Measurement of Dissolved Reactive Phosphorus in Water with

Nov 24, 2014 - ... Science, and Food Safety Key Laboratory of Liaoning Province, Bohai University, Jinzhou, Liaoning 121013, People's Republic of Chin...
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Measurement of Dissolved Reactive Phosphorus in Water with Polyquaternary Ammonium Salt as a Binding Agent in Diffusive Gradients in Thin-Films Technique Hong Chen, Meng-Han Zhang, Jia-Li Gu, Gang Zhao, Yu Zhang, and Jian-Rong Li* College of Chemistry, Chemical Engineering and Food Safety, Research Institute of Food Science, and Food Safety Key Laboratory of Liaoning Province, Bohai University, Jinzhou, Liaoning 121013, People’s Republic of China ABSTRACT: Diffusive gradients in thin-films (DGT) sampler with a polyquaternary ammonium salt (PQAS) aqueous solution as a binding phase and a dialysis membrane as a diffusive phase (PQAS DGT) was developed for the measurement of dissolved reactive phosphorus (DRP) in water. The performance of PQAS DGT was not dependent upon pH 3−10 and ionic strength from 1 × 10−4 to 1 mol L−1. The effective binding capacity of PQAS DGT containing 2.0 mL of 0.050 mol L−1 PQAS solution was estimated as 9.9 μg cm−2. The measurement of DRP in a synthetic solution by PQAS DGT over a 48 h deployment period demonstrated high consistency with the concentration of DRP in the synthetic solution measured directly by the ammonium molybdate spectrophotometric method. Field deployments of PQAS DGT samplers allowed for accurate measurement of the DRP concentration in situ. The advantages of PQAS DGT include no requirement of the elution steps and direct concentration measurements of the binding phase. KEYWORDS: passive sampling, diffusive gradients in thin films, dissolved reactive phosphorus, polyquaternary ammonium salt, water

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INTRODUCTION Phosphorus (P) is a nutrient that influences the biological productivity in a hydrophilic ecological system. P exists in organic and inorganic forms in water.1,2 The main species of P in water are dibasic phosphate and dihydric phosphate (HPO42− and H2PO4−), which are regarded as the most easily bioavailable species of P and constitute an important part of the generally measured dissolved reactive phosphorus (DRP).1,2 The determination of DRP in aquatic environments is of great importance for comprehending eutrophication processes and P biogeochemical cycling, assessing the quality of potable water, monitoring wastewater discharge compliance, and conducting nutrient management strategies for environmental waters.1,3 There are a lot of approaches available for the determination of the concentration of DRP in natural waters.2 However, most of the commonly used approaches for DRP monitoring are highcost, labor-intensive, time-consuming, and less sensitive.1−5 Furthermore, the concentrations of DRP measured by the above approaches may not reflect the real concentrations within the natural water because of the pretreatment of the sample prior to measurement.1,5 Therefore, it is preferable to use in situ sampling techniques for the accurate measurement of DRP concentrations in natural waters. An in situ sampling approach, the diffusive gradients in thinfilms (DGT) technique,6,7 was invented and applied for sampling dissolved labile species in natural waters, soils, and sediments.8−16 There are two kinds of DGT samplers, one with a solid binding phase and the other with a liquid binding phase. The solid-type DGT sampler integrates two processes of mass transport through a diffusive phase, such as a thin polyacrylamide hydrogel and accumulation within a solid binding phase, such as ferrihydrite, and has been developed rapidly. However, polyacrylamide hydrogel has some disadvantages, such as a weak mechanical resistance and not a well© 2014 American Chemical Society

defined gel structure, and the DGT method requires elution of analyte from the binding gel that may introduce analytical deviation. Li et al. invented a liquid-type DGT sampler with a diffusive phase, such as a dialysis membrane, and a liquid binding phase, such as poly(4-styrenesulfonate) solution, with some advantages, such as a good contact between the binding phase and the diffusive phase, ideal transportion and enrichment of analyte, a well-defined reproducible diffusive phase, and no need for the elution of analyte accumulated in the binding phase.17,18 Sodium polyacrylate solution,19,20 poly(vinyl alcohol) solution,21 thiol−poly(vinyl alcohol) solution,22 poly(aspartic acid),23,24 and polymer-bound Schiff base25 have been developed as liquid binding phases recently. Zhang et al. developed a DGT sampler using ferrihydrite as a binding agent for sampling DRP.26 The method was then applied to soil systems27 and aquatic systems.28,29 However, there have been comparatively few applications of the DGT sampler for the sampling of DRP. The restricted applications of the approach should be attributed to the comparatively low capacity of the Fe oxide gel.27 To increase the capacity of the DGT sampler, titanium-dioxide-based adsorbent (Metsorb)30 and amorphous zirconium hydroxide (Zr oxide)31 were developed as the binding agentes for the measurement of DRP in a wider variety of environments. However, the measurement of DRP by the DGT technique with a liquid binding phase has not been reported. Polyquaternary ammonium salt (PQAS) is a water-soluble cationic polymer and interacts with anionic substances present in aqueous solutions.32 A PQAS aqueous solution, as a liquid Received: Revised: Accepted: Published: 12112

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Samples were taken out from both chambers at a 30 min span up to 180 min and measured by the AMS method. Diffusion coefficients, D (cm2 s−1), were calculated from the slope of a linear plot of measured mass of DRP diffused through the diffusive phase versus time, using eq 1, where A is the exposed area of the diffusive phase, Δg is the thickness of the dialysis membrane, and C is the concentration of DRP originally existing in the source chamber of the diffusion cell.36,37

binding phase in the DGT sampler, has been applied to the measurement of dissolved Cr(VI).33,34 In this paper, A DGT technique with a dialysis membrane as the diffusive phase and a PQAS aqueous solution as the binding phase (PQAS DGT) was investigated for the sampling of DRP in water. The influences of solution pH and ionic strength on the properties of PQAS DGT were studied. The PQAS DGT performance for the sampling of DRP was investigated under laboratory conditions and then deployed in wastewater and natural water. PQAS DGT will be applied for the assessment of P bioavailability in soils, which, in turn, will help effective fertilization tactics and lessen the danger of environmental pollution, owing to excessive fertilization. When PQAS DGT is applied to evaluating bioavailable P in soils, a relation will be established between the plant response to P manure and the concentration of P in soil determined by PQAS DGT, and PQAS DGT can provide a more accurate suggestion of P fertilizer needs. The study of PQAS DGT for the sampling of DRP in water will lay the foundation for the assessment of P bioavailability in soils, and the assessment of P bioavailability in soils by PQAS DGT will be reported later.

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D=

slope Δg CA

(1)

The diffusion coefficients of DRP at different temperatures can be calculated by the Stokes−Einstein equation below (eq 2)

D1η1 T1

=

D2η2 T2

(2)

where D1 and D2 are the diffusion coefficients at temperatures T1 and T2 and η1 and η2 are the viscosities of water at those temperatures.38 Validation of DGT Performance in the Laboratory. A verification test for the binding phase of DGT was carried out following the programs stated previously.17 The DGT samplers were installed according to the procedures described by Chen et al.24 The samplers were immersed in 30 L of 0.01 mol L−1 NaNO3 spiked with 50 μg L−1 P (KH2PO4) at 20 °C; triplicate samplers were taken out at 4, 8, 12, 16, 24, 36, and 48 h. The PQAS solutions in the DGT samplers were removed at each time point and analyzed by the AMS method. The concentration gradient formed within the diffusive phase allows for the amount of analyte, M, that is enriched in the binding phase from a solution, after passing through a diffusive membrane of area (A) and thickness (Δg) with diffusive coefficient (D), over a deployment time (t), to be related directly to the concentration of analyte in the bulk solution measured by DGT (CDGT).6

MATERIALS AND METHODS

Materials. Cellulose acetate dialysis membrane (CDM, ∼14 000 or greater retain) was bought from Shanghai Yuanju Bio-Tech Co., Ltd., Shanghai, China. Cellulose nitrate membrane (0.45 μm) was bought from Dikma (Tianjin, China). Poly(quaternary ammonium salt) (PQAS; Mw = 2 × 104) was obtained from Henan Titaning Chemical Technology Co., Ltd., Zhengzhou, China. Potassium dihydrogen phosphate, antimony potassium tartrate, ammonium molybdate, hydrochloric acid, sodium hydroxide, and sodium nitrate were bought from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China. Apparatus. Ultraviolet−visible (UV−vis) spectroscopy (Beijing Royleigh Analytical Instrument Co., Ltd., China) was used for measurements of the absorbance of PQAS binding solutions containing phosphates at a wavelength of 700 nm by the ammonium molybdate spectrophotometric (AMS) method based on the National Standard of the People’s Republic of China (GB 11893-89).35 A PB-10 digital pH-meter (Sartorius, Germany) equipped with a combined glass electrode was used for the measurements of pH. Preprocessing of the Diffusive Phase and the Binding Phase. Cellulose acetate dialysis membrane has been used as the diffusive phase of the DGT sampler.17,18 The dialysis membrane was preprocessed according to the procedures suggested by Li et al.17 The treated diffusive phase was kept in deionized water. A 50.0 g PQAS solution was put in a dialysis membrane bag prepared as mentioned above, which was immersed in deionized water for 72 h with the water regularly supplemented.17 This method effectually got rid of all of the low-molecular-weight PQAS that went through the dialysis membrane. Capacity of PQAS DGT. The binding capacity of PQAS DGT was examined by immersing PQAS DGT for 24 h in 10 L KH2PO4 solutions containing 0.01 M NaNO3. The concentrations of KH2PO4 were in the range of 0.1−1.2 mg of P L−1. Measurement of the Diffusion Coefficient. The diffusion coefficient of H2PO4− in the dialysis membrane in contact with synthetic water containing 0.01 M NaNO3 at pH 7 was measured using a diffusion cell.17 The cell was made of two perspex chambers linked by a 2.0 cm diameter hole. A 3.0 cm diameter and 85 μm thickness disc of the new pretreated diffusive phase was put on the opening between the chambers, assuring that the diffusive phase was the only mass transmission medium. A total of 50 mL of 0.01 mol L−1 NaNO3 solution containing 30 mg L−1 P (KH2PO4) was put into the source solution chamber, and a total of 50 mL of 0.01 mol L−1 NaNO3 solution containing 0.050 mol L−1 PQAS, an optimum concentration of PQAS solution, was put into the receptor solution chamber. Both chambers were mixed constantly using a magnetic stirring apparatus.

M=

DAC DGTt Δg

(3)

PQAS DGT samplers are verified by investigating the relationship between the mass of analyte enriched in the binding phase (M) and the deployment time (t) with a solution of known concentration. The performance of PQAS DGT is also evaluated by calculating the percentage uptake (U%), defined by the following equation:25

U% =

C DGT × 100% C bulk

(4)

where Cbulk is the total concentration of DRP in the bulk solution directly measured by the AMS method.37 Effect of Solution pH and Ionic Strength on the DGT Performance. To evaluate the influence of various pH values (2, 3, 4, 5, 6, 7, 8, 9, and 10) and ionic strengths (0.0001, 0.001, 0.01, 0.1, and 1.0 mol L−1 as NaNO3) on the PQAS DGT performance, the PQAS DGT samplers were deployed in solutions containing 50 μg L−1 P (KH2PO4) at various pH values and ionic strengths for the deployment time from 4 to 48 h. The pH values of the bulk solutions were modulated using 2% NaOH or HNO3. The ionic strengths of the solutions were modulated with the proper addition of NaNO3 at pH ∼7. Field Deployment of the DGT Samplers in Wastewater and Natural Water. PQAS DGT samplers were deployed in triplicate in a wastewater canal (Jinzhou, China); triplicate samplers were taken out at 24, 48, 72, 96, and 120 h. The PQAS solutions were removed from the PQAS DGT samplers at each time point and measured by the AMS method, and 0.45 μm filtered grab samples were gathered daily and measured directly by the AMS method. PQAS DGT samplers were immersed in triplicate in local natural waters (Nuer River, Ling River, and North Lake, Jinzhou, China); triplicate samplers were taken out at 24, 48, 72, 96, and 120 h. The PQAS solutions were removed from the PQAS DGT samplers at each time point and measured by the AMS method, and 0.45 μm filtered 12113

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linearly with time up to 48 h (r2 = 0.9993; U% = 98.7%; Figure 2). These results demonstrated that PQAS DGT worked well

grab samples were gathered daily and measured directly by the AMS method.

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RESULTS AND DISCUSSION Capacity of PQAS DGT. There is a trend for the binding phase to become saturated because of the high cumulation of the analytes when the sampling is conducted over a long term (weeks or months) or in an environment with highconcentration analytes. The DGT capacity may be a restrictive factor for such applications. The DGT capacity was studied by immersing DGT samplers in stirred solutions with phosphate concentrations in the range of 0.1−1.2 mg of P L−1. A linear response (y = 35.99x + 4.50; r2 = 0.9985) was gained with the concentration up to 0.8 mg of P L−1 (Figure 1). The effective

Figure 2. Mass of phosphorus accumulated by PQAS DGT in a synthetic solution. Concentration of P (KH2PO4), 50 μg L−1; ionic strength, 0.01 mol L−1 NaNO3; pH, 7; deployment time, from 4 to 48 h; and temperature, 20 °C.

according to the DGT principle and PQAS satisfies the conditions of the DGT binding agent for the sampling of DRP. Therefore, DRP can be measured quantitatively by PQAS DGT. DRP can be enriched in the PQAS binding phase because of the electrostatic attraction between PQAS and DRP. PQAS is a water-soluble cationic polymer and can interact with anionic substances present in aqueous solutions, whereas DRP exists as various hydrophilic anionic species, such as H2PO4− and HPO42−, in a water environment and can interact with cationic substances present in aqueous solutions.32 DRP in water can go through the diffusive phase into the binding phase of the DGT sampler and bind with PQAS quickly; a diffusive gradient of DRP is thereby formed within the dialysis membrane between water and the interface with the binding phase, resulting in an accumulation of DRP in the binding phase. Effect of the pH. The DGT measurements of DRP were not dependent upon solution pH over the pH range of 3−10, which covers most of the pH conditions in natural water (Figure 3), consistent with the earlier findings that DGT measurements of anions were not dependent upon pH.11,33,41 With the increase of solution pH, more H2PO4− was transferred into HPO42− that can be combined by PQAS more strongly because of electrostatic interaction. However, with the increase of solution pH, more competing hydroxide anions must hinder the combination of PQAS and HPO42−. It was the above two opposite factors that resulted in no significant difference between the bindings of PQAS and anionic species of DRP that existed over the pH range of 3−10. The U% values increased significantly at pH 2 probably because PQAS can combine DRP more strongly with the increase of the hydrogen ion concentration. Effect of the Ionic Strength. The binding behavior of PQAS DGT for DRP was investigated in KH2PO4 aqueous solutions containing various ionic strengths (0.0001, 0.001,

Figure 1. Dependence of accumulated mass of phosphorus on the solution concentration for 24 h exposure of a DGT sampler.

binding capacity of PQAS DGT containing 2.0 mL of 0.05 mol L−1 PQAS solution was estimated as 9.9 μg cm−2 on the basis of Figure 1 compared to the binding gels used for phosphates reported in the literature, such as ferrous oxide gel (∼2 μg cm−2),26 titanium dioxide gel (∼12 μg cm−2),30 and zirconium oxide gel (∼100 μg cm−2).31 It can be estimated that, if the mean concentration of DRP in a water was 10 μg L−1, DGT could be deployed for up to 54 days. Furthermore, by increasing the volume of the PQAS solution, extended hours of deployment can be expected. Diffusion Coefficient of DRP in the Dialysis Membrane. The diffusion coefficient of DRP through the dialysis membrane in 0.01 mol L−1 NaNO3 solutions at 20 °C was (1.95 ± 0.17) × 10−6 cm2 s−1, lower than the value of D in the synthetic polyacrylamide hydrogel (6.05 × 10−6 cm2 s−1 at 25 °C). This can be explained by the structure of the dialysis membrane with lower porosity and lower water content.26,39 Validation of the DGT Performance for the Measurement of DRP. The DGT performance is evaluated in two aspects. First, a linear relationship between the mass of analyte enriched in the binding phase (M) and the deployment time (t) should be expected, if the DGT sampler works in principle. Second, the percentage uptake of the DGT sampler should be in the range of 90−110%.40 The uptake of DRP by PQAS in the synthetic solution containing 50 μg of P L−1 increased 12114

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sampling DRP in the majority of natural fresh and marine waters, although a further study in seawater is essential to guarantee that competing anions other than nitrate do not disturb the measurement of DRP by PQAS DGT. Field Deployment. PQAS DGT samplers were put in a local wastewater canal up to 5 days to investigate the robustness of the technique further. The concentrations of DRP in the wastewater were collected daily and measured directly by the AMS method. The concentration of DRP in the wastewater measured by PQAS DGT was 32.9 ± 0.9 μg L−1, and the CDGT value is in good agreement with the average 0.45 μm filtered measurement obtained from grab samples (Csol), as shown in Table 1. Therefore, DRP in the wastewater can be sampled and measured by PQAS DGT. Table 1. Comparison of DRP Measurement by PQAS DGT and Directly by the AMS Method in Wastewater and Natural Waters

Figure 3. Effect of pH on the performance of PQAS DGT by plotting percentage uptake of DRP versus the pH, Concentration of P (KH2PO4), 50 μg L−1; ionic strength, 0.01 mol L−1 NaNO3; deployment time, from 4 to 48 h; and temperature, 20 °C.

water sample wastewater Nuer River Ling River North Lake

0.01, 0.1, and 1.0 mol L−1 as NaNO3; Figure 4). The U% value of DRP increased with the increase of the ionic strength range

CDGTa (μg L−1)

Csolb (μg L−1)

± ± ± ±

33.5 ± 1.8 NDc ND ND

32.9 4.9 4.6 6.1

0.9 0.4 0.3 0.5

a Measured by PQAS DGT. bAverage value from 0.45 μm of filtered grab samples. cND = not detected.

PQAS DGT samplers were deployed in natural waters up to 5 days for sampling DRP in the natural water. The concentrations of DRP measured by PQAS DGT in Nuer River, Ling River, and North Lake were 4.9 ± 0.4, 4.6 ± 0.3, and 6.1 ± 0.5 μg L−1, respectively (Table 1). However, the concentrations of DRP in the natural waters cannot be detected directly by the AMS method because they are below the detection limit (Table 1). This work has demonstrated the feasibility of using PQAS solution as a binding phase for in situ sampling and measurement of DRP in water. PQAS is suitable as a liquid binding agent of the DGT technique for sampling DRP. The advantages of PQAS DGT include no requirement of the elution steps and direct concentration measurements of the binding phase. The measurement of DRP in a synthetic solution by PQAS DGT over a 48 h deployment period demonstrated high consistency with the concentration of DRP in the synthetic solution measured directly by the AMS method. A future study should focus on the application of this new technique to the sampling and measurement of DRP in soils and sediments.

Figure 4. Influence of the ionic strength on the performance of PQAS DGT by plotting percentage uptake of DRP versus the NaNO3 concentration. Concentration of P (KH2PO4), 50 μg L−1; pH, 7; deployment time, from 4 to 48 h; and temperature, 20 °C.

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from 0.0001 to 0.1 mol L−1, consistent with the experimental results reported by Panther and co-workers and Lucas and coworkers.42,43 Panther and co-workers found that the diffusion coefficients of As(V) in the negatively charged Nafion membrane increased with the increase of the ionic strength.42 Lucas and co-workers also found that the diffusion coefficients of Au(III) in a diffusive gel increased with the increase of the ionic strength.43 The U% values decreased at 1.0 mol L−1 solution of NaNO3 probably because the competitive diffusion between NO 3 − and DRP in the diffusive phase was strengthened at high ionic strength.33 However, accumulation was quantitative and consistent in the ionic strength range of 0.001−1.0 mol L−1, with U% values between 90 and 110%. These results suggest that PQAS DGT can be applied for

AUTHOR INFORMATION

Corresponding Author

*Telephone: +86-416-3400008. Fax: +86-416-3400159. E-mail: [email protected]. Funding

This study was supported by the National Key Technologies Research and Development Program of China during the 12th Five-Year Plan Period (2012BAD29B06), the Public-Interest Scientific Research Fund of Liaoning Province (2012003001), and the Food Safety Key Laboratory of Liaoning Province (LNSAKF2011038). Notes

The authors declare no competing financial interest. 12115

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(18) Li, W.; Zhao, H.; Teasdale, R. P.; Wang, F. Trace metal speciation measurements in waters by the liquid binding phase DGT device. Talanta 2005, 67, 571−578. (19) Fan, H. T.; Sun, T.; Li, W.; Sui, D. P.; Jin, S.; Lian, X. J. Sodium polyacrylate as a binding agent in diffusive gradients in thin-films technique for the measurement of Cu2+ and Cd2+ in waters. Talanta 2009, 79, 1228−1232. (20) Chen, H.; Dong, J.; Niu, Y. X.; Sun, T. Determination of Ni2+ in waters with sodium polyacrylate as a binding phase in diffusive gradients in thin-films. Chem. Res. Chin. Univ. 2011, 27, 703−707. (21) Fan, H. T.; Bian, Y. Q.; Sui, D. P.; Tong, G. F.; Sun, T. Measurement of free copper(II) ions in water samples with polyvinyl alcohol as a binding phase in diffusive gradients in thin-films. Anal. Sci. 2009, 25, 1345−1349. (22) Fan, H.; Sun, T.; Xue, M.; Tong, G.; Sui, D. Preparation of thiol−polyvinyl alcohol and its application to diffusive gradients in thin-films technique. Chin. J. Anal. Chem. 2009, 37, 1379−1381. (23) Liu, Y.; Chen, H.; Bai, F.; Gu, J.; Liu, L. Application of sodium poly(aspartic acid) as a binding phase in the technique of diffusive gradients in thin films. Chem. Lett. 2012, 41, 1471−1472. (24) Chen, H.; Guo, L.; Zhang, M. H.; Zhong, K. L.; Gu, J. L.; Bo, L.; Li, J. Determination of lead in soybean sauce by the diffusive gradients in thin films technique. Food. Chem. 2014, 165, 9−13. (25) Fan, H. T.; Liu, J. X.; Sui, D. P.; Yao, H.; Yang, F.; Sun, T. Use of polymer-bound Schiff base as a new liquid binding agent of diffusive gradients in thin-films for the measurement of labile Cu, Cd, and Pb. J. Hazard. Mater. 2013, 260, 762−769. (26) Zhang, H.; Davison, W.; Gadi, R.; Kobayashi, T. In situ measurement of dissolved phosphorus in natural waters using DGT. Anal. Chim. Acta 1998, 370, 29−38. (27) Menzies, N. W.; Kusumo, B.; Moody, P. W. Assessment of P availability in heavily fertilized soils using the diffusive gradients in thin films (DGT) technique. Plant Soil 2003, 269, 1−9. (28) Monbet, P.; McKelvie, I. D.; Worsfold, P. J. Combined gel probes for the in situ determination of dissolved reactive phosphorus in porewaters and characterization of sediment reactivity. Environ. Sci. Technol. 2008, 42, 5112−5117. (29) Pichette, C.; Zhang, H.; Sauve, S. Using diffusive gradients in thin-films for in situ monitoring of dissolved phosphate emissions from freshwater aquaculture. Aquaculture 2009, 286, 198−202. (30) Panther, J. G.; Teasdale, P. R.; Bennett, W. W.; Welsh, D. T.; Zhao, H. Titanium dioxide-based DGT technique for in situ measurement of dissolved reactive phosphorus in fresh and marine waters. Environ. Sci. Technol. 2010, 44, 9419−9424. (31) Ding, S.; Xu, D.; Sun, Q.; Yin, H.; Zhang, C. Measurement of dissolved reactive phosphorus using the diffusive gradients in thin films technique with a high-capacity binding phase. Environ. Sci. Technol. 2010, 44, 8169−8174. (32) Mazoniene, E.; Zemaitaitiene, R. J.; Buika, G.; Zemaitaitis, A. Interaction of polyquaternary ammonium salt and persulfate. Colloid Polym. Sci. 2004, 282, 209−214. (33) Chen, H.; Zhang, Y. Y.; Zhong, K. L.; Guo, L. W.; Gu, J. L.; Bo, L.; Zhang, M. H.; Li, J. R. Selective sampling and measurement of Cr(VI) in water with polyquaternary ammonium salt as a binding agent in diffusive gradients in thin-films technique. J. Hazard. Mater. 2014, 271, 160−165. (34) Guo, L. W.; Chen, H.; Zhang, Y. Y.; Bo, L.; Li, J. R. Determination of chromium speciation in tap water using diffusive gradients in thin film technique. Chem. Lett. 2014, 43, 849−850. (35) National Standards of the People’s Republic of China. Water Quality−Determination of Total Phosphorus−Ammonium Molybdate Spectrophotometric Method; National Standards of the People’s Republic of China: Beijing, China, 1989; GB 11893-89. (36) Scally, S.; Davison, W.; Zhang, H. Diffusion coefficients of metals and metal complexes in hydrogels used in diffusive gradients in thin films. Anal. Chim. Acta 2006, 558, 222−229. (37) Chen, H.; Sun, T.; Sui, D. P.; Dong, J. Effective concentration difference model to study the effect of various factors on the effective

ACKNOWLEDGMENTS The authors thank Henan Titaning Chemical Technology Co., Ltd. for supplying binding agent.

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REFERENCES

(1) Maher, W.; Woo, L. Procedures for the storage and digestion of natural waters for the determination of filterable reactive phosphorus, total filterable phosphorus and total phosphorus. Anal. Chim. Acta 1998, 375, 5−47. (2) Monbet, P.; McKelvie, I. D. Phosphates. In Handbook of Water Analysis, 2nd ed.; Nollet, L. M. L., Ed.; CRC Press: Boca Raton, FL, 2007. (3) Worsfold, P. J.; Gimbert, L. J.; Mankasingh, U.; Omaka, O. N.; Hanrahan, G.; Gardolinski, P.; Haygarth, P. M.; Turner, B. L.; KeithRoach, M. J.; McKelvie, I. D. Sampling, sample treatment and quality assurance issues for the determination of phosphorus species in natural waters and soils. Talanta 2005, 66, 273−293. (4) Gardolinski, P.; Hanrahan, G.; Achterberg, E. P.; Gledhill, M.; Tappin, A. D.; House, W. A.; Worsfold, P. J. Comparison of sample storage protocols for the determination of nutrients in natural waters. Water Res. 2001, 35, 3670−3678. (5) Jarvie, H. P.; Withers, P. J. A.; Neal, C. Review of robust measurement of phosphorus in river water: Sampling, storage, fractionation and sensitivity. Hydrol. Earth Syst. Sci. 2002, 6, 113−131. (6) Davison, W.; Zhang, H. In situ speciation measurements of trace components in natural waters using thin-film gels. Nature 1994, 367, 546−548. (7) Sui, D. P.; Fan, H. T.; Li, J.; Li, Y.; Li, Q.; Sun, T. Application of poly(ethyleneimine) solution as a binding agent in DGT technique for measurement of heavy metals in water. Talanta 2013, 114, 276−282. (8) Hutchins, C. M.; Panther, J. G.; Teasdale, P. R.; Wang, F.; Stewart, R. R.; Bennett, W. W.; Zhao, H. Evaluation of a titanium dioxide-based DGT technique for measuring inorganic uranium species in fresh and marine waters. Talanta 2012, 97, 550−556. (9) Liang, S.; Guan, D. X.; Ren, J. H.; Zhang, M.; Luo, J.; Ma, L. Q. Effect of aging on arsenic and lead fractionation and availability insoils: Coupling sequential extractions with diffusive gradients in thin-films technique. J. Hazard. Mater. 2014, 273, 272−279. (10) Mongin, S.; Uribe, R.; Puy, J.; Cecília, J.; Galceran, J.; Zhang, H. Key role of the resin layer thickness in the lability of complexes measured by DGT. Environ. Sci. Technol. 2011, 45, 4869−4875. (11) Panther, J. G.; Stewart, R. R.; Teasdale, P. R.; Bennett, W. W.; Welsh, D. T.; Zhao, H. Titanium dioxide-based DGT for measuring dissolved As(V), V(V), Sb(V), Mo(VI) and W(VI) in water. Talanta 2013, 105, 80−86. (12) Li, W.; Zhao, H.; Teasdale, P. R.; John, R.; Wang, F. Metal speciation measurement by diffusive gradients in thin films technique with different binding phases. Anal. Chim. Acta 2005, 533, 193−202. (13) Liu, J. L.; Feng, X. B.; Qiu, G. L.; Anderson, C. W. N.; Yao, H. Prediction of methyl mercury uptake by rice plants (Oryza sativa L.) using the diffusive gradient in thin films technique. Environ. Sci. Technol. 2012, 46, 11013−11020. (14) Huynh, T.; Zhang, H.; Noller, B. Evaluation and application of the diffusive gradients in thin films technique using a mixed-binding gel layer for measuring inorganic arsenic and metals in mining impacted water and soil. Anal. Chem. 2012, 84, 9988−9995. (15) Li, W.; Li, C.; Zhao, J.; Cornett, R. J. Diffusive gradients in thin films technique for uranium measurements in river water. Anal. Chim. Acta 2007, 592, 106−113. (16) Panther, J. G.; Bennett, W. W.; Teasdale, P. R.; Welsh, D. T.; Zhao, H. DGT measurement of dissolved aluminum species in waters: Comparing Chelex-100 and titanium dioxide-based adsorbents. Environ. Sci. Technol. 2012, 46, 2267−2275. (17) Li, W.; Teasdale, P. R.; Zhang, S.; John, R.; Zhao, H. Application of a poly(4-styrenesufonate) liquid binding layer for measurement of Cu2+ and Cd2+ with the diffusive gradients in thin-films technique. Anal. Chem. 2003, 75, 2578−2583. 12116

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diffusion coefficient in the dialysis membrane. Anal. Chim. Acta 2011, 698, 27−35. (38) Dorsey, N. E. Properties of Ordinary Water-Substance in All Its Phases: Water-Vapor/Water and All Ices; Reinhold Publishing Corporation: New York, 1940. (39) Bryan, N. D.; Hesketh, N.; Livens, F. R.; Tippinge, E.; Jones, M. N. Metal ion−humic substance interaction: A thermodynamic study. J. Chem. Soc., Faraday Trans. 1998, 94, 95−100. (40) Li, W.; Zhao, H.; Teasdale, P. R.; John, R. Preparation and characterization of a poly(acrylamidoglycolic acid-co-acrylamide) hydrogel for selective binding of Cu and application to diffusive gradients in thin films measurement. Polymer 2002, 43, 4803−4809. (41) Mason, S.; Hamon, R.; Nolan, A.; Zhang, H.; Davison, W. Performance of a mixed binding layer (MBL) for measuring anions and cations in a single assay using the diffusive gradients in thin films technique. Anal. Chem. 2005, 77, 6339−6346. (42) Panther, J. G.; Stillwell, K. P.; Powell, K. J.; Downard, A. J. Perfluorosulfonated ionomer-modified diffusive gradients in thin films: tool for inorganic arsenic speciation analysis. Anal. Chem. 2008, 80, 9806−9811. (43) Lucas, A.; Rate, A.; Zhang, H.; Salmon, S. U.; Radford, N. Development of the diffusive gradients in thin films technique for the measurement of labile gold in natural waters. Anal. Chem. 2012, 84, 6994−7000.

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dx.doi.org/10.1021/jf5040702 | J. Agric. Food Chem. 2014, 62, 12112−12117