| Phosphorus is an essential nutrient element used by all living organisms for growth and energy transport.In some oligotrophic areas,the concentration of phosphate exists at nanomolar levels due to the low solubility of phosphorus minerals and the uptake of phosphorus through phytoplankton photosynthesis.Many methods and systems for nanomolar dissolved reactive phosphorus(DRP)have been reported,however few simple procedures for all laboratories and long week-long continuous underway systems monitoring of DRP have been reported.Total phosphorus(TP)is identified as a significant index for water quality monitoring.At present,most of the reported determination techniques for TP have some disadvantages,such as low-solubility of reagent and time-consuming.To meet these requirements,we studied simple,reliable,sensitive methods for nanomolar DRP and TP analysis,the progresses have been as follows:(1)Based on classic phosphomolybdenum blue(PMB)chemistry and solid phase extraction(SPE),a convenient and practical method had been developed for the determination of nanomolar DRP in seawater.Under acidic conditions,the formed phosphomolybdenum blue can be preconcentrated on a hydrophilic-lipophilic balance(HLB)solid phase cartridge,eluted with 0.2 mol/L NaOH,and detected at 700 um after color recovery with the addition of more reagents.The limit of detection(LOD)was 3.0 nmol/L using 50 mL sample(which can be lowered by preconcentrating more volume),and the calibration curve showed a linear range between 10 and 900 nmol/L.The relative standard deviation(RSD)(n=81)was 2.6%with different operators at different days.The recoveries of the proposed method were found between 94.5-102.6%,and the analysis time was about 100 min/20 samples(sample volume was 100 mL).To evaluate the accuracy of established method,five types of phosphate standards and a series“blind”diluted phosphate standard solutions were detected,and the results were statistically analyzed,showing no significant difference.This method was free of interferences from salinity,silicate(up to 200 ?mol/L),and arsenate(up to 100 nmol/L),and suitable for different aqueous matrixes.The effect of a series of phosphorus-containing compounds(n=13)were evaluated.This method was applied to determine the phosphate concentration in samples(n=42)collected from the Western Pacific.(2)The SPE methodology and continuous flow analysis were combined for nanomolar DRP underway monitoring.The LOD and analysis time of this method was 1.0 nmol/L and 4-7 min/sample(which can be altered for different samples).The RSD(n=180)was 5.4%for a sample with concentration of 60 nmol/L.Two types of phosphate standard solutions were detected,and the results were statistically analyzed,showing no significant different from the certified concentration.The recovery of this method was 104.2%.This method was free of interferences from salinity,silicate(up to 80 ?mol/L),arsenate(up to 80 nmol/L),and phosphorus-containing compounds.With the long service life of HLB cartridge,the system worked stably and could meet the demand of long-term continuous analysis.This system has been successfully applied for a two-week continuous underway determination of DRP in surface seawater of the South China Sea.(3)A very simple method for the determination of TP had been developed,using a portable water boiler to substitute for autoclaving and highly water soluble sodium persulfate to replace of potassium persulfate.The digestion time was 3 h,which was followed by addition of ascorbic acid to eliminate free chlorine generated from the seawater samples,and then addition of the ammonium molybdate reagent for detection.This proposed method was used to analyze natural water samples(n=28)in comparison with standard autoclaving method.The proposed method had the superiorities of convenient,practical,rapid batch processing,and had successfully analyzed samples of three different matrix and a vertical profile at the transect A and SEATS(18°N,116°E)in the South China Sea. |
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