ABSTRACT
This article demonstrates how to prepare microfabricated columns (microcolumns) for organophosphonate and organosulfur compound separation that rival the performance of commercial capillary columns. Approximately 16,500 theoretical plates were generated with a 3 m long OV-5-coated microcolumn with a 0.25 microm phase thickness using helium as the carrier gas at 20 cm/s. Key to the advance was the development of deactivation procedures appropriate for silicon microcolumns with Pyrex tops. Active sites in a silicon-Pyrex microcolumn cause peak tailing and unwanted adsorption. Experimentally, we found that organosilicon hydride deactivation lowers adsorption activity in microcolumns more than silazane and silane treatments. But without further treatment, the phosphonate peaks continue to tail after the coating process. We found that heat treatment with pinacolyl methylphosphonic acid (PMP) eliminated the phosphonate peak tailing. In contrast, conventional resilylation employing N, O-bis(trimethylsilyl)acetamide, hexamethyldisilazane, and 1-(trimethylsilyl)imidazole does not eliminate peak tailing. Column activity tests show that the PMP treatment also improves the peaks for 2,6-dimethyl aniline, 1-octanol, and 1-decanol implying a decrease in the column's hydrogen bonding sites with the PMP treatment. FT-IR analysis shows that exposure to PMP forms a bond to the stationary phase that deactivates the active sites responsible for organophosphonate peak tailing.
Subject(s)
Chromatography, Gas/instrumentation , Organophosphonates/chemistry , Organophosphonates/isolation & purification , Organophosphorus Compounds/chemistry , Organophosphorus Compounds/isolation & purification , Sulfur Compounds/chemistry , Sulfur Compounds/isolation & purification , Soman/analogs & derivatives , Soman/chemistry , Spectroscopy, Fourier Transform Infrared , Time FactorsABSTRACT
Metal-organic frameworks (MOFs) have high surface areas and tailorable molecular properties so they have the potential of being selective adsorbents for preconcentrators. In this paper, IRMOF1 is tested as an adsorbent for preconcentration for the first time using dimethyl methylphosphonate (DMMP) as a test case. We find that DMMP is selectively adsorbed on IRMOF1 and is released upon heating to 250 degrees C. Concentration gains of more than 5000 are observed for DMMP with a 4-s sampling time. Sorption capacities are 0.95 g of DMMP/g of IRMOF1. By comparison, dodecane shows a preconcentration gain of approximately 5 under similar conditions. These results demonstrate that MOFs can be quite useful in selective preconcentrators.