Red meat followed by port followed by gout: Measuring uric acid levels with ion-exclusion chromatography

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  • Published: Jun 11, 2012
  • Author: Jon Evans
  • Channels: Ion Chromatography
thumbnail image: Red meat followed by port followed by gout: Measuring uric acid levels with ion-exclusion chromatography

Disease of kings

Red meat followed by port followed by gout: Measuring uric acid levels with ion-exclusion chromatography

Traditionally seen as an affliction of port-drinking old men, the painful, inflammation of the joints known as gout is actually becoming more common in the developed world, with 1–2% of the population developing the condition at some point during their lives. One of the reasons for the increasing frequency of what used to be called ‘the disease of kings’ and the ‘rich man’s disease’ is that we now all have the kind of rich diets that used to be the preserve of kings, comprising lots of meat, alcohol and sugary drinks.

Gout is caused by the accumulation of needle-like crystals of uric acid in the joints, and uric acid is the end product of the breakdown of the organic molecule purine. Normally, uric acid is excreted in urine, but if the body produces too much uric acid, as a result of ingesting rich food and sugary drinks that contain high amounts of purine, then it can accumulate in the blood and cause gout. And that’s not all, because if uric acid crystalizes in the kidneys then it produces kidney stones, while high levels of uric acid have also been linked with medical conditions such as diabetes, leukemia and lymphoma.

 

Pass the urine

Uric acid isn’t all bad though, as it’s a strong anti-oxidant and so at normal levels can help to protect against cardiovascular disease. This makes it all the more important to determine bodily concentrations of uric acid in at-risk individuals, ensuring that the concentrations don’t rise to potentially problematic levels. Fortunately, this can easily be done by measuring uric acid in urine, and a large number of methods have been developed for doing this, using analytical techniques such as colorimetry, anion-exchange chromatography (AEC) and reversed phase high performance liquid chromatography (RP-HPLC).

Less fortunately, these methods tend to have several shortcomings, requiring hazardous chemicals such as organic solvents and tending to suffer interference from other compounds in the urine. ‘In human urine, many kinds of inorganic ions and non-dissociated organic compounds coexist with uric acid,’ explains Mingyu Ding at Tsinghua University in Beijing, China. ‘The inorganic anions will interfere with the determination of uric acid when AEC is employed, and the non-dissociated organic compounds will interfere with the determination of uric acid if RP-HPLC is used.’

 

Pass the pure water

To produce a method that isn’t beset by these shortcomings, Ding turned to ion-exclusion chromatography. Almost the exact opposite of ion-exchange chromatography, ion-exclusion chromatography repels unwanted ionic analytes in a sample by utilising a stationary phase with the same charge as the analytes, while binding non-ionic analytes. When analysing uric acid in urine, this means that the interfering inorganic ions pass straight through the column, leaving the non-charged organic acids such as uric acid to be separated on the stationary phase. What is more, pure water can often be used as the mobile phase in ion-exclusion chromatography, removing the need for any organic solvents.

Together with scientists at Hiroshima University in Japan, Ding and his colleagues developed an ion-exclusion chromatography method for determining uric acid concentrations, with pure water as the mobile phase. Using this method, the scientists were able to detect uric acid at concentrations as low as 0.02mg/L and produce a calibration curve that allowed them to measure uric acid concentrations accurately.

When they then used this method on diluted urine samples without any pre-treatment, they found that they were clearly able to separate uric acid from other compounds in the urine within around six minutes and measure the average uric acid concentration as around 433mg/L. If the measured level is much above this, then you probably do want to consider cutting back on the port.

Related Links

Chinese Journal of Chemistry, 2012, 30, 1102–1104: "Determination of uric acid in human urine by ion-exclusion chromatography with UV detection using pure water as mobile phase"


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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