Comparison of soluble P in soil water extracts determined by ion chromatography, colorimetric, and inductively coupled plasma techniques in PPB range

Abstract

The determination of soil solution phosphate ions at trace levels is questionable with colorimetric method due to both limit of sensitivity and possible hydrolysis of organic soluble phosphate (P). A simple procedure was developed to determine orthophosphate at trace levels in soil solutions by single-column, suppressed-ion chromatography with conductivity detection without prior sample concentration. The procedure requires column capacity selection and use of a 500-mL injection loop. The method shows a detection limit of 0.05 mg P L 21 as well as a high resolution with a Dionex AS9SC column. The proposed method was tested by analyzing 45 soil samples (Colombian oxisols) 2241 ORDER REPRINTS differently P fertilized. Phosphorus levels in solutions were also determined by green-malachite colorimetry and inductively coupled plasma as reference methods. The linear correlation between the various methods showed that analysis of orthophosphate in the ppb range by ion chromatography are likely more acceptable that value obtained with colorimetry, which hydrolyzed organic P and caused systematic error. Examination of coefficients of variation for the IC method calculated from triplicate analyses of five randomized samples (situated between 7.4 and 16.3 mg P L 21 ) showed value ranged from 2.0 to 6.7%.The procedure allows precise measurements of trace amounts of orthophosphate in the presence of moderate background levels of salts such as chloride, nitrate, and sulfate ions and was adequate for routine analysis.

Effects of Soil Drying on Soil pH and Nutrient Extractability

“…Several researchers have documented differences between P measured colorimetrically and P measured by ICP (Khiari et al 2000;Masson et al 2001;Nathan et al 2002). Generally ICP P values are greater due to the presence of organic P (Nathan et al 2002) or other complexed forms of P in soil extracts.…”

In Situ Soil Phosphorus Monitoring Probe Compared with Conventional Extraction Procedures

“…Once a redox couple on the superficial surface is achieved, a constant and reproducible time-independent potential signal is provided. Moreover, this reference electrode has inherent advantages such as low cost, easy handling, and great in-soil stability (Masson et al 2001).…”

Ion Chromatography as an Alternative to Standard Methods for Analysis of Macro-nutrients in Mehlich 1 Extracts of Unfertilized Forest Soils

“…[21][22][23][24][25] During the 5-30 min contact period with the Mehlich 1 solution each of these P sources begins to approach an equilibrium state in the soil solution. [21][22][23][24][25] During the 5-30 min contact period with the Mehlich 1 solution each of these P sources begins to approach an equilibrium state in the soil solution.…”