Dual-Column\nStopped-Flow GC Method for Quantification\nof Permanent Gases, Water, and Organic Acids from a Single Injection

Analysis of permanent gases and organic acids is typically\nperformed\nwith separate methods due to challenges in achieving sufficient resolution\nwhen using GC columns that are chemically compatible with acids. We\ndeveloped a method to analyze samples containing high levels of water,\norganic acids, oxygenates, and permanent gases (CO, CO<sub>2</sub>, and C<sub>2</sub>H<sub>4</sub>) using a single injection. Resolution\nis achieved using two columns: (1) an HP-FFAP column resistant to\nwater and acids, which separates compounds based on hydrogen-bonding\naffinity, and (2) a GS-CarbonPLOT column capable of separating permanent\ngases. We employed a column isolation methodology using rotary valves\nto allow a heart cut of permanent gases, which coelute off the HP-FFAP\ncolumn, to be trapped on the CarbonPLOT column. After separation and\nanalysis of water, organic acids, and oxygenates via the HP-FFAP column,\nflow is resumed on the CarbonPLOT column, and the permanent gases\nare separated independently. By utilizing the unique combination of\ncolumns and the stopped-flow sequence, we achieved separation and\nquantification of the wide array of compounds occurring during lactic\nacid dehydration to acrylic acid from a single injection without the\nneed for a sophisticated flow modulator or multiple GCs or detector\narrays. This GC apparatus serves as an economical in-line analysis\nmethod for our catalytic studies and is applicable to a wide array\nof samples relevant to biobased fuels and chemicals.