Applicability of micro packed columns (1/16“ x 1 mm id) packed with DiatoSorb solid support and Porous Polymers configured for use in a dedicated capillary Agilent 6890 and 7890 GC

Barry Burger, Matt Lininger, Mike GossRestek Corporation, Bellefonte, Pa. 814.353.1300

GC Parameters

GC Parameters

DiatoSorb

GC Parameters

GC Parameters

DiatoSorb

GC Parameters

DiatoSorb

GC Parameters DiatoSorb

GC Parameters

GC Parameters

MicroPacked columns have been used for many years, most recently publicized in the late 90’s and continued well into the 21st century to measure planetary atmospheric constituents of Mars and Venus and Titan. Using conventional chromatography, retention times were long and prevented rapid sampling during the probes decent, thus limiting the number of samples. The same issues were anticipated on other missions such as the Galileo, Cassini, Mars Pathfinder, Mars Surveyor, and Rosetta missions. Sampling was just to slow using conventional chromatography and measuring low molecular weight HC’s, nitriles, dinitriles, CO, H2 and CO2 in large amounts of methane, N2 and Ar during decent.

Clearly such investigations require the development of analytical techniques that are both highly sensitive and precise for the identification of compounds that might be present in planetary atmospheres. Even though conventional chromatography was successfully used for in situ analyses of the atmospheric constituents of Mars, Venus and Titan for example, the relatively long period of time required to complete each analysis prevented the collection and analyses of a greater number of samples while the probe descends.

Also of concern was the chromatographic behavior of open tubular (PLOT) capillary columns for the analysis of light gases. While the columns produced good resolution of the test solutes in a relatively short time, they were, however, found unsuitable for gas chromatographic experiments aboard spacecraft due to their low sample loading and poor mechanical strength. A molesieve plot capillary column allows the separation of permanent gases in the presence of hydrocarbons and nitriles, however, its small id compromising sample load ability and also mechanical strength appears too weak to withstand the rigors of launch and space flight.

In the light of the aforementioned issues, micropacked columns are a suitable alternative for capillary columns because of their high sample load ability and low flow-rate.

The analysis of mixtures with component ratios at or near 100:1for instance require large sample volumes to detect minor components. These sample types easily overload a 0.25 mm id, 0.32 mm id or to some extent a 0.53 mm id capillary column. The advantage of a micropacked columns having id’s of 0.75 mm and 1.0 mm are a huge advantage in handling large

sample volumes without skewing peak symmetry. Also of significant importance is the inertness, particle size distribution and surface area relative to the solid support (DiatoSorb). Deactivation of the tubing (Sulfinert) and also a low RMS value of the stainless steel tubing surface is also very important in achieving high column efficiency, fast analysis times, low pressure drop and excellent peak symmetry.

Until recently micropacked columns could only be used in a GC with a dedicated packed column inlet and detector. However, now micropacked columns can quickly be installed in Agilent 6890 and 7890 dedicated capillary GC’s and accommodating both on column injection and split/splitless mode.

The use of diatomaceous earth (DE) solid support media for use in packed and micropacked columns was said to be obsolete back in the early 80’s with the introduction of borosilicate capillary columns and soon followed by the introduction of fused silica capillary columns. However, with numerous and robust packed column methods that were established and continue to perform well through the years, there hasn’t been the justification to revalidate methods utilizing plot or capillary columns. Process analyzer manufacturers, refineries, USP laboratories as well as numerous other private laboratories utilize both packed and micropacked columns. In either case the column performs only as good as the packing inside the tube. To resolve that issue Restek has developed DiatoSorb, a high quality chromatographic grade solid support that Restek has complete control of the manufacturing process. Beginning with the extraction from the earth and progressing through the calcination process, which removes the organics and increases both particle size as well as pore size, controlling a narrow particle size distribution range which translates into increased column efficiency and resolutions, stringent surface area control, which dictates polymer load ability and tightly controlled density to assure column to column retention time reproducibility and lastly, superior inertness. These stringent criteria are all necessary to assure product quality and reproducibility of packed and micropacked columns.

In conclusion, if your analysis requires columns with high sample load ability and must be mechanically robust to survive space travel or use here on earth, the MicroPacked column is the logical choice.

Figure 1. 2 meter x 1/16 x 1mm id MicroPacked column showing in situ analysis of light hydrocarbons by NASA using octyl and octadecyl phases

Figure 2. Maximum component volume on Capillary, packed and MicroPacked columns with various id’s

Figure 3. 2mm id packed column compared to 1mm id MicroPacked demonstrating inertness, efficiency and speed of analysis

Figure 4. 2mm id packed column compared to 1mm id MicroPacked demonstrating inertness in the analysis of steroids.

Figure 5. 2mm id packed column compared to 1mm id MicroPacked demonstrating inertness and speed of Volatile Fatty Acids analysis using a MicroPacked column.

Figure 6. 2mm id packed column compared to 1mm id MicroPacked demonstrating the speed of analysis using ASTM D-2887-18 method for the analysis of C5 to C44 hydrocarbons

Figure 7. 2 meter x 1/16 x 1mm id microPacked for Natural Gas analysis Figure 8. 2 meter x 1/16 x 1mm id for the analysis of Permanent Gases plus C1 and C2 hydrocarbons