{"id":86,"date":"2026-04-10T02:53:00","date_gmt":"2026-04-10T02:53:00","guid":{"rendered":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/chapter\/ch023-xhtml\/"},"modified":"2026-05-08T02:17:29","modified_gmt":"2026-05-08T02:17:29","slug":"3-3-sample-collection-and-analysis","status":"publish","type":"chapter","link":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/chapter\/3-3-sample-collection-and-analysis\/","title":{"raw":"3.3 Sample Collection and Analysis","rendered":"3.3 Sample Collection and Analysis"},"content":{"raw":"
\r\n
\r\n\r\nSamples for [latex]_{}^{3}H[\/latex] analysis should ideally be collected in glass bottles with minimal headspace and a tight\u2011fitting cap (e.g., a polyseal cap). However, when samples will be shipped to the laboratory, the use of high\u2011density polyethylene bottles\u2014or other plastic that has a low permeability to water vapor\u2014is generally acceptable as it avoids breakage issues associated with glass bottles. Typically, 1\u00a0L is sufficient volume, but readers are encouraged to contact their chosen laboratory for specific requirements.\r\n\r\n<\/div>\r\n
\r\n\r\nBecause the modern atmosphere may contain a [latex]_{}^{3}H[\/latex] concentration much higher than the sample, it is important to avoid contact between the sample and the atmosphere. However, extreme care to avoid contact such as submerging the collection bottle in a larger container that is filled with sample water is generally not required. Historically, some watches had luminescent dials that utilized [latex]_{}^{3}H[\/latex] gas and these should not be worn during sample collection. There are many different luminescent technologies used in modern watches, but, as [latex]_{}^{3}H[\/latex] gas is still used by several manufacturers, it is best to avoid wearing a watch during sample collection. When [latex]_{}^{3}H[\/latex] analyses are to be performed in the unsaturated zone, water must be first extracted using a suction lysimeter in situ or distillation from a core sample.\r\n\r\n<\/div>\r\n
\r\n\r\nTritium analyses are usually performed using liquid scintillation counting<\/em> (LSC), gas proportional counting<\/em> (GPC), or [latex]_{}^{3}{He}[\/latex] in\u2011growth. In a recent comparison of 78 international [latex]_{}^{3}H[\/latex] laboratories, 70 used LSC, seven used [latex]_{}^{3}{He}[\/latex] in\u2011growth, and one used GPC (Copia et al., 2020).\r\n\r\n<\/div>\r\n
\r\n\r\nA pre\u2011treatment using electrolytic enrichment of samples is commonly done for both the LSC and GPC methods for samples having [latex]_{}^{3}H[\/latex] values less than several TU. The electrolytic enrichment process decomposes water to oxygen ([latex]O_{2}[\/latex](g)) and hydrogen ([latex]H_{2}[\/latex](g)) gas that is depleted in [latex]_{}^{3}H[\/latex] relative to the remaining liquid phase. Typically, between 2,000 to 250\u00a0ml of sample is reduced to a volume of about 10 to 15\u00a0ml. The electrolysis process highly favors the formation of [latex]_{}^{1}H_{2}([\/latex]g) at the cathode over [latex]_{}^{2}H_{2}[\/latex](g) and [latex]_{}^{3}H_{2}[\/latex](g), leaving the remaining solution enriched in [latex]_{}^{2}{H\\ }[\/latex](deuterium) and [latex]_{}^{3}{H\\ }[\/latex] (Copia et al., 2021). A [latex]_{}^{3}{H\\ }[\/latex] enrichment factor of about 16 to 32 is common, but a factor as great as 175 can be obtained (Morgenstern & Taylor, 2009).\r\n\r\n<\/div>\r\n
\r\n\r\nThe enrichment process involves five steps:\r\n\r\n<\/div>\r\n
    \r\n \t
  1. predistillation to remove dissolved ions that might interfere with the electrolysis process,<\/li>\r\n \t
  2. the addition of an electrolyte to facilitate electrolysis,<\/li>\r\n \t
  3. electrolysis to enrich the sample in 2<\/sup>H and 3<\/sup>H,<\/li>\r\n \t
  4. alkalinity neutralization to lower the pH of the solution after electrolysis, and<\/li>\r\n \t
  5. final distillation to quantitatively recover the enriched water.<\/li>\r\n<\/ol>\r\n
    \r\n\r\nFor the GPC method, methane is synthesized (e.g., reaction of water with aluminum carbide at 150\u00a0\u00b0C; Horvatin\u010di\u0107, 1980) from either the raw water sample or from the residual solution following electrolytic enrichment. The produced methane is then placed into a counting cell along with quenching gas at pressures that are typically 5 to 7\u00a0atm.\r\n\r\n<\/div>\r\n
    \r\n\r\nFor the LSC method, about 10\u00a0ml of either the raw sample or the residual solution following electrolytic enrichment is added to a scintillation cocktail. The function of the scintillation cocktail is to absorb energy from radioactive decay and convert it into light pulses that can then be detected by a photomultiplier tube. Low background LSC are commercially available that employ both shielding and anti\u2011coincidence detection combined with sample blanks to reduce and correct for background radiation. The tritium detection limit for LSC of raw samples is typically between 2 to 10\u00a0TU and between 0.05 to 0.6\u00a0TU for enriched samples.\r\n\r\n<\/div>\r\n
    \r\n\r\nThe [latex]_{}^{3}{He}[\/latex] in\u2011growth method utilizes the child of [latex]_{}^{3}{H\\ }[\/latex] decay: [latex]_{}^{3}{He}[\/latex]. A sample is first placed into a container having low [latex]He[\/latex] permeability and degassed to remove dissolved [latex]He[\/latex] from the sample. The container is then sealed and stored for one to 12\u00a0months during which time [latex]_{}^{3}{He}[\/latex] is produced from [latex]_{}^{3}{H\\ }[\/latex] decay. After the in\u2011growth period, the evolved [latex]He[\/latex] is let into a final clean\u2011up line and then a sector\u2011field mass spectrometer where [latex]_{}^{3}{He}[\/latex] and [latex]_{}^{4}{He}[\/latex] are measured using peak\u2011height manometry. The purpose of the [latex]_{}^{4}{He}[\/latex] measurement is to correct for [latex]He[\/latex] leakage, outgassing, or insufficient degassing of the sample. While the [latex]_{}^{3}{He}[\/latex] in\u2011growth method is conceptually straight forward, several important factors affect the method\u2019s implementation:\r\n\r\n<\/div>\r\n
      \r\n \t
    • The sample must be 99.9995\u00a0percent degassed of its dissolved [latex]He[\/latex] content in a container that will not leak or outgas more than about 10,000\u00a0atoms of [latex]_{}^{3}{He}[\/latex] during the in\u2011growth period. Special glass with a high aluminum content that is stored at \u2212<\/em>20\u00a0\u00b0C to reduce helium diffusion, or an all\u2011metal flask is used.<\/li>\r\n \t
    • The sector\u2011field mass spectrometer must have a resolving power greater than about one in 400\u00a0amu to separate the [latex]_{}^{3}{He}^{+}[\/latex] peak from the hydrogen deuterium (HD) peak.<\/li>\r\n \t
    • The detection limit for the [latex]_{}^{3}{He}[\/latex] in-growth method depends on the sample size, holding time, and residual helium from the degassing procedure or leakage during storage. For a sample volume of 500\u00a0ml and in\u2011growth period of six\u00a0weeks, detection limits of 0.05\u00a0TU are common. For larger volumes (up to 3,000\u00a0ml) and\/or longer holding times (up to one\u00a0year) a detection limit of 0.003\u00a0TU has been reported (Jenkins, 1981). A significant advantage to the [latex]_{}^{3}{He}[\/latex] in\u2011growth method is that time and sample amount are interchangeable in terms of the detection limit. For example, Marston and others (2012) measured the [latex]_{}^{3}{He}[\/latex] content of structural waters in clay minerals on typical volumes of 20 to 30\u00a0ml with a detection limit of 0.5\u00a0TU by using an in\u2011growth time of 24\u00a0weeks compared with six\u00a0weeks typically used for 500\u00a0ml samples.<\/li>\r\n<\/ul>\r\n<\/div>","rendered":"
      \n
      \n

      Samples for [latex]_{}^{3}H[\/latex] analysis should ideally be collected in glass bottles with minimal headspace and a tight\u2011fitting cap (e.g., a polyseal cap). However, when samples will be shipped to the laboratory, the use of high\u2011density polyethylene bottles\u2014or other plastic that has a low permeability to water vapor\u2014is generally acceptable as it avoids breakage issues associated with glass bottles. Typically, 1\u00a0L is sufficient volume, but readers are encouraged to contact their chosen laboratory for specific requirements.<\/p>\n<\/div>\n

      \n

      Because the modern atmosphere may contain a [latex]_{}^{3}H[\/latex] concentration much higher than the sample, it is important to avoid contact between the sample and the atmosphere. However, extreme care to avoid contact such as submerging the collection bottle in a larger container that is filled with sample water is generally not required. Historically, some watches had luminescent dials that utilized [latex]_{}^{3}H[\/latex] gas and these should not be worn during sample collection. There are many different luminescent technologies used in modern watches, but, as [latex]_{}^{3}H[\/latex] gas is still used by several manufacturers, it is best to avoid wearing a watch during sample collection. When [latex]_{}^{3}H[\/latex] analyses are to be performed in the unsaturated zone, water must be first extracted using a suction lysimeter in situ or distillation from a core sample.<\/p>\n<\/div>\n

      \n

      Tritium analyses are usually performed using liquid scintillation counting<\/em> (LSC), gas proportional counting<\/em> (GPC), or [latex]_{}^{3}{He}[\/latex] in\u2011growth. In a recent comparison of 78 international [latex]_{}^{3}H[\/latex] laboratories, 70 used LSC, seven used [latex]_{}^{3}{He}[\/latex] in\u2011growth, and one used GPC (Copia et al., 2020).<\/p>\n<\/div>\n

      \n

      A pre\u2011treatment using electrolytic enrichment of samples is commonly done for both the LSC and GPC methods for samples having [latex]_{}^{3}H[\/latex] values less than several TU. The electrolytic enrichment process decomposes water to oxygen ([latex]O_{2}[\/latex](g)) and hydrogen ([latex]H_{2}[\/latex](g)) gas that is depleted in [latex]_{}^{3}H[\/latex] relative to the remaining liquid phase. Typically, between 2,000 to 250\u00a0ml of sample is reduced to a volume of about 10 to 15\u00a0ml. The electrolysis process highly favors the formation of [latex]_{}^{1}H_{2}([\/latex]g) at the cathode over [latex]_{}^{2}H_{2}[\/latex](g) and [latex]_{}^{3}H_{2}[\/latex](g), leaving the remaining solution enriched in [latex]_{}^{2}{H\\ }[\/latex](deuterium) and [latex]_{}^{3}{H\\ }[\/latex] (Copia et al., 2021). A [latex]_{}^{3}{H\\ }[\/latex] enrichment factor of about 16 to 32 is common, but a factor as great as 175 can be obtained (Morgenstern & Taylor, 2009).<\/p>\n<\/div>\n

      \n

      The enrichment process involves five steps:<\/p>\n<\/div>\n

        \n
      1. predistillation to remove dissolved ions that might interfere with the electrolysis process,<\/li>\n
      2. the addition of an electrolyte to facilitate electrolysis,<\/li>\n
      3. electrolysis to enrich the sample in 2<\/sup>H and 3<\/sup>H,<\/li>\n
      4. alkalinity neutralization to lower the pH of the solution after electrolysis, and<\/li>\n
      5. final distillation to quantitatively recover the enriched water.<\/li>\n<\/ol>\n
        \n

        For the GPC method, methane is synthesized (e.g., reaction of water with aluminum carbide at 150\u00a0\u00b0C; Horvatin\u010di\u0107, 1980) from either the raw water sample or from the residual solution following electrolytic enrichment. The produced methane is then placed into a counting cell along with quenching gas at pressures that are typically 5 to 7\u00a0atm.<\/p>\n<\/div>\n

        \n

        For the LSC method, about 10\u00a0ml of either the raw sample or the residual solution following electrolytic enrichment is added to a scintillation cocktail. The function of the scintillation cocktail is to absorb energy from radioactive decay and convert it into light pulses that can then be detected by a photomultiplier tube. Low background LSC are commercially available that employ both shielding and anti\u2011coincidence detection combined with sample blanks to reduce and correct for background radiation. The tritium detection limit for LSC of raw samples is typically between 2 to 10\u00a0TU and between 0.05 to 0.6\u00a0TU for enriched samples.<\/p>\n<\/div>\n

        \n

        The [latex]_{}^{3}{He}[\/latex] in\u2011growth method utilizes the child of [latex]_{}^{3}{H\\ }[\/latex] decay: [latex]_{}^{3}{He}[\/latex]. A sample is first placed into a container having low [latex]He[\/latex] permeability and degassed to remove dissolved [latex]He[\/latex] from the sample. The container is then sealed and stored for one to 12\u00a0months during which time [latex]_{}^{3}{He}[\/latex] is produced from [latex]_{}^{3}{H\\ }[\/latex] decay. After the in\u2011growth period, the evolved [latex]He[\/latex] is let into a final clean\u2011up line and then a sector\u2011field mass spectrometer where [latex]_{}^{3}{He}[\/latex] and [latex]_{}^{4}{He}[\/latex] are measured using peak\u2011height manometry. The purpose of the [latex]_{}^{4}{He}[\/latex] measurement is to correct for [latex]He[\/latex] leakage, outgassing, or insufficient degassing of the sample. While the [latex]_{}^{3}{He}[\/latex] in\u2011growth method is conceptually straight forward, several important factors affect the method\u2019s implementation:<\/p>\n<\/div>\n

          \n
        • The sample must be 99.9995\u00a0percent degassed of its dissolved [latex]He[\/latex] content in a container that will not leak or outgas more than about 10,000\u00a0atoms of [latex]_{}^{3}{He}[\/latex] during the in\u2011growth period. Special glass with a high aluminum content that is stored at \u2212<\/em>20\u00a0\u00b0C to reduce helium diffusion, or an all\u2011metal flask is used.<\/li>\n
        • The sector\u2011field mass spectrometer must have a resolving power greater than about one in 400\u00a0amu to separate the [latex]_{}^{3}{He}^{+}[\/latex] peak from the hydrogen deuterium (HD) peak.<\/li>\n
        • The detection limit for the [latex]_{}^{3}{He}[\/latex] in-growth method depends on the sample size, holding time, and residual helium from the degassing procedure or leakage during storage. For a sample volume of 500\u00a0ml and in\u2011growth period of six\u00a0weeks, detection limits of 0.05\u00a0TU are common. For larger volumes (up to 3,000\u00a0ml) and\/or longer holding times (up to one\u00a0year) a detection limit of 0.003\u00a0TU has been reported (Jenkins, 1981). A significant advantage to the [latex]_{}^{3}{He}[\/latex] in\u2011growth method is that time and sample amount are interchangeable in terms of the detection limit. For example, Marston and others (2012) measured the [latex]_{}^{3}{He}[\/latex] content of structural waters in clay minerals on typical volumes of 20 to 30\u00a0ml with a detection limit of 0.5\u00a0TU by using an in\u2011growth time of 24\u00a0weeks compared with six\u00a0weeks typically used for 500\u00a0ml samples.<\/li>\n<\/ul>\n<\/div>\n","protected":false},"author":7,"menu_order":10,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-86","chapter","type-chapter","status-publish","hentry"],"part":28,"_links":{"self":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters\/86","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\/86\/revisions"}],"predecessor-version":[{"id":339,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters\/86\/revisions\/339"}],"part":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/parts\/28"}],"metadata":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapters\/86\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/media?parent=86"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/pressbooks\/v2\/chapter-type?post=86"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/contributor?post=86"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/books.gw-project.org\/age-dating-young-groundwater\/wp-json\/wp\/v2\/license?post=86"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}