Chris English

Practical GC in gas chromatography: learn how PEG column bleed affects MS sensitivity, and when polar analytes still quantify reliably.

Gas chromatography (GC) liners are offered in dozens of different configurations and internal diameters. The liner is designed with baffles or glass wool to best vaporize and mix the sample prior to transferring it to the head of the analytical column. Split liners have considerably more flow and are designed to handle high split ratios. For example, some liners have a glass dimple at the bottom to allow for higher flow rates (low pressure drop). Some split liners have an outer diameter of 6.3 mm while splitless liners have an outer diameter of 6.5 mm. It has been reported that these liners have been used interchangeably, which begs the question: Does the outer diameter matter?

Injecting too little into a liner in splitless mode can cause band broadening and increased activity. This article examines these effects in split mode.

Column insertion distance is critical to good chromatography. What happens if the column is installed too low in the injection port? Is insertion distance more important when performing split injection or splitless injection? Does the position of the column in the injection port impact reproducibility?

This study replicates reports where the use of wool in the liner has resulted in poor reproducibility and low response for semi-volatile compounds.

Splitless modes of operation using an optimized pulse injection are described.

The impact of contamination on each part of the inlet is examined.

How physical and chemical characteristics are related to dirt in the GC system.

Small leaks may compromise column lifetime, increase maintenance, cause retention time shifts, and decrease sensitivity at elevated temperatures, but do they matter?

In this instalment of “Practical GC”, air leaks in a gas chromatography (GC) system and their impact on GC stationary phases are examined.

Identifying the source of siloxanes makes troubleshooting that much easier.

Since capacity is the maximum amount of sample on column before peak distortion occurs and is directly proportional to column dimensions, this instalment of “Practical GC” will expand our continuing evaluation to include narrow-bore and microbore columns with 0.25 mm, 0.18 mm, and 0.10 mm column internal diameters.

In the latest instalment of “Practical GC”, Chris English takes an empirical approach and examines concentrations for a wide range of compound polarities on several stationary phases, and determines overload as measured by symmetry.

Ethylene glycol is a particularly difficult compound to analyze because it is not easily extracted from water. Many environmental samples originate from water runoff at airports, where ethylene glycol is used as a de‑icing agent for airplanes during winter months. Hydraulic fracturing is a technique where pressurized fluid and sand or other solids (proppant) are used in gas drilling to allow gas extraction. Glycols are a common ingredient in most hydraulic fracturing fluid and play a key role in preventing emulsifications and stabilizing the solutions. The direct aqueous injection of ethylene glycol is challenging because it can be difficult to attain reproducibility and good peak shape. The large expansion volume of water can cause backflash, carryover can cause inconsistent results, and excess water can extinguish the flame ionization detection (FID) flame. This article describes a robust approach to analyze glycols in aqueous samples, which reduces downtime and maintains sensitivity.

Concurrent solvent recondensation–large volume splitless injection (CSR-LVSI), an alternative to programmed temperature vaporization (PTV), typically requires a special GC inlet. The technique described here uses an unmodified split/splitless inlet with CSR-LVSI to lower detection limits for the analysis of 1,4-dioxane in drinking water.