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Gas-diffusion separators

Gas-diffusion separations may be further divided into single and dual-phase separation systems. Single-phase systems are used for spectrophotometry, electrochemistry and chemiluminescence etc., with which liquid phase is used in both donor and acceptor channels. Dual-phase systems use a suitable gas as the acceptor stream, while the donor stream is liquid such systems are used with mass spectrometric (cf. Sec. 5.4.6) or electron capture detection [7J, but may also be used as a substitute for gas expansion separation in vapK ur generation atomic spectrometric determinations (cf. Sec. 5.5.1 FI hydride generation manifolds with dual phase gas diffusion separators) [Pg.131]

There are mainly two designs of gas diffusion separators, i.e., the sandwich type and the tubular type, the schematic diagrams of which are shown in Fig. 5.1 and 5.2. A common feature of the two designs is that they have separate channels for a donor and an acceptor stream separated by a membrane which is permeable to the gaseous analyte species. The difference between the two designs is in the form of the membrane. [Pg.131]

l A typical sandwich-type membrane gas-diffusion separator, a, side view A, B, plastic blocks with F. threaded fittings and G, engraved grooves M, microporous gas-diffusion membrane, b, top view showing position and configuration of a straight channel groove, c, a simplified schematic presentation of the sandwich-type gas-diffusion separator D, donor stream A, acceptor stream M, membrane. [Pg.132]

A typical structure of the sandwich type gas-diffiision separator is shown in Fig 5.1. As its name implies, the membrane which separates the donor and acceptor streams is sandwiched between two half blocks on which are engraved channels that are minor images of each other. An inlet and an outlet port, extending from the channels and furnished with connectors, are provided on each block. The blocks, usually made of [Pg.132]

2 Schematic figure of a tubular membrane gas-diffusion separator. DN, donor stream T, inner microporous membrane tubing W, waste O. outer tube of non-porous inateria) with inlet and outlet for acceptor stream. A D, to detection system. [Pg.133]


Zhu Z, Fang Z. 1987. Spectrophotometric determination of total cyanide in waste waters in a flow-injection system with gas-diffusion separation and pre-concentration. Anal Chim Acta 198 25-36. [Pg.273]

Separators based on diffusion of the gas phase across a permeable membrane, which are known as dual-phase gas diffusion separators , can be of two types, namely ... [Pg.86]

Z. Zhu and Z. Fang, Gas Diffusion Separation Flow Injection Analysis of Cyanide in Waste Waters [in Chinese]. Kexue Tongbao, 31 (1986) 800. [Pg.461]

Spectrophotometric Determination of Carbon Dioxide in Blood with Gas Diffusion Separation 231... [Pg.1]

In 1979, Baadenhuijsen and Seuren-Jacobs [2] were the first to report on a FI gas diffusion separation system with a semi-permeable dimethylsilicone rubber membrane, used for the determination of carbon dioxide in plasma. In the same year. Zagatto et al.[3] introduced an isothermal distillation FI system in which ammonia diffused from a flowing donor liquid film across an air-gap and absorbed by a flowing acceptor film on the opposite side of the gap. However, later developments on gas diffusion separations mainly followed the approach of Baadenhuijsen and Seuren-Jacobs, obviously due to its simpler design and higher versatility. The first theoretical study on an FI gas-diffusion separation system was attempted by van der Linden [4], who used a tank-in-series model for the mathematical evaluation of the separation process. [Pg.129]

Fig 5.2 is a schematic diagram of a tubular type gas-diffusion separator. The separator is column shaped, with two concentric channels. The tubular membrane forms the inner channel, usually reserved for the donor stream, and extends beyond the outer channel to be connected to the suppK and waste conduits. The terminals of the outer channel are extended to inlet and outlet ports on the column which are furnished with connectors for the acceptor stream conduits. [Pg.133]

Another approach for on-line degassing of solutions is to use a standard sandwich type gas-diffusion separator. One of the ports of the acceptor channel is blocked and the other connected to a vacuum source or to a pump which evacuates the gas from the channel. Such an arrangement was used by Hinkamp and Schwedt [13] in the determination of total phosphorus in waters with amperometric detection to remove gas bubbles generated in the reaction stream after an on-line continuous digestion in a microwave oven. [Pg.134]

Gas-diffusion separators have been integrated with detection cells to produce more compact systems both in optical sensing and atomic absorption spectrometry. These will be described in more detail in the sections on the coupling to individual detectors (cf. Sec. 5.4.2, 5.5.2)... [Pg.134]

The membranes used in FI gas-diffusion separation systems may be classified according to the mechanism of mass transfer of gaseous components across them. Microporous or heterogeneous membranes, usually made of PTFE or polypropylene, allow penetra-... [Pg.134]

Fig. 5 Schematic diagram of a typical FI manifold with gas-diffusion separation and volume-based sampling. CR. carrier stream S, sample R. reagent for formation of volatile analyte species SP. membrane gas-diffusion separator, A. acceptor stream D, detector and W, waste outlets for donor and acceptor streams. Fig. 5 Schematic diagram of a typical FI manifold with gas-diffusion separation and volume-based sampling. CR. carrier stream S, sample R. reagent for formation of volatile analyte species SP. membrane gas-diffusion separator, A. acceptor stream D, detector and W, waste outlets for donor and acceptor streams.
Fig. 6 FI manifold with gas-diffusion separator nested in sample loop of the injection valve used for preconcentration of volatile species by time-bas sampling (sample loading sequence). AS, autosampler, T, heating thermostat (optional) CDS, gas-diffusion separator, V, injection valve Ri, reagent for generation of volatile species R2. acceptor reagent stream R3. derivatization reagent (optional) D, detector W, waste a, valve position in sample injection sequence. Crossed circles in valve represent blocked channels [20]. Fig. 6 FI manifold with gas-diffusion separator nested in sample loop of the injection valve used for preconcentration of volatile species by time-bas sampling (sample loading sequence). AS, autosampler, T, heating thermostat (optional) CDS, gas-diffusion separator, V, injection valve Ri, reagent for generation of volatile species R2. acceptor reagent stream R3. derivatization reagent (optional) D, detector W, waste a, valve position in sample injection sequence. Crossed circles in valve represent blocked channels [20].
Factors Influencing Mass Transfer in FI Gas-diffusion Separation Systems... [Pg.140]

Factors influencing the mass transfer and performance of FI gas-diffusion separation systems were studied in detail, and discussed by Karlberg and Pacey [22] using chlorine dioxide as the gaseous analyte. Some important observations mainly based on their results include ... [Pg.140]

Coupling of FI Gas-diffusion Separation Systems to Various Detectors... [Pg.142]

The most frequently used detector in FI systems with gas-diffusion separation is the spectrophotometer. Quite often the gas-diffusion process offers sufficient selectivity to allow relatively non-specific chemical reactions in the acceptor stream to detect the analyte. Thus, carbon dioxide, sulfur dioxide, hydrogen sulfide, ammonia may all be determined using suitable acid-base indicators in appropriate buffer solutions used as the acceptor streams. The concentration of the buffer solutions may be adjusted to suit a certain concentration range for the analyte. In order to further enhance the selectivity and/or sensitivity more specific reagents may be introduced in the acceptor streams. In the previously mentioned example on the determination of cyanide [20] a modified pyrazolone-isonicotinic acid reaction was used for such purposes. Interferences due to Schlieren effects seem not to have been reported in gas diffusion spectrophotometric systems. This is understandable, since the matrix composition of acceptor streams is usually quite uniform, and the refractive index is little affected after absorbing the gaseous analytes. [Pg.142]

For the gas-diffusion spectrophotometric determination of carbonate, sulfide, sulfite and ammonium nitrogen, the volatile compounds generated under suitable pH conditions penetrate the membrane in a gas-diffusion separator and are collected in acceptor streams containing the appropriate chromogenic reagents. When the separation process is sufficiently selective, the determination may be based on a protolytic reaction, with the... [Pg.142]

The combination of gas-diffusion separation and enzyme reactions in spectrophotometry produced methods with outstanding selectivity by combining the high selectivity of enzyme reactions with that of gas-diffusion separations. The selectivity is further enhanced through specific chemical derivatizations in the acceptor streams. Petersson et al.[30] were the first to use such an approach for the selective determination of urea in whole blood. [Pg.144]

Tits Schematic diagram of an integrated gas-diffusion separation optosensing detection system. A. acceptor stream with reagent S, reacted sample with generated volatile species ... [Pg.145]

The combination of FI gas-diffusion separation with chemiluminescence has produced selective methods for the determination of chlorine and chlorinated species. Hollowell ct al.[33] determined chlorine dioxide by a chemiluminescent reaction with luminol, following a gas-diffusion separation. A T-spiral flow cell was mounted directly in front of the photomultiplier to maximize the detection of the light emission. Potential interferences from transition metals were removed by the gas-diffusion process, since they do not pass... [Pg.145]

In 1981, Meyerhoff and Fraticelli [35] appear to be the first to report on the coupling of a gas-diffusion separation system to a flow-through potentiometric detector. Ammonia was isolated from the donor stream containing the sample by penetrating a microporous membrane and collection in an acceptor buffer stream, and then determined selectively using a tubular nonactin p>olymer membrane electrode. The precision (<7% r.s.d.) and sample throughput (30 h ) of this early application was rather low. [Pg.146]

Coeuee and Gunaratna [36] reported on the potentiometric determination of free chlorine in water using a silver/silver chloride electrode following a gas diffusion separation using a acceptor stream buffered at pH 4.5. [Pg.146]

Figuerola et al.[37] determined free cyanide and cyanide present in weak complexes sequentially using two silver iodide/silver sulfide electrodes with an intervening gas> diffusion separator. Following the potentiometric determination of free cyanide with the first flow-through electrode, the effluent was acidified, and the evolved hydrogen cyanide from weakly complexed species w as transferred through the membrane of the gas-diffusion separator, collected in an alkaline acceptor stream and determined with the second electrode. [Pg.147]

More recently, in the determination of cyanide with a metallic silver-wire electrode Frenzel ei al.[38] have shown that relatively non-selective potentiometric sensors may be used to make selective determinations by enhancing the selectivity using gas-diffusion separations. Potential interferences from sulfide, sulfite and nitrite which may form interfering gaseous species were removed by a pre-oxidation with permanganate and dichromate. [Pg.147]

The combination of gas-diffusion separation with conductimetry, recently reported by de Faria and Pasquini [39], pro ided a selective, precise and economic approach for the determination of ammonia, and also for nitrates and nitrites, after pre-reduction using an on-line zinc column. This approach appears to be a good substitute for the spectrophotometric methods on the determination of ammonia nitrogen. [Pg.147]

Kunnecke and Schmid [40] introduced a gas-diffusion separation system combined with an immobilized alcohol oxidase column used for the determination of ethanol in beverages by amperometry. Ethanol vapour from the samples diffused through a silicone-modified polypropylene membrane and was collected in a potassium phosphate buffer acceptor stream before passing through the immobilized enzyme column where the ethanol was transformed into hydrogen peroxide. The peroxide was determined using an amperometric detector with excellent precision (cf. Sec. 8.4). [Pg.147]

The feasibility of FI mass spectrometry was demonstrated by Canham and Pacey [41] using a gas-diffusion separator as an interface between the FI system and a quadrupole mass spectrometer. [Pg.147]

The same woiiters [42] used the dual phase gas diffusion FI system with a mass spectrometer to study the formation of different species of volatile hydrides of selenium and arsenic. The combined technique offered extremely high selectivity and sensitivity through the synergistic combination of the selectivity of FI gas diffusion separation and... [Pg.147]

FI Hydride Generation Manifolds with Dual-phase Gas-diffusion Separators... [Pg.151]

Gas-liquid separation in FI hydride generation have also been achieved using dualphase gas-diffusion separators both in a sandwich and tubular configuration. Yamamoto et al.[47] were the first to report on such a system using a tubular PTFE microporous separator (cf. Sec. 5.2.2) in the hydride generation AAS determination of arsenic, achieving a characteristic concentration of 0.06 The system is shown schematically in Fig. [Pg.151]

Fig. lO Schematic figure of a FI hydride generation AAS system with segmented carrier stream and tubular membrane dual phase gas diffusion separator reponed in ref. 48. S. sample At, aigon flow T, microporous PTFE tubing G, dual-phase gas-diffusion separator, BH, borohydride reductant W, waste and AAS, quartz atomizer cell. [Pg.152]


See other pages where Gas-diffusion separators is mentioned: [Pg.107]    [Pg.131]    [Pg.133]    [Pg.134]    [Pg.138]    [Pg.138]    [Pg.138]    [Pg.139]    [Pg.140]    [Pg.141]    [Pg.143]    [Pg.144]    [Pg.144]    [Pg.145]    [Pg.146]    [Pg.152]   
See also in sourсe #XX -- [ Pg.131 ]




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Factors Influencing Mass Transfer in FI Gas-diffusion Separation Systems

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Gas-diffusion separation systems

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Spectrophotometric Determination of Total Nitrogen in Soils with On-line Gas-diffusion Separation

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