Table 2.

Repeatability of isotopic enrichments (isotope ratios and mole % excess) and nitrate concentrations from samples of urine, saliva and standards within a run, across runs, following various volumes of injection on to the GCMS and a 2-fold serial dilution.

Sample	n	Isotope Ratio (% ± SD)	Mole % Excess (% ± SD)	Nitrate Concentration (mmol/L ± SD)	CV (%)
Intra-run repeatability
Aqueous standard*	10	10.34 ± 0.30	-	-	1.13
Aqueous standard 10.5 mole % excess	10	-	10.79 ± 0.45	-	1.59
Saliva*	10	10.71 ± 0.03	-	-	0.30
Saliva (a)	10	-	-	0.88 ± 0.004	0.46
Urine (a)	10	-	-	1.98 ± 0.008	0.44
Inter-run repeatability
Saliva*	6	10.64 ± 0.09	-	-	0.83
Saliva (a)	6	67.15 ± 0.51	36.12 ± 0.24	0.88 ± 0.008	0.90
Urine (a)	6	35.52 ± 0.22	19.95 ± 0.20	2.01 ± 0.017	0.87
Urine (b)	6	45.58 ± 0.33	25.91 ± 0.26	1.43 ± 0.013	0.94
Injection volume
Aqueous standard*	6	10.38 ± 0.29
Saliva (a)	6	67.7 ± 0.51	36.46 ± 0.20	0.87 ± 0.008
Saliva (b)	6	56.16 ± 0.58	31.43 ± 0.27	1.09 ± 0.014
Urine (a)	6	35.58 ± 0.73	20.17 ± 0.47	1.98 ± 0.057
Urine (b)	6	48.50 ± 3.24	27.60 ± 1.68	1.32 ± 0.108
2-fold serial dilution
Aqueous standard*	15	10.45 ± 0.05	-	-
2mmol/l Aqueous standard	15	61.59 ± 0.20	33.89 ± 0.09	1.95 ± 0.01
Saliva (a)	15	67.18 ± 0.33	36.25 ± 0.13	0.88 ± 0.005
Saliva (b)	15	55.60 ± 0.18	31.17 ± 0.08	1.11 ± 0.008
Urine (a)	15	35.81 ± 0.21	20.32 ± 0.65	1.96 ± 0.014
Urine (b)	15	45.00 ± 0.14	25.76 ± 0.08	1.44 ± 0.013

All values are expressed as Mean ± SD; all samples and standards were spiked with 0.1mmol/L Na¹⁵NO₃ unless stated

^*natural abundance.