Fate of pyrazines in the flavored liquids of e-cigarettes

Figures & data

Table 1. Quality control and quality assurance measurements for pyrazine quantification.

Pyrazine	CAS Number	Molecular weight (g/mol)	LOD (µg/mL)	LOQ (µg/mL)	Repeatability (%RSD of n = 6)	%Recovery from liquids (n = 9)^*	%Recovery fromfilters (n =9)^*
Ethylpyrazine (EP)	13925–00-3	108.14	0.03	0.10	11.8	89–100	85–90
2,5-dimethylpyrazine (DMP)	123–32-0	108.14	0.04	0.12	7.4	76–98	85–92
2,3-diethylpyrazine (DEP)	15707–24-1	136.19	0.05	0.16	6.8	88–102	80–100
2,3,5-trimethylpyrazine (TMP)	14667–55-1	122.17	0.04	0.12	8.8	81–99	64–82
2,3,5,6-tetramethylpyrazine (TeMP)	1124–11-4	136.19	0.04	0.13	7.3	81–103	76–104
Acetylpyrazine (AcP)	22047–25-2	122.12	0.02	0.08	6.8	66–86	67–88

* Recoveries were estimated on three different concentrations, each repeated in triplicates.

Table 2. Pyrazine concentration in e-liquid (µg/mL) of commercial ECIG brands with nicotine label listed in µg/mL for comparison.

Sample	Brand	Flavor	Nicotine label	EP	DMP	DEP	TMP	TeMP	AcP	Total
I	wow	Hazelnut coffee	18000	5.3	—	—	48.6	—	48.0	101.9
II	wow	Peanut butter	18000	—	13.6	—	37.3	—	19.3	70.2
III	EC blend	Kettle corn	18000	—	—	—	8.8	—	1702.4	1711.2
IV	EC blend	Buttered keoke rum coffee	18000	—	—	—	—	11.4	26.3	37.7
V	EC blend	Dragon's milk	0	—	—	—	—	—	20.6	20.6
VI	Apollo	Blubery kona coffee	12000	—	—	—	8.6	—	—	8.6
VII	Apollo	Tobacco	12000	—	—	—	100.9	508.4	62.3	671.6
VIII	Halo	Tribeca	18000	—	—	—	9.3	13.5	75.4	98.2
IX	Halo	Malibu	18000	—	—	—	—	—	—	—
X	Retro	Cheese cake walts	3000	—	—	—	—	—	138.4	138.4
XI	Retro	Roots	12000	—	—	—	—	—	—	—
XII	Vaporzone	Red tobacco	18000	—	—	—	—	—	—	—
XIII	South beach	Red tobacco	18000	—	—	—	—	—	—	—
XIV	Medusa	Charon liquorice	18000	—	—	—	25.3	35.2	—	60.5
XV	STD3		18000	81.6	81.6	76.1	81.1	90.8	78.8	490

EP: ethyl pyrazine, DMP: 2,5-dimethyl pyrazine, DEP: 2,3-diethyl pyrazine, TMP: 2,3,5-trimethyl pyrazine, TeMP: 2,3,5,6-tetramethyl pyrazine, and AcP: acetyl pyrazine. *The measured nicotine content for seven samples agreed with the label within a 5% error (data not shown).

Table 3. Pyrazine concentration (µg/mL) in aerosols (A) for several commercial e-cigarette (ECIG) brands and standard solutions (STD) Measured PG/VG ratio (v/v) in the parent liquid is also shown. Values below the limit of detection are indicated by a dash.

Sample	PG/VG	EP	DMP	DEP	TMP	TeMP	AcP	Total
Wow, Hazelnut	71.9/28.1	—	—	—	15.8 ± 0.4	—	19.8 ± 0.2	35.6 ± 0.3
Wow, Peanut Butter	84.1/15.9	—	2.6 ± 0.47	—	10.4 ± 2.4	—	12.8 ± 3.1	25.8 ± 1.4
ECBlend, Kettle Corn	70.2/29.8	—	—	—	—	—	714.3 ± 23.6	714.3 ± 23.6
Halo, Tribeca	72.0/28.0	—	—	—	0.2 ± 0.1	0.1 ± 0.0	27.8 ± 1.3	28.1 ± 1.4
Retro, Cheese Cake Waltz	52.2/47.8	—	—	—	—	—	61.2 ± 1.9	61.3 ± 1.9
STD1	71.0/29.0	—	—	—	—	—	—	—
STD2	71.0/29.0	—	—	—	—	—	—	—
STD3	71.0/29.0	26.5 ± 2.9	32.6 ± 3.8	29.0 ± 2.7	36.3 ± 3.8	40.1 ± 3.3	37.8 ± 2.0	202.3 ± 18.4

EP: ethyl pyrazine, DMP: 2,5-dimethyl pyrazine, DEP: 2,3-diethyl pyrazine, TMP: 2,3,5-trimethyl pyrazine, TeMP: 2,3,5,6-tetramethyl pyrazine, and AcP: acetyl pyrazine. L: liquid phase; A: aerosol phase.

Figure 1. Fourier-Transform-Infrared (FTIR) plots of evaporated acetylpyrazine (AcP) during thermogravimetric analysis (TGA) between 80 and 130°C. The plots show no new peaks indicative of possible degradation products and confirm that AcP evaporation was completed by 130°C.

Figure 2. Plot of the measured pyrazine concentration in aerosol particulate matter versus the concentration measured in the parent e-cigarette liquids.