title: Determination of phosphate in soil extracts in the field: A green chemistry enzymatic method.
abstract: Measurement of ortho-phosphate in soil extracts usually involves sending dried samples of soil to a laboratory for analysis and waiting several weeks for the results. Phosphate determination methods often involve use of strong acids, heavy metals, and organic dyes. To overcome limitations of this approach, we have developed a phosphate determination method which can be carried out in the field to obtain results on the spot. This new method uses: •Small volumes.•An enzymatic reaction.•Green chemistry. First, the soil sample is extracted with deionized water and filtered. Next, an aliquot of the soil extract (0.5 mL) is transferred to a disposable cuvette, containing 0.5 mL of reaction mixture [200 mM HEPES, pH 7.6, 20 mM MgCl2, with 80 nmol 2-amino-6-mercapto-7-methylpurine ribonucleoside (MESG) and 1 unit of recombinant purine nucleoside phosphorylase (PNP; EC 2.4.2.1)], mixed, and incubated for 10 min at field temperature. Absorbance of the completed reaction is measured at 360 nm in open-source, portable photometer linked by bluetooth to a smartphone. The phosphate and phosphorus content of the soil is determined by comparison of its absorbance at 360 nm to a previously prepared standard phosphate curve, which is stored in the smartphone app.
authors.affiliation: NECi, Lake Linden, MI 49945, USA.
authors.forename: Ellen R
authors.initials: ER
authors.lastname: Campbell
authors.affiliation: NECi, Lake Linden, MI 49945, USA.
authors.forename: Kayla
authors.initials: K
authors.lastname: Warsko
authors.affiliation: NECi, Lake Linden, MI 49945, USA.
authors.forename: Anna-Marie
authors.initials: AM
authors.lastname: Davidson
authors.affiliation: NECi, Lake Linden, MI 49945, USA.
authors.forename: Wilbur H
authors.initials: WH
authors.lastname: Bill Campbell
keywords: Enzymatic; Field; Green chemistry; HEPES, 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid; IMAC, immobilized metal-ion affinity chromatography; MESG, 2-amino-6-mercapto-7-methylpurine ribonucleoside; Open-source portable photometer; PNP, purine nucleoside phosphorylase (EC 2.4.2.1); Soil phosphate; Soil phosphate determination in the field; Soil phosphorus