Microcoulometric titration

Detection mode microcoulometric titration. c Detection mode UV fluorescence. 

Microcoulometric titration is used as the detection mode in some commercial sulfur-specific analysers. Sulfur in PP and waxes (range from 0.6 to 6 ppm S) were determined by means of an oxidative coulometric procedure [537]. The coulometric electrochemical array detector was used for determining a variety of synthetic phenolic antioxidants (PG, THBP, TBHQ, NDGA, BHA, OG, Ionox 100, BHT, DG) in food and oils [538],... 

GC/FID has been used for quantifying sulfur volatiles such as hydrogen sulfide in human saliva (Solis and Volpe 1973). This method included microcoulometric titrations and a procedure for incubation of saliva and sampling of headspace sulfur volatile components. The amount of total sulfur volatiles detected in control samples of saliva incubated at 37°C for 24 hours ranged from 4.55 to 13.13 ppm. 

Solis MC, Volpe AR. 1973. Determination of sulfur volatiles in putrefied saliva by a gas chromatography-microcoulometric titrating system. J Periodontal 44 775-778. 

Christian, G. D. A Sensitive Amperometric Endpoint Detection System for Microcoulometric Titrations. Microchem. J. 9, 484 (1965). 

FIGURE 30 Microcoulometric Titrating System for the Determination of Sulfur in Hexanes. 

Apparatus Use the Dohrmann Microcoulometric Titrating System (MCTS-30), or equivalent (shown in Fig. 30), unless otherwise specified in an individual monograph. It consists of a constant rate injector, A, a pyrolysis furnace, B, a quartz pyrolysis tube, C, a granular-tin scrubber, D, a titration cell, E, and a microcoulometer with a digital readout, F. 

Extracts from all samples were analyzed by gas chromatography as described by Hindin, May, and Dunstan (5). After the residue had been taken up in a measured volume (0.1 or 1.0 ml.) of petroleum naphtha, a 10-/Jiter aliquot was injected into a Beckman temperature programmer coupled with a Dohramann microcoulometric titration detector. The column-packing material used for the separation of the insecticides was 5% by weight of EPON 1001 on 60/80-mesh acid-washed, flux-calcined diatomite (Chromosorb P). This material was packed in aluminum tubing % inch in o.d. by 3 feet. 

The postulated catalytic cycles for pterin-containing molybdenum enzymes involve a two-electron change at the molybdenum atom (Mo(VI) Mo(IV)). Microcoulometric titrations of nitrate reductase Chlorella vulgaris) (76), milk xanthine oxidase (77), and sulfite oxidase (78) show that their molybdenum centers are reduced by two electrons. The reduction potentials for the molybdenum center of chicken liver sulfite oxidase are strongly dependent upon pH and upon anion concentration (78). 

Microcoulometric titrations of sulfite oxidase suggest that both the magnitude and the direction of the driving force for intramolecular electron transfer between the molybdenum and the iron centers of sulfite oxidase can be modulated by pH and anion concentration (78). At low pH and/or high chloride the Mo(VI) center appears to be reduced... 

Structure and electrochemical studies of the cluster ligandation and interaction with small molecules in mammalian PAPs by NMR, EXAFS, and microcoulometric titrations. 

The eluted halogen-organic compounds are pyrolized the resultant hydrogen halide is quantified selectively by microcoulometric titration. 

Test Method B covers the determination of organic chloride in the washed naphtha fraction of. crude oil by oxidative combustion followed by microcoulometric titration. 

In this automatic system, the authors preferably used coulometric generation of titrant (cf., microcoulometric determination of deviations in the above end-point titration ), e.g., H, OH, Ag, Hg2+, Br2,12, Fe(CN) (cf., Table 1 in ref. 63). The detection method may be potentiometric (logarithmic signal), amperometric (linear signal), biamperometric, conductometric, oscillometric, etc. Moreover, the authors evaluated triangle programmed titration curves by... 

Recently, Van der Schoot and Bergveld74 developed an ISFET-based microlitre titrator by combination with a microcoulometric pH actuator. As a result of integrated circuit technology they could integrate ten pH-sensitive ISFETs... 

Oxidative microcoulometry has become a widely accepted technique for the determination of low concentrations of sulfur in petroleum and petroleum products (ASTM D3120). The method involves combustion of the sample in an oxygen-rich atmosphere followed by microcoulometric generation of a triiodide ion to consume the resulting sulfur dioxide. It is intended to distinguish the technique from reductive microcoulometry, which converts sulfur in the sample to hydrogen sulflde that is titrated with coulometrically generated silver ion. 

Table II. Microcoulometric and Titration Data for Syncrude Fractions...

Some techniques may offer selective screening as well as specificity —e.g., microcoulometric methods described by Coulson et al. (24). This technique consists of a combination of gas chromatography, combustion, and continuous coulometric titration for chlorine or sulfur. The development of the flame photometric detector offers a similar potential for the selective screening and specificity of pesticides which contain phosphorus or sulfur (25). Even so, one or more tests in addition to the initial... 

A selective thermionic specific detector (TSD) was developed by Albert (107) but it is more commonly referred to as a nitrogen-phosphorous detector (NPD). It is basically an alkali FID. Figure 13.36 compares the TSD and the microcoulometric detector. More resolution is obtained through the TSD with elimination of the mixing in the transfer line, reactor tube, and titration cell of the... 

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