92
Exercise 7
6. Measure the extinction of the butyl acetate solution with a 1-cm (or 10-cm) cell at a
wavelength of 885 nm. Use pure butyl acetate for a blank.
7. Standard solutions are prepared and measured as above, to prepare a standard
curve.
8. Since very small concentrations are being measured, reagent and double distilled
water contamination must be substracted. Separate analyses using double-distilled
water and the reagents yield a blank (OD b ). Then,
ODcorr = ODsample - ODb
9. Proceed with the computation of a standard curve and calculations of concentrations as in the previous methods.
Total Phosphorus
In this method the total phosphorus in a water sample is oxidized by persulfate, which
liberates organic phosphorus as inorganic phosphate (Menzel and Corwin, 1965). The
total phosphate then is determined by the methods described above for inorganic
phosphate.
Total phosphorus concentration of an unfiltered water sample minus that of the
dissolved P0 4 -P fraction, as determined above, approximately equals the concentration of organic phosphorus. The organic component may be separated further
into dissolved and particulate fractions by filtration (glass fiber filters, Reeve Angel
984A, 0.5-J1m pore size or Whatman GF/F, 0.6-0.7-J1m pore size). Here we shall deal
only with the total phosphorus content of the sample.
Any filtration should be done within 1 h of sample collection. When analysis cannot
be performed immediately, the filtrate should be frozen at once to - 20°C in
polyethylene bottles. All analyses should be performed immediately once the samples
are quick-thawed; do not thaw and refreeze the samples.
Reagents
1. All reagents as used for inorganic phosphate analyses discussed above.
2. Persulfate solution: Mix 5% w/v K1S10 g in distilled water; prepare daily.
Procedures
1. Add 16 ml of the 5% persulfate solution to 100-ml samples in 250-ml borosilicate
flasks.
2. Place flasks in a boiling water bath for 1 h (or autoclave for i hat 15lbs/in 2 or
1055 g/cm 1 ).
3. Cool and adjust the volume to 120ml with accurate i50-ml graduated cylinders.
4. The liberated P0 4 -P then is analyzed according to the methods used for inorganic
P0 4 -P above (use procedures for concentrations > 10 J1g P0 4 -P/I). When you
suspect that you have concentrations < 10 J1g P /I, the extraction procedures
discussed above can be used to measure the liberated P04 -P by increasing the
sample and reagent volumes appropriately.
5. P0 4 -P standards and reagent blanks should be made and submitted to identical
boiling and volume adjustment procedures.
6. Proceed with the computation of a standard curve and calculations of sample
concentrations.
Note: See also the "Automated Analyses" section below.
Exercise 7
6. Measure the extinction of the butyl acetate solution with a 1-cm (or 10-cm) cell at a
wavelength of 885 nm. Use pure butyl acetate for a blank.
7. Standard solutions are prepared and measured as above, to prepare a standard
curve.
8. Since very small concentrations are being measured, reagent and double distilled
water contamination must be substracted. Separate analyses using double-distilled
water and the reagents yield a blank (OD b ). Then,
ODcorr = ODsample - ODb
9. Proceed with the computation of a standard curve and calculations of concentrations as in the previous methods.
Total Phosphorus
In this method the total phosphorus in a water sample is oxidized by persulfate, which
liberates organic phosphorus as inorganic phosphate (Menzel and Corwin, 1965). The
total phosphate then is determined by the methods described above for inorganic
phosphate.
Total phosphorus concentration of an unfiltered water sample minus that of the
dissolved P0 4 -P fraction, as determined above, approximately equals the concentration of organic phosphorus. The organic component may be separated further
into dissolved and particulate fractions by filtration (glass fiber filters, Reeve Angel
984A, 0.5-J1m pore size or Whatman GF/F, 0.6-0.7-J1m pore size). Here we shall deal
only with the total phosphorus content of the sample.
Any filtration should be done within 1 h of sample collection. When analysis cannot
be performed immediately, the filtrate should be frozen at once to - 20°C in
polyethylene bottles. All analyses should be performed immediately once the samples
are quick-thawed; do not thaw and refreeze the samples.
Reagents
1. All reagents as used for inorganic phosphate analyses discussed above.
2. Persulfate solution: Mix 5% w/v K1S10 g in distilled water; prepare daily.
Procedures
1. Add 16 ml of the 5% persulfate solution to 100-ml samples in 250-ml borosilicate
flasks.
2. Place flasks in a boiling water bath for 1 h (or autoclave for i hat 15lbs/in 2 or
1055 g/cm 1 ).
3. Cool and adjust the volume to 120ml with accurate i50-ml graduated cylinders.
4. The liberated P0 4 -P then is analyzed according to the methods used for inorganic
P0 4 -P above (use procedures for concentrations > 10 J1g P0 4 -P/I). When you
suspect that you have concentrations < 10 J1g P /I, the extraction procedures
discussed above can be used to measure the liberated P04 -P by increasing the
sample and reagent volumes appropriately.
5. P0 4 -P standards and reagent blanks should be made and submitted to identical
boiling and volume adjustment procedures.
6. Proceed with the computation of a standard curve and calculations of sample
concentrations.
Note: See also the "Automated Analyses" section below.