Microcoulometry

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. 

Trace Quantities of Sulfur in Light Liquid Petroleum Hydrocarbons by Oxidative Microcoulometry... 

The electrode reaction of triamterene 15 was elucidated by means of DCP, Tast polarography, cyclic voltammetry, microcoulometry, controlled potential electrolysis, and spectroscopy (ultraviolet/visible (UVA is), NMR). Two steps of reduction independent of pH were observed two-electron reduction of 15 resulted in the formation of 17. The first reduction wave of 15 was assumed to be due to irreversible two-electron reduction forming unstable 16, which tautomerized to 17, and the second reduction wave was ascribed to two-electron reduction of 17 to the tetrahydro product, 18 (Scheme 2). 

Chemical Analyses. Organic halogens of drinking water concentrates were analyzed by microcoulometry (19) by direct injection of 100 /zL of the organic concentrate. 

Terpene catalytic hydrodesulfurization was performed in a pilot-plant reactor at 200°C, 1 atm. The volume of catalyst was 70 cm the liquid hourly space velocity of terpene 0.4 h"1 and the hydrogen to terpene molar ratio of 7. The catalysts were pretreated in situ in a flow of N2 at 260°C then sulfided in H2S/H2 (1 9) from 260°C to 370°C. After 5 h-on-stream, the catalysts were cooled down to the reaction temperature in H2S/H2. The hydrocarbons were analyzed by GC on a CP Wax 57 CB capillary column at 65°C and the sulfur contents were determined by microcoulometry using the ASTM D312077 norm. The... 

Microcoulometry, see Polarographic coulometry Mi 11icoulometry, see Polarographic coulometry Multisweep polarography (PM)... 

SULFUR (by Oxidative Microcoulometry) (Based on ASTM D3120)... 

Raney Nickel Reduction Apparatus in Appendix IIIC under Sulfur by Oxidative Microcoulometry). On top of the boiling flask, fit a water-jacketed distillation column with hooks. To the distillation column, fit a piece of glass tubing with ground ST inner joints with hooks, and connect the distillation column and a gas dispersion tube with ST outer joints with hooks. 

Values of n have been based on a combination of the polarographic wave heights and on the results of microcoulometry, in which a small volume of solution containing a known concentration of the substrate is partially (15-20%) reduced by application of the... 

The reason for the different number of electrons, and consequently for the differences in products found in the two studies, may be the difference in the applied coulometric methods. The microcoulometric method applied in Reference 64 is not exhaustive as is the coulometric method applied in Reference 65, and the products formed in the former study may therefore be of an intermediate nature. Insoluble products formed in the bulk solution during microcoulometry precipitate and never get in contact with the electrode, whereas precipitation onto the mercury pool electrode in the exhaustive electrolysis allows further reduction of an insoluble intermediate. 

Hydrocarbon impurities in propylene can be determined by gas chromatographic methods (ASTM D-2712, ASTM D-2163), and another test is available for determination of traces of methanol in propylene (ASTM Test Method D4864). A gas chromatographic method (ASTM D-5303) is available for the determination of trace amounts of carbonyl sulfide in propylene with a flame photometric detector. Also, sulfur in petroleum gas can be determined by oxidative microcoulometry (ASTM D-3246). 

Several test methods are available for determining sulfur in diverse petroleum product and lubricant matrixes from sub-mg/kg to m% concentration levels. One of the earliest methods issued by the D02 committee was for the sulfur determination by an oxygen bomb method (D 129) first issued in 1922. This was the 15 standard ever issued by the D02 Committee. The techniques currently used for the sulfur determination include classical wet chemistry (D 129, D 1266, D 1552, and D 2784), X-ray fluorescence (D 2622, D 4294, D 4927, D 6334, D 6443, D 6445, and D 7039), atomic spectroscopy (D 4951 and D 5185), and various thermal combustion microelemental methods using various detection techniques such as microcoulometry (D 3120 and D 3246), UV-fluorescence (D 5453 and D 6667), electrochemistry (D 4045 and D 6920), GC-FPD (D 7041), etc. A list of such available test methods is given in Table 4 along with other pertinent details as to the applicability of the method. 

D3120 Oxidative pyrolysis microcoulometry Light liquid hydrocarbons Chlorine and nitrogen may interfere precision is not very good... 

D3246 Oxidative pyrolysis microcoulometry LPG fuels Chlorine and nitrogen may interfere... 

There are about 20 laboratory based ASTM standard test methods available for the determination of sulfur in various petroleum products and lubricant samples [6]. These utilize diverse analytical techniques and have applicability range sparming from m% to low mg/kg levels. However, at the very low end of sulfur analysis there are only three or four test methods which can adequately determine sulfur in such fuels. These lab-based standard test methods include ASTM D 2622 - wavelength dispersive X-ray fluorescence, D 3120 - oxidative microcoulometry, D 5453 - combustion UV-fluorescence, and D 6920 - oxidative combustion electrochemical detection methods. Without a doubt, the most widely used two methods out of these in oil industry laboratories are D 2622 and D 5453. Studies have shown that at truly ultra-low levels of sulfur only D 5453 can deliver accurate and precise results. This conclusion has... 

ABSTRACT Current and upcoming regulations worldwide require maximum concentrations of sulfur in fuels to be in the range 10-50 mg/kg. This paper describes a new on-line analyzer for ultra low sulfur, the first to etrqtloy Pyro-electrochemical technology, which is significantly sinyler than other pyrolysis methods such as Pyro-microcoulometry and Pyro-UV fluorescence. 

Nadkarni (Symposium Chairman) reviewed the alternate methods available for sulfur determination in fuels. Out of about 20 ASTM standard test methods available, only about five (D 2622 WDXRF, D 3120 microcoulometry, D 5453 UV-fluorescence, D 6920 pyro-electrochemical, D 7039 MWDXRF) are appropriate for ultratrace amounts of sulfur in gasoline or diesel. However, in their actual industrial use only D 2622 and D 5453 predominate. 

The number of electrons involved in the electrode process are found to be six and four in acetate buffer (pH = 4.0) and carbonate buffer (pH = 10.0) respectively from the results of microcoulometry. The products of controlled potential electrolysis (carried out at —1.50 V and —1.30 V vs. SCE) in the above mentioned supporting electrolytes are identified as amine and hydroxylamine respectively. The nitro group in EPN exists in different forms depending on the supporting electrolyte. The change in colour of depolariser to yellow at... 

Ch. ZBINDEN (1904-1983) publishes a copper determination which can be termed chronopotentiometric stripping microcoulometry (1931) Bull de la soc chim biol 13 35. This can be regarded as the key step towards anodic stripping voltammetry. 

Oxidative microcoulometry is used to determine trace quantities of sulphur in aromatic hydrocarbons. An oxidative pyrolysis converts sulfur to sulfur dioxide which is titrated in titration cell with the triiodide ion present in the electrolyte. 

ASTM D 3961-98. Standard test method for trace quantities of suUur in hquid aromatic hydrocarbons by oxidative microcoulometry. 

ASTM D 5808-95. Standard test method for determining OTganic chloride in aromatic hydrocarbons and related chemicals by microcoulometry. 

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