Improved 63Ni radiochemical assay of free fatty acids in plasma.
We have modified the 63Ni radiochemical method of Ho (Anal Biochem 1970;36:105) for determination of free fatty acids (FFA) in plasma. Extracting 1 or 0.1 mL of plasma with Dole's mixture (J Biol Chem 1960;235:2595) and washing the "heptane" layer with two volumes of isopropanol/water/dilute (0.5 mol/L) H2SO4 (25/25/1, by vol) removes about 90% of the lipid phosphorus from the "heptane" layer without removing any FFA and is more convenient than treatment with silicic acid. The following modifications decrease background radioactivity and improve separation of the organic phase from the water phase containing the uncomplexed 63Ni: (a) use glassware instead of plastic test tubes; (b) evaporate the organic phase to dryness before adding the 63Ni (this removes the isopropanol, which interferes with the 63Ni assay); and (c) add anhydrous sodium sulfate before the final centrifugation step.
D005230:Fatty Acids, Nonesterified / Q000097:blood* / Q000302:isolation & purification; D006801:Humans; D007202:Indicators and Reagents; D009532:Nickel; D010743:Phospholipids / Q000302:isolation & purification; D011786:Quality Control; D011854:Radiochemistry; D011868:Radioisotopes; D012588:Scintillation Counting; D012824:Silicic Acid; D012996:Solutions; D013431:Sulfates
D005230:Fatty Acids, Nonesterified; D007202:Indicators and Reagents; D010743:Phospholipids; D011868:Radioisotopes; D012996:Solutions; D013431:Sulfates; C012036:sodium sulfate; D012824:Silicic Acid; C022838:nickel chloride; D009532:Nickel