Ste-by-step guide

Collecting samples

Collect suspended particles by filtration on precombusted (450°C for 4 h) Whatman GF/F (or similar) 25 mm glass fibre filters. Store filters either dried (60°C for 24 h) or frozen until analysis.

Oxidizing reagent

• 15 g of potassium persulfate (K₂S₂O₈)
• 5 g of boric acid (H₃BO₃)
• dissolved with 70 ml of 1.5 M (60 g l^-1) sodium hydroxide
• made up to 250 ml with ultrapure water (Milli-Q)

Oxidation procedure

Place filters in acid-washed 50 ml Duran bottles with blue screw caps (see figure below).

Add reagents:

• 20 ml of ultrapure water
• 5 ml of reagent

Cap bottles tightly capped and autoclave at 120°C for 30 min.

Note that the pH of the extract is very low, ca 1.7 to 2.3. This will not affect phosphate analysis, but will affect nitrate analysis. Therefore, neutralization is needed prior to nitrate analysis (target pH: 8).