Molecular Sieve 5A and 13X Packed GC Columns for Permanent Gas Separations

Molecular sieves, synthetic forms of Zeolite packing, have been used since the 1950s for separating light gases (oxygen, nitrogen, methane, and carbon monoxide) and inert gases (helium, argon, neon, krypton, and xenon), yet there have been few changes or improvements in their basic composition or performance. Restek has designed the two most common molecular sieves—5A and 13X, as high-performance packings that feature batch-to-batch inertness and consistency. These packings are used in a wide range of packed and PLOT column analyses.

Molecular sieve 5A and 13X packings differ in pore size and composition, causing differences in retention and selectivity for many gases. The 5A packing provides greater retention, which improves the separation of argon, oxygen, and nitrogen, and is a better choice for analyzing the trace impurities in inert gases typically used in the semiconductor industry. The 13X packing often is preferred for analysis of carbon monoxide, particularly at trace concentrations, because lower retention results in sharper chromatographic peaks and improved detection limits.

Molecular Sieve 5A or 13X Packing in Silcosteel Treated Tubing Exhibits Excellent Chromatography for Permanent Gas Analysis

Figure 1 compares a gas mixture analyzed using a 1-meter, high-performance molecular sieve 5A column and a 2-meter, high-performance molecular sieve 13X column. Notice the excellent peak symmetry for carbon monoxide on each column, indicating that the packing and column tubing are extremely inert. Combining high-quality molecular sieves with Silcosteel-treated tubing produces a packed column optimized for trace analysis of the difficult components oxygen and carbon monoxide.

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