The estimation of low levels of 14C in biological samples by alkaline extraction and liquid scintillation counting.
A liquid extraction method capable of accurately estimating low levels of 14C in blood and faecal samples is described. The lower limit of detection is about 4 pCi of 14C per g wet wt of ovine faeces and the lowest level of quantitative determination is 33 pCi per g. Extraction of soluble material is efficient and 14C present in the extract as n-[1-14C]hexadecane, D-[U-14C]glucose, [1-14C]stearic acid, [1-14C]methionine, or Na2 14CO3 is estimated without loss. The aqueous extraction medium used contains 2.5% (v/v) Synperonic NP9 (a non-ionic emulsifier) and 3.5% NaOH and samples are decolorised using hydrogen peroxide. The extract is counted without neutralisation in an inexpensive scintillation mixture based on an emulsifiable oil rather than on an aromatic solvent. It consists of White Spirit 100 (53.8% v/v), Synperonic NP9 (30.8% v/v), octan-2-ol (10.8% v/v), benzyl alcohol (4.6% v/v) and 2,5-diphenyl oxazole (3 g/l). Ethanediol added with the aqueous alkaline extract acts as a third cosurfactant. The advantage of this mixture over one based on an aromatic solvent is that it has a much larger capacity for the concentrated blood and faecal extracts.
D000818:Animals; D002250:Carbon Radioisotopes / Q000032:analysis* / Q000097:blood; D005243:Feces / Q000032:analysis; D012588:Scintillation Counting / Q000379:methods; D012756:Sheep
D002250:Carbon Radioisotopes