Preliminary observations on the use of a novel low duty cycle flow modulator for comprehensive two-dimensional gas chromatography.

The present research is focused on the preliminary evaluation, in particular in relation to the advisable operational conditions, of a novel low duty cycle flow modulator. In such a respect, a fast comprehensive two-dimensional gas chromatography-mass spectrometry method is herein proposed. Applications on a C7-C30 series of alkanes, 64 fragrance allergens (plus 2 internal standards), and 5 perfumes, were carried out by using two different column sets, low-polarity + medium-polarity and low-polarity + low-polarity. In both cases, the first column was of dimensions 10 m × 0.25 mm ID × 0.25 µm df, while the second one was of dimensions 1 m × 0.10 mm ID × 0.10 µm df. A modulation period of 700 ms, with a re-injection period of 80 ms, was used in order to obtain a higher duty cycle (measured to be approx. 0.04). Absolute quantification of the allergens was carried out by using two internal standards, namely 1,4-dibromobenzene and 4,4'-dibromobiphenyl. In terms of limits of quantification the instrumental response was characterized by a wide variability, ranging between 9 ppb and 5.4 ppm for both column sets. A total number of 97 fragrance allergens were identified and quantified in five commercial perfumes.

Towards the determination of an equivalent standard column set between cryogenic and flow-modulated comprehensive two-dimensional gas chromatography.

This preliminary research is focused on the task of defining an equivalent standard column set between cryogenic and flow-modulation comprehensive two-dimensional gas chromatography (GC × GC) combined with mass spectrometry (MS). Cryogenic modulation (CM) was carried out by using a loop-type device, while the flow modulator used was a seven-port wafer chip, equipped with an external accumulation loop. Initially, a common low-polarity + mid-polarity CM GC × GC column set was selected (30 m × 0.25 mm ID × 0.25 µm df + 1.5 m × 0.25 mm ID × 0.25 µm df), a method was developed, and a GC × GC-MS fingerprint was attained (on a sample of bio-oil derived from coconut fibers). After, a column set with the same stationary phases was selected for the flow modulation GC × GC-MS method (20 m × 0.18 mm ID × 0.18 µm df + 5 m × 0.32 mm ID × 0.25 µm df), with the capability to provide a-similar-as-possible separation. A side-by-side measurement of several chromatography parameters (efficiency, peak capacity, resolution, peak widths, retention factors, elution temperatures) was made.

Comprehensive two-dimensional gas chromatography-mass spectrometry using milder electron ionization conditions: A preliminary evaluation.

The present research is based on the use of comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC × GC-QMS), using "milder" electron ionization (EI) conditions. The term milder refers to the use of lower energy EI conditions (e.g., 20 eV), instead of the most common electron energy of 70 eV. The effects of using lower source temperatures were also evaluated. Within such an analytical context, GC × GC-QMS was applied to the analysis of a variety of different molecular-mass compounds with various polarities (sterols, linear alkanes, fatty acid methyl esters, vitamin E, squalene, a linear alcohol, and a group of fifteen pesticides). In general, the results attained indicate that milder EI conditions, and lower source temperatures, generate mass spectra with a higher relative abundance of ions at higher mass-over-charge (m/z) values, comprising the molecular ion, and reduced fragmentation at lower m/z values. The extent to which such a phenomenon occurred was obviously related to the chemical structure of each analyte. Spectral repeatability was also assessed, and was found to be satisfactory. Finally, with regard to analyte signal-to-noise ratios these were generally comparable in applications involving different electron ionization energies.