Experimental design-based isotope-dilution SPME-GC/MS method development for the analysis of smoke flavouring products

Figures & data

Table 1. Identification and characterisation of liquid smoke flavouring components.

	Compounds	CAS no.	Identification method^a	RI (Lit.)^b	RI (Obs.)	Qualifier ion	Quantifier ion	Calibration equivalent^c
	Furan/pyran derivatives
1	3-Furancarboxaldehyde (3-furaldehyde)	498–60-2	Std, RI, MS	831	821	96	95	3-Furaldehyde
2	2-Methoxymethylfuran	13,679–46-4	RI, MS	829	828	112	81	3-Furaldehyde
3	2-Furancarboxaldehyde (furfural)	98–01-1	RI, MS	831	833	67	96	3-Furaldehyde
4	2-Furanmethanol (furfuryl alcohol)	98–00-0	Std, RI, MS	851	858	81, 69	98	Furfuryl alcohol
5	1-(2-Furanyl)-ethanone	1192–62-7	RI, MS	909	909	110	95	3-Furaldehyde
6	g-Butyrolactone	96–48-0	RI, MS	913	926	56	86	3-Furaldehyde
7	5-Methyl-2-furancarboxaldehyde (5-methylfurfural)	620–02-0	Std, RI, MS	963	964	81, 109	110	5-Methylfurfural
8	2-Methylfuroate	611–13-2	Std, RI, MS	969	975	68, 126	95	2-Methylfuroate
9	5-Methyl-2(5H)-furanone	591–117	RI, MS	997	998	98, 83	55	3-Furaldehyde
10	1-(2-Furanyl)-1-propanone	3194–15-8	RI, MS	1005	1007	124	95	3-Furaldehyde
11	2-Acetyl-5-methylfuran	1193–79-9	RI, MS	1039	1036	124	109	3-Furaldehyde
12	5-Methyl-4-hydroxy-3(2H)-furanone	19,322–27-1	RI, MS	1046	1047	98	69	3-Furaldehyde
13	3-Hydroxy-2-methyl-4H-pyran-4-one (maltol)	118–71-8	RI, MS	1085	1097	97, 71	126	3-Furaldehyde
14	2-Methylbenzofuran	4265–25-2	Std, RI, MS	1109	1114	77, 103	131	2-Methylbenzofuran
15	5-Acetoxymethyl-2-furaldehyde	10,551–58-3	RI, MS	1295	1305	109, 79	126	3-Furaldehyde
	Phenols
16	Phenol	108–95-2	Std, RI, MS	990	984	66, 79	94	Phenol
17	2-Methylphenol	95–48-7	Std, RI, MS	1038	1054	90, 107	108	2-Methylphenol
18	Acetophenone	98–86-2	Std, RI, MS	1065	1069	77,120	105	Acetophenone
19	3-Methylphenol	108–39-4	Std, RI, MS	1075	1074	79, 107	108	3-Methylphenol
20	2,5-Dimethylphenol	105–67-9	Std, RI, MS	1105	1109	91, 107	122	2,5-Dimethylphenol
21	2-Ethylphenol	90–00-6	Std, RI, MS	1132	1133	91, 122	107	2-Ethylphenol
22	2,4-Dimethylphenol	105–67-9	RI, MS	1136	1147	77, 107	122	Phenol
23	4-Ethylphenol	123–07-9	RI, MS	1156	1163	77, 107	122	Phenol
24	3,5-Dimethylphenol	108–68-9	RI, MS	1169	1169	107, 121	122	Phenol
25	2,3-Dimethylphenol	203–321-6	Std, RI, MS	1185	1187	107	122	2,3-Dimethylphenol
26	3-Ethylphenol	620–72-7	Std, RI, MS	1190	1193	122	107	3-Ethylphenol
27	3,4-Dimethylphenol	95–65-8	RI, MS	1201	1209	122	107	Phenol
28	2,4,6-Trimethylphenol	527–60-6	Std, RI, MS	1236	1219	136, 91	121	2,4,6-Trimethylphenol
29	2-Propylphenol	644–35-9	RI, MS	1229	1225	136, 77	107	Phenol
30	2-Ethyl-6-methylphenol	1687–64-5	RI, MS	1237	1237	121	136	Phenol
31	4-Propylphenol	645–56-7	RI, MS	1260	1255	136, 77	107	Phenol
32	2,3,6-Trimethylphenol	2416–94-6	Std, RI, MS	1275	1262	136	121	2,3,6-Trimethylphenol
33	Thymol	89–83-8	Std, RI, MS	1295	1295	150, 91	135	Thymol
34	2,4,5-Trimethylphenol	496–78-6	RI, MS	1310	1310	136	121	Phenol
35	2-Methyl-6-(2-propenyl)-phenol	3354–58-3	MS	–	1323	133	148	Phenol
	Guaiacol and derivatives
36	2-Methoxyphenol (guaiacol)	90–05-1	Std, RI, MS	1089	1092	81, 109	124	Guaiacol
37	4-Methoxy-3-methylphenol	14,786–82-4	RI, MS	1142	1155	95, 123	138	Guaiacol
38	2-Methoxy-4-methylphenol (4-methylguaiacol)	93–51-6	Std, RI, MS	1181	1181	67, 138	123	4-Methylguaiacol
39	2-Methoxy-5-methylphenol	1195–09-1	RI, MS	1195	1190	95, 123	138	Guaiacol
40	2-Methoxy-3-methylphenol	18,102–31-3	RI, MS	1203	1194	95, 123	138	Guaiacol
41	2-Methoxy-4-vinylphenol (4-vinylguaiacol)	7786–61-0	Std, RI, MS	–	1257	135, 150	107	4-Vinylguaiacol
42	4-Ethyl-2-methoxyphenol (4-ethylguaiacol)	2785–89-9	Std, RI, MS	1283	1283	122, 152	137	4-Ethylguaiacol
43	1-(3-Hydroxy-2-methoxyphenyl)-ethanone	703–23-1	RI, MS	1329	1334	166	151	Guaiacol
44	2-Methoxy-4-(2-propenyl)-phenol (eugenol)	97–53-0	Std, RI, MS	1360	1364	131, 149	164	Eugenol
45	4-Ethyl-6-methyl-2-methoxyphenol	120,550–70-1	RI, MS	1363	1365	151	166	Guaiacol
46	2-Methoxy-4-propylphenol (4-propylguaiacol)	2785–87-7	Std, RI, MS	1356	1372	166, 122	137	4-Propylguaiacol
47	4-Hydroxy-3-methoxybenzaldehyde (vanillin)	121–33-5	Std, RI, MS	1405	1404	81, 109	152	Vanillin
48	1,2-Dimethoxy-4-(2-propenyl)-benzene (methyl eugenol)	93–16-3	RI, MS	1410	1418	163, 91	178	Guaiacol
49	2-Methoxy-4-(1-propenyl)-phenol (isoeugenol)	97–54-1	RI, MS	1451	1454	131, 149	164	Isoeugenol
50	4-(2-Hydroxyethyl)-2-methoxyphenol (homovanillyl alcohol)	2380–78-1	Std, RI, MS	1446	1463	168, 122	137	Homovanillyl alcohol
51	1-(4-Hydroxy-3-methoxyphenyl)-ethanone (acetovanillone)	498–02-2	Std, RI, MS	1491	1492	166	151	Acetovanillone
52	4-Hydroxy-3-methoxybenzoic acid methyl ester (methylvanillate)	3943–74-6	Std, RI, MS	1526	1523	182, 123	151	Methylvanillate
53	1-(4-Hydroxy-3-methoxyphenyl)-2-propanone (2-propiovanillone)	2503–46-0	Std, RI, MS	1536	1536	180	137	2-Propiovanillone
	Benzenediol and derivatives
54	1,2-Dimethoxybenzene (veratrole)	91–16-7	Std, RI, MS	1147	1143	77, 123	138	Veratrole
55	1,4-Dimethoxybenzene	150–78-7	Std, RI, MS	1163	1155	95, 138	123	1,4-Dimethoxybenzene
56	1,2-Benzenediol (pyrocatechol)	120–80-9	Std, RI, MS	1197	1194	64	110	Pyrocatechol
57	2-Methoxy-1,4-benzenediol (2-methoxy hydroquinone)	824–46-4	RI, MS	1207	1210	125, 97	140	Syringol
58	3,5-Dimethoxytoluene	4179–19-5	Std, RI, MS	1242	1237	109, 123	152	3,5-Dimethoxytoluene
59	3-Methyl-1,2-benzenediol (3-methylcatechol)	488–17-5	Std, RI, MS	1255	1260	95, 78	124	3-Methylcatechol
60	3-Methoxy-1,2-benzenediol (3-methoxy-pyrocatechol)	934–00-9	Std, RI, MS	1268	1265	125, 97	140	3-Methoxy-pyrocatechol
61	4-Methyl-1,2-benzenediol (4-methylcatechol)	452–86-8	RI, MS	1344	1349	78	124	3-Methylcatechol
62	2,6-Dimethoxyphenol (syringol)	91–10-1	Std, RI, MS	1357	1353	111, 139	154	Syringol
63	2,6-Dimethoxy-4-methylphenol (4-methylsyringol)	6638–05-7	RI, MS	1383	1381	153	168	Syringol
64	3,4-Dimethoxybenzoic acid (veratric acid)	93–07-2	RI, MS	1528	1524	167	182	Syringol
65	4-Ethyl-2,6-dimethoxyphenol (4-ethyl syringol)	14,059–92-8	RI, MS	1528	1529	139, 182	167	Syringol
66	2,6-Dimethoxy-4-(2-propenyl)-phenol (4-allylsyringol)	6627–88-9	Std, RI, MS	1609	1610	167, 179	194	4-Allylsyringol
67	4-Propyl-2,6-dimethoxyphenol (4-propyl syringol)	6766–82-1	RI, MS	1616	1618	196	167	Syringol
68	4-Hydroxy-3,5-dimethoxybenzaldehyde (syringaldehyde)	134–96-3	RI, MS	1678	1675	181	182	Syringol
69	1-(4-Hydroxy-3,5-dimethoxyphenyl)-ethanone (acetosyringone)	2478–38-8	Std, RI, MS	1748	1758	196	181	Acetosyringone
	Aldehydes and ketones
70	2-Methyl-2-butenal	1115–11-3	RI, MS	753	739	55	84	2-Cyclohexen-1-one
71	3-Hydroxy-2-butanone	513–86-0	RI, MS	729	724	45	88	2-Cyclohexen-1-one
72	Cyclopentanone	120–92-3	RI, MS	767	787	55	84	2-Cyclohexen-1-one
73	2-Methyl-cyclopentanone	1120–72-5	RI, MS	848	840	69	98	2-Cyclohexen-1-one
74	1-(Acetyloxy)-2-propanone	592–20-1	RI, MS	859	864	73, 116	86	3-Furaldehyde
75	3-Methyl-2-cyclopenten-1-one	2758–18-1	MS	–	875	81, 67	96	2-Cyclohexen-1-one
76	2-Methyl-2-cyclopenten-1-one	1120–73-6	RI, MS	906	905	67	96	2-Cyclohexen-1-one
77	2,5-Hexanedione	110–13-4	MS	–	927	71, 114	99	2-Cyclohexen-1-one
78	2-Cyclohexen-1-one	930–68-7	Std, RI, MS	935	932	96	68	2-Cyclohexen-1-one
79	3,4-Dimethyl-2-cyclopenten-1-one	30,434–64-1	MS	–	938	67, 110	95	2-Cyclohexen-1-one
80	2,3-Dimethyl-2-cyclopenten-1-one	1121–05-7	MS	–	945	67, 95	110	2-Cyclohexen-1-one
81	Benzaldehyde	100–52-7	RI, MS	961	961	77, 51	106	3-Furaldehyde
82	4-Methyl-2-cyclopenten-1-one	–	MS	–	965	98	68	2-Cyclohexen-1-one
83	2,3-Dimethyl-2-cyclopenten-1-one	1121–05-7	MS	–	999	67, 95	110	2-Cyclohexen-1-one
84	2,3,4-Trimethyl-2-cyclopenten-1-one	28,790–86-5	MS	–	1011	81, 124	109	2-Cyclohexen-1-one
85	3-Methyl-1,2-cyclopentanedione (cyclotene)	765–70-8	RI, MS	1032	1033	69, 83	112	2-Cyclohexen-1-one
86	3,4,5-Trimethyl-2-cyclopenten-1-one	55,683–21-1	MS	-–	1036	81, 124	109	2-Cyclohexen-1-one
87	2,3-Dimethyl-2-cyclopenten-1-one	1121–05-7	RI, MS	1040	1040	67, 95	110	2-Cyclohexen-1-one
88	Benzene acetaldehyde	122–78-1	Std, RI, MS	1043	1043	120, 65	91	Benzene acetaldehyde
89	2-Hydroxybenzaldehyde	90–02-8	Std, RI, MS	1041	1045	93	122	2-Hydroxybenzaldehyde
90	2,3-Dimethyl-2-cyclopenten-1-one	1121–05-7	RI, MS	1042	1047	67, 95	110	2-Cyclohexen-1-one
91	3,4-Dimethyl-2-hydroxy-2-cyclopenten-1-one	21,835–00-7	MS	–	1060	83, 111	126	2-Cyclohexen-1-one
92	3-Methyl-2-cyclohexene-1-one	1193–18-6	RI, MS	1077	1063	54, 82	110	2-Cyclohexen-1-one
93	2,3,5-Trimethyl-2-cyclopenten-1-one	54,562–24-2	RI, MS	1071	1067	81, 124	109	2-Cyclohexen-1-one
94	3-Ethyl-2-cyclopenten-1-one	5682–69-9	MS	–	1083	95	110	2-Cyclohexen-1-one
95	3,5-Dimethyl-2-cyclohexene-1-one	1123–09-7	RI, MS	1111	1116	124, 54	82	2-Cyclohexen-1-one
96	3-Ethyl-2-hydroxy-2-cyclopenten-1-one	21,835–01-8	MS	–	1122	83, 111	126	2-Cyclohexen-1-one
97	2-Hydroxy-3-propyl-2-cyclopenten-1-one	25,684–04-2	MS	–	1210	112, 125	140	2-Cyclohexen-1-one
98	2,3-Dihydro-1H-Inden-1-one	83–33-0	RI, MS	1292	1288	104	132	3-Furaldehyde
99	2,3-Dihydro-2-methyl-1H-inden-1-one	17,496–14-9	MS	-	1314	146	131	3-Furaldehyde
100	Piperonal	120–57-0	Std, RI, MS	1339	1342	150, 121	149	Piperonal
101	2,3-Dihydro-7-hydroxy-3-methyl-1H-inden-1-one	40,513–50-6	MS	–	1390	147	162	3-Furaldehyde
	Other related compounds
102	3-Methyl-1-butanol	123–51-3	RI, MS	734	731	70	55	Phenol
103	α-Pinene	80–56-8	Std, RI, MS	939	936	77,136	93	α-Pinene
104	1-Methylcyclopentene	693–89-0	MS	–	945	82	67	2-Cyclohexen-1-one
105	2-Pyrimidinol	51,953–13-0	MS	–	974	68	96	Phenol
106	β-Pinene	19,902–08-0	Std, RI, MS	981	981	77, 121	93	β-Pinene
107	2-Acetyloxyethyl acetate	111–55-7	RI, MS	988	992	116, 103	86	Phenol
108	α-Phellandrene	99–83-2	Std, RI, MS	1007	1006	77, 136	93	α-Phellandrene
109	Limonene	5989–27-5	Std, RI, MS	1030	1031	121, 136	68	Limonene
110	Eucalyptol	470–82-6	Std, RI, MS	1033	1035	108, 81	154	Eucalyptol
111	Benzyl alcohol	100–51-6	Std, RI, MS	1038	1037	79, 91	108	Benzyl alcohol
112	Phthalan	496–14-0	MS	–	1082	120	91	Phenol
113	Linalool	78–70-6	Std, RI, MS	1094	1095	93, 121	71	Linalool
114	2-Methoxy-3-methylpyrazine	2847–30-5	Std, RI, MS	1131	1135	81, 109	124	2-Methoxy-3-methylpyrazine
115	Benzoic acid	65–85-0	Std, RI, MS	1171	1175	122, 77	105	Benzoic acid
116	1,2,3-Trimethoxybenzene	634–36-6	Std, RI, MS	1309	1311	125, 153	168	1,2,3-Trimethoxybenzene
117	1,2,3-Trimethoxy-5-methylbenzene	6443–69-2	Std, RI, MS	1409	1401	139, 167	182	1,2,3-Trimethoxy-5-methylbenzene
118	Caryophyllene	87–44-5	Std, RI, MS	1435	1437	93, 161	133	Caryophyllene
119	3-Phenoxybenzaldehyde	39,515–51-0	RI, MS	1711	1714	169	198	Phenol

^aIdentification via: Std: reference substance, RI: retention index, MS: mass spectrum.

^bRetention indices for DB-5 column were retrieved from online databases including www.odour.org, www.pherobase.com, www.flavornet.org, and www.vcf-online.nl.

^cCalibration equivalent: the respective substance was quantified as equivalent to the listed compound, respectively, if available, quantified with reference substance.

Figure 1. Heat map representing the sensitivity and precision in terms of intensity and RSD% for different commercial SPME fibres including CAR/PDMS, DVB/CAR/PDMS, PDMS, PDMS/DVB, and polyacrylate coatings.

Figure 2. Chromatographic elution pattern of the liquid smoke components and response surfaces of high- (furfural), medium- (4-methylguaiacol), and low (4-ethylsyringol)-volatile compounds in liquid smoke.

Table 2. Method performance characteristics associated with liquid smoke components.

		LOD^b		LOQ			Precision (RSD%)
Sl.	Compound^a	pg/vial	(µg/L)	pg/vial	(µg/L)	Coefficient of determination	Intra-day	Inter-day
	Furan derivatives
1	3-Furancarboxaldehyde	14.3	(1.4)	40.9	(4.1)	0.989	1.9	3.1
2	2-(Methoxymethyl)-furan	–	–				3.0	3.8
3	2-Furancarboxaldehyde	–	–				4.1	4.6
4	5-Methyl-2-furancarboxaldehyde (5-methylfurfural)	5.7	(0.6)	16.3	(1.6)	0.988	4.4	5.5
5	3-Hydroxy-2-methyl-4H-pyran-4-one	–	–				4.5	3.3
6	2-Methylbenzofuran	18.2	(1.8)	52.1	(5.2)	0.990	2.1	3.8
	Phenols
7	Phenol	30.5	(3.0)	87.0	(8.7)	0.990	1.9	2.3
8	2-Methylphenol	8.2	(0.8)	23.4	(2.3)	0.976	0.8	2.7
9	Acetophenone	38.0	(3.8)	108.7	(10.9)	0.988	2.5	3.7
10	2-Ethylphenol	6.0	(0.6)	17.5	(1.8)	0.990	2.5	2.4
11	2-Propylphenol						3.0	3.6
	Guaiacol derivatives
12	2-Methoxyphenol	123.9	(12.4)	354.1	(35.4)	0.993	1.9	2.5
13	4-Methoxy-3-methylphenol	–	–				3.9	3.2
14	2-Methoxy-4-methylphenol (4-methylguaiacol)	4.2	(0.4)	12.1	(1.2)	0.989	3.8	2.7
15	2-Methoxy-5-methylphenol	–	–				4.1	4.9
16	2-Methoxy-3-methylphenol	–	–				5.0	4.1
17	2-Methoxy-4-vinylphenol (4-vinylguaiacol)	6.5	(0.6)	18.5	(1.8)	0.999	1.8	2.2
18	4-Ethyl-2-methoxyphenol (4-ethylguaiacol)	5.2	(0.5)	14.9	(1.5)	0.975	2.3	3.6
19	1-(3-Hydroxy-2-methoxyphenyl)-ethanone	–	–				3.7	4.1
20	2-Methoxy-4-(2-Propenyl)-phenol (eugenol)	3.9	(0.4)	11.1	(1.1)	0.987	2.2	2.4
21	2-Methoxy-4-propylphenol (4-propylguaiacol)	3.3	(0.3)	9.5	(1.0)	0.978	2.1	2.1
22	4-Hydroxy-3-methoxybenzaldehyde (vanillin)	31.7	(3.2)	90.5	(9.1)	0.971	2.3	2.6
23	2-Methoxy-4-(1-propenyl)-phenol (trans-isoeugenol)	81.3	(8.1)	232.2	(23.2)	0.965	2.8	2.1
24	1,2-Dimethoxy-4-(2-propenyl)-benzene (methyl eugenol)	–	–				2.9	3.9
25	2-Methoxy-4-(1-propenyl)-phenol (cis-isoeugenol)	–	–				2.1	3.1
26	4-Hydroxy-3-methoxybenzoic acid methyl ester (methylvanillate)	7.2	(0.7)	20.5	(2.0)	0.987	3.6	2.7
	Syringol derivatives
27	2,6-Dimethoxyphenol (syringol)	33.9	(3.4)	96.8	(9.7)	0.988	2.6	3.6
28	2,6-Dimethoxy, 4-methylphenol (4-methylsyringol)	–	–				4.0	4.5
29	3,4-Dimethoxybenzoic acid (veratric acid)	–	–				3.4	2.5
30	2,6-Dimethoxy-4-ethylphenol (4-ethyl syringol)	–	–				2.8	3.4
	Other related compounds
31	2-Methoxy-3-methylpyrazine	351.9	(35.2)	1005.4	(100.5)	0.996	1.3	2.2
32	1,2-Dimethoxybenzene (veratrole)	11.8	(1.2)	33.7	(3.4)	0.990	2.1	3.5
33	3,5-Dimethoxytoluene	10.8	(1.1)	30.8	(3.1)	0.986	5.3	5.0
34	1,2,3-Trimethoxybenzene	6.9	(0.7)	19.6	(2.0)	0.986	4.3	4.8

^aCompounds (34 out of 119 identified substances) used for method optimisation and evaluation purposes.

^bInstrumental LODs, LOQs, and coefficients of determination were estimated where reference substances were available.

Table 3. Contents of smoke flavouring compounds in several commercial primary smoke flavouring products.^b

Sl.	Compounds	Smoke flavourings
		Type 1	Type 2	Type 3	Type 4	Type 5	Type 6
	Furan/pyran derivatives
1	3-Furancarboxaldehyde (3-furaldehyde)	2.0 ± 0.3	7.5 ± 0.3	4.1 ± 0.1	4.9 ± 0.2	4.7 ± 0.2	4.5 ± 0.2
2	2-Methoxymethylfuran^a	0.1	ND^c	ND	ND	0.8	13.5
3	2-Furancarboxaldehyde (furfural)^a	36.4	307.0	158.5	185.5	187.7	184.8
4	2-Furanmethanol (furfuryl alcohol)	<LOQ^d	0.1 ± 0.2	0.1 ± 0.1	0.2 ± 0.0	0.2 ± 0.2	2.7 ± 0.1
5	1-(2-Furanyl)-ethanone^a	4.7	35.3	22.4	24.5	26.8	65.4
6	g-Butyrolactone^a	ND	0.8	0.3	1.0	1.0	0.8
7	5-Methyl-2-furancarboxaldehyde (5-methylfurfural)	8.3 ± 0.7	66.3 ± 0.4	40.9 ± 0.3	60.4 ± 0.0	43.5 ± 3.0	64.7 ± 3.9
8	2-Methylfuroate	0.7 ± 0.1	4.8 ± 0.1	3.2 ± 0.1	3.6 ± 0.0	3.7 ± 0.1	4.3 ± 0.3
9	5-Methyl-2(5H)-furanone^a	0.5	3.7	2.8	3.2	4.1	22.2
10	1-(2-Furanyl)-1-propanone^a	0.9	7.7	4.7	5.0	5.1	7.5
11	2-Acetyl-5-methylfuran^a	0.5	5.8	3.6	3.7	4.7	12.5
12	5-Methyl-4-hydroxy-3(2H)-furanone^a	ND	0.9	1.1	1.6	0.9	57.0
13	3-Hydroxy-2-methyl-4H-pyran-4-one (maltol)^a	0.5	4.1	3.4	4.0	4.0	15.3
14	2-Methylbenzofuran	0.1 ± 0.0	0.2 ± 0.0	0.1 ± 0.0	0.1 ± 0.0	0.1 ± 0.0	0.7 ± 0.0
15	5-Acetoxymethyl-2-furaldehyde^a	ND	ND	ND	ND	ND	7.9
	Phenols
16	Phenol	18.2 ± 0.5	77.7 ± 1.2	50.8 ± 0.2	59.5 ± 1.3	55.2 ± 0.5	325.4 ± 14.6
17	2-Methylphenol	9.3 ± 0.3	49.6 ± 0.3	30.9 ± 0.3	33.3 ± 0.4	30.6 ± 1.4	116.0 ± 7.7
18	Acetophenone	0.5 ± 0.1	3.2 ± 0.1	1.9 ± 0.1	2.0 ± 0.0	2.1 ± 0.1	5.5 ± 0.4
19	3-Methylphenol	0.3 ± 0.3	2.5 ± 0.1	1.7 ± 0.0	1.8 ± 0.0	2.0 ± 0.3	6.7 ± 0.5
20	2,5-Dimethylphenol	2.2 ± 0.0	13.8 ± 0.1	8.4 ± 0.2	8.8 ± 0.0	8.5 ± 0.5	20.3 ± 1.4
21	2-Ethylphenol	0.7 ± 0.0	2.9 ± 0.0	1.9 ± 0.0	2.0 ± 0.0	1.9 ± 0.1	5.3 ± 0.4
22	2,4-Dimethylphenol^a	3.2	26.4	17.1	17.9	16.1	46.1
23	4-Ethylphenol^a	0.6	3.6	2.8	3.6	2.8	8.3
24	3,5-Dimethylphenol^a	ND	2.2	1.1	1.1	1.1	2.6
25	2,3-Dimethylphenol	ND	2.0 ± 0.0	0.8 ± 0.1	0.9 ± 0.0	0.8 ± 0.1	2.8 ± 0.3
26	3-Ethylphenol	ND	2.1 ± 0.0	1.4 ± 0.1	1.6 ± 0.0	1.3 ± 0.1	5.2 ± 0.6
27	3,4-Dimethylphenol^a	0.5	5.0	3.0	3.0	2.9	7.1
28	2,4,6-Trimethylphenol	ND	0.3 ± 0.0	ND	ND	ND	0.7 ± 0.1
29	2-Propylphenol^a	0.3	1.5	1.1	1.1	1.0	2.3
30	2-Ethyl-6-methylphenol^a	ND	4.9	2.8	2.8	2.6	10.5
31	4-Propylphenol^a	ND	0.5	0.3	0.3	0.1	1.5
32	2,3,6-Trimethylphenol	ND	2.4 ± 0.0	1.6 ± 0.0	1.6 ± 0.0	1.4 ± 0.1	3.6 ± 0.6
33	Thymol	0.5 ± 0.0	0.9 ± 0.0	0.8 ± 0.0	0.8 ± 0.0	0.7 ± 0.0	1.2 ± 0.1
34	2,4,5-Trimethylphenol^a	ND	ND	ND	ND	ND	0.4
35	2-Methyl-6-(2-propenyl)-phenol^a	ND	ND	ND	ND	ND	0.3
	Guaiacol derivatives
36	2-Methoxyphenol (guaiacol)	25.9 ± 0.2	290.1 ± 0.4	189.7 ± 0.5	204.9 ± 0.3	202.9 ± 0.6	304.4 ± 19.5
37	4-Methoxy-3-methylphenol^a	1.3	8.7	5.5	5.3	5.9	7.7
38	2-Methoxy-4-methylphenol (4-methylguaiacol)	15.0 ± 1.7	251.1 ± 1.3	179.4 ± 0.6	192.8 ± 1.7	181.6 ± 2.7	211.9 ± 15.1
39	2-Methoxy-5-methylphenol^a	3.2	2.6	2.1	2.4	2.2	2.1
40	2-Methoxy-3-methylphenol^a	3.2	51.9	30.3	31.6	31.1	40.5
41	2-Methoxy-4-vinylphenol (4-vinylguaiacol)	3.1 ± 0.1	25.0 ± 0.5	21.2 ± 0.6	20.6 ± 0.6	18.3 ± 1.3	42.6 ± 4.5
42	4-Ethyl-2-methoxyphenol (4-ethylguaiacol)	1.6 ± 0.2	35.6 ± 0.3	26.9 ± 0.1	28.4 ± 0.2	25.9 ± 0.8	23.1 ± 1.9
43	1-(3-Hydroxy-2-methoxyphenyl)-ethanone^a	ND	1.9	1.3	1.4	1.2	1.0
44	2-Methoxy-4-(2-propenyl)-phenol (eugenol)	0.6 ± 0.0	8.8 ± 0.1	6.7 ± 0.0	6.8 ± 0.1	6.2 ± 0.3	5.9 ± 0.6
45	4-Ethyl-6-methyl-2-methoxyphenol^a	ND	4.8	3.4	3.6	3.3	3.7
46	2-Methoxy-4-propylphenol (4-propylguaiacol)	0.5 ± 0.0	3.8 ± 0.1	3.1 ± 0.0	3.1 ± 0.0	2.9 ± 0.1	2.1 ± 0.2
47	4-Hydroxy-3-methoxybenzaldehyde (vanillin)	0.2 ± 0.4	0.7 ± 0.4	1.2 ± 0.8	1.7 ± 0.8	6.3 ± 1.0	12.5 ± 1.4
48	1,2-Dimethoxy-4-(2-propenyl)-benzene (methyl eugenol)^a	0.1	0.2	0.2	0.2	0.2	0.3
49	2-Methoxy-4-(1-propenyl)-phenol (isoeugenol)	1.4	15.0	11.0	10.5	8.5	13.6
50	4-(2-Hydroxyethyl)-2-methoxyphenol (homovanillyl alcohol)	0.5 ± 0.2	3.0 ± 0.2	2.8 ± 0.1	2.7 ± 0.1	2.4 ± 0.2	2.7 ± 0.3
51	1-(4-Hydroxy-3-methoxyphenyl)-ethanone (acetovanillone)	<LOQ	0.3 ± 0.3	0.9 ± 1.1	1.4 ± 1.4	0.5 ± 0.3	9.8 ± 1.3
52	4-Hydroxy-3-methoxybenzoic acid methyl ester (methylvanillate)	0.3 ± 0.0	0.7 ± 0.1	0.7 ± 0.1	0.6 ± 0.3	0.8 ± 0.0	0.8 ± 0.2
53	1-(4-Hydroxy-3-methoxyphenyl)-2-propanone (2-propiovanillone)	0.2 ± 0.0	0.5 ± 0.4	0.9 ± 0.7	1.2 ± 0.8	0.6 ± 0.1	3.5 ± 0.7
	Benzenediol and derivatives
54	1,2-Dimethoxybenzene (veratrole)	0.5 ± 0.0	1.0 ± 0.0	0.8 ± 0.0	0.8 ± 0.0	0.8 ± 0.0	1.0 ± 0.0
55	1,4-Dimethoxybenzene	0.1 ± 0.0	0.2 ± 0.0	0.2 ± 0.0	0.2 ± 0.0	0.2 ± 0.0	0.3 ± 0.0
56	1,2-Benzenediol (pyrocatechol)	0.2 ± 0.1	1.1 ± 0.4	1.3 ± 0.1	1.6 ± 0.0	0.9 ± 0.1	0.8 ± 0.0
57	2-Methoxy-1,4-benzenediol (2-methoxy hydroquinone)^a	0.1	0.2	0.2	0.3	0.2	0.8
58	3,5-dimethoxytoluene	0.3 ± 0.0	2.6 ± 0.0	2.1 ± 0.0	2.2 ± 0.0	2.1 ± 0.1	2.0 ± 0.1
59	3-Methyl-1,2-benzenediol (3-methylcatechol)	0.1 ± 0.0	0.1 ± 0.0	0.1 ± 0.1	0.2 ± 0.1	0.1 ± 0.0	0.3 ± 0.0
60	3-Methoxy-1,2-benzenediol (3-methoxy-pyrocatechol)	ND	0.2 ± 0.0	0.4 ± 0.0	0.8 ± 0.1	0.3 ± 0.0	1.0 ± 0.0
61	4-Methyl-1,2-benzenediol (4-methylcatechol)^a	ND	ND	ND	4.2	0.6	1.6
62	2,6-Dimethoxyphenol (syringol)	1.4 ± 0.3	7.4 ± 0.2	9.8 ± 0.5	12.6 ± 0.5	9.2 ± 0.1	34.2 ± 0.5
63	2,6-Dimethoxy-4-methylphenol (4-methylsyringol)^a	0.8	1.8	1.7	1.6	1.6	9.9
64	3,4-Dimethoxybenzoic acid (veratric acid)^a	0.1	0.1	0.1	0.1	0.1	0.1
65	4-Ethyl-2,6-dimethoxyphenol (4-ethyl syringol)^a	ND	4.5	8.5	10.4	7.3	9.7
66	2,6-Dimethoxy-4-(2-propenyl)-phenol (4-allylsyringol)	0.4 ± 0.0	0.8 ± 0.2	1.3 ± 0.6	1.6 ± 0.6	1.1 ± 0.1	1.5 ± 0.4
67	4-Propyl-2,6-dimethoxyphenol (4-propyl syringol)^a	ND	0.1	1.0	1.2	0.7	0.2
68	4-Hydroxy-3,5-dimethoxybenzaldehyde (syringaldehyde)^a	0.1	0.1	0.1	0.1	0.1	0.1
69	1-(4-Hydroxy-3,5-dimethoxyphenyl)-ethanone (acetosyringone)	0.4 ± 0.0	0.4 ± 0.0	0.4 ± 0.0	0.4 ± 0.0	0.4 ± 0.0	0.5 ± 0.1
	Aldehydes and ketones
70	2-Methyl-2-butenal^a	0.1	ND	ND	ND	ND	1.7
71	3-Hydroxy-2-butanone^a	ND	0.2	ND	0.1	0.2	15.8
72	Cyclopentanone^a	0.9	3.6	2.0	2.3	2.6	6.9
73	2-Methyl-cyclopentanone^a	0.4	0.6	0.3	0.4	0.3	1.6
74	1-(Acetyloxy)-2-propanone^a	0.7	0.2	0.4	0.4	0.1	92.4
75	3-Methyl-2-cyclopenten-1-one^a	0.1	0.4	0.2	0.3	0.4	2.8
76	2-Methyl-2-cyclopenten-1-one^a	4.8	17.2	10.2	11.4	12.9	43.4
77	2,5-Hexanedione^a	ND	0.6	0.4	0.7	0.4	15.1
78	2-Cyclohexen-1-one	0.7 ± 0.2	2.7 ± 0.1	1.5 ± 0.0	1.7 ± 0.0	1.9 ± 0.2	13.9 ± 0.8
79	3,4-Dimethyl-2-cyclopenten-1-one^a	0.5	1.8	1.2	1.3	1.3	3.2
80	2,3-Dimethyl-2-cyclopenten-1-one^a	0.3	1.3	0.7	0.8	0.8	3.4
81	Benzaldehyde^a	2.3	2.7	1.6	8.4	2.2	3.0
82	4-Methyl-2-cyclopenten-1-one^a	1.6	6.7	4.9	4.5	6.2	65.0
83	2,3-Dimethyl-2-cyclopenten-1-one^a	1.4	6.6	4.0	4.3	4.5	10.6
84	2,3,4-Trimethyl-2-cyclopenten-1-one^a	ND	0.8	0.5	0.5	0.5	0.1
85	3-Methyl-1,2-cyclopentanedione (cyclotone)^a	2.8	12.9	13.9	18.6	13.0	29.7
86	3,4,5-Trimethyl-2-cyclopenten-1-one ^a	0.3	4.7	2.9	3.1	4.1	10.3
87	2,3-Dimethyl-2-cyclopenten-1-one^a	1.8	9.7	6.7	6.9	7.7	39.5
88	Benzene acetaldehyde	ND	0.8 ± 0.0	ND	ND	ND	ND
89	2-Hydroxybenzaldehyde	0.9 ± 0.1	2.6 ± 0.1	1.5 ± 0.0	1.7 ± 0.0	1.5 ± 0.1	3.1 ± 0.2
90	2,3-Dimethyl-2-cyclopenten-1-one^a	1.8	9.7	6.7	7.0	7.7	39.5
91	3,4-Dimethyl-2-hydroxy-2-cyclopenten-1-one^a	0.2	1.5	1.4	1.8	1.1	18.7
92	3-Methyl-2-cyclohexene-1-one^a	0.2	0.9	ND	ND	0.6	2.2
93	2,3,5-Trimethyl-2-cyclopenten-1-one^a	0.8	3.4	1.5	2.3	2.5	10.5
94	3-Ethyl-2-cyclopenten-1-one^a	12.4	1.9	1.2	1.1	2.0	10.4
95	3,5-Dimethyl-2-cyclohexene-1-one^a	ND	2.0	1.4	1.4	1.3	1.3
96	3-Ethyl-2-hydroxy-2-cyclopenten-1-one^a	0.5	3.0	3.2	4.2	2.5	36.5
97	2-Hydroxy-3-propyl-2-cyclopenten-1-one^a	ND	0.1	0.1	0.2	0.2	1.8
98	2,3-Dihydro-1H-Inden-1-one^a	0.4	3.9	2.7	2.9	2.7	8.8
99	2,3-Dihydro-2-methyl-1H-inden-1-one^a	ND	1.0	0.8	0.8	0.7	1.1
100	Piperonal	0.4 ± 0.0	0.4 ± 0.0	0.4 ± 0.0	0.4 ± 0.0	0.4 ± 0.0	0.5 ± 0.0
101	2,3-Dihydro-7-hydroxy-3-methyl-1H-inden-1-one^a	ND	0.2	0.1	0.1	0.1	0.5
	Other related compounds
102	3-Methyl-1-butanol^a	ND	ND	ND	13.3	ND	ND
103	α-Pinene	0.2 ± 0.0	0.2 ± 0.0	0.2 ± 0.0	0.2 ± 0.0	0.2 ± 0.0	0.2 ± 0.0
104	1-Methylcyclopentene^a	0.3	1.3	0.7	1.3	0.8	3.4
105	2-Pyrimidinol^a	10.0	7.1	7.0	0.3	5.5	9.4
106	β-Pinene	0.3 ± 0.0	0.3 ± 0.0	0.3 ± 0.0	0.3 ± 0.0	0.3 ± 0.0	0.7 ± 0.1
107	2-Acetyloxyethyl acetate^a	ND	ND	ND	ND	ND	34.6
108	α-Phellandrene	0.2 ± 0.0	0.2 ± 0.0	0.2 ± 0.0	0.2 ± 0.0	0.2 ± 0.0	0.2 ± 0.0
109	Limonene	0.2 ± 0.0	0.4 ± 0.0	0.3 ± 0.0	0.3 ± 0.0	0.3 ± 0.0	0.4 ± 0.0
110	Eucalyptol	ND	ND	ND	0.1 ± 0.0	0.1 ± 0.0	0.1 ± 0.0
111	Benzyl alcohol	2.9 ± 0.5	0.7 ± 0.0	0.5 ± 0.0	3.4 ± 0.1	0.5 ± 0.0	0.8 ± 0.1
112	Phthalan^a	ND	0.8	0.3	0.3	0.4	1.0
113	Linalool	0.4 ± 0.0	0.4 ± 0.2	0.4 ± 0.0	0.4 ± 0.0	0.5 ± 0.1	2.4 ± 1.5
114	2-Methoxy-3-methylpyrazine	8.4 ± 0.8	39.4 ± 1.3	27.9 ± 0.7	27.1 ± 1.1	30.2 ± 0.2	49.2 ± 0.7
115	Benzoic acid	ND	5.1 ± 0.4	ND	0.4 ± 0.1	ND	ND
116	1,2,3-Trimethoxybenzene	0.3 ± 0.0	0.4 ± 0.0	0.4 ± 0.0	0.4 ± 0.0	0.4 ± 0.0	0.5 ± 0.0
117	1,2,3-Trimethoxy-5-methylbenzene	1.5 ± 0.2	16.4 ± 0.3	18.5 ± 1.2	19.8 ± 0.1	17.7 ± 0.8	20.7 ± 2.4
118	Caryophyllene	0.2 ± 0.0	0.3 ± 0.0	0.3 ± 0.0	0.3 ± 0.0	0.3 ± 0.0	0.3 ± 0.0
119	3-Phenoxybenzaldehyde^a	1.8	0.4	ND	0.1	ND	2.0

^aPseudo-content: content calculated with relative response factors of compound (see ‘calibration equivalent’ in Table 1).

^bConcentrations of compounds calibrated with reference substances are expressed as mean ± SD (mg/L) of primary liquid smoke. Only mean values were presented for all other compounds.

^cND: not detected.

^d<LOQ: below limit of quantification.