Total organic sulfur, direct determination

RILEY ET AL. Direct Determination of Total Organic Sulfur in Coal... 

A method for the direct determination of the organic sulfur in coal using extraction with hot nitric acid was developed. The method yields total organic sulfur values that are much closer to the sulfur values found in deep cleaned coals and with greater precision than the organic sulfur values obtained by ASTM Method D 2492. 

In the method for determining the forms of sulfur in coal (ASTM D-2492 ISO 157), the sulfate and pyrite sulfur are determined directly, and the organic sulfur is taken as the difference between the total sulfur and the sum of the sulfate and pyrite sulfur. 

Buffle, J., Zali, O., Zumstein, J. and De Vitre, R.R. (1987) Analytical methods for the direct determination of inorganic and organic species seasonal changes of iron, sulfur, and pedogenic and aquogenic organic constituents in the eutrophic Lake Bret, Switzerland. Sci. Total Environ., 64, 41-59. 

A procedure for the direct determination of the sulfate, sulfide, pyritic, and organic sulfur in a single sample of coal has been reported by McGowan and Markuszewski (17). The method uses various strengths of perchloric acid as the selective oxidizing agent. The results obtained for the analysis of three coals were comparable to ASTM results and the relative standard deviations for nine sulfate, four pyritic, six organic, and four total recovered sulfur determinations were 2.7, 3.4, 2.4, and 2.4%, respectively. 

There are methods for the direct determination of organic sulfur in coal (3.4), but details regarding individual molecular structures are much harder to obtain. Much of the research designed to obtain this information has concentrated on the analysis of coal extracts (5.6) and pyrolysis products (7.8). Unfortunately the sulfur species from pyrolysis processes may be highly modified and usually account for only a very small percentage of the total sulfur in the coal. 

It appears that adding to all these difficulties is the lack of a satisfactory method for the direct determination of organic sulfur in coal that could be routinely applied to all coals under all conditions. The commonly used ASTM procedure (7) for organic sulfur is an indirect method, based on the difference between the total sulfur and the total inorganic... 

This test method covers the determination of total sulfur in liquid petroleum products and in solid petroleum products that can be liquefied with moderate heating or dissolved in a suitable organic solvent. The applicable concentration range will vary to some extent with the instrumentation used and the nature of the sample. Optimum conditions will allow the direct determination of sulfur in essentially paraffinic samples at concentrations exceeding 0.0010 mass %. 

Evans et al. [98] has described a method for the determination of total copper, iron, manganese and zinc in various plant materials. Organic matter is destroyed by wet oxidation and measurement is made directly upon the sulfuric acid digests by flame atomic absorption spectrophotometry. In the measurement, direct interferences from the inorganic species found in plant... 

Altliough methods involving organic solvent extraction or protein precipitation wfil estimate both free and protein-bound cortisol in tlie circulation, immunoassay-based methods that determine cortisol directly from serum have essentially replaced all extraction-based methods for routine cortisol measurements save for urine free cortisol methods. Flistorically four general methods have been used for the quantitative estimation of total blood cortisol concentrations in the clinical laboratory. These are the Porter-Silber color reaction method modified for plasma,the use of sulfuric acid-induced fluorescence, HPLC methods, or immunoassay. In general, HPLC and immunoassay are now used in both clinical laboratories and reference laboratories for the quantitative determination of cortisol in serum or urine. 

Digestion of fossil fuel samples is the most labor-intensive and time-consuming step in the analytical procedures described so far. Techniques with direct introduction of the isotope-diluted sample would therefore be much more attractive and suitable for use as routine methods. In this context, Heumann and co-workers developed two different methods which avoid the digestion step and rely on direct introduction of the isotope-diluted sample into the ICP. LA-ICP-IDMS was applied for the determination of sulfur and metals in petroleum products and crude oils [47, 48] and thermal vaporization (TV)-ICP-IDMS was used for the determination of trace amounts of sulfur in petroleum products [36]. To totally mix a petroleum or crude oil sample with the spike, the spike needs to be in an organic form. A " S-labeled dibenzothiophene spike in xylene and isotope-enriched organometallic compounds of the metals of interest in isobutyl methyl ketone were used for LA-ICP-IDMS purposes. For sulfur determination via TV-ICP-IDMS, the same spike was applied, but n-hexane was used as the... 

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