Direct Analysis of Beer by HR ICP-OES Application Note · PlasmaQuant 9100 Elite

Introduction

Beer is traditionally brewed from water, malted barley and hop. Often yeast is added during the fermentation process. Other base ingredients such as rice, wheat or corn are also used to brew beers of a huge variety with a wide range of different tastes. Since the brewing ingredients affect the taste and quality of the final beer, their quality is of highest importance. Metal contamination originating from the raw materials or the brewing process itself can adversely affect the final quality of the beer.

Copper contamination originating from the brewing kettle and increased iron contents may result in an unwanted metallic taste. Iron significantly contributes to the characteristics of the froth, which is important especially in regions where beer is traditionally served in a glass. Other elements to be monitored in beer and its precursors are sodium, zinc, manganese and calcium. Similar to iron, calcium affects the froth of the beer. Since calcium or zinc salts (CaSO4, ZnSO4) are added intentionally as a pH buffer, their final concentration needs to be adjusted.

Monitoring metallic contents in final beer products as well as in precursors of the brewing process by the use of inductively coupled plasma optical emission spectroscopy (ICP-OES) demonstrates a routine task of quality control laboratories in the brewing industry. The main focus is on highly precise and accurate measurements with minimum sample preparation and data evaluation efforts.

Major challenges in the analysis of beer are the varying contents of alcohol (typically 4–6% (v/v)), the high amount of total dissolved solids (TDS) and the carbon dioxide (CO2) contents. CO2 causes unsteady sample introduction and thus poor precision of the obtained results. Therefore it must be removed before the analysis.

Running high TDS samples in combination with moderate amounts of alcoholic components additionally requires a highly robust sample introduction and plasma system to avoid poor precision due to plasma-based signal fluctuation. To account for these effects, many ICP-OES systems require dilution of the samples. The resulting dilution factors eventually compromise limits of detection (LOD), which is a limitation for trace elemental analysis.

The presented methodology describes a direct analysis of beer for calcium, sodium, copper, zinc, manganese and iron contents by the use of a high-resolution ICP-OES, the PlasmaQuant 9100 Elite. The exceptionally high resolution allows for interference-free analysis of all investigated analytes in the demanding matrix of undiluted beer samples. The dedicated introduction kit for high matrix samples combined with the robust plasma of the high-frequency generator enables precise and accurate measurements of demanding matrices with LODs in the sub-ppb range.