Spectrophotometric determination of iron, aluminum, and phosphorus in soiland sediment extracts after their nitric and perchloric acid digestion

Pyrocatechol violet and thiocyanate methods used in the water analysis for spectrophotometric determination of aluminum (AI) and iron (Fe), respective ly, were modified for the determination of these elements in different type s of commonly used extracts of soils and sediments. The extracts were diges ted with nitric and perchloric acid in an Al-heating block as for the total phosphorus (P) analysis and aliquots of the digests were analyzed for Al a nd Fe. Comparison of the spectrophotometric methods with inductively couple d plasma method was demonstrated using (I) oxalate, citrate-dithionite, and pyrophosphate extracts of 25 samples of acid forest soils, and (ii) water, sodium hydroxide, dithionite-bicarbonate, and hydrochloric acid extracts o f eight fresh water sediments.