Potentiometric Detection of Anions Separated by Liquid Chromatography Using a Metallic Silver Wire Electrode

Abstract

A silver metallic wire electrode, coated with AgCl, used for potentiometric detection of inorganic anions in liquid chromatography, is described. The electrode response to the anions was evaluated by both static and flow injection measurements, and results have shown that the electrode exhibits sensitive response to CI^? and SCN^? with a detection limit of 10^?6 M. The electrode was used as a potentiometric detector for the determination of anions following separation by ion chromatography using the eluent containing 5 mM phthalate at pH 4.2. Calibration plots were not linear, but give a useful working range of 5 x10^?5 to 3 x10^?2 M. It also demonstrated to be a useful detector for the detection of anions separated, where the separation of anions was preformed with a C₁₈ column using a 0.1 mM octylammonium salicylate as an ion-paring reagent, by ion-pair chromatography. The determination of chloride in waste water samples were demonstrated by proposed method.

     

MEASUREMENT OF RADIATION INDUCED LOCALIZED ABSORPTION IN CHROMATOGRAPHIC ELUENTS BY MEANS OF THE CO LASER AND THE PZT PYROELECTRIC DETECTOR

Abstract

Combined use of the CO laser and PZT piezoelectric detector is proposed as a sensitive and specific detector for gas chromatography. The feasibility of this detection scheme is demonstrated for a model mixture containing varying proportions of acetone in water. After separation on a GC column, spectra of both constituents were recorded in the 1600 cm^?1 to 1900 cm^?1 range that encompasses the characteristic frequency of C=O bond in acetone. Reasonably high sensitivity (mass concentration limit is 1.2x10^?8 g acetone) and a good degree (factor 530) of spectral discrimination was achieved by a proper selection of analytical wavelengths.     

A Raster thermal-neutron scintillation multidetector of modular type

A 100-channel scintillation multichannel detector of thermal neutrons has been designed and manufactured for modernizing the D7a neutron diffractometer on the IVV-2M reactor. The detector is built in accordance with the modular approach and allows arrangement of sensitive surfaces of channels on a cylindrical surface of arbitrary radius. The sensitive volume of a channel is a multilayer composition of stripes of an ND scintillation screen and wavelength-shifting fibers. The dimensions of the entrance aperture of the channel’s sensitive volume are 3 × 120 mm. The average detection efficiency in channels for neutrons of wavelength λ = 1.53 Å is 70%. The gamma sensitivity of the detector channels is no higher than 1 × 10^?7. The maximum counting rate of an individual channel is ≥ 1 × 10⁵ neutrons/s. Each module of the detector is an independent device and contains ten channels for neutron detection, signal-processing electronics, a high-voltage supply system, and computer-interfacing electronics. A CAN interface is used to acquire data from the modules, set the registration parameters, and control the modules.     

A Single Particle Photometric Detector For Steric Field-Flow Fractionation

ABSTRACT

A single particle photometric detector is described for use with steric field-flow fractionation. By counting individual particles, the detector circumvents the difficult problem of calibrating detector response for particulate systems. The system is based on the detection of light from a He-Ne laser scattered by particles flowing through a thin flow cell. It was designed for monitoring particles in the 1-70 μm size range. The flow cell, which is easily constructed, has a total volume of 4.6 μl and an optical viewing volume of only 2.8 x 10^-3 μl. A low power compound microscope is a major component of the system. The performance characteristics of the detector are determined by using polystyrene latex beads of different diameters carried through the cell at different flow rates. Measurements are reported for relative signal response as a function of particle diameter, cell time constant as it depends on flow rate, and particle count in relationship to particle concentration. Examples of the detector's response are shown.     

A MINIATURIZED,HIGH COLLECTION EFFICIENCY CHEMILUMINESCENCE DETECTOR FOR CAPILLARY ZONE ELECTROPHORESIS

ABSTRACT

A miniaturized, high collection efficiency, post-column, sheath flow chemiluminescence (CL) detector for use with capillary zone electrophoresis (CZE) is described. The stainless steel detector body significantly cuts down the electrical noise associated with the AC power lines. The inner wall of this CL detector was carefully machined to a high smoothness to increase retro-reflection. The other advantage of this novel CL detector arises because the PMT is placed extremely close to the separation capillary to increase the solid angle for light collection. Calculations indicate that the collection efficiency of this chemiluminescence detector is ≈58%.

The miniaturized CE-CL detector is characterized using transition metal cations as the sample species. The major problem for the separation of transition metal cations is their strong adsorption to the surface of the fused silica capillary. A theoretical plate number of 340,000 for 1.0 × 10^?11 M Co²⁺ is demonstrated. Detection limits of 1.5 × 10^?12 M for Co²⁺, 5.0 × 10^?8 M for Cr³⁺, and 3.0 × 10^?8 M for Cu²⁺ are reported.     

Evaluation of Halogen‐Specific Detector (XSDTM) for Trace Analysis of Chlorinated Fatty Acids in Fish

Abstract

The applicability of a halogen‐specific detector (XSD?, manufactured by OI Analytical) was evaluated for GC analysis of chlorinated fatty acid methyl esters (FAMEs) that are present at trace levels in transesterified fish extract, a complex matrix consisting of similar but nonchlorinated compounds. A characteristic of the XSD working principle is that thermal electron emission, negative surface ionization and positive surface ionization are all operative in a concerted manner. While the XSD is not superior to other GC detectors in terms of signal‐to‐noise, its merit is in its high selectivity (10⁶) and low detection limit (2 pg Cl) for chlorinated fatty acids, and ease of operation and maintenance. Its reasonably wide linear range (up to 10 ng Cl) is desirable for trace analysis of chlorinated FAMEs. A major drawback of this detector is a certain degree of peak broadening and peak tailing of eluted compounds with concentrations larger than ～1 ng Cl/µL in the injected solution even though this value does not exceed the upper limit of the XSD linear range. Nevertheless, in trace analysis of chlorinated compounds, the concentrations of analytes are usually well below 1 ng Cl/µL. Parallel use of the XSD and a universal detector such as FID in gas chromatography is useful for optimizing operation conditions for trace analysis and simultaneously analyzing nonchlorinated major components.     

Digitally Controlled Potentiostat for Electrochemical Studies

ABSTRACT

A potentiostat employing digital selection of sweep range, sweep rate, and cell current measurement time has been built for use in staircase voltammetry, square wave polarography and voltammetry, and tast polarography. The use of these techniques enables background current reduction and therefore provides high sensitivity. The method of cell potential generation and control allows very high measurement precision. The instrument can be operated either manually or under complete computer control.     

Slow-neutron detector based on thin CVD diamond film

A slow-neutron detector based on thin CVD diamond film is discussed. A deep graphitized layer in the diamond film acts as one of the electrodes in the detector. The detector demonstrates low sensitivity to γ radiation, at the background level. The detector is tested with a laboratory neutron source based on the isotope ²⁵²Cf in a moderator. Slow neutrons are detected by means of the boron isotope ¹⁰В and lithium isotope ⁶Li. In both cases, slow neutrons are recorded with about 3% efficiency. The efficiency of slow-neutron recording is also assessed theoretically.     

A pyroelectric detector of pulsed γ rays

A theory of a pyroelectric pulsed-γ-ray detector and results of experimental tests thereof are presented. The detector contains a capacitor, which is filled with a dielectric made of a polarized ferroelectric material that serves as a sensitive element; does not require external power-supply units; and has a temporal resolution of up to 10^?9 s, a sensitivity of ～10^?8 C Gy^?1, an amplitude characteristic linear in the range of absorbed doses 10^?1?5 × 10³ Gy, and high radiation stability and noise immunity.     

A Low Cost Lock-In Amplifier for Ac Polarography

ABSTRACT

The electronics, construction and use of a low cost lock-in amplifier suitable for AC polarography are described. The device operates from 10 Hz to 10 kHz in 1,2,5 multiples of frequency. Components for the unit cost about $150.     

A neutron semiconductor detector based on TIInSe<Subscript>2</Subscript>

A new semiconductor detector of neutron radiation based on a TIInSe₂ crystal has been investigated. The detector is produced from a homogeneous semiconductor sample with two electric contacts and operates in an integrating mode. It is shown that, owing to its high sensitivity (～10^?13 A/(neutron cm^?2 s^?1)) and small size (the volume of the sensitive crystal element is ～7 mm³), the detector is capable of monitoring spatial, time, and intensity distributions of γ rays and neutrons in pulse research reactors.     

Efficiency Determination for NaI (Tl) Detectors in the 23 keV to 1333 keV Energy Range

Abstract

The photopeak efficiency of a NaI (Tl) detector was determined experimentally for 23‐1333 keV photon energy by using polyester coated radioisotopes ²²Na, ⁵⁴Mn, ⁵⁷Co, ⁶⁰Co, ¹⁰⁹Cd, ¹³⁷Cs, and ¹³³Ba. The energy resolution of the NaI (Tl) detector was also measured. The data were analyzed using the Genie‐2000 from Canberra. The experimental values were fitted to an analytical function of photon energy and an agreement was observed for the entire range of the studied energies. The results have shown that the NaI (Tl) detector is a particularly attractive detector for field application, as it works at room temperature and has a high probability of detecting gamma radiation.     

Reversed‐Phase Liquid Chromatography with Electrokinetic Flow Analysis System

Abstract

An electrokinetic flow analysis system was introduced for reversed‐phase chromatography separation. It consisted of a C₈‐modified silica monolithic column, a UV‐Vis detector, and a pressurizing electroosmosis pump (EOP) to deliver mobile phase steadily and continuously. Acetonitrile was used as the organic solvent component of the mobile phase, i.e., the pump carrier, to improve the separation resolution of three aromatic compounds. The effect of acetonitrile concentration on the separation resolution and flow rate of mobile phase was investigated. When 35% acetonitrile (v/v) solution, containing 0.5 mmol/L hexamethylene tetraamine, was used as the mobile phase, three aromatic components could be baseline separated by the electrokinetic flow analysis system.     

Evaluation of a Linear Self-Scanned Photodiode Array Detector for Direct Detection of 6-8 Kev X-Rays

ABSTRACT

The performance of a commercially available 1-dimensional x-ray detector based on a directly bombarded self-scanned photo-diode array has been evaluated for x-rays in the 6-8 KeV range. The detector consists of a linear array of 1024 pixels, each approximately 25 μm wide by 2000 μm tall. Modifications to allow cooling to -55°C, which is required for long x-ray exposures, are described. The signal yield is 0.63 ADC counts/Fe⁵⁵ x-ray, resulting in a detective quantum efficiency greater than 0.5 for doses over a range of 10 to 10⁴ x-rays per pixel per scan when operated at -55°C. The resolution is about 3 pixels (75 μm FWHM) and the response with respect to dose is linear up to 1.5 x 10⁴ x-rays integrated per pixel per scan. There is some non-linearity at doses below about 1000 x-rays/pixel/scan. The detector has very little geometric distortion. The uncorrected uniformity of response of the individual pixels (field flatness) is good to about 2%. However, the variation in responsiveness is stable and a field flatness calibration can be readily used to correct the uniformity of response.     

1‐Pyrenemethanol,a Useful Fluorometric Reagent for the Detection and Determination of Carboxylic Acids in Atmospheric Samples

Abstract

A rapid fluorometric procedure for the selective and sensitive determination of carboxylic acids, based on pre‐column derivatization using 1‐pyrenemethanol, was optimized and applied to atmospheric sampling. The optimum conditions for derivatization were determined to be: reaction solvent–dichloromethane, temperature ?44°C, reaction time ?30 min, and reagent/total acid ratio ?15. Separation of the derivatives of acids up to twenty carbons by reversed‐phase (C₈) chromatography was achieved in 25 min using a water/acetonitrile gradient with a limit of detection for the derivatives of 20 pg for a 20 µL injection. A scanning detector with good spectral resolution allows qualitative identification of the components in complex samples. When used in atmospheric analysis, the recoveries of carboxylic acids from spiked samples were >80% with repeatabilities below 10% RSD. Low molecular weight acids were encountered predominantly in the vapor phase (0.20 to 92 ng/m³), whereas higher molecular weight acids were found mostly in particulate form (0.15–129 ng/m³).     

A sectioned spectrometer of fast neutrons

Development of a capture gated spectrometer on the basis of a liquid organic scintillator doped with enriched ⁶Li is discussed. Particular interest is evoked by the good pulse height resolution of the spectrometer for 14-MeV neutrons, which is expected to be very high, ～10–15%. This resolution is attained by compensating for the nonlinearity of the light yield in the scintillator owing to the use of separate optically isolated sections, which independently detect scintillations from each recoil proton. The detector is sensitive to fluence rates ranging from 10^?4 to 10² cm^?2 s^?1 above a threshold of 500 keV under conditions of uncorrelated γ-ray background at a level of up to 10² s^?1 (E > 100 keV). A pilot model of the detector based on a scintillator without a lithium dopant has been produced and tested. The detector efficiency is governed by the scintillator volume (～1.2 l); for 3-MeV neutrons, its value is 0.2–0.5%. The response of the pilot detector to neutrons from a Pu-α-Be source with energies of up to 10 MeV has been measured. Initial testing indicates a low threshold at an ～600-keV energy of a recoil proton. A good spectral response is obtained using the criterion that three optical sections of the detector operate at a time. This spectrometer can find application in low-background experiments in basic physics research, as well as in space research and nuclear medicine for measuring the parameters of the neutron flux.     

Development of a Setup for the Discrimination of β+ and γ Rays

Abstract

A β⁺–γ discrimination set‐up was developed and applied to the ²²Na radioisotope. The radioisotope emits positrons (β⁺) and these positrons create γ rays by annihilating with electrons. These annihilation γ rays were used here, and the discrimination between these positrons and γ rays was investigated by the coincidence measurement between time signals and the energy signals. The detection system presented here uses a 3 inch (diameter) by 3 inch (length) NaI(Tl) inorganic scintillation detector for γ detection and 3 inch (diameter) by 3 inch (length) plastic scintillation detector for β⁺ detection.     

Low-cost potentiometric sensor based on a molecularly imprinted polymer for the rapid determination of matrine in herbal medicines

Abstract

A low-cost potentiometric sensor based on a molecularly imprinted polymer was developed for the determination of matrine in herbal medicine samples. The imprinted material was synthesized by the use of matrine as template, methacrylic acid (MAA) as the monomer, ethylene glycol dimethyl acrylate (EGDMA) as the cross linker, 2,2′-azo-bisisobutyronitrile (AIBN) as the initiator, and toluene and dodecanol as the porogenic agent. The electrode sensing membrane was fabricated by incorporating the ground imprinted particles into the polyvinyl chloride substrate that was subsequently incorporated into a laboratory constructed ion-selective electrode. The prepared imprinted sensor exhibited a rapid Nernst response across the concentration range from 1?×?10^?5 to 1?×?10^?1 M with a detection limit equal to 9.3?×?10^?6 M. The analytical capabilities support the direct determination of matrine in herbal medicine. The analytical results were verified by a standard ultraviolet absorption spectrophotometry protocol. The proposed sensor manifested a series of advantages, including high selectivity and sensitivity, enhanced stability and low cost, that provides a wide number of potential applications for herbal analysis.     

An Improved Sensitive Nonselective Radiofrequency Detector for Gas Chromatography

SUMMARY

A dielectric-constant-response radiofrequency detector for gas chromatography is described. The detector is extremely sensitive to organic vapors; it should display general response to compounds which have a dielectric constant different than the carrier gas. Limits of detection have been significantly decreased when compared to previously suggested designs for radio-frequency detectors. The detector is physically small and readily compatible with commercially available chromatographs. A theory for the signal response of the detector is proposed.     

The Use of Second Derivative and Digital Readout in Fast-Sweep Polarography†

SUMMARY

The use of the second derivatives of the polarographic waves for analytical work in fast-sweep polarography has been investigated. Three-electrode potentiostatic control circuitry and controlled-drop-time dropping mercury electrode apparatus was used. With active, operational amplifier derivative and filter circuitry, the theoretically greater resolution of overlapping waves and freedom from base-line effects can be realized. A circuit has been designed which makes possible the high-precision readout of polarographic peak heights on a digital voltmeter. With the digital readout system and second derivative waves, a short-term reproducibility of the measurements approaching 0.1% can be achieved for concentrations above 10^?4 M. Above about 10&^?5 M, analyses can be performed with 1% accuracy, using only a single polarographic cell with blank corrections or by peak-to-peak measurement of the second derivative wave. Below 10^?5 M it is advantageous to use a combination of second derivative and two-cell differential operation.