Fast and simultaneous ultrasound-assisted extraction of exchangeable-NH4+, NO3−and NO2−species from soils followed by ion chromatography determination

A method for the determination of exchangeable-ammonium, nitrate and nitrite species in soils by using a fast and simultaneous ultrasound-assisted extraction procedure followed by ion chromatography with conductimetric detection is proposed. Variables such as extraction method (ultrasonic bath or orbital shaker) and extractant type (water or acetic acid solution) were studied. The ultrasound-assisted reaction time was optimized. The best extraction efficiency was found when 0.5 g of soil sample was ultrasonically treated with 30 mL of acetic acid solution at pH 4.0 for 20 min. The results for acid soils or moderately basic (pH ≤ 8.1) were in agreement with those obtained by a classical method. The proposed method is preferable to the classical method because it is less laborious, faster, requires lower amount of sample and reagents and no carcinogenic reagent is used. The detection limits were 1.3 μg g-1 for NH4+–N, 0.06 μg g-1 for NO3-–N, and 0.08 μg g-1 for NO2-–N. The relative standard deviations were lower than 7% (n = 3) for all nitrogen species.