World market of alcoholic drinks is extensive and plays a great role in each state budgetary recharge. According to the statistics more than 500 million litres of spirits are produced worldwide every day. This fact leads us to understanding of high necessity of quality control of this production. Quantity of volatile compounds is the topmost quality parameter of these products. Further we will cite few legislative documents concerning methods of volatiles quantification with GC.

According to the legislations volatile compounds concentrations must be expressed in mg/L (or g/L, or g/hL) of absolute alcohol (AA).

Ethanol as Internal Standard

Oppositely to the generally adopted practices, the suggested “Ethanol as Internal Standard” method applies the major volatile compound as IS.

As ethanol always presents in alcohol-containing products, there is no necessity in its artificial addition into analysed sample. Also its concentration in mg/L AA units is known with a 100 % guarantee in each and every ethanol containing product and is equal to ethanol density. The process of sample analysis is similar to that in the traditional IS method as relative response factors (RRF) are to be determined:

(1)

where and are the values of detector response, for example, peak areas, for the i-th individual compound and ethanol in standard solution, respectively; is the concentration of the i-th analysed compound in mg/L AA units; = 789300 mg/L is ethanol density.

Method fully eliminates the necessity of sample density measurement and ABV determination as concentrations of volatiles in mg/L AA units are determined directly from GC data:

(2)

Algorithm of application

The suggested method is very simple and can be easily used in each laboratory equipped with instrumentation necessary for traditional method application. The concrete algorithm of “Ethanol as IS” method usage is the following:

• Prepare SS for calibration. For this aim gravimetrically add all analyzed volatile compounds to water-ethanol solution. The concrete algorithm of SS preparation is performed in legislation EC 2870/2000.
Note: no IS compound addition required, simply dilute the concentrated SS “A” with water-ethanol mixture to receive calibration solution “C”. Calculate volatile concentrations in mg/L AA units.
• Measure the prepared solution “C” with GC and use formula (1) to calculate calibration coefficients RRF.



Compound	Calibration
	Concentration "C", mg/L AA	Response 1, a.u.	Response 2, a.u.	Response3, a.u.	RRF
Acetaldehyde	428.250	26.548	26.676	26.955	1.224
Methyl acetate	682.510	34.498	33.961	34.613	1.517
Ethyl acetate	616.510	43.492	42.927	43.733	1.085
Acetal	552.980	52.283	51.473	52.633	0.810
Methanol	481.410	31.720	31.521	31.966	1.159
Ethanol	789300	60268	59835	60761	1.000
2-butanol	497.890	60.212	59.785	60.769	0.631
1-propanol	484.060	57.201	56.777	57.634	0.646
2-methyl-1-propanol	474.360	66.381	65.845	66.873	0.546
3-propanol	536.020	71.437	70.809	71.924	0.573
1-butanol	496.770	64.686	64.272	65.238	0.586
2-methyl-1-butanol	514.010	72.918	72.392	73.344	0.539
3-methyl-1-butanol	492.710	69.622	69.173	70.083	0.541

• Put the analysed spirit sample to the standard microvial of 2 ml volume and analyse it by GC. Use formula (2) to calculate volatile compounds concentrations directly from GC data without any preliminary manual procedures. The obtained concentrations in mg/L AA units are in full compliance with international legislative documents.