Experiment was carried out as follows:
- 1g of plant waste (already grand/crushed) was diluted in 250ml of distilled H2O.
- 3ml aliquot of the dilution was used for the digestion in the COD reagent, and afterwards (intermediate steps), the COD was read with the spectrophotometer.
- reading was taken as 750 mgO2/l.
Please, how do I express this in mgO2/kg sample?
Both mg/L and mg/kg are equal to 1 ppm, except that mg/L refers to mass in liquid and mg/kg is mass in solid sample. You already converted your solid sample (1 g of plant waste) to liquid, that's why your result is in mg/L.
Yes. The concentration is in mg/L. Your volume is 250 mL, which is 0.25 L, i.e. if you multiply the reading by 0.25 you will have the quantity in the 250 mL. Now that quantity came from 1 g of solid. Therefore multiply the mg/g by 1000 to get mg/kg
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