Determination of carbon number distributions of complex phthalates by gas chromatography-mass spectrometry with ammonia chemical ionization.

An assay method for phthalate esters with a complex mixture of isomer of varying carbon numbers, such as di-isononyl phthalate (DINP) and di-isodecyl phthalate (DIDP), using gas chromatography-mass spectrometry (GC-MS) positive chemical ionization (PCI) with 5% ammonia in methane is described. GC-MS-PCI-NH3, unlike GC-MS electron ionization (EI) (GC-MS-EI) that produces generally m/z 149 ion as the main base peak and low intensity M(+) peaks, produces higher intensity (M + 1) ions that allow the determination of total (R + R') carbon number distributions based on the various R and R' alkyl groups of the di-esters moiety. The technique allows distinguishing among the various commercial DINP and DIDP plasticizers. The carbon number distributions are determined in the acceptable range of <0.1 mole percent to >85 mole percent (m/m). Several examples of analysis made on commercial DINP and DIDP are presented. The use of only 5% instead of 100% ammonia simplifies use of GC-MS-PCI-NH3 but still produces sufficient M + 1 ion intensities that are appropriate for the assay. In addition, use of low concentrations of ammonia mitigates potential safety aspects related to use of ammonia and provides less corrosion for the instrument hardware.

Determination of aromatic hydrocarbons in gasolines by flow modulated comprehensive two-dimensional gas chromatography.

Valve based/flow modulated comprehensive two-dimensional gas chromatography-flame ionization detection (GC x GC-FID) was used for quantification of C6 through C12 aromatic hydrocarbons by carbon number in gasolines. A 0.53 mm i.d. non-polar first dimension column was coupled to a 0.53 mm i.d. polar second dimension column through a double loop eight port valve modulator. Depending on the sample type, normalized percent and internal standard (I.S.) quantification was performed. For normalized percent quantification, a one-point calibration performed with one aromatic compound per carbon number/class provided an average % accuracy of 2.1% and a short-term n--1 relative standard deviation of 1.0%. For total aromatic compounds good agreement with the more complex conventional multidimensional GC technique was obtained. However, GC x GC has certain advantages over most other methods, mainly increased selectivity for total and carbon number aromatic content. The identification of the aromatic hydrocarbons was confirmed by GC x GC-MS.

Speciation of sulfur-containing compounds in diesel by comprehensive two-dimensional gas chromatography.

Sulfur-containing compounds in diesel have been speciated by comprehensive two-dimensional gas chromatography (GCxGC) with a sulfur chemiluminescence detector (SCD). The advantages of GCxGC technique are higher resolution and greater sensitivity. GCxGC-SCD can achieve the class separation of sulfur-containing compounds with an appropriate separation column combination. The major classes of sulfur-containing compounds in diesel are benzothiophenes and dibenzothiophenes. Relative concentration of each class as well as each carbon number family can be quantitated by the summation of the integrated areas corresponding to the individual group(s) in the GCxGC space. In practical applications, GCxGC-SCD can be used to characterize different diesels and to reflect desulfurization process efficiency. In this study, GCxGC-SCD has demonstrated its value in speciation of sulfur-containing compounds classes, which is difficult to accomplish by any other single technique.