{"id":113,"date":"2026-04-10T02:53:06","date_gmt":"2026-04-10T02:53:06","guid":{"rendered":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/chapter\/ch039-xhtml\/"},"modified":"2026-05-11T22:22:08","modified_gmt":"2026-05-11T22:22:08","slug":"5-3-sample-collection-and-analysis","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/chapter\/5-3-sample-collection-and-analysis\/","title":{"raw":"5.3 Sample Collection and Analysis","rendered":"5.3 Sample Collection and Analysis"},"content":{"raw":"
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\r\n\r\nLike all dissolved gas tracers, samples for [latex]{SF}_{6}[\/latex] must be collected such that gas exchange with the atmosphere does not occur and bubbles are not trapped within the sample container. Numerous sample containers have been used including custom\u2011made metal cylinders with valves on each end (Figure 22<\/span><\/a>). A simple and effective sampling method uses a one\u2011liter glass bottle with a narrow mouth as shown in Figure 22<\/span><\/a>. The bottles are filled using a submersible pump with the discharge tube extending to near the bottom of the bottle. The bottle is purged with 3 to 4\u00a0L of water before slowly removing the discharge tube such that the bottle is totally filled\u2014no headspace is left. A polyethylene cone-shaped liner inside a cap (i.e., a polyseal<\/em> cap), is then installed onto the bottle. The cone\u2011shaped liner displaces a small amount of water that was at the water\u2013atmosphere interface upon installation, resulting in minimal contamination of the remaining water by the modern atmosphere.\r\n\r\n<\/div>\r\n
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\r\n\r\n<\/span>Figure 22\u00a0\u2011<\/strong>\u00a0Sampling SF6<\/sub> a) stainless steel cylinder for SF6<\/sub> samples and b) glass narrow\u2011mouth bottle with c) polyseal<\/em> cone\u2011shaped cap. Samples for the bottles should be filled by d) inserting a tube to the bottom and flushing more than 3L, then e) installing the cap with no headspace and f) wrapping electrical tape counterclockwise around the cap to prevent it from moving,\r\n\r\n<\/div><\/blockquote>\r\n<\/div>\r\n
\r\n\r\nHeadspace and purge\u2011and\u2011trap are the two primary analytical methods used for [latex]{SF}_{6}[\/latex] age dating. The headspace technique introduces a known amount of [latex]{SF}_{6}[\/latex] free gas into a sample container of known volume. The container is shaken resulting in a partitioning of [latex]{SF}_{6}[\/latex] between the water and gas headspace. Because of its low solubility, there is a strong preference for [latex]{SF}_{6}[\/latex] to reside in the gas phase. After equilibration, the headspace gas is subsampled with a syringe or gas sampling valve and then quantified with a gas chromatograph<\/em> (GC) using an electron capture detector.\r\n\r\n<\/div>\r\n
\r\n\r\nWith the purge\u2011and\u2011trap technique, a known amount of water is introduced into a sparging chamber. [latex]{SF}_{6}[\/latex]free carrier gas\u2014typically [latex]N_{2}[\/latex] or [latex]He[\/latex]\u2014is bubbled through the water inside the sparging chamber and then through a trap that retains [latex]{SF}_{6}[\/latex] but not the carrier gas or oxygen. Traps are typically filled with a porous polymer (e.g., Porapak\u2122 Q) and are held at \u2212<\/em>70 to \u2212<\/em>80\u00a0\u00b0C. After sufficient stripping, the trap is warmed to release [latex]{SF}_{6}[\/latex], which is then routed into a GC for analysis.\r\n\r\n<\/div>\r\n
\r\n\r\nBoth the headspace and purge\u2011and\u2011trap methods have been used for low\u2011level [latex]{SF}_{6}[\/latex] analyses (Bullister & Wisegarver, 2008; Busenberg & Plummer, 2000; Busenberg & Plummer, 2010; Wanninkhof et al., 1987; Wanninkhof et al., 1991). The headspace method is particularly useful for higher concentrations that exist in injected tracer studies (Clark et al., 1994; Cook, Lamontagne, et al., 2006; Wanninkhof et al., 1990).\r\n\r\n<\/div>\r\n<\/div>","rendered":"
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Like all dissolved gas tracers, samples for [latex]{SF}_{6}[\/latex] must be collected such that gas exchange with the atmosphere does not occur and bubbles are not trapped within the sample container. Numerous sample containers have been used including custom\u2011made metal cylinders with valves on each end (Figure 22<\/span><\/a>). A simple and effective sampling method uses a one\u2011liter glass bottle with a narrow mouth as shown in Figure 22<\/span><\/a>. The bottles are filled using a submersible pump with the discharge tube extending to near the bottom of the bottle. The bottle is purged with 3 to 4\u00a0L of water before slowly removing the discharge tube such that the bottle is totally filled\u2014no headspace is left. A polyethylene cone-shaped liner inside a cap (i.e., a polyseal<\/em> cap), is then installed onto the bottle. The cone\u2011shaped liner displaces a small amount of water that was at the water\u2013atmosphere interface upon installation, resulting in minimal contamination of the remaining water by the modern atmosphere.<\/p>\n<\/div>\n

\n

\"\"<\/p>\n<\/div>\n

\n
\n
\n

<\/span>Figure 22\u00a0\u2011<\/strong>\u00a0Sampling SF6<\/sub> a) stainless steel cylinder for SF6<\/sub> samples and b) glass narrow\u2011mouth bottle with c) polyseal<\/em> cone\u2011shaped cap. Samples for the bottles should be filled by d) inserting a tube to the bottom and flushing more than 3L, then e) installing the cap with no headspace and f) wrapping electrical tape counterclockwise around the cap to prevent it from moving,<\/p>\n<\/div>\n<\/blockquote>\n<\/div>\n

\n

Headspace and purge\u2011and\u2011trap are the two primary analytical methods used for [latex]{SF}_{6}[\/latex] age dating. The headspace technique introduces a known amount of [latex]{SF}_{6}[\/latex] free gas into a sample container of known volume. The container is shaken resulting in a partitioning of [latex]{SF}_{6}[\/latex] between the water and gas headspace. Because of its low solubility, there is a strong preference for [latex]{SF}_{6}[\/latex] to reside in the gas phase. After equilibration, the headspace gas is subsampled with a syringe or gas sampling valve and then quantified with a gas chromatograph<\/em> (GC) using an electron capture detector.<\/p>\n<\/div>\n

\n

With the purge\u2011and\u2011trap technique, a known amount of water is introduced into a sparging chamber. [latex]{SF}_{6}[\/latex]free carrier gas\u2014typically [latex]N_{2}[\/latex] or [latex]He[\/latex]\u2014is bubbled through the water inside the sparging chamber and then through a trap that retains [latex]{SF}_{6}[\/latex] but not the carrier gas or oxygen. Traps are typically filled with a porous polymer (e.g., Porapak\u2122 Q) and are held at \u2212<\/em>70 to \u2212<\/em>80\u00a0\u00b0C. After sufficient stripping, the trap is warmed to release [latex]{SF}_{6}[\/latex], which is then routed into a GC for analysis.<\/p>\n<\/div>\n

\n

Both the headspace and purge\u2011and\u2011trap methods have been used for low\u2011level [latex]{SF}_{6}[\/latex] analyses (Bullister & Wisegarver, 2008; Busenberg & Plummer, 2000; Busenberg & Plummer, 2010; Wanninkhof et al., 1987; Wanninkhof et al., 1991). The headspace method is particularly useful for higher concentrations that exist in injected tracer studies (Clark et al., 1994; Cook, Lamontagne, et al., 2006; Wanninkhof et al., 1990).<\/p>\n<\/div>\n<\/div>\n","protected":false},"author":7,"menu_order":24,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-113","chapter","type-chapter","status-publish","hentry"],"part":33,"_links":{"self":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters\/113","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/users\/7"}],"version-history":[{"count":2,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters\/113\/revisions"}],"predecessor-version":[{"id":414,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters\/113\/revisions\/414"}],"part":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/parts\/33"}],"metadata":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters\/113\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/media?parent=113"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapter-type?post=113"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/contributor?post=113"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/license?post=113"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}