Isolation of ammonium-N as 1-sulfonato-iso-indole for measurement of delta15N.
The conversion of ammonium (NH(4) (+)) to 1-sulfonato-iso-indole has been examined as a method for natural abundance measurement of delta(15)N of NH(4) (+). The reaction is complete within 2 h and is based on the derivatisation of NH(4) (+) by o-phthaldialdehyde and sodium sulfite at a high pH, 11.2. The product is readily concentrated from dilute solutions by reverse-phase solid-phase extraction (SPE). The method is compound-specific despite partial derivatisation of potentially interfering amino acids, as their derivatives are not extracted by SPE. delta(15)N values of NH(4) (+) in KCL soil extracts can be measured within 48 h by automated continuous-flow IRMS with a precision of 0.23 per thousand (1 SD). Parallel measurements of NH(4) (+) standards of known delta(15)N are made to allow correction for the isotopic dilution by non-sample NH(4) (+). The practicality of this method is demonstrated by measuring the changes in NH(4) (+) concentration and delta(15)N following the addition of urea as a nitrogen source to inorganic N-depleted soil.
Johnston
Andrew M
AM
Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK. ajohnston@upstate.com
Scrimgeour
Charles M
CM
Kennedy
Hilary
H
Handley
Linda L
LL
D000596:Amino Acids / Q000032:analysis; D007211:Indoles / Q000032:analysis* / Q000737:chemistry*; D009587:Nitrogen Isotopes; D009994:Osmolar Concentration; D000644:Quaternary Ammonium Compounds / Q000032:analysis* / Q000737:chemistry* / Q000302:isolation & purification; D012680:Sensitivity and Specificity; D014508:Urea / Q000737:chemistry
C475528:1-sulfonato-iso-indole; D000596:Amino Acids; D007211:Indoles; D009587:Nitrogen Isotopes; D000644:Quaternary Ammonium Compounds; C030374:indole; D014508:Urea