On-line calculator AlcoDrinks on correct determination of volatile compounds, including ethanol, in alcohol products

Using this calculator, you can perform a quantitative determination of the content of volatile compounds, using ethanol as internal standard.

You should only specify the value of the area under the peaks of the analyzed compound and ethanol. As a result, you will immediately receive the concentration of analyzed compound in mg per liter of absolute alcohol (AA). Given values RRF are approximate. For more accurate results, you should enter the improved values for the calculation of RRF, corresponding to your gas chromatography.

Name of the sample:

Compound	Density*, mg/L	RRF		Area, arb. units	Concentration,
Compound	Density*, mg/L	Average**	Custom	Area, arb. units	Concentration,
acetaldehyde	783400	1.337			75.844 0.0038594447726036534
isobutyraldehyde	793800	1.109			0 0
ehtylformate	916800	1.321			0 0
acetone	784500	1.300			0 0
methyl acetate	934200	1.387			8.774 0.0003755751125583793
ethyl acetate	900300	1.117			246.401 0.010898196285665596
methanol	786600	1.223			52.800 0.0026569699787106905
2-butanone	805000	0.900			0 0
2-propanol	785000	0.969			1.615 0.00008206456845288083
ethanol	789300	1.000			789300 (39.89 v/v %)
diacetyl	990000	2.019			0 0
2-butanol	806300	0.853			0 0
1-propanol	805300	0.679			581.619 0.028860279150986864
isobutanol	801800	0.581			618.270 0.03071712321590331
isoamyl acetate	876000	0.707			0 0
1-butanol	809800	0.648			5.232 0.00025769057483797267
isoamylol	813000	0.632			891.095 0.04394340125465448
hexanol	815300	0.600			0 0
ethyllactate	1032800	1.908			0 0
cyclohexanol	962400	0.556			0 0
benzyl alcohol	1041900	0.909			0 0
phenylethanol	1013000	0.730			0 0
water	998230				59.98339618967539
sample

*Densities are given according to TOXNET - Toxicology Data Network, U.S. National Library of Medicine http://toxnet.nlm.nih.gov/.
**Average coefficients RRF are calculated on results obtained on gas chromatographs Crystal (JSC SDB Chromatec, Yoshkar-Ola, Russia).

Theoretical background and calculation

Concentration of the volatile compounds in alcohol products should be presented in mg per 1 liter of anhydrous alcohol (Absolute Alcohol - AA) in strict accordance with the regulations documents of OIV, Commission Regulation (EC) and AOAC Official Methods /1-4/. The mass concentration of ethanol in anhydrous alcohol (AA) is well known and its density is 789300 mg/L (AA). Since ethanol is present in the sample and its concentration in the anhydrous alcohol is well known, for quantitative calculation of the volatiles should use the method of internal standard (IS).
The value of the concentration of the i-th volatile compound of the test sample may be written by the following formula

(1)

(2)

where C_IS is the concentration of IS in the test sample; A_i and A_IS are peak areas of the i-th component and IS in the test sample; respectively, RF_i and RF_IS are coefficients of the detector response of i-th component and of IS in the standard working solution, respectively; C^st_i and C^st_IS are the concentrations of the i-th component and IS, respectively, expressed in mg per 1 liter of AA; A^st_i and C^st_IS the peak area of the i-th component and IS, respectively, in the standard working solution; RRF_i is relative response factor for the i-th component relative to IS.
Since in this case ethanol is the IS then C^st_ethanol = ρ_ethanol = 789300 mg/L is the value of the density of ethanol and the expressions (1) and (2) may be represented as follows /5/

(3)

(4)

where A^st_ethanol and A_ethanol are the peak areas of ethanol in the standard solution and in the test sample, respectively.

It should be noted that in the expression (3) there are not parameters such as:

name (kind/type) of sample
injection value
split ratio
values of air and hydrogen flows for flame-ionization detector (FID)
model, technical characteristics and methodic parameters of used gas chromatograph (GC)
volume concentration (v/v) of ethanol (strength) in sample
name of IS
quantity of injected IS

Determination of coefficients RRF

Values of coefficients RRF are calculated on experimental data of standard solutions with known values of concentration of volatile compounds by formula (4).

**Table 1** Results of determination of coefficients **RRF** on experimental data presented in **Figure 1**
Compound	C_i, mg/L (AA)	A_i(1), arbitrary units (a.u.)	A_i(2), arbitrary units (a.u.)	RRF_i(1)	RRF_i(2)	RRF_i(aver)
acetaldehyde	1093.7	2242.73	1928.25	1.357	1.316	1.337
methyl acetate	1051.1	2102.54	1762.88	1.391	1.384	1.387
ethyl acetate	1058.4	2628.58	2204.95	1.121	1.114	1.117
methanol	1119.1	2583.30	2092.81	1.206	1.241	1.223
2-propanol	1047.1	2990.90	2520.33	0.974	0.964	0.969
ethanol	789300	2196575	1831688	1.000	1.000	1.000
1-propanol	1029.0	4173.81	3553.94	0.686	0.672	0.679
isobutanol	1035.1	4910.14	4170.46	0.587	0.576	0.581
1-butanol	1042.8	4450.13	3764.17	0.652	0.643	0.648
isoamylol	1054.0	4621.50	3883.01	0.635	0.630	0.632
cyclohexanol	117.36	590.93	486.77	0.553	0.560	0.556
benzyl alcohol	1051.1	3218.04	2683.40	0.909	0.909	0.909
phenylethanol	1074.2	4100.24	3406.19	0.729	0.732	0.730

Determination of concentrations of volatile compounds in the alcohol-containing sample

Determination of concentrations of volatile compounds in test sample is performed in accordance with equation (3).

**Table 2** Experimental data and data from certificate **CRM LGC5100 Whisky - Congeners**
Compound	RRF_i(aver)	A_i(1), arbitrary units (a.u.)	A_i(2), arbitrary units (a.u.)	C_i(1), mg/L (AA)	C_i(2), mg/L (AA)	C_i(cp), mg/L (AA)	Repr, %	C_i(cert), mg/L (AA)	Uncert, %	Bias, %
acetaldehyde	1.337	32.132	30.300	75.35	76.34	75.84	1.3	-	-	-
methyl acetate	1.387	3.714	3.247	9.04	8.49	8.77	6.3	-	-	-
ethyl acetate	1.117	129.678	113.097	254.18	238.15	246.17	6.5	-	-	-
methanol	1.223	24.131	23.382	51.79	53.91	52.85	4.0	52.00	6.2	1.6
2-propanol	0.969	0.918	0.916	1.56	1.67	1.62	7.0	-	-	-
ethanol	1.000	449900	418776	789300	789300	789300	0.0	-	-	-
1-propanol	0.679	489.899	452.824	583.59	579.51	581.55	0.7	570.00	4.2	2.0
isobutanol	0.581	607.886	563.278	619.96	617.17	618.56	0.5	588.00	5.3	5.2
1-butanol	0.648	4.657	4.228	5.29	5.16	5.23	2.5	4.80	22.9	8.9
isoamylol	0.632	806.883	744.870	895.08	887.70	891.39	0.8	795.80	3.5	12.0

Peak area of analyzing volatile compounds are recorded in Table 2 in arbitrary units, for example, in "mV * min" or in "pA * s".

The bias between the values of the concentrations from the certificate and the experimentally measured are not more than 12.0% relative.

References

International Organization of Vine and Wine (OIV). Compendium of international methods of wine and must analysis, 2009; Vols. 1 and 2.
Commission Regulation (EC) No 2870/2000 of 19 December 2000 laying down Community reference methods for the analysis of spirits drinks, 2000.
AOAC (Association of Official Analytical Chemists) Official Methods 972.10. Alcohol (higher) and ethyl acetate in distilled liquors. Alternative gas chromatographic method, 1975.
AOAC Official Methods 972.11. Methanol in distilled liquors. Gas chromatographic method, 1973.
Charapitsa S.V. et al. Direct Determination of Volatile Compounds in Spirit Drinks by Gas Chromatography. J. Agricultural and Food Chemistry, 2013, 61 (12), 2950–2956 DOI:10.1021/jf3044956.
Tables for determining of ethanol content in alcohol-water solutions (in Russian).