Molecular formula determination of capillary column gas chromatographic effluents using combined microwave-induced plasma emission and mass spectral data

Abstract

The use of elemental composition Information derived from microwave-induced plasma emission as a complement to mass spectral data for the determination of molecular formulas of materials eluted from a gas chromatograph was explored. This evaluation was conducted using the atomic emission responses obtained from large (GMW 200-400 range) molecules of varying structure that were composed of three to six elements. The emission responses were calibrated by using a set of small molecules of unrelated chemical structure. The results obtained Indicate that, If an accurate mass has been measured, the molecular formula can be determined by using only a subset of the elemental ratios available from the atomic emission. If, however, only a lowresolution determination of the molecular weight has been made, all of the elemental ratios are required for the determination of a molecular formula. Of the examples reported here, all but one molecular formula could be determined unambiguously from the low-resolution molecular weight and the atomic emission data. In that particular case, possible molecular formulas could be limited to three, while an accurate mass determination alone for this molecule would produce 23 molecular formulas.

Environmental Applications of Gas Chromatography/Atomic Emission Detection

“…There is disagreement regarding the prospects for empirical formula determinations, [4][5][6] and it is postulated that GC/ AED elemental ratios are best used in conjunction with mass spectrometric molecular weights. 7 There is also disagreement whether GC/AED can be used to minimize the number of standards required for quantification. The disagreement ranges from whether to require only a single internal standard for a chemical family with the same elemental distribution 8 to the need for standards with the same molecular structure and retention time as those of the analyte to be quantified.…”

“…The application of GC/AED as a routine environmental screening tool has not yet been reported for actual environmental samples. There is disagreement regarding the prospects for empirical formula determinations, − and it is postulated that GC/AED elemental ratios are best used in conjunction with mass spectrometric molecular weights . There is also disagreement whether GC/AED can be used to minimize the number of standards required for quantification.…”

Selective detection of carbon-13-labeled compounds by gas chromatography/emission spectroscopy

“…by changing the reagent and makeup gas flows. This combination of 13C specificity with atomic information is useful in the identification of unknown compounds, especially when combined with mass spectral data, as shown by Hooker and DeZwaan (6).…”