Fast, high peak capacity separations in comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry

Second-Dimension Temperature Programming System for Comprehensive Two-Dimensional Gas Chromatography. Part 1: Precise Temperature Control Based on Column Electrical Resistance

A second-dimension temperature programming system (²DTPS) for comprehensive two-dimensional gas chromatography (GC × GC) is introduced, and its performance is characterized. In the system, a commercial stainless-steel capillary column was used for the separation, as a heating element, and as a temperature sensor. The second dimension (²D) column was resistively heated and controlled using an Arduino Uno R3 microcontroller. Temperature measurement was accomplished by measuring the overall ²D column's electrical resistance. A diesel sample was used to compare the ²D peak capacity (²n_c) and resolution (²R_s), while a perfume sample was used to compare the reproducibility of the system for within-day (n = 5) and day-to-day (n = 5) results. The ²n_c improved by 52% with the ²DTPS compared to the secondary oven. The GC × GC system utilizing the ²DTPS had an average within-day and day-to-day relative standard deviation (RSD) of 0.02 and 0.12% for the ¹D retention time (¹t_R), 0.56 and 0.58% for the ²D retention time (²t_R), and 1.18 and 1.53% for the peak area, respectively.

Cryogenic trapping as a versatile approach for sample handling, enrichment and multidimensional analysis in gas chromatography

Cryogenic methods - those that employ cryogenic fluids/gases but also other approaches to generate reduced temperature - are versatile, functional and relatively easily implemented as part of a total gas chromatographic method. The general utility of a cold region is almost invariably as a trapping or focussing step, to collect analyte into a sharp zone. The success in effectively trapping analyte depends on analyte volatility and the temperature of the cold region. Analytes collection into a sorbent phase supported by cryotrapping usually provide a greater capacity trapping for the sorption step. Stripping analyte from a sample into a cryogenic trap, with subsequent introduction to GC as in a purge-and-trap method, sample introduction into an injector with incorporation of a cooling zone, manipulation and management of chromatographic bands during chromatography elution such as employed in multidimensional gas chromatography, and focussing analyte just prior to the detector, all have the same goal of concentrating the band, reducing its dispersion, and maximising response. This review summarises various approaches that demonstrate how cryogenic methods have been incorporated into gas chromatographic analysis.

Development of an improved method to estimate the days of continuous drug ingestion, based on the micro-segmental hair analysis

To prove drug-related crimes, it is important to estimate the date on which a specific drug was ingested. Previously, we developed a method, "micro-segmental hair analysis," to estimate the day of ingestion of a single-dose drug by segmenting a hair strand into 0.4-mm segments, which correspond to daily hair growth. In this study, the method was improved to estimate the days of continuous drug ingestion. The subjects ingested four hay-fever medicines (fexofenadine, epinastine, cetirizine, and loratadine) continuously (1-18 days) and chlorpheniramine as a single dose at intervals of several weeks as an internal temporal marker (ITM). The hair strands of the subjects were collected and subjected to a micro-segmental analysis. The distribution curves of each hay-fever medicine in a hair strand had broad peaks reflecting the number of days of drug ingestion. The positions on the curves corresponding to the first and final ingestion days of hay-fever medicines were identified using the ITM. The positions were near the hair segments on both ends of full width at half maximum (W₂ ) of the broad peak. When the first and final days of continuous ingestion were estimated using W₂ , independent of peak shape, the absolute average error from the actual ingestion days was approximately 2 days. Overall, we established a method to estimate the days of both single-dose and continuous drug ingestions. Furthermore, the method would be useful to investigate drug ingestion history in various scenes such as drug-related crimes and therapeutic drug monitoring.

Implications of phase ratio for maximizing peak capacity in comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry

The relationship between the phase ratio, β, of the primary (¹D) and secondary (²D) separation dimensions of comprehensive two-dimensional (2D) gas chromatography (GC×GC) separations, and the implications of β on realization of maximal 2D peak capacity, n_c,2D, are examined. A GC×GC chromatographic system with time-of-flight mass spectrometry, TOFMS, was otherwise held constant for the separation of a multi-component test mixture spanning a range of chemical functionalities, while only the β of the two analytical columns were changed, ¹β for ¹D and ²β for ²D. Six column sets were studied using common, commercially available β values. The β ratio, β_R=¹β/²β, is defined as a quantitative metric to facilitate this study. It is demonstrated that β_R plays a key role in maximizing n_c,2D. Overall, β_R substantially affected n_c,2D by influencing retention factors on the ²D column, ²k, and thereby changing the modulation period, P_M, necessary for proper ²D column separations. The necessary changes to P_M modify the modulation ratio, M_R, which affects the ¹D column peak widths and ¹n_c due to the impact of undersampling. Through changes to ¹β, the range of ²k can be controlled, with subsequent effects to both ²n_c and ¹n_c. These effects were opposite in direction, such that improvements to ²n_c may result in declines in ¹n_c. It is observed that due to the pseudo-isothermal nature of the ²D separation, there are diminishing returns to extending the ²n_c at the cost of ¹n_c. In this particular study, column set 3 (¹D: 20m length, 250μm i.d., 0.25μm film; ²D: 2m, 180μm i.d., 0.2μm film; β_R=1.11) with a P_M of 3s provided the highest theoretical n_c,2D of ∼8200, though this was at a relatively low M_R of ∼1.8. Column set 2 (¹D: 20m length, 250μm i.d., 0.5μm film; ²D: 2m, 180μm i.d., 0.2μm film; β_R=0.56) with a P_M of 1.5s provided a high theoretical n_c,2D of ∼5800, at a much higher M_R of ∼3.7. Though column set 2 had a lesser total peak capacity than column set 3, its higher M_R suggests that by improving the ¹D column efficiency (i.e., narrowing the ¹D column peak widths) to improve ¹n_c, can result in an increased theoretical n_c,2D.

High-Speed, Comprehensive, Two Dimensional Separations of Peptides and Small Molecule Biological Amines Using Capillary Electrophoresis Coupled with Micro Free Flow Electrophoresis

Two-dimensional (2D) separations are able to generate significantly higher peak capacities than their one-dimensional counterparts. Unfortunately, current hyphenated 2D separations are limited by the speed of the second dimension separation and the consequent loss of peak capacity due to under sampling of peaks as they elute from the first dimension separation. Continuous micro free flow electrophoresis (μFFE) separations eliminate under sampling as a limitation when incorporated as the second dimension of a 2D separation. In the current manuscript we describe the first coupling of capillary electrophoresis (CE) with μFFE to perform 2D CE × μFFE separations. The CE separation capillary was directly inserted into the μFFE separation channel using an edge on interface. Analyte peaks streamed directly into the μFFE separation channel as they migrated off the CE capillary. No complicated injection, valving, or voltage changes were necessary to couple the two separation modes. 2D CE × μFFE generated an ideal peak capacity of 2 592 in a 9 min separation of fluorescently labeled peptides (7.6 min separation window, 342 peaks/min). Data points were recorded every 250-500 ms (>8 data points/peak), effectively eliminating under sampling as a source of band broadening. CE × μFFE generated an ideal peak capacity of 1885 in a 2.7 min separation of fluorescently labeled small molecule bioamines (1.8 min separation window, 1053 peaks/min). Peaks in the 2D CE × μFFE separation of peptides covered 30% of the available separation space, resulting in a corrected peak capacity of 778 (102 peaks/min). The fractional coverage of the 2D CE × μFFE separation of small molecule bioamines was 20%, resulting in a corrected peak capacity of 377 (209 peaks/min).

Fully Automated Portable Comprehensive 2-Dimensional Gas Chromatography Device

We developed a fully automated portable 2-dimensional (2-D) gas chromatography (GC x GC) device, which had a dimension of 60 cm × 50 cm × 10 cm and weight less than 5 kg. The device incorporated a micropreconcentrator/injector, commercial columns, micro-Deans switches, microthermal injectors, microphotoionization detectors, data acquisition cards, and power supplies, as well as computer control and user interface. It employed multiple channels (4 channels) in the second dimension (²D) to increase the ²D separation time (up to 32 s) and hence ²D peak capacity. In addition, a nondestructive flow-through vapor detector was installed at the end of the ¹D column to monitor the eluent from ¹D and assist in reconstructing ¹D elution peaks. With the information obtained jointly from the ¹D and ²D detectors, ¹D elution peaks could be reconstructed with significantly improved ¹D resolution. In this Article, we first discuss the details of the system operating principle and the algorithm to reconstruct ¹D elution peaks, followed by the description and characterization of each component. Finally, 2-D separation of 50 analytes, including alkane (C₆-C₁₂), alkene, alcohol, aldehyde, ketone, cycloalkane, and aromatic hydrocarbon, in 14 min is demonstrated, showing the peak capacity of 430-530 and the peak capacity production of 40-80/min.

Methods of discovery-based and targeted metabolite analysis by comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry detection

The investigation of naturally volatile and derivatized metabolites in biological tissues by comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC-TOFMS) can provide highly complex and information-rich data for comprehensive metabolomics analysis. The addition of the second separation dimension with GC × GC provides additional chemical selectivity, and the fast scanning time of TOFMS offers benefits in chemical selectivity and overall peak capacity compared to traditional one-dimensional (1D) GC. Furthermore, methods of derivatization to facilitate volatility and thermal stability, the most prominent being the silylation of organic compounds, have extended the use of GC as an important metabolomics tool. The highly information-rich data from GC × GC-TOFMS benefits from sophisticated comprehensive targeted and nontargeted algorithmic software methods. Herein, we detail a robust derivatization and instrumental method for metabolomics analysis and provide a brief overview of possible methods for data analysis.