A simple and rapid in situ preconcentration method for the determination of phosphate in environmental waters by use of solid-phase extraction, and its applications to brackish lake waters

A new method for phosphate purification for oxygen isotope ratio analysis in freshwater and soil extracts using solid-phase extraction with zirconium-loaded resin

RATIONALE

Phosphate (PO₄ ) oxygen isotope (δ¹⁸ O_PO4 ) analysis is increasingly applied to elucidate phosphorus cycling. Due to its usefulness, analytical methods continue to be developed and improved to increase processing efficiency and applicability to various sample types. A new pretreatment procedure to obtain clean Ag₃ PO₄ using solid-phase extraction (SPE) with zirconium-loaded resin (ZrME), which can selectively adsorb PO₄ , is presented and evaluated here.

METHODS

Our method comprises (1) PO₄ concentration, (2) PO₄ separation by SPE, (3) cation removal, (4) Cl^- removal, and (5) formation of Ag₃ PO₄ . The method was tested by comparing the resulting δ¹⁸ O_PO4 of KH₂ PO₄ reagent, soil extracts (NaHCO₃ , NaOH, and HCl), freshwater, and seawater with data obtained using a conventional pretreatment method.

RESULTS

PO₄ recovery of our method ranged from 79.2% to 97.8% for KH₂ PO₄ , soil extracts, and freshwater. Although the recovery rate indicated incomplete desorption of PO₄ from the ZrME columns, our method produced high-purity Ag₃ PO₄ and accurate δ¹⁸ O_PO4 values (i.e., consistent with those obtained using conventional pretreatment methods). However, for seawater, the PO₄ recovery was low (1.1%), probably due to the high concentrations of F^- and SO₄ ^2- which interfere with PO₄ adsorption on the columns. Experiments indicate that the ZrME columns could be regenerated and used repeatedly at least three times.

CONCLUSIONS

We demonstrated the utility of ZrME for purification of PO₄ from freshwater and soil extracts for δ¹⁸ O_PO4 analysis. Multiple samples could be processed in three days using this method, increasing sample throughput and potentially facilitating more widespread use of δ¹⁸ O_PO4 analysis to deepen our understanding of phosphorus cycling in natural environments.

A new sampling method with zirconium-loaded resin for phosphate oxygen isotope analysis in oligotrophic freshwater systems

RATIONALE

The phosphate oxygen isotope ratio ( δ 18 O PO 4 ) is a useful technique to trace the sources and biogeochemical cycles of phosphorus (P) in aquatic ecosystems. However, δ 18 O PO 4 has not been widely used in oligotrophic freshwater systems due to technical and methodological difficulties in collecting sufficient phosphate (PO₄ ) for the δ 18 O PO 4 analysis, which sometimes requires hundreds of liters of the water sample. In this study, a new approach (PaS-Zir) was developed for the δ 18 O PO 4 analysis in oligotrophic freshwater systems using zirconium (Zr)-loaded (ZrIRC) resin, which has a high affinity for PO₄ .

METHODS

ZrClO₂ was added to Amberlite IRC748 to obtain the ZrIRC resin. The adsorption/desorption experiment using KH₂ PO₄ with a known value of δ 18 O PO 4 was conducted to determine the adsorption/desorption properties of the resin and the likelihood of isotopic fractionation. By installing mesh bags filled with the resin, the PaS-Zir approach was used in two rivers with low PO₄ concentrations (0.2 and 5.3 μmol/L). A conventional sampling method was also performed in the study river with a higher PO₄ concentration to validate the efficacy of the PaS-Zir method.

RESULTS

The adsorption/desorption experiment demonstrated that the ZrIRC resin possessed a sufficient adsorption capacity (153 μmol/resin-mL) and exhibited little isotopic fractionation during the adsorption/desorption processes. Using the PaS-Zir method, we were able to collect sufficient PO₄ samples for the δ 18 O PO 4 analysis from the rivers within at least 4 days of mesh bag installation. The δ 18 O PO 4 values (14.2‰ ± 0.2‰) obtained using the PaS-Zir method were comparable to those obtained using the conventional method (14.0‰ ± 0.03‰).

CONCLUSION

We proved that the PaS-Zir method is applicable to oligotrophic freshwater systems and is generally more efficient than the conventional method. In addition, our method is useful for improving the understanding of the P dynamics of oligotrophic ecosystems because of the extremely low concentration of PO₄ commonly found in them, which are often prone to P pollution.

Preparation of resin-based composites containing Ce and cationic polymers with abundant promotional affinity sites for phosphate capture

A new type of composite, D301-Ce+, for efficient and selective phosphate removal.

The alternative use of layered double hydroxides as extraction medium coupled with microcomplexation for determination of phosphate in water samples

A simple, rapid, in situ, and green extraction combined with a microcomplexation has been developed for the spectrophotometric determination of phosphate in water samples. Through their formation, layered double hydroxides (LDHs) were employed as the extraction medium, instantly commenced by a rapid addition of a mixed solution of Mg²⁺ and Al³⁺ ions into alkaline phosphate solution. After the extraction, LDH precipitate containing phosphate was dissolved by sulfuric acid and the released phosphate was subsequently detected via its complexation with molybdate in the presence of antimonyl and ascorbic acid. Under optimum conditions, the linearity in the range of 5-200μgL^-1, with the correlation coefficient (r²) of 0.9969, and the enrichment factor (EF) of 14 were obtained. The limit of detection (LOD) of 5μgL^-1 and good precision, with the relative standard deviations (RSDs) less than 8.16%, were achieved. The proposed method was successfully applied to determine phosphate in water samples and the relative recoveries of 72.97-115.32% were obtained.

Concentrations of Arsenic in Brackish Lake Water: Application of Tristimulus Colorimetric Determination

The evaluation of a simple and rapid tristimulus colorimetric method for the determination of arsenic in brackish waters and its application to brackish water samples taken from brackish Lake Nakaumi are described. The determinations of arsenic in brackish water samples were made satisfactorily independent of sample salinity. By applying this method to lake water samples, the distributions and behaviors of arsenic in the lake and their controlling factors were clarified, such as seasonal variations of arsenic and the effect of a typhoon.

A Simple and Rapid in situ Preconcentration Method for Trace Ammonia Nitrogen in Environmental Water Samples Using a Solid-Phase Extraction Followed by Spectrophotometric Determination

A simple and rapid in situ preconcentration method for the spectrophotometric determination of trace ammonia nitrogen in environmental water samples has been developed based on solid-phase extraction using a small column packed with octadecyl group-bonded silica gel (Sep-Pak C18 cartridge). A water sample was taken into a graduated syringe for easy and simple operation and prevention of contamination immediately after sample collection. Ammonia in the sample was reacted with hypochlorite and thymol to be converted into indothymol blue; then the formed indothymol blue was collected as an ion pair between indothymol blue and tetrabutylammonium ion on a Sep-Pak C18 cartridge. The indothymol blue on the cartridge was stable for 4 days. The retained indothymol blue was easily eluted with a mixture of methanol and 0.01 mol/l sodium hydroxide solution. The color intensity due to the indothymol blue was spectrophotometrically measured at 725 nm. The proposed method was successfully applied to environmental water samples such as river water.

Diffuse Reflectance Spectroscopic Determination of Phosphate with Applications of Chromaticity Coordinates and Color Temperature

A simple and sensitive method has been developed for the determination of phosphate in the ng ml(-1) concentration range. The method utilizes the quantitative extraction of the Molybdenum Blue species of phosphate by polyurethane foam (PUF) discs prior to a diffuse reflectance spectrometric (DRS) measurement of the colored foam. A preconcentration factor of 150 has been achieved for a 100 ml sample volume. The effect of the pH of the solution on the rate of color development of the phosphomolybdenum blue has been carefully examined. A calibration graph has been established based on the Kubelka-Munk function (F(R)695), which was found to favorably correlate with the phosphate concentration. The lower detection limit (3sigma) was found to be 5 ng ml(-1), with a working analytical range of 5-70 ng ml(-1). At the same time, the chromaticity coordinates y (CIE 1931) and v' of the CIELUV (1976) were found to show good correlation with the concentration of phosphate in water. On the other hand, the calculated color temperature has been found to excellently correlate with the phosphate concentration. The different experimental parameters were thoroughly investigated.

A simple and rapid in situ preconcentration method using solid-phase extraction for the determination of dissolved manganese in brackish lake water samples

A simple and rapid in situ preconcentration method for the determination of dissolved manganese in environmental waters has been developed based on solid-phase extraction using a Sep-Pak C18 cartridge. Manganese in water samples, which was taken into a graduated syringe to easily perform the operation for collecting manganese at sampling sites, was converted into a stable complex with 4-(2-pyridylazo)resorcinol (PAR) at pH 10 immediately after sample collection. The formed Mn-PAR complex was collected by a Sep-Pak C18 cartridge, which was packed with C18-bonded silica. The complex was stable in the Sep-Pak C18 cartridge for at least one month. The retained complex was quantitatively eluted with 0.5 M hydrochloric acid. The manganese was determined by graphite-furnace AAS. The proposed method was successfully applicable to brackish lake water samples to investigate the behavior of dissolved manganese in brackish lakes.