Rapid, Sensitive, Microscale Determination of Phosphate in Water and Soil

Abstract

A rapid and sensitive analysis of inorganic and organic phosphorus (P) is needed to analyze water and soil extracts at submicromolar concentrations. The proposed method, based on the complexation of malachite green with phosphomolybdate under acidic conditions, was adapted to a 96-well microtiter plate format, and was tested for matrix interferences using 15 soils and some common extractants, including water, KCI, CaCl2, NaOH, and HCl. The accuracy of P determination was affected when CaCl2 and HCl concentrations were greater than 0.1 M and when NaOH concentration exceeded 0.4 M. Potassium chloride concentration up to 1 M did not interfere with P determination. The molar absorptivity was 46 841 M(-1) cm(-1) and the reagent blank absorbance was 0.071+/-0.003 (n = 10). At the 99% confidence limit, the method detection limit was calculated to be 0.006 mg P L(-1). Recovery of added inorganic P in different types of soils and extracts ranged between 95 and 112% with an average of 102%. The proposed microplate method allows P to be determined rapidly in a wide range of soil types and extracts and requires limited volume (20-200 microL). The procedure uses limited quantities (40 microL) of two stable reagents (>1 yr), and generates low amounts of hazardous waste.

Quantification of pyrophosphate in soil solution by pyrophosphatase hydrolysis

“…The final buffer concentration in each well was 15 mM. Solutions of authentic phosphorus compounds (200 mg P l À1 ) were incubated at 35 C with pyrophosphatase (final activity 0.1 nkat ml À1 ) for 24 h and the soluble reactive phosphate (SRP) concentration determined colorimetrically by the malachite green method (Irving and McLaughlin, 1990) with a detection limit of 6 mg P l À1 (D'Angelo et al, 2001). The difference between SRP in control and enzymetreated solutions was assumed to represent pyrophosphatasehydrolyzable phosphorus.…”

Determination of phosphate using a highly sensitive paired emitter–detector diode photometric flow detector

“…The malachite green method has been shown to enhance sensitivity by approximately 4 times when compared to the aforementioned methods [12,18]. A significant advantage of the malachite green method is its lack of sensitivity to experimental conditions such as changes in heating, reagent addition sequence or reaction time [12,19]. Additional advantages include higher sensitivity compared to the molybdenum blue method and the longer optimum detection wavelength than the yellow method [20].…”

A simple miniaturised photometrical method for rapid determination of nitrate and nitrite in freshwater

“…Microscale analysis using the microplate reader has also been applied to the determination of nutrients in environmental samples [14,24,25]. In the present study, at least 48 nitrate-containing samples could be simultaneously measured in duplicate within 90 min.…”