30 samples/hr possible.     

SELECTIVE S-ALKYLATION IN PHASE TRANSFER CATALYSIS OF 2-PYRIDINE-, -PYRIMIDINE- AND BENZOXAZOLE-THIONE

Abstract

Alkylation via phase transfer catalysis of several ambident anions of the |N–C–S|^? type leads exclusively to S-substitution. Yields obtained are better or equal to those given by conventional methods and experimental work-up is very much simplified compared to the latter.     

Catalytic-Fluorimetric Determination of Ti(IV) by Flow Injection Analysis

Abstract

Two flow injection analysis catalytic-fluorimetric methods for the determination of titanium are suggested, based on the measurement of the peak height and of the peak width, respectively. Both methods allow the determination of titanium at the ng.mL^?1 level with good selectivity. A comparison between both method is also established.     

A dansyl-based optical probe for detection of singly and doubly charged anions

This paper reports the synthesis of a new molecule, 5-(dimethylamino)naphthalene-1-sulfonic acid 2,3-bis(3-phenylureido)phenyl ester (1), as an optical probe for anions. The effect of the presence of various anions on the spectroscopic properties of 1 was examined using UV–vis absorption spectroscopy, fluorescence and ¹H NMR titration experiments. Strong binding of 1 to carboxylate, oxalate, cyanide and dihydrogen phosphate anions resulted in an increase in the emission of 1 and changes in its ¹H NMR chemical shifts. Binding constants of 1 to anions were also calculated based on the binding isotherms derived from the spectroscopic titrations.     

New Algorithm of Spectral Analysis of Elements in Presence of Matrix Interferences

Abstract

This work suggests a new algorithm for the elemental analysis, which permits taking into account both the multiplicative and additive matrix effects, a matrix composition being unknown. The use of this algorithm in the development of analysis techniques at any set of objects may appear to be successful at arbitrarily selected measurement conditions. The basis of the algorithm consists of a combination of pattern recognition and standard addition technique (PRSA). The main concept of PRSA is to predict a function approximating satisfactorily a calibration dependence for a specific object and then to determine an unknown concentration using a nonlinear addition technique, all the aforementioned being based on easily obtained information on an analyzed object and measurement conditions. The abilities of the proposed algorithm were demonstrated by the example of strontium determination by the flame atomic absorption spectrometry in superconducting systems.     

Comparison of simulated and actual DSC measurements for first-order transitions

A system of differential equations modeling a heat flux DSC is solved and the results are compared with those obtained using a TA Instruments Q1000™ DSC.¹ It incorporates a new heat flow rate measurement technique that determines the heat flow rate between the sample and its pan. Two types of first-order transitions are investigated: melting of a pure substance and solidification of a pure substance including super-cooling. In both transitions, the peak shape obtained using the new heat flow rate measurement and predicted by the model is quite different from that measured using conventional DSC. It is shown that the differences are the result of simplifications implicit in the conventional heat flow rate measurement that is based solely on the difference between sample and reference calorimeter temperatures. Heat flow rates measured using the improved measurement agree very well with the model predictions for heat exchange between the sample and its pan.     

Voltammetric approach to multicomponent electrochemical systems at platinum electrode surfaces

Adsorption interactions of different systems on electrodispersed and smooth platinum electrodes were explored through anodic stripping voltammetry using a conventional flow cell technique at 25°C. A first adsorbate was formed at the platinum electrode in contact with the solution containing the adsorbable species I, and subsequently the platinum—adsorbate I system was put into contact with a solution containing the adsorbable species II, where I CO, CH₃OH and reduced CO₂, and II C₂H₄, C₂H₂ and CO, and vice versa. The anodic stripping voltammograms revealed either a total or partial displacement of adsorbate I by adsorbate II, or chemical interactions among adsorbed residues I and Il. The following decreasing platinum—adsorbate interaction sequence was established C₂H₂-2 > CO > C₂H₄ > CH₃OH ≈ CO₂.     

Simultaneous Ion Chromatographic Determination of Weakly and Strongly Retained Inorganic Anions using Aminoacids as Eluents

Abstract

At present eluents that are most widely used in ion chromatography of inorganic anions are salts with carbonate and hydroxyl eluting ions. But these eluents appear to be of no efficiency when samples containing both weakly and strongly retained inorganic anions are to be analyzed. In this case, one should use either expensive and complicated gradient elution technique or double injection with different eluents separately for weakly and strongly retained anions.

In this work, the simultaneous ion chromatographic determination of weakly and strongly retained inorganic anions without gradient elution is considered. The most common eluent for ion chromatography of anions, carbonate and aminoacids are compared. Dependence of the chromatographic behaviour of the strongly retained inorganic anions upon the concentration of the organic components in the eluent is shown.     

Ultraviolet Spectrometric Determination of Phenols as Phenolate Anions

Abstract

The determination of phenols is important in many areas, such as the characterization of hazardous waste products and the analysis of coal gasification by-products and the analysis of coal gasification by-product waters. Ultraviolet spectrometric phenolate anion measurement is a simple and reliable technique for the selective determination of phenol concentrations in water. For most common phenols, the difference in absorptivity at 291 nm caused by raising the pH from 7 to 12 and converting unionized phenols to phenolate anions provides an accurate measure of phenol concentrations despite variable sample compositions. This technique may be applied directly to aqueous samples or to other samples after extraction of phenols with a solvent.