Freeze-drying: an alternative method for the analysis of volatile organic compounds in the headspace of urine samples using solid phase micro-extraction coupled to gas chromatography - mass spectrometry

Table 2 Average number of compounds identified per sample per class of compound and treatment tested (n ≥ 12)

Class	Fresh	Frozen	NaCl	NaOH	HCl	Freeze-dry	Mann–Whitney \| p values
Class	Fresh	Frozen	NaCl	NaOH	HCl	Freeze-dry	A vs. F	B vs. F	C vs. F	D vs. F	E vs. F
Alcohol	1	1	1	1.2	7.7	7.5	0.001	0.001	0.001	<0.001	0.889
Acid	0	0	0	1	5.3	3.1	NA	NA	NA	0.112	0.001
Aldehyde	1.9	1.9	2.2	4	7.8	1.1	0.002	0.009	0.003	<0.001	<0.001
Aromatic	5.9	5.6	5.5	10.3	30.2	21.3	<0.001	<0.001	<0.001	<0.001	<0.001
Halogen	0	0	0	0	1	0	NA	NA	NA	NA	NA
Ketone	8.1	8.1	7.9	22.6	20.6	36.9	<0.001	<0.001	<0.001	<0.001	<0.001
Furan	1.7	1.6	1.3	1.1	9.8	8.7	<0.001	<0.001	0.001	<0.001	0.048
N-Containing*	2.1	2.1	2.1	8.3	2	11.2	<0.001	<0.001	<0.001	0.003	<0.001
O-Containing**	12.2	12.5	12.5	29.6	62.9	63.2	<0.001	<0.001	<0.001	<0.001	0.849
S-Containing***	1	1	1	3.6	7.7	3.2	0.124	0.029	0.124	0.203	<0.001
Hydrocarbon	3.9	3.7	4.2	6.5	37.2	14	<0.001	<0.001	<0.001	<0.001	<0.001
Ester	0	1	1	1	2.3	2.9	NA	0.007	0.024	<0.001	0.198
Amide	0	0	0	0	0	1	NA	NA	NA	NA	NA
Pyrrole	1	1	1	2.5	0	1.8	<0.001	<0.001	<0.001	0.011	NA

ISSN: 2661-801X