Wine, rum and lead

Sailors and wine buffs beware. A novel method for the direct determination of lead in rum and wine could reveal their favourite tipple to be contaminated with potentially harmful quantities of the toxic heavy metal. The technique uses a flow injection hydride generation system coupled to an atomic absorption spectrometer with flame-quartz atomizer (FI-HG-AAS).

The ancient Romans added lead to their wine to give a sweeter taste to the often sour product of grape fermentation, pewter tankards contain a small amount of lead and were common until the advent of glass and ceramic drinking vessels. Even today, lead crystal glasses are often the choice of wine and liquor connoisseurs. But, lead accumulates in the body and has toxic effects so avoiding its ingestion makes sense

Chemists Latif Elçi of the University of Pamukkale, in Denizli, Turkey, Zikri Arslan of Jackson State University, Missouri, and Julian Tyson of the University of Massachusetts, Amherst, Massachusetts, USA, have looked at approaches to analysing lead content in the popular alcoholic beverages rum and wine. "An excess of ingested lead is a real health hazard affecting both the nervous system and the biosynthesis of haemoglobin," the team points out.

To carry out the test, the team acidifies the samples (0.40% by volume hydrochloric acid for wine samples and to 0.30% by volume HCl for rum samples. They then mix a 3% solution of oxidant potassium ferrocyanate [K₃Fe(CN)₆] in hydrochloric acid and then neutralise with alkaline sodium borohydride solution as reductant. The result is formation of lead hydride (PbH₄).

The team then determine the amount of lead in the original sample based on FI-HG-AAS of the lead hydride produced. They found that the values agree with those that can be obtained by the more complicated procedure of inductively coupled plasma mass spectrometry. The team says that their calibration curve is linear up to 8.0 micrograms per litre of lead, and has an error margin of just 4.58%.

The current threshold value for lead contamination of wine, as stipulated by the International Organization of Vine and Wine (OIV) is as low as it has ever been a 200 micrograms per litre. This is well below the concentration accessible to conventional AAS, the researchers point out, affirming that their direct, as opposed to batch, approach reduces the detection limit to a mere 0.16 micrograms per litre.

Generation of lead hydride in samples suspect of containing lead is, the team says, " an attractive method for analysis of non-aqueous solutions". Hydride generation can be used to determine lead in gasoline, for instance while chloroform extracts of lead pyrrolidine-1-carbodithioate can be used to determine lead content in particulate matter.

Given that wine is a complex mixture containing a variety of inorganic as well as organic substances in an aqueous-ethanol solution, much effort has been focused on developing a robust test method. The method developed by Elçi and colleagues is, the team says, "simple, fast and provides accurate." Their success with two disparate alcoholic beverages rum and wine suggest that the technique should be useful for testing a range of drinks.