Skip Navigation Links.



























Total Phosphorus by In-line UV Digestion  

FIAlab standard method for total phosphorus through in-line UV digestion using the FIAlab-2500/2600/2700  and FIAlab's IL-UV In-line Digestion Unit.  Note, this method is also compatible with Sequential Injection Systems (please inquire).

Assay Typical Throughput Concentration Range Notes
Total Phosphorus (High) 30 samples/hour 1 to 10 ppm 1 cm flowcell
Total Phosphorus (Low) 30 samples/hour 0.1 to 2 mg (N)/L 10 cm flowcell

 

 Principle:

Phosphorus is released as PO43- in the digester. PO43- is then detected using the standard assay (formation of phosphomolybdate, reduction to heteropoly blue; detection at 880 nm, reference at 490 nm).

 Comments:
 
           
Interferences and limitations:

The colorimetric molybdenum blue reaction is sensitive to changes in acidity, and works best in the pH 6-8 range.  The sample should not have a strong matrix absorbance at the selected detection wavelength.  Turbidity will cause high phosphate results and noisy data.  This can be a problem with acid digested samples.  High iron concentrations (>50 mg/L) will decrease the phosphate signal.  While the presence of As3+ can cause high phosphorus results. 

The inline UV digestion conversion does not work well for polyphosphates.

For longer digestions bubbles may form.  Use of FIAlab's DB10 debubbler prior to the injection loop is recommended if this becomes an issue.

Special Hardware:

FIAlab - IL-UV In-line Digestion Unit for In-line digestion of total nitrogen, total phosphorous, total cyanide. Includes secondary two channel peristaltic pump.

Programming: 

Please contact FIAlab for details on the programming/timing of the sample digestion period within the IL-UV coil.

Reagents:

Persulfate Digestion Solution:

7.6 g of sodium tetraborate decahydrate

16.0 g of potassium persulfate

Dissolve in 1 L DI water

Carrier: DI Water
1-Liter Degassed DI Water.    Matrix matching is required for salt water and soil extract samples.

Reagent 1:   6 mM Ammonium Molybdate.
 10.0 grams Ammonium molybdate tetra-hydrate [1235.81 FW]
 0.2 grams Antimony Potassium Tartrate half-hydrate [333.94 FW] catalyst

40 mL conc. H2SO4 acid (36N) ACS grade (Sigma-Aldrich 38,337-6)

1-Liter Degassed DI Water. Place acid into 800mL of DI water, mix and let cool to room temperature.  Add molybdate and antimony potassium tartrate and mix until dissolved.  Fill flask to the mark.  Transfer solution into a dark and airtight glass bottle for maximum longevity. This solution is stable for several weeks.

Reagent 2: Reagent Carrier Stream of 300mM Ascorbic Acid.
30 grams Ascorbic acid  [176.12 FW]
 1.0 grams Sodium dodecyl sulfate  [288.38 FW] surfactant (Sigma-Aldrich 436143-25G)
  

1-Liter Degassed DI Water. Place the ascorbic acid into a 1-liter volumetric flask and mix with 600 cc of DI water until dissolved.  Add the sodium dodecyl sulfate and mix slowly (prevent foaming) until dissolved.  Fill flask to the mark.  Transfer solution into an airtight light sensitive glass bottle for maximum longevity.  Minimize exposure to air and prepare fresh weekly since this solution is unstable.

 

Standards:

100ml  ICPHO-100   (Phosphate standard)
Source: 727-524-7732 - www.exaxol.com 

Please email or phone FIAlab Instruments for additional product information.
 Email: fialab@flowinjection.com, Voice: 425-376-0450 or 1-800-963-1101,  Fax: 425-376-0451