Inorganic and organic phosphorus in sediment

Inorganic and organic phosphorous in sediment

Source: Strickland and Parsons (1972) with modification by Aspila (1976)

 

Reagents

  • Stock Ammonium Molybdate Solution
  • Dissolve 30g of ammonium molybdate tetrahydrate in 1l of DI water
  • Keep in a cool dark place

 

  • Stock Antimony Potassium Tartrate Solution
  • Dissolve 1.5g of antimony potassium tartrate in 1l of DI water
  • Keep in a cool dark place

 

  • 10% Sulphuric acid

 

  • Ascorbic Acid Solution
  • Dissolve 60g of ascorbic acid in 1l of DI water
  • Keep in a cool dark place. Stable for about a month

 

  • Working Colour Reagent
  • Carefully mix 100mls of ammonium molybdate stock solution, 250mls of 10% sulphuric acid 100mls of ascorbic acid and 50mls of antimony potassium tartrate solution.
  • Keep in a cool dark place. Stable for about 6 hours

 

  • 1M Hydrochloric acid

 

  • Potassium orthophosphate (KH2PO4) 10mM stock solution
  • Accurately weigh 136mg into 100mls of 1M hydrochloric acid.

 

  • Potassium orthophosphate standards
  • Prepare 0, 50, 100, 200, 400 and 800uM solutions by pipetting 0.5, 01.0, 2, 4 and 8mls of potassium orthophosphate standard into 1M hydrochloric acid and making up to 100mls. This will give a calibration able to measure phosphorus between 0 and 0.1% in a 0.3g dried sample aliquot

 

Procedure

Inorganic phosphorus

Weigh accurately between 0.2 and 0.3g of dried, homogenised and sieved (200 um) sediment into a centrifuge tube and add 12mls of 1M HCl. Place on a shaking table for 16 hours and then centrifuge or filter. To 10mls of extract add 1ml or working colour reagent and let stand for 20 min before measurement by spectrophotometer at 885nm. Prior to measurement, calibrate the spectrophotometer with standards and the blank.

 

Calculate inorganic phosphorus content of sediment:

 

                                    (u-molarity of extract) x (12/1000) x 31       x       100%

                                                1000000 x wt. of sample (g)

 

 

Total phosphorus

Weigh accurately between 0.2 and 0.3g of dried, homogenised and sieved (200 um) sediment into a crucible and ignite at 550 C for 1hour. After the crucible has cooled empty contents into a centrifuge tube and add 12mls of 1M HCl. Repeat extraction and measurement procedure of inorganic phosphorus determination.

 

Organic phosphorus content can then be calculated from:

Organic phosphorus = Total phosphorus – Inorganic phosphorus

 

References

Aspila, K.I. Agemain, H and Chau, A. 1976. A semi-automated method for the determination of inorganic, organic and total phosphorus in sediments. Analyst, 101 187-197

Strickland J. and Parsons T.  1972. A practical handbook of seawater analysis. Bulletin 167 Fisheries Research Board of Canada, Ottawa

 

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