Detection of geothermal phosphite using high-performance liquid chromatography

Abstract

Little is known about the prebiotic mechanisms that initiated the bioavailability of phosphorus, an element essential to life. A better understanding of phosphorus speciation in modern earth environments representative of early earth may help to elucidate the origins of bioavailable phosphorus. This paper presents the first quantitative measurements of phosphite in a pristine geothermal pool representative of early earth. Phosphite and phosphate were initially identified and quantified in geothermal pool and stream samples at Hot Creek Gorge near Mammoth Lakes, California, using suppressed conductivity ion chromatography. Results confirmed the presence of 0.06 +/- 0.02 microM of phosphite and 0.05 +/- 0.01 microM of phosphate in a geothermal pool. In the stream, phosphite concentrations were below detection limit (0.04 microM) and phosphate was measured at 1.06 +/- 0.36 microM. The presence of phosphite in the geothermal pool was confirmed using both chemical oxidation and ion chromatography/mass spectrometry.

FIGURE 1

Ion chromatograph of phosphite and phosphate standards, each at concentrations of 0.40 μM, solvated in synthetic geothermal water. The peak assignments are: (1) fluoride; (2) chloride; (3) bromide; (4) nitrate; (5) phosphite; (6) hydrogen carbonate; (7) sulfate; and (8) phosphate.

FIGURE 2

Representative chromatographs of (a) geothermal pool (solid line), (b) stream (dashed line), and (c) 18.2 MΩ water (dotted line). Data is offset for clarity.

FIGURE 3

Iodate oxidation results. Panel (a) presents typical chromatographs of geothermal pool water prior to oxidation (solid line) and 96 minutes after the addition of iodate oxidation solution (dashed line). Panel (b) presents typical chromatographs of stream water prior to oxidation (solid line) and 45 minutes after the addition of iodate oxidation solution (dashed line). Peak 9 is arsenate. Data are offset for clarity.

FIGURE 4

Representative chromatographs of a spiked geothermal pool (dashed line), geothermal pool (solid line), and 18.2 MΩ water (dotted line) samples. Each were acquired using conductivity detection in series with mass spectrometer (MS) detection. The three panels present (a) conductivity detector data, (b) single ion monitoring data at m/z = 81 ± 1, and (c) single ion monitoring data at m/z = 97 ± 1, respectively. Shaded areas represent the retention times of (peak 5) phosphite and (peak 8) phosphate, respectively. IC effluent was directed to the MS only during time intervals bracketed between the dotted lines. Data are offset for clarity.