Heavy metals: Atomic coffee analysis

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  • Published: Jul 15, 2015
  • Author: David Bradley
  • Channels: Atomic
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Digesting coffee

Researchers in Poland have developed a simple alternative to the wet digestion sample preparation for roasted ground and instant coffee samples that allows them to carry out inductively coupled plasma optical emission spectrometry and flame atomic absorption spectrometry for more effective elemental analysis.

Researchers in Poland have developed a simple alternative to the wet digestion sample preparation for roasted ground and instant coffee samples that allows them to carry out inductively coupled plasma optical emission spectrometry and flame atomic absorption spectrometry for more effective elemental analysis.

In a previous issue, SpectroscopyNOW reported on the use of FAAS for the determination of mineral ion content in unroasted, green, coffee beans. In more recent work, the same team - Anna Szymczycha-Madeja, Maja Welna and Pawel Pohl of the Faculty of Chemistry, Division of Analytical Chemistry and Chemical Metallurgy, Wroclaw University of Technology, Wroclaw, Poland - has turned their attention to roasted ground coffee and instant coffee and the development of analytical procedures that allow them to obtain quantitative measurements for aluminium, barium, cadmium, cobalt, chromium, copper, manganese, nickel, lead, strontium and zinc using ICP-OES and calcium, iron, potassium, magnesium and sodium using FAAS.

Royal prep

They explain that their proposed procedure, which basically involves the use of ultrasound to assist in the solubilisation of ground coffee their mineral content in aqua regia (a fuming mixture of concentrated nitric and hydrochloric acids, 1:3 ratio). Aqua regia is well known for its ability to dissolve noble metals, hence the name, "regal water". The team points out that their approach is both fast and simple and does not require additional reagents. They have demonstrated good analytical performance with an accuracy of between −4.7 to 1.9%, the precision within 0.5–8.6% and recovery in the range 93.5–103%, as they report in the journal Food Additives & Contaminants: Part A. The team adds that their detection limits for the various metal elements analysed ranged from 0.086 nanograms per millilitre for strontium to 40 nanograms per millilitre for iron.

Precision and proof

With this level of precision and proof of principle, the researchers have carried out a preliminary classification of some eighteen coffee samples by employing principal component analysis (PCA) and a hierarchic cluster analysis. It is important for food quality control to be able to assess with precision the mineral content of a wide range of foods and beverages. Coffee is a common target of adulteration and food fraud and so obtaining baseline mineral profiles for different types of coffee from different regions will provide the authorities and others with useful information. In addition, different concentrations of physiologically relevant minerals, whether from the perspective of nutritional or toxicological studies is also important.

"In our opinion, this is the first study, where a non-digestion procedure was proposed for ground and  instant  coffee  samples  for  such  a  large  number  of  elements," the team reports. They suggest that their procedure represents an interesting  alternative  to  the routine wet sample preparation or dry-ashing processes used for ICP-OES and FAAS experiments."The suitability of the mentioned procedure could also  be  particularly  important  in  case  of  multi-element  analyses  combined  with  the multivariate data treatment of analytical results, where a great number of samples have to be pre-treated and measured," the team concludes. 

Related Links

Food Additives Contaminants: Part A 2015, xonline: "Simplified multi-element analysis of ground and instant coffees by ICP OES and FAAS"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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