{"id":73080,"date":"2020-06-08T18:43:00","date_gmt":"2020-06-08T18:43:00","guid":{"rendered":"https:\/\/discover.restek.com\/?p=73080"},"modified":"2025-12-11T14:13:41","modified_gmt":"2025-12-11T14:13:41","slug":"optimizing-splitless-injections-splitless-purge-valve-time","status":"publish","type":"post","link":"https:\/\/discover.restek.com\/de\/blogs-de\/gnbl5440\/optimizing-splitless-injections-splitless-purge-valve-time","title":{"rendered":"Optimizing Splitless Injections: Splitless Purge Valve Time"},"content":{"rendered":"\n<p>In my&nbsp;previous blog, I discussed optimizing inlet temperature for splitless injections.&nbsp; Today I would like to discuss another critical parameter for splitless injections: splitless purge valve time.&nbsp; The key feature of a splitless injection is that all the carrier gas flow is directed to the column and the splitless valve is closed during injection.&nbsp; This allows for maximum recovery of the injected sample, making splitless injections ideal for trace level analyses.<\/p>\n\n\n\n<p>The split valve remains closed during and after sample injection for a predetermined amount of time to allow for full volatilization and transfer of the analytes to the column.&nbsp; While this time is essential for achieving the best recoveries of trace analytes, keep in mind you are also injecting a very large amount of solvent in the case of liquid injections.&nbsp; Because of this, at some point, you must open the split vent to rid the inlet of excess solvent vapor.&nbsp; Without doing this, the large solvent peak can potentially interfere with your compounds of interest.<\/p>\n\n\n\n<p>So just as in selecting an ideal inlet temperature, selecting an ideal splitless hold time can also involve compromise.&nbsp; You must select a hold time that is long enough to ensure complete vaporization and transfer of your analytes to the column, but not so long as to introduce excess solvent into your column, which can result in excessive tailing of the solvent peak, leading to an elevated baseline and potential interference with analytes.&nbsp; The figure below provides an example showing peak areas over a wide molecular weight range of hydrocarbons vs splitless hold time.&nbsp; Note that the liner is single taper with wool and the carrier gas flow is 1.5 mL\/min.&nbsp; As a general rule, you should allow the liner to be swept 1.5-2 full volumes with carrier gas, prior to opening the split vent.&nbsp; Notice that after a certain amount of time, gains start to become insignificant.&nbsp; Eventually C8 is lost in the solvent and cannot be detected.<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img loading=\"lazy\" decoding=\"async\" width=\"1024\" height=\"699\" src=\"https:\/\/discover.restek.com\/wp-content\/uploads\/blog-optimizing-splitless-injections-splitless-purge-valve-time-01-1024x699.png\" alt=\"\" class=\"wp-image-73086\" title=\"-\" srcset=\"https:\/\/discover.restek.com\/wp-content\/uploads\/blog-optimizing-splitless-injections-splitless-purge-valve-time-01-1024x699.png 1024w, https:\/\/discover.restek.com\/wp-content\/uploads\/blog-optimizing-splitless-injections-splitless-purge-valve-time-01-300x205.png 300w, https:\/\/discover.restek.com\/wp-content\/uploads\/blog-optimizing-splitless-injections-splitless-purge-valve-time-01-768x524.png 768w, https:\/\/discover.restek.com\/wp-content\/uploads\/blog-optimizing-splitless-injections-splitless-purge-valve-time-01.png 1274w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p><em>Figure 1<\/em>: Experiment to test response of early, middle and late eluting hydrocarbons, as well as solvent peak area, vs splitless valve time. The \u201cideal\u201d split time is between 60 and 75 seconds, which correlates to a 1.5 to 2x sweep of the inlet liner. The solvent peak eventually interferes with C8, completely masking it. Column flow was set at 1.5 mL\/min and liner was a single taper with wool.<\/p>\n\n\n\n<p>To make your life easy, Restek has a free tool that calculates this ideal range for you: The&nbsp;EZGC Method Translator and Flow Calculator.&nbsp; Check out the short webinar below to see how to use it:<\/p>\n\n\n\n<figure class=\"wp-block-embed is-type-video is-provider-youtube wp-block-embed-youtube wp-embed-aspect-16-9 wp-has-aspect-ratio\"><div class=\"wp-block-embed__wrapper\">\n<iframe loading=\"lazy\" title=\"Calculating Splitless Hold Time Using Restek\u2019s EZGC Method\" width=\"720\" height=\"405\" src=\"https:\/\/www.youtube.com\/embed\/9uqeEklQrjU?feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe>\n<\/div><\/figure>\n\n\n\n<p>Here are a few key points from the video to remember when filling in the EZGC Flow Calculator to calculate splitless valve time:<\/p>\n\n\n\n<ol class=\"wp-block-list\">\n<li>For \u201cTemperature\u201d, under the Column section, enter your initial oven temperature.<\/li>\n\n\n\n<li>In the \u201cControl Parameters\u201d section, only enter one of the values, based upon your control mode. For instance, if you are using constant flow, fill in your column flow, whereas if you are using constant pressure, only fill in pressure.\u00a0 The other values will be automatically calculated.\u00a0 Be sure to select the correct outlet pressure.\u00a0 For an MS detector select \u201cvacuum\u201d and for detectors such as FID or TCD, select \u201catmospheric\u201d.<\/li>\n\n\n\n<li>In the \u201cInlet\u201d section, you must enter inlet temperature and liner volume. An exact liner volume is not necessary, as having something relatively close should result in an acceptable recommendation.\u00a0 The simplest way to obtain an estimate is to assume that your liner is a cylinder and apply the following formula:\u00a0<em>V<\/em>\u00a0=\u00a0<em>\u03c0 r<sup>2\u00a0<\/sup>h<\/em>\u00a0, where\u00a0<em>V<\/em>\u00a0is volume,\u00a0<em>r<\/em>\u00a0is the radius (1\/2 of the internal diameter), and\u00a0<em>h<\/em>\u00a0is the height (length) of the liner.\u00a0 Some common liner configuration volumes are listed in\u00a0<em>Figure 2.\u00a0<\/em>\u00a0 Note that this table is in \u00b5L, whereas the\u00a0<em>Flow Calculator<\/em>\u00a0uses mL.\u00a0 Simply place a decimal point before the \u00b5L value to convert to mL (i.e. 900 \u00b5L = 0.900 mL). \u00a0Use the values listed under \u201cPhysical\u201d volume.<\/li>\n\n\n\n<li>Note that after entering a value into a field, you must click outside of the field or into another field in order for the calculation to update.<\/li>\n<\/ol>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"482\" height=\"259\" src=\"https:\/\/discover.restek.com\/wp-content\/uploads\/blog-optimizing-splitless-injections-splitless-purge-valve-time-02.png\" alt=\"\" class=\"wp-image-73093\" title=\"-\" srcset=\"https:\/\/discover.restek.com\/wp-content\/uploads\/blog-optimizing-splitless-injections-splitless-purge-valve-time-02.png 482w, https:\/\/discover.restek.com\/wp-content\/uploads\/blog-optimizing-splitless-injections-splitless-purge-valve-time-02-300x161.png 300w\" sizes=\"auto, (max-width: 482px) 100vw, 482px\" \/><\/figure>\n\n\n\n<p><em>Figure 2<\/em>: Liner volumes for some common configurations. Use the value under &#8220;Physical&#8221; for calculating splitless valve time.<\/p>\n\n\n\n<p>You now have an understanding of why optimizing splitless purge valve time is important.&nbsp; Using Restek\u2019s Flow Calculator makes this an easy task.&nbsp; If you ever want to verify that you are in fact using the best hold time for your analysis, you can easily set up an experiment like the one shown in&nbsp;<em>Figure 1<\/em>, where you plot peak areas vs hold time.<\/p>\n\n\n\n<p>For the next installment of this blog series I am going to discuss initial oven temperature.&nbsp; Hope you enjoy!<\/p>\n\n\n\n<div style=\"height:100px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n","protected":false},"excerpt":{"rendered":"<p>In my&nbsp;previous blog, I discussed optimizing inlet temperature for splitless injections.&nbsp; Today I would like to discuss another critical parameter for splitless injections: splitless purge valve time.&nbsp; The key feature of a splitless injection is that all the carrier gas flow is directed to the column and the splitless valve is closed during injection.&nbsp; This&#8230;<\/p>\n","protected":false},"author":5,"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":[2324,2325],"ppma_author":[598],"class_list":["post-73080","post","type-post","status-publish","format-standard","hentry","category-blogs-de","resource-technique-gaschromatographie-gc","resource-technique-injektionstechniken"],"acf":[],"taxonomy_info":{"category":[{"value":792,"label":"Blogs"}],"resource-technique":[{"value":2324,"label":"Gaschromatographie (GC)"},{"value":2325,"label":"Injektionstechniken"}]},"featured_image_src_large":false,"author_info":{"display_name":"Brenda Cogan","author_link":"https:\/\/discover.restek.com\/de\/author\/brenda-coganrestek-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":444,"filter":"raw","cat_ID":792,"category_count":444,"category_description":"","cat_name":"Blogs","category_nicename":"blogs-de","category_parent":0}],"tag_info":false,"authors":[{"term_id":598,"user_id":0,"is_guest":1,"slug":"linx-waclaski","display_name":"Linx Waclaski","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\/de\/wp-json\/wp\/v2\/posts\/73080","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/users\/5"}],"replies":[{"embeddable":true,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/comments?post=73080"}],"version-history":[{"count":2,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/posts\/73080\/revisions"}],"predecessor-version":[{"id":73392,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/posts\/73080\/revisions\/73392"}],"wp:attachment":[{"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/media?parent=73080"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/categories?post=73080"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/tags?post=73080"},{"taxonomy":"industries-application","embeddable":true,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/industries-application?post=73080"},{"taxonomy":"post-badge","embeddable":true,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/post-badge?post=73080"},{"taxonomy":"resource-type","embeddable":true,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/resource-type?post=73080"},{"taxonomy":"product-library","embeddable":true,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/product-library?post=73080"},{"taxonomy":"resource-technique","embeddable":true,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/resource-technique?post=73080"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/discover.restek.com\/de\/wp-json\/wp\/v2\/ppma_author?post=73080"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}