Over the years we have worked with many customers on their packed column gas analysis troubleshooting requests. \u00a0In some cases, customers were having coelution issues with several of their gases and were hoping that Restek could help. \u00a0For many of these requests, a different packing was all that was needed to achieve the required separations. \u00a0In other cases, substituting a similar but more efficient column, such as using a PLOT (Porous Layer Open Tubular) column in place of a less-efficient packed column, resolved the issue. \u00a0However, achieving certain separations was not as simple as switching GC columns and may have required multiple columns connected to a column switching device.<\/p>\n\n\n\n
Below are several of the more common coeluting gases customers ask us about. Hopefully after you have reviewed this post, you will not only be aware of common gas coelutions when using packed columns, but also how you may wish to proceed if you are experiencing these coelutions.<\/p>\n\n\n\n
One of the more popular requests we receive is a column recommendation for separating argon and oxygen. \u00a0A molecular sieve 5A is a popular choice of packing because these two gases will very likely coelute using all other packings. \u00a0Even though this separation is possible using a 5A packed column, often a very long column and\/or cryo-cooling is needed. \u00a0That is why we recommend a 30-meter Rt-MSieve 5A PLOT column for this difficult separation instead of a packed column, as mentioned in the link below. \u00a0The additional theoretical plates you will obtain by using a PLOT column instead of a packed column will be noticeable (as long as you do not<\/span> overload the PLOT column).<\/p>\n\n\n\n Another difficult separation is helium, neon, and hydrogen. \u00a0Once again, the molecular sieve 5A is often the go-to packing. \u00a0If you are not having success separating these compounds using a packed column, your time and energy may be better spent using a 30-meter Rt-MSieve 5A PLOT column. This separation may also be possible if using a PLOT or micropacked carbon<\/span> molecular sieve column, as long as the column is not overloaded and the instrument is optimized. <\/p>\n\n\n\n You may be asking yourself why nitrogen\/krypton and methane\/krypton are listed in this blog post. The reason is because many gas analysis customers who use molecular sieve 5A (and 13X) packed columns have noticed that separating nitrogen and krypton can be difficult. Similarly, when using carbon<\/span> molecular sieve packed columns (like the ShinCarbon), analysts are often surprised that separating methane and krypton can be difficult. Also note, it is not unusual to see an elution order change between these compound pairs when the starting GC oven temperature and\/or carrier gas flow rate are changed.<\/p>\n\n\n\n The good news, carbon<\/span> molecular sieve columns (like the ShinCarbon) will easily separate nitrogen from krypton and molecular sieve 5A and 13X columns will easily separate methane from krypton.<\/p>\n\n\n\n This section will discuss challenging gas separations using Hayesep and Porapak porous polymer packed columns. The Hayesep packings reviewed for this post include A, B, C, D, DB, N, Q, S and T. The Porapak packings include N, P, Q, R, S and T.<\/p>\n\n\n\n Please note that each of these packings will often show poor performance separating the lightest gases. For example, unless the columns are very long, separating several of the primary components of air (nitrogen\/oxygen\/argon\/carbon monoxide) is very difficult. In addition, depending upon the dimensions of the column and the concentration of the air in the standard(s)\/sample(s), methane (and possibly carbon dioxide) may coelute with a high concentration air peak, even when using a porous polymer PLOT column.<\/p>\n\n\n\n Listed below are challenging hydrocarbon gas separations for certain Hayesep and Porapak packings. Your column may be able to separate these gases without issue, or if there are coelutions, separation may be possible with optimization of your analytical instrument conditions (temperatures and\/or carrier gas flow rate). Or, depending upon compound concentrations and your specific instrument, you may need to switch to an alternative column to achieve separation while keeping analysis (run) times reasonably short and\/or to avoid the need for cryo-cooling. Because packed column separation performance is not always predicable or consistent (packings and their mesh size range may vary slightly from batch to batch), do not be surprised if the compound elution order (or coelutions) on your instrument differs from those shown in published documentation.<\/p>\n\n\n\n If a compound peak seems to be missing, do not assume column\/instrument activity is the issue, especially if the compound is an inert compound like a straight-chain hydrocarbon. Instead, consider that the missing compound may be coeluting with another peak.<\/p>\n\n\n\n Finally, to obtain the most consistent results from column to column, always<\/span> measure the carrier gas column flow rate exiting the packed column. \u00a0Do not<\/span> simply set the head pressure and expect reproducibility. \u00a0Each packed column is different. \u00a0You must<\/span> adjust the head pressure for each column, even for those with the same catalog number, to obtain the proper carrier gas flow. \u00a0<\/p>\n\n\n\n The information below will summarize much of the preceding information in addition to showing the most likely elution order of common gases for several molecular sieve and porous polymer packings. \u00a0<\/p>\n\n\n\n Thank you for your time. I hope you have found this interesting and useful.<\/p>\n\n\n\n <\/p>\n\n\n\n Molecular Sieve 5A\/13X: Oxygen\/Argon and Helium\/Neon\/Hydrogen<\/p>\n\n\n\n Carbon Molecular Sieve (ShinCarbon): Oxygen\/Argon and Helium\/Neon\/Hydrogen<\/p>\n\n\n\n All porous polymers: Helium\/Neon\/Hydrogen and Nitrogen\/Oxygen\/Argon\/Carbon Monoxide<\/p>\n\n\n\n Hayesep A: Propylene\/Propane and Iso-butane\/n-Butane<\/p>\n\n\n\n Hayesep B: Ethylene\/Ethane<\/p>\n\n\n\n Hayesep C: Ethane\/Acetylene<\/p>\n\n\n\n Hayesep N: Propane\/Propylene and Iso-butane\/n-Butane<\/p>\n\n\n\n Porapak N: Propane\/Propylene<\/p>\n\n\n\n Porapak P: Acetylene\/Ethane and Propane\/Propylene<\/p>\n\n\n\n Hayesep Q: Ethylene\/Acetylene<\/p>\n\n\n\n Porapak Q: Ethylene\/Acetylene<\/p>\n\n\n\n Porapak R: Acetylene\/Ethane<\/p>\n\n\n\n Hayesep S: Iso-butane\/n-Butane<\/p>\n\n\n\n Hayesep T: Propane\/Propylene<\/p>\n\n\n\n Porapak T: Propane\/Propylene<\/p>\n\n\n\n <\/p>\n\n\n\n Molecular Sieve 5A\/13X: Nitrogen\/Krypton<\/p>\n\n\n\n Carbon Molecular Sieve (ShinCarbon): Oxygen\/Nitrogen and Methane\/Krypton<\/p>\n\n\n\n Hayesep B: Ethylene\/Ethane\/Acetylene<\/p>\n\n\n\n Hayesep C: Ethylene\/Ethane\/Acetylene and Propylene\/Propane<\/p>\n\n\n\n Hayesep D: Acetylene\/Ethylene<\/p>\n\n\n\n Hayesep DB: Acetylene\/Ethylene<\/p>\n\n\n\n Troubleshooting coeluting compounds during packed column gas analyses can be a difficult task. In this post, we look at the more common coeluting gas issues you may face and recommend steps to overcome them.<\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_kad_blocks_custom_css":"","_kad_blocks_head_custom_js":"","_kad_blocks_body_custom_js":"","_kad_blocks_footer_custom_js":"","_kadence_starter_templates_imported_post":false,"_kad_post_transparent":"","_kad_post_title":"","_kad_post_layout":"","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false,"footnotes":""},"categories":[792],"tags":[],"industries-application":[],"post-badge":[],"resource-type":[],"product-library":[],"resource-technique":[],"hf_cat_post":[623],"ppma_author":[582],"class_list":["post-76412","post","type-post","status-publish","format-standard","hentry","category-blogs-de"],"acf":[],"taxonomy_info":{"category":[{"value":792,"label":"Blogs"}]},"featured_image_src_large":false,"author_info":{"display_name":"Audrey Crater","author_link":"https:\/\/discover.restek.com\/fr\/author\/audrey-craterrestek-com\/"},"comment_info":0,"category_info":[{"term_id":792,"name":"Blogs","slug":"blogs-de","term_group":0,"term_taxonomy_id":792,"taxonomy":"category","description":"","parent":0,"count":442,"filter":"raw","cat_ID":792,"category_count":442,"category_description":"","cat_name":"Blogs","category_nicename":"blogs-de","category_parent":0}],"tag_info":false,"authors":[{"term_id":582,"user_id":0,"is_guest":1,"slug":"alan-sensue","display_name":"Alan Sensue","avatar_url":"https:\/\/secure.gravatar.com\/avatar\/?s=96&d=mm&r=g","0":null,"1":"","2":"","3":"","4":"","5":"","6":"","7":"","8":""}],"_links":{"self":[{"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/posts\/76412","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/comments?post=76412"}],"version-history":[{"count":5,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/posts\/76412\/revisions"}],"predecessor-version":[{"id":89758,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/posts\/76412\/revisions\/89758"}],"wp:attachment":[{"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/media?parent=76412"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/categories?post=76412"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/tags?post=76412"},{"taxonomy":"industries-application","embeddable":true,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/industries-application?post=76412"},{"taxonomy":"post-badge","embeddable":true,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/post-badge?post=76412"},{"taxonomy":"resource-type","embeddable":true,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/resource-type?post=76412"},{"taxonomy":"product-library","embeddable":true,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/product-library?post=76412"},{"taxonomy":"resource-technique","embeddable":true,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/resource-technique?post=76412"},{"taxonomy":"hf_cat_post","embeddable":true,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/hf_cat_post?post=76412"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/discover.restek.com\/fr\/wp-json\/wp\/v2\/ppma_author?post=76412"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}Helium\/Neon\/Hydrogen<\/h2>\n\n\n\n
Nitrogen\/Krypton and Methane\/Krypton<\/h2>\n\n\n\n
Permanent and Hydrocarbon Gases<\/h2>\n\n\n\n
Summary<\/h2>\n\n\n\n
Very likely coelutions when using packed columns<\/h3>\n\n\n\n
Somewhat likely coelutions when using packed columns<\/h3>\n\n\n\n