Total hydrocarbon determination

The determination of hydrocarbon contaminants in soil is one of the most frequently performed analyses in the study of contaminated sites and is also one of the least standardized. Given the wide variety of hydrocarbon contaminants that can potentially enter and exist in the soil environment, a need exists for methods that quantify these chemicals satisfactorily. Formerly, the idea of total hydrocarbon determination in soil was seen as providing a satisfactory tool for assessing contaminated sites, but the nature of the method and the site specificity dictate a risk-based approach in data assessment. Quantitation of particular hydrocarbon species may be required. 

Figure 13. Plot of concentrations of C] to 5 hydrocarbons at 300°C in the gaseous products determined by gas chromatography (GC) and total hydrocarbons determined by NMR [53], GC data are for LHSV = 0.3 hri. NMR and GC data are adjusted so that the concentrations of methane coincide.

A flame-ionization, total hydrocarbon analyzer determines the THC, and the total carbon content is calculated as methane. Other methods include catalytic combustion to carbon dioxide, which may be deterrnined by a sensitive infrared detector of the nondispersive type. Hydrocarbons other than methane and acetylene are present only in minute quantities and generally are inert in most appHcations. 

Most of the hydrocarbon emissions from iron and steel facilities are not captured by TRI. The EPA Office of Air Quality Planning and Standards has compiled air pollutant emission factors for determining the total air emissions of priority pollutants (e.g., total hydrocarbons, SO, NO, CO, particulates, etc.) from many iron and steel manufacturing sources. 

The definitions above are an abbreviated version of those used in a veiy complex and financially significant exercise with the ultimate goal of estimating resei ves and generating production forecasts in the petroleum industry. Deterministic estimates are derived largely from pore volume calculations to determine volumes of either oil nr gas in-place (OIP, GIP). This volume when multiplied by a recovery factor gives a recoverable quantity of oil or natural gas liquids—commonly oil in standard barrels or natural gas in standard cubic feet at surface conditions. Many prefer to use barrels of oil equivalency (BOE) or total hydrocarbons tor the sum of natural gas, natural gas liquids (NGL), and oil. For comparison purposes 6,000 cubic feet of gas is considered to be equivalent to one standard barrel on a British thermal unit (Btu) basis (42 U.S. gallons). 

Zsolnay and Kiel [26] have used flow calorimetry to determine total hydrocarbons in seawater. In this method the seawater (1 litre) was extracted with trichlorotrifluoroethane (10 ml) and the extract was concentrated, first in a vacuum desiccator, then with a stream of nitrogen to 10 pi A 50 pi portion of this solution was injected into a stainless steel column (5 cm x 1.8 mm) packed with silica gel (0.063-0.2 mm) deactivated with 10% of water. Elution was effected, under pressure of helium, with trichlorotrifluoroethane at 5.2 ml per hour and the eluate passed through the calorimeter. In this the solution flowed over a reference thermistor and thence over a detector thermistor. The latter was embedded in porous glass beads on which the solutes were adsorbed with evolution of heat. The difference in temperature between the two thermistors was recorded. The area of the desorption peak was proportional to the amount of solute present. 

Zsolnay A (1974) Determination of aromatic and total hydrocarbon content in submicrogram and microgram quantities in aqueous systems by means of high-performance liquid chromatography. Special publication no. 409. National Bureau of Standards, Washington, DC, p 119... 

The detailed model was constructed as described by Carslaw et al. (1999, 2002). Briefly, measurements of NMHCs, CO and CH4 were used to define a reactivity index with OH, in order to determine which NMHCs, along with CO and CH4, to include in the overall mechanism. The product of the concentration of each hydrocarbon (and CO) measured on each day during the campaign and its rate coefficient for the reaction with OH was calculated. All NMHCs that are responsible for at least 0.1% of the OH loss due to total hydrocarbons and CO on any day during the campaign are included in the mechanism (Table 2). Reactions of OH with the secondary species formed in the hydrocarbon oxidation processes, as well as oxidation by the nitrate radical (NO3) and ozone are also included in the... 

The widespread use of -hexanc as an extractant in the laboratory creates problems in interpreting concentration readings at low levels. Even with good quality control, it may often be impossible to determine whether to attribute a measured value to the actual levels in a sample or to contamination from M-hexanc in the laboratory environment (Otson et al. 1994). For the most part, -hexane is not a common target analyte from water or soil samples. While data based on ambient air samples or sampling in the air of various workplace or residential environments are more numerous, most EPA regulatory programs rely on bulk measurements of total hydrocarbons or total volatile compounds rather than on measurements of specific compounds such as -hexane (Bishop et al. 1994 DeLuchi 1993). 

Petroleum pollution monitoring laboratories in the Mediterranean region participated (1984-1986) in two intercalibration exercises (MEDCALI and II) to evaluate the International Oceanographic Commission (IOC) Manual for petroleum hydrocarbon determination in sediment (IOC, Manuals and Guides, No. 11). The main source of error in the analysis was the extraction/ partition step. When the results were corrected for recoveries, relative standard deviations for w-alkancs, UCM (unresolved complex mixture) and total aromatics, which had previously been 60, 56 and 49%, respectively, were reduced to 17, 30 and 6%, respectively. 

Each k is given by an Arrhenius expression, k = A exp(-E/RT), and the fraction of the tighdy bound component is a parameter. For the high temperature results in Figure 6, some charring of toluene was observed at the highest wall temperature (790°C). The fraction of toluene remaining in the bed was determined from gas-phase total hydrocarbon, 02, and C02 measurements. 

The TOC content can also be determined in air. However, the parameter used in this case is called total hydrocarbons (TH) rather than TOC. One significant difference between the OC in air and in other matrices is that the atmosphere contains a nearly constant background concentration of methane ( 1.7 u.g g 1 v/v),14 derived mostly from natural sources. Thus, any TH measurement will... 

FIGURE 17.7 Diagram of apparatus of ISO TS 19700. The secondary oxidizer (inside dotted line) is for the determination of total hydrocarbons in the ISO standard. (From Hull, T.R. and Paul, K.T., Fire Saf.42, 353, 2007. With permission.)... 

Figure 4 presents selectivity data for these two fused catalysts. The selectivity was determined from the average composition of the product obtained during the second to eighth week of testing. The product distributions are plotted as per cent of the total hydrocarbons, the... 

Common Whole Mixtures There are few systematic studies of mixtures that are strictly based on the approach of the mixture of concern or similar mixtures as defined under human risk assessment of mixtures. Most ecological effect studies have more characteristics in common with a component-based or unique whole mixture approach than with the common mixture approach. A rare example of the common whole mixture approach in ecological risk assessment is the hydrocarbon block method. In this case, mixture effects are predicted on the basis of partial characterization of hydrocarbon mixtures. The hydrocarbon block method is used to determine the risks of a total hydrocarbon mixture on the basis of discriminating different chain length fractions of hydrocarbons, for each of which toxicities are known (King et al. 1996). 

Differences In hydrolysis characteristics are used in analytical test procedures to Identify the easily dissociated esters by polymer and tltratable acidity, amd the less reactive by total acidity procedures. Total hydrocarbon content is determined by carbon analysis,and uncombined by the aniline sulfate procedure. 

The products from these hydrogenations were separated into gases (analyzed by G.C.), water (analysed by azeotropic distillation), insolubles (CH2CI2 insolubles), asphaltene (CH2CI2 soluble/X4 insoluble) (Shell X4 40-60 C b.p. light petroleum), oils (CH2CI2 soluble/X4 soluble). Hydrogen transferred from the donor solvent was determined by G.L.C. analysis of the ratio of tetralin to naphthalene in the total hydrocarbon liquid product. 

Hasty E, Revesz F. 1995. Total petroleum hydrocarbon determination by microwave solvent extraction. American Laboratory 27(4) 66. 

Gas samples were collected in Tedlar gas sample bags and analyzed for their content of CO, C02, H-, CL, and total hydrocarbons using the process analyzer described lh Cw Moisture content of the gas was determined by the condensation method (15). 

Saturated hydrocarbons were quantified with perdeuterated tet-racosane as a co-xnjectlon standard. Total hydrocarbon concentrations were determined by electronically Integrating the area above a blank baseline resolved hydrocarbon concentrations were determined by Integrating peak areas above an unresolved envelope. Individual n-alkanes were Identified by comparison of sample peak retention times to those of an external standard mixture. 

BS 7164-11.1 Part 11 Determination of the microstructure of butadiene BS 7164-13 Part 13 Determination of total hydrocarbon content BS 7164-21 (=ISO 1656) Part 21 Determination of nitrogen content (see Section 7.5.1, Test for nitrogen)... 

Partition coefficients of gases and hydrocarbons are presented in Tables 6.4 and 6.5. The partition coefficients of gases have mainly been determined from solubilities. Most of the data were obtained by King and co-workers, and King has also reviewed the data available. " It was previously demonstrated that the partition coefficient of alcohols at the solubility limit was significantly lower than at infinite alcohol dilution. Eor the gases and hydrocarbons, however, the solubility is very low, even in surfactant solutions typically, the mole fraction at the solubility limit is of the order lO " to 10 whereas for the alcohols it is of the order 10 fi Initially, we might thus expect that the variation of partition coefficients with total hydrocarbon concentration would be of minor importance, and that values at the solubility limit and at infinite dilution could be compared. However,... 

For many strained hydrocarbons and alkenes, heats of formation are not known. In these cases, computational methodology may be used. For a number of molecules, the total energies determined by ab initio calculations and transformed into heats of formation by special group equivalents may be used (81b). Strain energies have also been obtained via isodesmic reactions, which measure deviations from the additivity of bond energies (224). 

An example of Li amide-imide pressure cycling data is presented, although there are detailed presentations in this book on thermodynamics and structure of these materials by other authors. Chandra et al. [148] determined the effect of long-term pressure cycling between (1, 56, 163, 501, and 1100 cycles) for the Li-N-H system using industrial hydrogen [hydrogen min% (v/v) 99%, water 32 ppm, O2 10 ppm, N2 400 ppm. Total hydrocarbons ... 

Total hydrocarbons in the air may be determined using infrared spectrophotometry. The hydrocarbons are collected in a condensation trap immersed in liquid oxygen. The hydrocarbons absorb in the 3- to A-jxnx region of the infrared spectrum using a 20-m pathlength cell. They are expressed as parts per million hexane, and the instrument is calibrated using a hexane standard. 

The studies described above give evidence that the XAD-2 method provides a useful determination of the hydrocarbon components in dilute seawater-oil suspensions. The quantity of "total oil reported in Table I is in sharp contrast to the total hydrocarbons found in the water by the combined helium extraction/XAD extraction techniques. The discrepancy between total oil by IR and hydrocarbons found in water by component analysis was previously reported (5,11) and can be explained by the low contribution to the IR absorbance at 2927 cm 1 of the soluble aromatic constituents relative to the saturate hydrocarbons. The difference between IR analytical result and component analysis by GC becomes much greater in the filtered systems, where the total hydrocarbons found are three times that reported by the IR method. It is clear that the IR analytical technique is only useful in systems where there is a preponderance of particulate, bituminous petroleum or where it is used as a monitoring tool. It provides no information about actual levels of hydrocarbons in systems where there is a preponderance of water-soluble aromatic compounds. 

The analysis of Prudhoe Bay Crude Oil for the hydrocarbon components under study is presented in Table V, together with the percentage of the total hydrocarbons found represented by each of the hydrocarbon types. For comparison, the contribution of component types to the total hydrocarbon is listed for both a filtered and unfiltered seawater suspension. The comparison is somewhat biased because benzene was not determined in the crude oil, being poorly separated from the hexane solvent, and because C4-benzenes were not determined in the unfiltered sample. However, it can be readily seen from the results that while aromatic hydrocarbon types are present in the crude oil in roughly equal concentrations, the preponderance of the total hydrocarbons in the seawater suspension is composed of the low-molecular-weight aromatic hydrocarbons. In both unfiltered and filtered systems, 90% of the water-soluble aromatic hydrocarbons found are composed of benzene, toluene, ethyl benzene, and the xylenes. This is in contrast to their concentration in the whole crude oil, which is at most a few percent and where their contributions to the hydrocarbons analyzed for is probably less than 30%. 

An example of an automatic analyser for the determination of organic pollutants is the Meloy HC 500-2C from Columbia Scientific Industries. It is a self-contained system for monitoring ambient concentrations of non-methane hydrocarbons (NMHC), methane and total hydrocarbons. Sample air Is first introduced directly into the flame ionization detector to yield a total hydrocarbon reading which Is stored In an electrical circuit. The pneumatic system Is automatically switched so that the sample air passes through a catalytic converter before It Is Introduced Into the detector, which converts ail the NMHC Into a non-detectable species. Hence, only the methane in the sample Is... 

Various analytical techniques used for hydrocarbon analyses of sea water samples, ultraviolet and fluorescence spectrophotometry (Keizer and Gordon, 1973), infrared spectrometry (Carlberg and Skarstedt, 1972), liquid column chromatography together with the determination of heat of adsorption (Zsolnay, 1977b) provide only data about a fraction of the hydrocarbons or yield a value equivalent to the total hydrocarbon concentration. Thus, we will only consider studies where hydrocarbons are precisely determined by gas—liquid chromatography and mass spectrometry. 

---