Determination of Phosphate by Batch Analysis
FIA peristaltic pump, Injection valve, 1 ml grad. syringes, Eppendorf pipette, Flow-cell, UV-VIS spectrophotometer, recorder.
Pump tubing 2.75 mm id, PTFE tubing 0.8 mm id, test tubes 10 ml, test tube rack, 50 ml volumetric flasks.
Potassium dihydrogen orthophosphate, (KH2PO4) FW = 136.09
Di sodium hydrogen phosphate (Na2 HPO4) FW = 141.96
Potassium antimony tartrate, FW = 324.92
Ammonium molybdate, (ammonium molybdate(V1)tetrahydrate, FW = 1235.86
Ascorbic acid, FW = 176.12
1.0g of a phosphate salt sample:
disodium hydrogen phosphate (Na2HPO4 FW = 141.96) or
Fertilizer sample (0.1 g)
Mixed reagent (mix fresh daily):
- 50 ppm stock phosphate solution: dilute from 1000 ppm stock prepared as follows: weigh out accurately 1.43 g of dried KH2PO4 and dissolve in one liter distilled water. Pipette 2.5 mls into a 50 ml volumetric flask and make up to the mark with distilled water.
- Soln. A = potassium antimony tartrate: 1.3715 g in 50ml distilled water.
- Soln. B = ammonium molybdate: 10 g in 250 ml distilled water.
- Soln. C = ascorbic acid: 1.76 g in 100 ml distilled water (prepare fresh daily)
- Soln. D = 5N sulphuric acid: 35 ml to 250 ml distilled water.
50ml D + 5ml A + 15ml B + 30ml C
Operation of instrument:
- All glassware used in this experiment must be acid washed (1 % nitric acid bath) and dried thoroughly (glassware oven) before use!
- Use eppendorf pipette with plastic tips to measure exactly 0.8 mls of mixed reagent.
- Color development: color develops fully within an hour. There is no need to leave samples and standards overnight for color development.
- 50 ppm phosphate standard: dry salt in oven @ 80°C, cool in desiccator and then weigh out the required amount.
- Sample: weigh out 1.00g of salt in triplicate in 100 ml volume solutions. Dilution is x 100 ( dilute 0.50ml in 50ml volumetric flask)
- Measure @ 830 nm or 825 nm.
- Blank: 5ml distilled water and 0.8ml mixed reagent.
- Pump: flow rate of distilled water = 5ml per minute (Pump setting = 500)
- Tubing: single piece pump tubing = 2.75 mm id. for distilled water.
Injector loop: 60cm x 0.8mm id PTFE tubing.
Manifold loop: 30cm x 0.8 mm id PTFE tubing from injector to flow cell.
Follow User guide or get help from Technician or Demonstrator
Signature: Dhanlal De Lloyd, Chem. Dept, The University of The West Indies, St. Augustine campus
The Republic of Trinidad and Tobago.
Copyright: delloyd2000© All rights reserved.