Photometric Detection System Research Articles

Comparison of segmentors for liquid—liquid extraction flow-injection analysis

The segmentation of two immiscible solvents in a continuous liquid—liquid extraction flow system has been studied with a computer-controlled photometric detection system (resolution time ∼3 msec). The T-shaped segmentors tested were made of fluoroplastic, glass (A4-T fitting) and a modified glass (A8-T fitting). The modified A8-T fitting gave the most repeatable segmentation (rsd ∼2%).

Design of coaxial segmentors for liquid-liquid extraction/flow-injection analysis

The process of the segmentation of two immiscible solvents by newly introduced coaxial segmentors of different geometry was studied in a continuous liquid-liquid extraction flow system. A fast reading «on-tube» photometric detection system (∼3 ms time resolution) controlled by a computer was used to measure optical transparency directly across the flowing stream. The influence of flow rates, flow rate ratio, the density and interfacial tension of the phases as well as the geometry of the segmentors was studied

Calculation of equilibrium constants from multiwavelength spectroscopic data—IV: Model-free least-squares refinement by use of evolving factor analysis

The newly developed algorithm of evolving factor analysis has been supplemented by iterative refinement. It allows the completely model-free calculation of concentration profiles and spectra from spectrophotometric and other spectroscopic data. Not even implicit use is made of the law of mass action. The results are practically identical with those based on a specific chemical model and classical least-squares refinement. Iterative evolving factor analysis is based on applying factor analysis successively to the set of the first 1,2 ⋯ M spectra of a spectrometric titration. The analysis is repeated from the opposite end and the eigenvalues thus calculated are combined into “concentration profiles” of completely abstract “species”. These “concentration profiles” are iteratively refined by normalization, calculation of the absorption spectra from the normalized concentrations and recalculation of the concentration profiles from the absorption spectra. Evolving factor analysis is not restricted to spectrometric titrations, and can also be applied to peak resolution in chromatography using a multiwavelength (diode array) photometric or mass-spectrometric detection system, or to any other ordered set of multichannel data.

Pyrolysis gas-liquid chromatography of the pathotypes of the potato cyst nematodesGlobodera rostochiensisandG. pallida

SUMMARYCurie-point pyrolysis gas-liquid chromatography (PGLC) was used to detect gross chemical differences between the 8 European pathotypes of the potato cyst nematodesGlobodera rostochiensisandG. pallida. No qualitative differences were seen with either flame ionization or flame photometric detection systems, although quantitative differences between pathotypes were detected. Cluster analysis of these differences failed to group the pathotypes into species, but separation of some economically important pathotypes was achieved. The potential of PGLC for nematode identification is discussed.

Intercomparison of concentration results from fine particle sulfur monitors

A one week intercomparison study was carried out to evaluate the ability of selected analytical instruments to measure fine paniculate sulfur concentrations. The instruments compared included five modified flame photometric detection systems and an automated dichotomous sampler that was coupled to an on-line, wavelength dispersive X-ray fluorescence analyzer tuned to measure sulfur on fine particle filters. All instruments were connected to a common duct. Concentrations were obtained in periods ranging from 1 to 30 min, but data were reported and intercompared on an hourly basis. Paniculate sulfur concentrations varied from 1 to 9 μg m −3. Results at all concentration levels from four of the six systems agreed to better than ± 5 % throughout the study; while all six agreed within ± 25 % of their composite-mean concentration values at the higher concentrations measured. Linear regression between the composite means and each sampler system's data set showed that the standard estimate of errors ranged from 0.2 to 0.6μgm −3, correlation coefficients from 0.979 to 0.994, and slopes ranged from 0.88 to 1.22. Sulfate concentrations were also determined every 6 h from the fine particle stage of another dichotomous sampler. They were 26 % lower than expected relative to the aerosol sulfur concentrations; thus it appears that either the aerosol sulfur was not entirely in sulfate form, or sulfate was not completely extractable by conventional procedures.

Determination of ambient aerosol sulfur using a continuous flame photometric detection system. II. The measurement of low-level sulfur concentrations under varying atmospheric conditions

Principles involved in the measurement of sulfur concentrations using a flame photometric detector (FPD) are described along with factors other than sulfur which affect FPD response. Variations in inlet pressure and sample water vapor concentration are both shown to alter zero air response and instrument calibration to SO 2. Daily atmospheric fluctuations in barometric pressure and water partial pressure are found to significantly affect low-level (< 20 ppb) measurements. Possible solutions to these problems investigated in this paper include an inlet drying system, mass flow control and increased sensitivity through sulfur addition to the hydrogen stream. The FPD exhibits no detectable change in sensitivity up to an altitude of 1400 m when the mass flows of air and H 2 are held constant although a slight increase in baseline response is observed. The use of a 66 ppb SF 6-H 2 mixture results in a 13-fold increase in signal/noise at 1 ppb and lowers the limit of detection for sulfur to about 0.1 ppb.

Flow injection determination of trace vanadium with catalytic photometric detection

A catalytic photometric detection system based on the chromotropic acid—bromate reaction is adapted to a flow injection system for the rapid, simple and sensitive determination of vanadium. Vanadium in the range 0.3–4.8 ng (10–160 ppb) can be determined at a rate of ca. 60 samples per hour.

Determination of ambient aerosol sulfur using a continuous flame photometric detection system. I. Sampling system for aerosol sulfate and sulfuric acid

A system for measurement of ambient levels of aerosol sulfur using a flame photometric sulfur analyzer (FPD) with a heated denuder for SO 2 removal has been developed. Cyclic addition of ammonia permits discrimination between sulfuric acid and other sulfate aerosols. The effects of changes in ambient water vapor concentration and barometric pressure on the FPD sulfur response have been quantitatively evaluated, and it is shown that other environmental effects on sulfur response may be eliminated by frequent and proper zeroing. Calibration plots and ambient data are presented which demonstrate the specificity and sensitivity of the system to < 1.0 ppb aerosol sulfur.

Sources and fates of aromatic compounds in urban stormwater runoff

Petroleum-derived aromatic hydrocarbons and associated sulfur compounds in urban storm-water runoff and Delaware River sediment samples were characterized with a gas chromatograph equipped with a flame ionization/sulfur specific flame photometric detection system. Total petroleum hydrocarbon concentrations were determined gravimetrically in storm water emanating from a northern Philadelphian storm sewer. Comparison of hydrocarbon and sulfur fingerprints of the aromatic fractions of environmental samples with reference oils indicated that crankcase oil was the most likely source of aromatics in storm-water runoff. A weathering study on used crankcase oils showed a loss of diaromatics which accounted for their absence in the environmental samples. Since aromatic sulfur compounds were preferentially associated with particulate matter in urban runoff, a mechanism was proposed in which fuel oils and lubricating oils released to the environment are adsorbed onto particulate matter. The lower boiling diaromatics are lost through natural weathering, and during a storm, the particulates are washed into sewers and then into receiving waters.

Studies on retinal blood flow. I. Estimation of human retinal blood flow by slit-lamp fluorophotometry.

This article describes a new direct method for estimation of human retinal blood flow by slit-lamp fluorophotometry. The apparatus consists fundamentally of a modified slit lamp with an eye piece containing two fiberoptic probes connected to a double photometric detection system. Both optic fibers are focused on a retinal arterial segment, and the passage of a fluorescein bolus is automatically registered, giving, after correction, the mean transit time. Fluorescein angiography allows the determination of the volume of the arterial segment under study. Values for superior temporal retinal blood flow in healthy individuals show a mean value of 4.2 +/- 0.5 microliter/min. Studies in anemic patients show an increase of approximately 52% in the retinal blood flow. The potential causes of error associated with this technique, apart from the slight increase in intraocular pressure induced by the contact lens used, do not appear to be significant.

A Liquid-Laser Temperature-Jump Apparatus for the Study of Fast Reactions in Solution

A temperature-jump apparatus was made utilizing a neodymium liquid-laser as the energy source for heating. By employing a special arrangement of a photometric detection system consisting of a He-Ne laser as a probe light source and PIN photodiodes as detectors for a double-beam difference method with nearly-coaxial beam alignment, it was possible to measure chemical relaxations quantitatively even with small temperature jumps produced by 1.05 µm pulse. Temperature rises of 0.07 K within 100 ns in Q-switched mode and 1.0 K within 400 µs in normal mode were achieved in a volume of 5 mmφ×2 mm in an aqueous solution. The chemical relaxations of reactions between nickel and ammonia, and between nickel and tiron were measured, and it was shown that the laser T-jump method was effective for the study of kinetic salt effects, etc.

Removal of Sulfur in Environmental Samples Prior to Gas Chromatographic Analysis for Pesticide Residues

Abstract Extracts of soil, water, and sediment often contain large amounts of elemental sulfur. This sulfur causes considerable interference in the GLC analysis of early eluting compounds by electron capture or flame photometric detection systems. A method is described whereby sulfur is removed by refluxing with a copper-aluminum alloy. Using a sample volume of 1 ml, up to 50 ppm elemental sulfur can be removed. Recovery of chlorinated pesticides from desulfurized extracts is &amp;gt;80%. Parathion and malathion gave recoveries of approximately 50%.

Direct gas chromatographic analysis of sulphur compounds in mouth air in man

A gas Chromatograph equipped with a sensitive photometric detection system was successfully applied to the direct determination of sulphur compounds in mouth air. A measurable amount of sulphur-containing compounds, that is detectable by organoleptic perception, was found in air samples of all 15 subjects studied. Large differences in concentration were observed among subjects and in the individual subjects during different periods of day. The maximum levels correspond to the reported peaks of objectionability of mouth odour. The gas Chromatographic analysis of mouth air revealed the presence of three sulphur-containing compounds. Two of these, which accounted for approximately 90 per cent of the sulphur content, were positively identified as hydrogen sulphide and methyl mercaptan. Both compounds emanate an objectionable putrid odour. The third, a minor odoriferous component, was tentatively identified on the basis of retention time on a Teflon column as dimethyl sulphide. The saliva tests indicate that the same three components are produced during the initial 60—90 min of putrefaction. Since the oral hygiene measures markedly reduced the sulphur content of mouth air, it is concluded that the determined sulphur compounds are produced by a putrefactive process occurring within the oral cavity.

A universal automatic recording titrator

A universal automatic macro-micro recording titration unit is described which has the capabilities of a multitude of commercial single-purpose titration instruments without the attendant duplication of hardware. It is based on a modified Precision Dow Recording Titrator and offers the operator a choice of liquid or coulometrically generated titrants and potentiometric, amperometric, thermometric, photometric, or conductometric end-point detection systems. The potentiometric system gives straightforward curve-presentation; the photometric mode employs a monochromator for maximum sensitivity and is equally adaptable to colorimetric, turbidometric, and chemiluminescent titrimetry; the conductometric mode employs a novel electrolytic conductivity transducer which produces a d.c. signal proportional to the 60-cycle a.c. current between the electrodes. All components are easily constructed or are commercially available.