A comparison of sample extraction procedures for the determination of inorganic anions in soil by ion chromatography

Three different extraction techniques were used for aqueous extraction of anions from soil of the type Ranker that was sampled from a serpentine site. The first technique involved the use of a rotary mixer (rotary mixer assisted extraction), the second, a microwave digestion system (microwave assisted extraction), with different extraction temperatures for every cycle during the procedure as follows: 50, 100 and 150 degrees C. An ultrasonic bath (ultrasonic assisted extraction) was used for the last technique in which the durations of the extraction process were: 10, 20, 30, 40 and 50 min. The concentrations of inorganic anions in the soil extracts after filtration were determined by ion chromatography. The results showed that the microwave-assisted extraction was highly efficient, giving, at a temperature of 150 degrees C, several times higher amounts of extracted anions in water than the other two techniques. Moreover, the extracted amounts of anions obtained by means of an ultrasonic bath with an extraction time ranging from 10 to 50 min were similar to those obtained by means of the rotary mixer with an extraction time of 22 h. However, extraction using the rotary mixer was more reliable, since the extracted amounts of anions obtained by means of an ultrasonic bath do not correlate with prolongation of the extraction time.