Continuum in MDGC Technology: From Classical Multidimensional to Comprehensive Two-Dimensional Gas Chromatography

Development and Application of a Novel Multiloop Splitter-Based Non-cryogenic Artificial Trapping Modulation System in Comprehensive Two-Dimensional Gas Chromatography

A multiloop splitter-based non-cryogenic artificial trapping (M-SNAT) modulation technique was established, which applied the first (¹D) nonpolar and the second (²D) polar columns, deactivated fused silica (DFS) columns, a microfluidic Deans switch (DS), and splitters located between the ¹D column outlet and the DS. The splitters were connected into multiple loops with a progressively doubled perimeter of the next loop. This enabled a duplex splitting mechanism within each loop consisting of splitting of analyte pulses, the pulse delay, and their combination which led to equally split peaks of the same analytes with the number of split peaks (n_split) equal to 2^m (m = number of loops). This system resulted in local profiles of artificially split-and-trapped analytes prior to their selective transfers onto the ²D column by means of periodic multiple heart-cuts (H/C). The developed SNAT approach can be successful, providing that the ratio of modulation period to sampling time (P_M/t_samp) is equal to n_split. The approach with n_split = 16 was further developed into a single device platform and applied for the modulation of a wide range of compounds in waste tire pyrolysis samples with the RSD of ≤0.01 and <10% for the one-dimensional modulated peak times and peak areas, respectively (n = 50). The method enabled an artificial modulation mechanism without cryogen consumption and enhanced the ²D peak capacity (²n_c) and ²D separation by use of a longer ²D column.

A multi-location peak parking approach for calculation of second dimensional retention indices for improved volatile compound identification with cryogen-free comprehensive heart-cut two-dimensional gas chromatography

Comprehensive heart-cut multidimensional gas chromatography (CH/C MDGC) without a cryogenic trapping device was developed with an established approach for calculation of first and second dimensional retention indices (¹I and ²I) for improved compound identification. A first dimensional (¹D) DB-1MS column (60 m) and a second dimensional (²D) DB-WAX column (60 m) were applied with a Deans switch (DS) using a constant H/C window of 0.2 min and a periodic multiple heartcut strategy comprising 225H/C throughout the CH/C. ¹I was calculated based on comparison of the middle of the heartcut time with the alkane retention times on the ¹D column. A multi-location peak parking approach using sixteen sets of automated injections of alkane references was also established with the least square curve fitting method for construction of the alkane isovolatility curves which were applied for ²I calculation. The untargeted compound analysis of a perfume sample was then performed according to comparison with the libraries of mass spectra, ¹I and ²I. The CH/C MDGC system with a 25 h analysis time showed a peak capacity (n_c) of 9198 and 128 separated peaks with 71 compounds successfully identified according to MS, ¹I and ²I library match under the established error approximation criteria. Furthermore, relationship between the analysis time and number of separated peaks was proposed based on the set of 84 identifiable compounds. With the compensation of lower separation performance and greater I errors, the analysis time could be reduced by applying a 2.5 min H/C window with a total analysis time of 2 h and n_c of 1134.

Strategies towards simpler configuration and higher peak capacity with comprehensive multidimensional gas chromatography

Experimental and data analysis approaches in multidimensional gas chromatography (MDGC) comprising comprehensive multiple heart-cut (H/C) and comprehensive two dimensional GC (GC × GC) were developed with an example application illustrated for analysis of a technical glycol precursor sample. The GC × GC system employed a long ¹D (30 m) and a short ²D (5 m) column with a flow modulator and a Deans switch (DS) as a splitter; meanwhile. The H/C system was applied solely as a DS located between long ¹D (30 m) and ²D (60 m) columns without use of cryogenic trapping devices. The effects of injection time and ²D column flow in GC × GC and the impacts of H/C window and number of injections (total analysis time) in H/C analysis were investigated. The analysis performance for each condition was evaluated according to peak capacity and number of separated compounds. The continuum between the two techniques was then established via the relationship between analysis time and analysis performance. The separation performances were improved with longer analysis time so that the suitable condition was selected within this compromise. Under the selected conditions, volatile compounds in the technical glycol precursor sample were identified according to the match between the experimental MS spectra and first dimensional retention indices (¹I) with that from the NIST2014 database and literature. An hour analysis with GC × GC resulted in a total peak capacity of 798, number of separated peaks of 61 and average MS match score of 887 ± 35; meanwhile, the corresponding numbers were improved to be 9198, 107 and 898 ± 24, respectively, with the 25 h comprehensive H/C analysis.

Experimental and data analysis approaches in MDGC comprising comprehensive H/C and GC × GC were developed with an example application illustrated for analysis of a technical glycol precursor sample.

Cryogen-free comprehensive heartcut multidimensional gas chromatography using a Deans switch for improved analysis of petrochemical products derived from palmitic acid oxidation

Comprehensive heartcut multidimensional gas chromatography was applied with example application for analysis of a sample obtained from palmitic acid oxidation in a Rancimat instrument. The system utilized a single Deans switch (DS) located between first dimensional semi-standard nonpolar (30 m) and second dimensional polar (60 m) columns. A cyclic multiple heartcut strategy consisting of 150 heartcuts with a 0.2 min window was applied offering comprehensive analysis and injection of a narrow band of compounds onto the second column without use of cryogenic trapping devices. Untargeted compound analysis of the sample prepared by solid phase micro-extraction was performed based on match between the experimental MS spectra and first dimensional retention indices with that from the NIST library. The sample contained the major compounds of 2-octanone, 1-methylcyclohexanol, 2,3,6-trimethylphenol, 3-phenylpropanol and 2-nonanone. This approach was then evaluated based on peak capacity and the number of identified compounds. Compared with one dimensional gas chromatography providing a total peak capacity of 172 and 43 identified compounds, the analysis performance was much more improved with a capacity of 5840 and 235 identified compounds by using comprehensive heartcut multidimensional gas chromatography with the total analysis time of 15.3 h. By comparison within the same set of identified compounds, the one dimensional and multidimensional approaches provided the MS match scores of 769 ± 81 and 836 ± 88, respectively. In addition, the nonlinear relationship between the analysis time and number of identifiable peaks was calculated according to the set of 235 compounds. This revealed that the analysis time could be shortened with the compensation of lower separation performance, where application of a 2.5 min heartcut window with the total analysis time of 1.2 h could result in the total peak capacity of 390 with 150 identifiable compounds.