Miniaturization of a standard liquid chromatographic system

Summary Methods for the construction of micro-columns equipped with low dead volume end fittings and an easy way to miniaturize a standard flow-cell to a volume of 0.67 mm³ are described. Operation characteristics of the microcolumns were evaluated by plate height versus linear velocity and plate height versus capacity factor plots. The influence of the volume of the flow-cell on the resolution is also demonstrated. An improvement of the resolution factor (R_S) from 0.9 to 1.45 between sulphapyridine and sulphamerazine was obtained by using the 0.67 mm³ flow-cell instead of the 12.5 mm³ original flow-cell. The influence of the sample volume on the separation efficiency is also shown.     

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.     

Titrating apparatus for the detection of soft β-emitting isotopes

The measuring devices reported in the literature allow only radiometric titrations indicated by hard β or γ-radiating isotopes. The authors developed an apparatus also suitable for the detection of soft β-emitting isotopes. In the course of the analysis, the activities are measured in a scintillation system in which the great surface of a mass of anthracene crystals provides excellent contact with the active solution. In studies on the linearity of the scintillation system the sources of error and their elimination were also examined. The sensitivity of the scintillation system was determined with³H,¹⁴C,³⁵S,⁴⁵Ca,³⁶Cl and³²P isotopes, frequently applied in organic chemical practice. The method of adjusting the specific activities of reagent solutions prepared from the various isotopes is discussed. The apparatus makes it possible to extend the applications of radiometric titration in the analysis of organic compounds.     

A Simple Low-Cost Conductivity Cell for Flow Analysis Measurements

Abstract

A versatile low-cost conductivity flow-cell design is proposed. Its characteristics permit discrete variations in the cell volume and in the electrode area/distance ratio by varying the sealing gasket thickness, favoring high sensitivity applications in continuous flow measurements. Its dynamic characteristics as a flow conductivity detector were observed using a single-line FIA system and standard KC1 solutions, while its performance in routine work was tested by determining the NH₄ ⁺ content in plant Kjeldahl digests using FIA processing. These results are in good agreement with those obtained by the usual distillation/titration method.     

KMnO4-OP Chemiluminescence system for FIA determination of hydrogen peroxide

A fast and simple KMnO₄-OP chemiluminescence system for flow-injection analysis of hydrogen peroxide is described. When a mixture of sample and OP is injected into acidic KMnO₄, solution in a flow-cell, strong chemiluminescence occurs. The response is linear to the concentration of hydrogen peroxide in the range of 1.0 × 10^–8 to 6.0 × 10^–5 mol/l with 0.1 mol/l permanganate, and the upper limit of linear response could be extended to 6 × 10^–3 mol/l by increasing the permanganate concentration. The relative standard deviation of the method is between 1.6 and 2.3%. The detection limit is 6.0 × 10^–9 mol/l. This method is suitable for automatic and continuous analysis and has been successfully tested for determination of hydrogen peroxide in rain water. The chemiluminescence intensity was found to be remarkably enhanced in the presence of the OP micellar system.     

Quantitative Separation of Hg(11) From Several Metal Ions on Zr(IV) Antimonate Papers

Abstract

The chromatographic behaviour of 32 metal ions has been studied on paper Impregnated with Zirconium(IV) antimonate in aqueous HCI and mixed solvent system containing dimethyisul phoxide and dioxane. Several Important binary and ternary separations have been achieved. Quantitative separation of Hg(ll) from Ni²⁺, Pb²⁺, Pd²⁺, Ru³⁺, Rh³⁺, Bi³⁺, Co²⁺, Cd²⁺ and Gd³⁺ is described.     

The simultaneous determination of Th,Pu, Ra isotopes, 210Pb, 55Fe, 32Si and 14C in marine suspended phases

An efficient and systematic chemical procedure for the simultaneous measurement of Th, Pu, Ra isotopes, ²¹⁰Pb, ⁵⁵Fe, ³²Si and ¹⁴C in the same sample has been developed. This method has been applied successfully to the measurement of these isotopes in oceanic particulate samples collected from several tons of sea water. This procedure should find application in the analysis of geochemical samples.     

Direct Combination of a High Performance Liquid Chromatograph and a Circular Dichroism Spectrometer for Separation and Structural Analysis of Proteins

Abstract

Basic studies of the combined system of a high performance liquid chromatograph (HPLC) and a circular dichroism (CD) spectrometer for separation and analysis of proteins are described. The HPLC-CD measurement of standard protein mixture was easily carried out by using a micro flow-cell device with a beam condenser and with a thin cell of a 1 mm-optical path. The effluent was firstly monitored at 280 nm by using an UV detector and subsequently monitored at 220 nm by using a CD spectrometer. The CD spectrum at each chromatographic peak by CD was measured in the wavelength region of 250–195 nm by a stopped flow method.     

A Liquid Chromatographic-Fluorometric Method for the Analysis of Picogram Amounts of Tryptophan Metabolites in Cerebrospinal Fluid

Abstract

A system employing reverse-phase high-performance liquid chromatography and a fluorescence flow-cell has been used to determine tryptophan (TRP) and several of its metabolites in cerebrospinal fluid (CSF). Absolute detection limits of 25, 12, 15, and 70 pi-cograms have been obtained for TRP, indoleacetic acid (IAA), indolepropionic acid (IPA), and 5-hydroxyindoleacetic acid (HIAA), respectively. Both 5HIAA and TRP have been quantitated in 1.0 ul of untreated CSF. IAA and IPA have been determined in 100 ul of CSF after a one-step extraction.     

Molecular constants of OCS isotopes in the (0110) vibrational state measured by molecular-beam electric-resonance spectroscopy

The ΔJ = 0,l-doublet transitions of OCS isotopes (¹⁶O¹²C³²S, ¹⁶O¹²C³³S, ¹⁶O¹²C³⁴S, ¹⁶O¹³C³²S and ¹⁸O¹²C³²S) in the (01¹0) vibrational state have been measured in a molecular-beam electric-resonance spectrometer equipped with a nozzle source. Rotation-vibration coupling constants and electric dipole moments have been determined for all isotopes, and the spin-rotation and the quadrupole coupling constants for the ³³S nucleus in ¹⁶O¹²C³³S in the υ₂=0 and υ₂=1 states.     

Flow-Through Photometric Sensor for the Determination of Cadmium at the Nanogram per Millilitre Level

Abstract

A sensor for the determination of cadmium based on retention of the CdI₄ ^? complex on a QAE Sephadex resin located in the flow-cell of a conventional photometric detector and on subsequent complex displacement reaction with 4-(2-pyridylazo)-resorcinol is proposed. Formation of the colored chelate and detection take place simultaneously. The method features a determination range between 30 and 500 ng/ml of Cd(II) with relative standard deviations of 1.8% and 3.4% for 200 and 50 ng/ml of Cd(II), respectively. The selectivity involved in the use of the proposed sensor is shown in the study of interference.     

Characterization of a TeflonÒcoated semiconductor detector flow cell for monitoring of pertechnetate in groundwater

Summary A new flow-cell detection system using a Teflon^òcoated passivated ion-implanted planar silicon semiconductor detector was developed for detection of pertechnetate (⁹⁹TcO₄^-E_b     

Integrated Retention/Spectrophotometric Detection Method for the Determination of Formaldehyde

Abstract

An integrated-sensor method for the determination of formaldehyde based on retention of the reaction product of the analyte with p-rosaniline and sulfite in a flow-cell packed with Dowex 1-X-8 anion exchange resin was developed. The method has a good selectivity with a detection limit of 0.3 μg ml^?1 (1 ml sample) or 75 ng ml^?1 (2 ml sample), and a linear range between 1–30 μg ml^?1. The relative standard deviations (n = 11) were 2.8 and 1.3% for 2 and 20 μg ml^?1 formaldehyde, respectively. Depending on the working conditions, the sampling frenquency ranged between 10 and 18 h^?1. The method was applied to the determination of formaldehyde in well water.     

Ultratrace analysis of calcium with high isotopic selectivity by diodelaser resonance ionisation mass spectrometry

A resonance ionisation mass spectrometer for the ultratrace determination of calcium isotopes is presented. It achieves high overall efficiency, ultra-high isotopic abundance sensitivity of more than 10¹⁰ and complete suppression of isobars. The system can be used for isotope ratio studies on stable and long-lived trace isotopes with the final goal of radiodating via ⁴¹Ca-determination. For the different applications optical one-, two- or three-step resonance excitation and subsequent ionisation is applied using simple and inexpensive diodelasers. Additional mass analysis is accomplished in a commercial quadrupole mass spectrometer. The experimental set-up and first results on synthetical and meteorite samples are described.     

Automation of the Photodegradation Spectrophotometric Method for the Determination of Diethylstilbestrol by Flow Injection

ABSTRACT

An spectrophotometric determination of diethylstilbestrol is proposed on the basis of on-line photo-degradation and measurement at 330 nm. The procedure is accomplished by means of flow-injection assembly including a photo-reactor formed by a PTFE 168 cm long coil around a low-pressure mercury lamp 6 w; this photo-reactor was nested between the injection valve and the spectrophotometric flow-cell. The sample solution was injected into a carrier stream of aqueous di-potassium hydrogen ortophosphate flowing at 5.0 ml min^?1. Influence of the physic-chemical and hydrodynamic parameters was studied and optimised. The calibration graph was linear up to 65 mg l^?1, and the procedure presented a reproducibility (rsd of the calibration slope) 1.4%, and a sample throughput of 52 h^?1. The influence of foreign compounds was tested.     

Distribution of plutonium isotopes in sediments of Melanesian Basin,Central Pacific

The anthropogenic plutonium isotopes are important geochemical tracers for environmental studies. The distributions and sources of the Pu isotopes in water column or sediments of the North Pacific have been intensively studied. However, knowledge on the distribution of Pu isotopes in sediments of the Central Pacific, when available, is limited. To study the composition of Pu isotopes in the ocean, thus to identify the sources of radioactive pollution, sediment core samples were collected in the Central Pacific by R/V Hakuho Maru in the KH-04-5 cruise. The activity concentrations of ^239+240Pu and the ²⁴⁰Pu/²³⁹Pu atom ratio were determined using a sector-field inductively coupled mass spectrometry (SF-ICP-MS) combined with a high efficiency sample introduction system (APEX-Q). Possible sources and sedimentation behavior of Pu isotopes are discussed.     

Laser Ablation Molecular Isotopic Spectrometry: Strontium and its isotopes

The experimental details are reported of Laser Ablation Molecular Isotopic Spectrometry (LAMIS) and its application for performing optical isotopic analysis of solid strontium-containing samples in ambient atmospheric air at normal pressure. The LAMIS detection method is described for strontium isotopes from samples of various chemical and isotopic compositions. The results demonstrate spectrally resolved measurements of the three individual ⁸⁶Sr, ⁸⁷Sr, and ⁸⁸Sr isotopes that are quantified using multivariate calibration of spectra. The observed isotopic shifts are consistent with those calculated theoretically. The measured spectra of diatomic oxide and halides of strontium generated in laser ablation plasmas demonstrate the isotopic resolution and capability of LAMIS. In particular, emission spectra of SrO and SrF molecular radicals provided clean and well resolved spectral signatures for the naturally occurring strontium isotopes. A possibility is discussed of using LAMIS of strontium isotopes for radiogenic age determination.     

A Fluorescence Quenching Method for the Determination of Chromium(VI) with L-Tyrosine

Abstract

A fluorescence quenching method for the determination of Cr(VI) in aqueous solution is described. The fluorescence intensity of the system is linear ever the range 5×10^?6 - 1.0×10^?4 M Cr(VI). The method has been applied to the determination of Cr(VI) In cast iron and waste water.     

Flow-injection extraction with a microvolume module based on integrated conduits

A self-contained module for liquid—liquid extractions is described. The module contains engraved conduits for mixing of sample and ragent, an engraved segmentor, a detachable extraction coil, a membrane separator, and a rinsing system for the flow cell. The membrane in the separator is supported by a teflon-coated steel grid and can be replaced rapidly. The segmented stream enters at the centre of the circular membrane and travels through an engraved, coiled channel in contact with the membrane before leaving the membrane area at the periphery. The volume of the receptor chamber for the organic phase is 10 μl. For a detector flow-cell volume of 8 μl, an aqueous flow rate of 2.0 ml min^?1 and an organic flow rate of 1.2 ml min^?1, the “loss factors” caused by analyte dispersion are 3.2 and 1.5 for caffeine sample volumes of 40 μl and 100 μl, respectively, compared with batch extraction. The system is also tested for extraction of anionic surfactants as their ion-pairs with methylene blue.     

Determination of Chlorpyrifos by a Multicommutated Photochemically Induced Fluorescence Optosensor

Abstract

We propose a multicommutated flow-through optosensor for the quantitation of the organophosphate pesticide chlorpyrifos in dried chili peppers. We used photochemically induced fluorescence detection to overcome the negligible native fluorescence of the target pesticide. Firstly, the photodegradation of chlorpyrifos was performed online with an ultraviolet lamp. Then, the fluorescent photoproduct was retained on a solid support (Sephadex QAE A-25) inside the flow-cell in order to record the analytical signal. The online photodegradation and preconcentration of the photoproduct on the solid support were critical for the automation, speed, and high sensitivity obtained. A QuEChERS procedure was selected for sample treatment, obtaining recovery yields close to 100%. The method proposed presents a quantitation limit of 18?mg?kg^?1 in real samples, hence fulfilling the maximum residue limit of Codex Alimentarius, 20?mg?kg^?1. Therefore, this approach offers a novel method for screening purposes in the agricultural and food industries.