Table 4. The stability of HCAAs at various conditions.

	Nominal concentrations (pg/mL)	Determined concentrations (pg/mL)
		Room temperature for 24 hrs			Four freeze–thaw cycles			Auto-sampler for 24 hrs
AαC	150	149.7	±	3.1	142.7	±	2.9	152.7	±	1.5
	20	21.1	±	0.5	18.9	±	0.4	21.0	±	0.7
MeAαC	150	151.3	±	2.1	139.0	±	2.0	163.7	±	3.2
	20	20.5	±	0.5	18.8	±	0.1	21.2	±	0.2
IQ	150	155.0	±	2.6	152.7	±	1.5	156.7	±	2.5
	20	21.6	±	0.7	21.1	±	0.2	20.8	±	0.7
Trp-P-1	150	149.3	±	2.5	149.3	±	3.8	152.3	±	2.1
	20	19.6	±	0.9	18.8	±	0.6	20.5	±	0.5
Trp-P-2	150	149.3	±	2.5	148.0	±	1.0	148.7	±	2.1
	20	19.6	±	0.2	18.6	±	0.2	19.5	±	0.3
Glu-P-1	150	151.7	±	6.1	148.3	±	4.2	153.3	±	2.1
	20	21.0	±	0.2	19.3	±	0.2	21.2	±	0.5
Glu-P-2	150	148.7	±	2.3	146.0	±	2.6	150.0	±	1.7
	20	19.9	±	0.6	20.1	±	0.5	21.1	±	0.5
PhIP	150	152.3	±	4.9	149.7	±	2.1	151.3	±	4.7
	20	21.2	±	0.5	20.7	±	0.5	20.0	±	0.2
Harman	1487	1563	±	21	1507	±	23	1493	±	15.3
	257	282	±	9.5	266	±	9.5	261	±	8.5
Norharman	1493	1580	±	10	1537	±	5.8	1477	±	15.3
	287	278	±	2.9	297	±	11	272	±	5.1