Phosphates

CONTENTS 8.1 Introduction ....................................................................................................................... 220

8.1.1 Physical and Chemical Properties ..................................................................... 220 8.2 Sample Preservation, Storage, and Pretreatment ........................................................ 223

8.2.1 Filtration ................................................................................................................. 223 8.2.2 Container Type and Pretreatment ..................................................................... 225 8.2.3 Physical Condition of Storage ............................................................................ 225

8.2.3.1 Chemical Preservation .......................................................................... 225 8.2.3.2 Freezing ................................................................................................... 226

8.2.4 Preconcentration ................................................................................................... 226 8.2.5 Digestion ................................................................................................................ 227

8.2.5.1 Thermal Digestion Methods ................................................................ 227 8.2.5.2 UV Photooxidation ................................................................................ 228 8.2.5.3 Combined Thermal Hydrolysis and Photooxidation Digestion .... 229

8.3 Analytical Techniques...................................................................................................... 229 8.3.1 Colorimetry and Spectrophotometry................................................................. 229

8.3.1.1 Direct Photometry, Based on Formation of Phosphomolybdate or Phosphomolybdenum Blue ......................... 229

8.3.1.2 Detection as Unreduced Vanadomolybdophosphoric Acid........... 230 8.3.1.3 Detection as Phosphomolybdenum Blue........................................... 230 8.3.1.4 Detection as a 12-MPA Ion Association Complex ........................... 230 8.3.1.5 Solvent Extraction of Phosphomolybdenum Blue

or Phosphomolybdate Ion Association Complexes ......................... 230 8.3.1.6 Solvent Extraction of Phosphomolybdate.......................................... 231 8.3.1.7 Interferences in Photometric Techniques Based on Formation

of Phosphomolybdate and Phosphomolybdenum Blue ................. 231 8.3.2 Photoluminescence Techniques.......................................................................... 232 8.3.3 Atomic Spectrometry ........................................................................................... 232 8.3.4 Electrochemical Techniques ................................................................................ 236 8.3.5 Separative Techniques ......................................................................................... 236

8.3.5.1 Ion Chromatography............................................................................. 236 8.3.5.2 Capillary Electrophoresis ..................................................................... 237

8.3.6 Automated Techniques........................................................................................ 237 8.3.6.1 Segmented Continuous Flow Analysis .............................................. 237 8.3.6.2 Flow Injection and Sequential Injection Analysis ............................ 238 8.3.6.3 Automated Batch Analyzers ................................................................ 238

8.4 Applications in Water Analysis ..................................................................................... 238 8.4.1 Potable Waters....................................................................................................... 239 8.4.2 Wastewaters........................................................................................................... 239 8.4.3 Brackish and Estuarine Waters .......................................................................... 239 8.4.4 Marine Waters ....................................................................................................... 241 8.4.5 Development of Portable and In Situ Analysis Systems................................ 242

8.5 Conclusions........................................................................................................................ 242 Abbreviations ............................................................................................................................. 243 References ................................................................................................................................... 243

8.1.1 Physical and Chemical Properties

Although phosphorus is the eleventh most abundant element in the Earth’s crust, where it forms approximately 1120 mg kg1, it is geochemically classed as a trace element [1,2]. In the lithosphere, it occurs as phosphates, and these may be leached by weathering processes into the hydrosphere. Phosphorus may then be precipitated as insoluble metal phosphates, which are incorporated into sediments and cycled on a geological timescale (millions of years), or it can participate in the rapid terrestrial and aquatic biological phosphorus cycles.