Rate of phosphoantimonylmolybdenum blue complex formation in acidic persulfate digested sample matrix for total dissolved phosphorus determination: importance of post-digestion pH adjustment.
Acidic persulfate oxidation is one of the most common procedures used to digest dissolved organic phosphorus compounds in water samples for total dissolved phosphorus determination. It has been reported that the rates of phosphoantimonylmolybdenum blue complex formation were significantly reduced in the digested sample matrix. This study revealed that the intermediate products of persulfate oxidation, not the slight change in pH, cause the slowdown of color formation. This effect can be remedied by adjusting digested samples pH to a near neural to decompose the intermediate products. No disturbing effects of chlorine on the phosphoantimonylmolybdenum blue formation in seawater were observed. It is noted that the modification of mixed reagent recipe cannot provide near neutral pH for the decomposition of the intermediate products of persulfate oxidation. This study provides experimental evidence not only to support the recommendation made in APHA standard methods that the pH of the digested sample must be adjusted to within a narrow range of sample, but also to improve the understanding of role of residue from persulfate decomposition on the subsequent phosphoantimonylmolybdenum blue formation.
Huang
Xiao-Lan
XL
Ocean Chemistry Division, Atlantic Oceanographic and Meteorological Laboratory, National Oceanic and Atmospheric Administration, Miami, FL 33149, USA. xiaolan.huang@noaa.gov
Zhang
Jia-Zhong
JZ
D000143:Acids / Q000737:chemistry*; D000965:Antimony / Q000032:analysis* / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008982:Molybdenum / Q000032:analysis* / Q000737:chemistry; D010758:Phosphorus / Q000032:analysis* / Q000737:chemistry*; D012996:Solutions; D013431:Sulfates / Q000737:chemistry*
D000143:Acids; D012996:Solutions; D013431:Sulfates; C532628:phosphoantimonylmolybdenum blue; D010758:Phosphorus; D008982:Molybdenum; D000965:Antimony