Analysis of vodka by ion chromatography

A number of major minerals and trace elements may be declared as part of the nutritional information for food labelling, but those alkali metals and alkaline earth metals present in the finished vodka product are there as a result of unwanted impurities gained during the manufacturing processes.

These can alter both the taste of the final product as well as causing instability problems if the levels present are not within strictly defined tolerance limits.

Vodka is thought to have its origins in medieval times when alchemists held the secrets of distillation. It is synonymous with the Slavic word meaning water.

It was perceived to have been first produced in Eastern Europe sometime in the fourteenth or fifteenth century.

Over time the equipment was gradually improved until in 1771 the German chemist Christian Ehrenfried Weigel developed the Liebig Condenser that is the forerunner of the condensing equipment of today.

Vodka is a clear spirit of high purity and can be made from a wide range of raw materials.

It can be manufactured from anything that contains starch, such as sugar beet, molasses, rye, wheat, potatoes or maize.

The cheaper western vodkas are often produced from molasses with the premium vodkas usually being made from grain or potatoes.

Water is perhaps the most crucial element in the production of a quality vodka product.

In the majority of bottles of vodka, water makes up 60% of its contents.

The water used to dilute the rectified spirit must be completely odourless and without any foreign taste otherwise precipitation of the liquor can occur.

Water is demineralised through the removal of iron and manganese compounds by aeration and filtering.

To ensure a quality product the hard materials, for example calcium ions, are softened with deionisation columns and in many cases pumped through activated charcoal.

The purity of the vodka is achieved through a highly controlled distillation process.

The process of fermentation produces a wash that contains many flavoured compounds and different alcohols.

To achieve a high purity and alcohol content, many vodkas are triple distilled, some even more.

Most vodkas are produced in continuous stills with rectification columns to remove the unwanted products.

The vodka is passed through a number of columns, each of which removes a certain impurity.

This can pose the problem of producing vodka that is very nearly pure ethanol having little or no defined characteristic taste.

To overcome this, the pure product is sometimes added to one that has been aged in wood allowing the vodka to retain some character and identification.

The distillate is then filtered and purified, most commonly through activated charcoal, where the rough edge is taken off the vodka to leave a clean, crisp taste.

The charcoal can be made from any tree, although it is generally perceived that hardwood trees such as maple, birch or beech produce the best results.

The actual method of filtration depends upon the individual vodka manufacturer, some opt for repeated filtration over silver birch and quartz sand, while one particular manufacturer is said to filter through seven columns packed with charcoal.

The spirit after purification is usually at a very high proof (often 190 proof, equivalent to 95% alcohol) before being diluted with demineralised water usually to about 80 proof (40% alcohol) for bottling.

Some manufacturers verify vodka not only by proof, existence of ethers and other harmful components, but also by the absence of heavy metals and other elements.

Chromatography is a method for separating mixtures of substances using two phases, one of which is stationary and the other mobile moving in a particular direction.

Chromatography techniques are divided up according to the physical states of the two participating phases.

The term Ion Exchange Chromatography or Ion Chromatography (IC) is a subdivision of High Performance Liquid Chromatography (HPLC).

A general definition of ion chromatography can be applied as follows: "ion chromatography includes all rapid liquid chromatography separations of ions in columns coupled online with detection and quantification in a flow-through detector".

A stoichiometric chemical reaction occurs between ions in a solution and a solid substance carrying functional groups that can fix ions as a result of electrostatic forces.

In cation chromatography these are sulphonic acid groups.

In theory ions with the same charge can be exchanged completely reversibly between the two phases.

The process of ion exchange leads to a condition of equilibrium, the side to which the equilibrium lies depends on the affinity of the participating ions to the functional groups of the stationary phases.

No sample pre-treatment was necessary and 100ml of the vodka sample was injected directly into the ion chromatograph and the response for the peaks recorded using a mobile phase eluent of tartaric acid/dipicolinic acid with the Metrohm Cation 1-2 analytical column.

The calculation was carried out automatically using integration software 761 Compact IC 1.1 against a previously prepared calibration plot.

The Metrohm 761 Compact IC is, as the name suggests, a small instrument that compromises neither in terms of its power or price.

The dimensions of 25x38x45cm house everything that is required in terms of ion chromatography to allow detection limits down to low parts per billion without the need for pre-concentration.

There are no external displays or switches, and all the hardware is fully controlled via a single RS232 connection between the IC and the PC.

All instrument parameters can be called up by mouse-click.

80 system configurations and more than 300 applications are already permanently stored within the software and it is also possible to download further systems from the Metrohm homepage for direct use with the software.

The 761 Compact IC contains everything that a high performance ion chromatograph requires; low pulsation dual piston pump, pulsation damper, electromagnetic injection valve, a two-channel peristaltic pump, high performance conductivity detector, and eluent organiser, as well as a data recording and processing module.

All the components that come into contact with the eluent and sample are metal-free.

The detector is the heart of every ion chromatograph.

The detector temperature varies by less than 0.01C and can be optimally adapted to the ambient conditions.

The outstanding temperature stability reduces interference and allows exact conductivity measurements.

Two different systems are available: with direct conductivity detection, or additionally with chemical suppression using the Metrohm Suppressor Module (MSM).

When a large sample throughput is required, it is recommended to automate the system with one of three Metrohm autosamplers: the 766 IC Sample Processor, the 788 IC Filtration Sample Processor or the 813 Compact Autosampler. The analysis produced a result of the order of approximately one mg l-1 for sodium, potassium and calcium and about 0.1 mg l-1 for magnesium.

Ion chromatography plays an important role in the analysis of alkali metals and alkaline earth metals in finished samples of vodka confirming both their presence and actual quantities.

One of the major advantages of ion chromatography as an analytical technique is that often little or no sample preparation is required, and it uses only a small amount of sample.

Results can be obtained for the four metals within ten minutes.

If the values of the metals obtained for the finished product are not within defined levels, then this gives a rapid indicator that there is a problem somewhere within one of the manufacturing processes.

The monitoring of the level of calcium and magnesium in the finished product is particularly important. High levels of these two metals can lead to instability problems with the finished vodka product, which affects both the quality of the actual vodka, and the lifetime for which it can be stored. If the levels of sodium and potassium are out of specification then this can also lead to problems affecting the distinctively defined taste characteristics for a particular brand that the consumer expects.

References: The following internet sites were used extensively as references and can be used to obtain further information: www.metrohm.ch, www.fluidfoundation.com, www.smirnoff.com, www.polishvodkas.com, www.cocktails.about.com