Last Month's Most Accessed Feature: Do feed the animals: An IC method for detecting phosphorus and sulfur in animal feed

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  • Published: Mar 1, 2018
  • Categories: Ion Chromatography
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Essential nutrients

Do feed the animals: An IC method for detecting phosphorus and sulfur in animal feed

A team of Brazilian chemists has developed an ion chromatography (IC) method for detecting phosphorus and sulfur in animal feed that is not only greener than current recommended methods, but also faster, cheaper and more sensitive.

Phosphorus and sulfur are essential nutrients for most animals, including humans, and so are regularly added to animal feed, both for livestock and domestic pets. If ingested at too high levels, however, phosphorus and sulfur can also cause health problems such as raised blood pressure and neurological disease. So manufacturers of animal feed need to make sure that phosphorus and sulfur are present at just the right concentrations, which differ for the feed for different animals.

Several methods have been developed for detecting the concentration of phosphorus and sulfur in animal feed, but they tend to be quite time-consuming, comprising a large number of steps, and require large amounts of toxic chemicals. These chemicals include acids for releasing the phosphorus and sulfur from the animal feeds and reagents for converting the phosphorus and sulfur into forms that can be detected, usually phosphates and sulfates.


Dilute nitric acid

Ion chromatography with conductivity detection can also sensitively detect phosphates and sulfates, raising the possibility that it could form the basis for a simpler, more efficient detection method. But the phosphorus and sulfur would still need to be released from the animal feed with an acid, which creates background noise that can easily mask the conductivity signal from the phosphates and sulfates.

So Marcia Mesko and her colleagues at the Universidade Federal de Pelotas decided to look for a way to reduce the amount of acid required to release phosphorus and sulfur from animal feed. The solution they came up with involves mixing the animal feed with a diluted solution of nitric acid and then heating this mixture in a microwave while applying oxygen under pressure. This creates oxygen radicals that help the dilute nitric acid to break down the animal feed, releasing the phosphorus and sulfur.

The released phosphorus and sulfur still have to be converted into phosphates and sulfates. But because IC is able to work with small sample sizes (500mg of animal feed, compared with 2g for the conventional methods), far lower amounts of reagents are required: milligrams rather than grams.


Cows, chickens, rabbits and fish

With oxygen under pressure, Mesko and her colleagues found that a nitric acid solution with a concentration of just 2mol/L was able to release the phosphorus and sulfur.  This nitric acid solution was too weak to produce much background noise, allowing the phosphorus and sulfur, once converted into phosphate and sulfate, to be detected at concentrations of 100mg/kg and 160mg/kg respectively. Increasing the concentration of the nitric acid to just 4mol/L greatly increased the background noise, raising the detection levels to 550mg/kg for phosphorus and 750mg/kg for sulfur.

As well as enhancing the sensitivity, the dilute nitric acid ensured that, compared with conventional methods, this IC method used up to seven times less acid. When added to the reductions in the amount of reagents used, this makes the IC method much greener and cheaper than conventional methods. It is also faster, taking 35 minutes rather than two and half hours, and over twice as sensitive.

As a final test, Mesko and her colleagues used their new IC method to assess the concentration of phosphorus and sulfur in various animal feeds, including feed for cows, chickens, rabbits and fish. Because these animals differ substantially in size, the chemists found that the concentrations varied quite a bit (10,026–28,357mg/kg for phosphorus and 2259–4601mg/kg for sulfur), but closely matched the values specified by the manufacturers.

Related Links

Food Chemistry, 2018, 246, 422–427: "A novel and eco-friendly analytical method for phosphorus and sulfur determination in animal feed"

Article by Jon Evans

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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