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Methods for Determining Heavy Metals in Cocoa Powder

Much of today's cocoa powder comes from underdeveloped countries, like the Ivory Coast, Indonesia and Nigeria. Since many of these countries have none or only a few enforced environmental regulations, contaminants such as lead and other heavy metals can accumulate in the cocoa and pollute the foods made from it. Several methods can be used for the determination of heavy metals in cocoa powder so they can be eliminated before the cocoa reaches the consumer.

  1. Trace Metal Clean Technique

    • To use the trace metal clean technique, a clean room, or "bubble," is needed. The bubble can be created within a room and can be partitioned off with plastic. All metal must be removed from the room or bubble or it must be covered up with tape. A ventilation system in the clean room filters the air through a large HEPA filter, which filters out any metal particles already in the air. Inside the clean room, the glass or plastic containers for the cocoa powder are then washed with ultra-pure water and air dried, so no metal particles will adhere to them. Within the clean room, different methods to determine the heavy metals in cocoa powder can then be used without fear of contamination.

    Aqua Regia Digestion

    • "Aqua regia" consists of 1 volume of concentrated nitric acid mixed with 3 to 4 volumes of concentrated hydrochloric acid. It's so corrosive that it easily dissolves gold and platinum. Because of the toxic fumes, aqua regia digestion is done under a fume hood. A sample of cocoa powder is put into a plastic or glass container, mixed with the right amount of aqua regia and then gently heated in a water bath. A pre-determined amount of the solution is then taken out and put into a test tube, where it is mixed with an organic solvent and gently shaken. This solvent collects any heavy metals in the solution. This process can also be done in a microwave instead of hot water.

    Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

    • In Inductively Coupled Plasma Mass Spectrometry (ICP-MS), a cocoa sample is turned into an aerosol, which is then ionized with high-temperature argon plasma, which decomposes it to neutral elements. This ionizes the sample. The sample is then analyzed with a mass discriminator and detector. The analysis is based on the mass-to-charge ratios of the ionized samples. This process is an effective and precise way to determine the presence of heavy metals in a variety of foods, including cocoa powder. It is the most commonly used method to determine heavy metal content in food and is FDA-approved.

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