The GC–C-IRMS/MS measurements were carried out
with a Hewlett-Packard 5890 Series II gas chromatograph,
connected via a split with a combustion interface to the
IRMS system (MAT 252, Finnigan MAT; Germany) for
the isotopic determination of nitrogen, and, via a transfer
line, with a mass spectrometer (GCQ, Finnigan MAT; Ger-
many) for qualitative analysis and quantification of the
amino acids. The capillary column for GC was
50 m 0.32 mm i.d. 0.5 lm BPX5 (SGE), operating
with a carrier gas flow of 1.5 ml min1
at the following
temperature and pressure: initial 50 C (1 min), increased
to 100 Cat10 C min1
(10 min), increased to 175 Cat
3 C min1
(10 min), increased to 250 C min1
(10 min);
head pressure, 13 psi (90 kPa).