Hydrocarbons Standard samples

If simple sample pretreatment procedures are insufficient to simplify the complex matrix often observed in process mixtures, multidimensional chromatography may be required. Manual fraction collection from one separation mode and re-injection into a second mode are impractical, so automatic collection and reinjection techniques are preferred. For example, a programmed temperature vaporizer has been used to transfer fractions of sterols such as cholesterol and stigmasterol from a reversed phase HPLC system to a gas chromatographic system.11 Interfacing gel permeation HPLC and supercritical fluid chromatography is useful for nonvolatile or thermally unstable analytes and was demonstrated to be extremely useful for separation of compounds such as pentaerythritol tetrastearate and a C36 hydrocarbon standard.12... 

Nonurban oxidant measurements in Ohio were reported by Neligan and Angus. Concentrations of 0.18 and 0.12 ppm were reported for rural sites in Wilmington and McConnelsville, respectively. At the same time, urban sites had similar concentrations. However, the nonurban sites violated the ambient air quality standard more frequently than the urban sites. Trajectory analysis showed that ozone concentrations of 0.04-0.06 ppm were found in air masses that had not passed over anthropogenic hydrocarbon sources. These may have been examples of naturally occurring oxidant. Airborne hydrocarbon bag samples were obtained over 6-min... 

The charcoal tubes were broken open and the charcoal transferred into a stoppered glass test tube. One milliliter of carbon disulfide was pipetted into each tube, and 1.5 ml of carbon disulfide was pipetted into each 3M vapor monitor badge. After 30 minutes, aliquots of carbon disulfide were injected into the gas chromatograph and compared versus hydrocarbon standards prepared in carbon disulfide. The total areas of the sample and standard peaks were measured by the data system. 

The accuracy of the method has been assessed by analysis of a standard sample of bovine liver from the National Bureau of Standards and a standard sulfonated hydrocarbon. For the bovine liver the sulfur content by combustion/ ion chromatography was about 1.2% below the accepted value whereas for the standard hydrocarbon, with a reported sulfur content of 0.97%, combustion/ion... 

Standard Samples. The positive identification of the individual hydrocarbons isolated from petroleum created an early demand for known hydrocarbon compounds of the highest purity. An impetus was given to this need for pure hydrocarbons during World War II, when it became imperative to have standard samples for the calibration of spectrometers. 

The above paragraphs are quoted from the paper prepared by Shaffer and Rossini 159) as a report for APIRP 6 for the Session on Fundamental Research. Table 3 of then-paper is a list of the API Standard Samples of hydrocarbons arranged by type of hydrocarbon. The formula, name, and purity of each hydrocarbon is shown. 

More than half of the synthetic hydrocarbon products made at Ohio State have been sent to APIRP 6 for purification to make the two series of high purity standard samples of hydrocarbons prepared, first at the National Bureau of Standards, now at the Carnegie Institute of Technology. Most of the hydrocarbon compounds that have been purified by APIRP 6 were prepared by APIRP 45. 

Chemicals. The o-xylene was an American Petroleum Institute standard sample, with stated impurities of 0.005 0.004 mole %. Other hydrocarbons were purified by gas chromatography. Purity was checked by gas chromatography on three columns of different selectivity except for 0.02% p-xylene in the m-xylene, no more than 0.002% of any impurity was detected. Samples were stored in vacuo. 

The repeatability of the Ir values for various monoterpene hydrocarbons was examined. The concentrations of the standard samples for GC-MS of ot-pinene, P-pinene, sabinene, myrcene, a-phellandrene, a-terpinene, limonene, y-terpinene and terpinolene were within the range of 0.5-1.8% (w/w). The Ir value for each monoterpene hydrocarbon was plotted in Fig. 1, where the coefficient of variation (CV) is also presented. These Ir values only seem to vary over a narrow range, since their CVs were not more than 0.61% (limonene). 

The nonvolatile organic compounds that remain in the UOC after the milling process can help identify the type of purification and preconcentration methods that were used (Kennedy et al. 2012). A solution of 20 80 methanobwater with internal deuterated hydrocarbon standards was used to extract the organic compounds from a slurry of UOC and analysis was carried out with a GC-MS. As expected, di-octylamine, tri-isooctylamine, and alamine 336 were found in a UOC sample that was processed with amines. 

After successful application of enantioselective GC to the analysis of enantiomeric composition of monoterpenoids in many essential oils (e.g., Werkhoff et al., 1993 Bicchi et al., 1995 and references cited therein), the studies have been extended to the sesquiterpene fraction. Standard mixtures of known enantiomeric composition were prepared by isolation of individual enantiomers from numerous essential oils by preparative GC and by preparative enantioselective GC. A gas chromatographic separation of a series of isolated or prepared sesquiterpene hydrocarbon enantiomers, showing the separation of 12 commonly occurring sesquiterpene hydrocarbons on a 2,6-methyl-3-pentyl-P-cyclodextrin capillary column has been presented by Konig et al. (1995). Further investigations on sesquiterpenes have been published by Konig et al. (1994). However, due to the complexity of the sesquiterpene pattern in many essential oils, it is often impossible to perform directly an enantioselective analysis by coinjection with standard samples on a capillary column with a chiral stationary phase alone. Therefore, in many cases two-dimensional GC had to be performed. 

The argentometric titration of mercaptans, described in Chapter VI, can also be used for the determination of mercaptanes in hydrocarbons. ) Liquid samples are dissolved in ammoniacal acetone and titrated with a standard solution of silver nitrate gaseous samples are absorbed in a solution eontaining excess of silver nitrate and the unreacted silver is titrated with standard dodecyl mercaptan. 

Working Standards—For working standard hydrocarbons, reasonably well purified samples of n-hexadecane, fra/i -decahydronaphthalene, and 1-methylnaphthalene may be used. Their exact values are determined by comparison with standard samples of the same hydrocarbons having certified values of refractive index. 

Precision—The precision statements are based on an interlaboratory study in which analysts in each of six laboratories analyzed seven hydrocarbon solvent samples, including heptane, VM P naphtha, mineral spirits, toluene, and aromatic solvent 100 on two different days. To each solvent, initially containing essentially no benzene, 0.1 to 0.5 volume % benzene was added. The within-laboratory standard deviation was found to be 0.0094 % absolute with 42 df and the between-laboratory standard deviation was 0.022 % absolute with 49 df. Based on these standard deviations, the following criteria should be used forjudging the acceptability of results at the 95 % confidence level ... 

Standards for Calibration and Identification—Standard samples of normal paraflins covering the carbon number range (through C44) of the sample are needed for establishing the retention times of the individual paraffins and for calibration for quantitative measurements. Hydrocarbons used for standards must be greater than 95 % purity. 

Figure 5 Stacked chromatograms showing the GC analysis of a series of n-hydrocarbons isolated by headspace SPME at various temperatures. The sample was prepared by transferring l-pl of individual hydrocarbon standards into a 4-mL vial and sealing with a Teflon-coated septum. After 10 minutes equilibration at the indicated temperature, the headspace vapor was extracted using a 100-lim polydimethylsiloxane fiber and was analyzed by GC with flame ionization detection. The injector temperature for this sample was set at 300°C, and the fiber was desorbed for 1 minute.

This method follows the ASTM D 1159 and D 2710 procedures and the AFNOR M 07-017 standard. It exploits the capacity of the double olefinic bond to attach two bromine atoms by the addition reaction. Expressed as grams of fixed bromine per hundred grams of sample, the bromine number, BrN, enables the calculation of olefinic hydrocarbons to be made if the average molecular weight of a sufficiently narrow cut is known. 

The actual Russian standards allow presentation of hydrocarbon components of UGC as individual compounds only for C -C hydrocai bons. The rest is described as pseudo-compound C,, although its content may reach 60 % m/m. Apparently, the detailed determination of composition of hydrocarbons C, in UGC allows essentially to raise quality of both its processing and its record. The best method for the determination of heavy hydrocai bons is capillary gas chromatography. Typical approach is based on preliminary sepai ation of UGC samples to gaseous and liquid phases. 

Sodium hydroxyalkanesulfonates may be determined in the presence of an unsaturated hydrocarbon, including sodium alkenesulfonate. The sulfonates are converted to the free sulfonic acids using a slight excess of 2,4-dinitrobenzene-sulfonic acid. The hydroxyl group of the sulfonic acid liberated is acetylated in ethyl acetate solution by a known excess of acetic anhydride. The unconsumed anhydride is hydrolyzed by a pyridine-water mixture and the acids titrated potentiometrically with standard sodium hydroxide solution. The hydroxy-alkanesulfonate content is calculated after correction for any traces of acidity or alkalinity in the original sample. 

Another useful standard Is SRM 1647, priority pollutant polynuclear aromatic hydrocarbons (in acetonitrile). It can be used to calibrate liquid chromatographic Instruments (retention times. Instrument response), to determine percent recoveries, and to fortify aqueous samples with known PAH concentrations. Figure 8 Illustrates the HPLC separation and UV detection (fluorescence is also used extensively) for the 16 priority pollutants. 

Another complicating characteristic of materials from the environment is that the size and nature of the residue to be analyzed in the mass spectrometer will change from sample to sample. To determine if this might have an effect on the observed TCDD signal, we analyzed identical samples of TCDD with differing amounts of squalane, a saturated hydrocarbon selected as a model for residues obtained from standard extraction and cleanup procedures. As is indicated in Table I (Part A), there was... 

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