Two-step method to assess water safety

Researchers investigating nutrient runoff can now access an American Society for Testing and Materials (ASTM) standard that utilises the separation capabilities of ion chromatography for the simultaneous determination of total nitrogen and phosphorous concentrations.

Developed in conjunction with Thermo Fisher Scientific, the ‘Standard Test Method for Determination of Total Nitrogen, Total Kjeldahl Nitrogen by Calculation, and Total Phosphorus in Water, Wastewater by Ion Chromatography’ allows users to concurrently monitor total nitrogen (organic nitrogen, ammonia, nitrate and nitrite) as nitrate and total phosphorus as orthophosphate in unfiltered water samples.

“Excess amounts of essential nutrients such as nitrogen and phosphorous can cause algal blooms, leading to the generation of toxic microcystins,” explained ASTM member Richard Jack, senior director, Environmental and Industrial Marketing, Chromatography and Mass Spectrometry, Thermo Fisher Scientific. “With this new method, scientists should be able to identify excess nutrients in waterways from water treatment and agricultural run-offs.”

Currently, laboratories use two methods to determine total kjeldahl nitrogen (TKN) and total phosphate. The new test method can be incorporated into existing ion chromatography protocols with the addition of a simple two-step process — sample digestion and analysis — to determine total nitrogen and total phosphate simultaneously.

During the digestion step, a water sample is digested with alkaline persulfate, which results in oxidation of nitrogen compounds to nitrate and hydrolysis of phosphorus to orthophosphate. Following this, the sample can be analysed using an ion chromatography platform to produce reproducible determination of nutrients at high throughputs. By comparing digested and undigested samples, the TKN digestion method can be eliminated — saving time and disposal costs of acidic reagents as well as reducing some of the false positives from TKN that occur with the use of acidic reagents.

“Thermo Fisher’s method provides a single, reliable instrumental method for the determination of the target analytes in water, in place of traditional multiple and complex wet chemical methods, with the opportunity for accumulative errors,” said Robert Joyce, chairman of the ASTM International Subcommittee D19.06. “We expect the method should deliver labour savings, as well as improved sensitivity and accuracy.”

The method can be found at the ASTM website.