Orthophosphate is the available form of phosphorus in environment and is required for biological processes being a part of ATP to nucleic acid. Microbes utilize orthophosphate for their vital activities. To make a precise analysis of TP in the water samples it is the best way to keep the fresh samples at -20 degree C to check the microbial activity in the water samples. If the samples are collected from a distantly located site it is always good to add acid in the samples which do not affect the analytical procedures.

Hi Nitish

by convention the orthophosphate is contained in the below 0.45um fraction(FP), the orthophosphate is the dissolved unbound form, although there are some organic and inorganic fractions that contain phosphate below this fraction. Adding acid may well assist in releasing the " bound" phosphorus fraction. We generally freeze this fraction as a preservation technique. Mind you this may also cause some cell structures, below this size fraction, to fracture and release the phosphorus. Now the interesting part, your analysis drives what you get. ie if you then analyse the sample using ICPOES or ICPMS(destructive techniques) you end up with total dissolved phosphorus(TDP) as apposed to filtered reactive phosphorus(FRP), you get with colourometric techniques....they are often quite different in concentration.

Cheers

Frank PS.....I hope this helps.

For more info on effects of sample preservation, you might read this article:

http://www.aslo.org/lo/toc/vol_12/issue_2/0332.pdf

H2SO4 preservation is not tested, but freezing is: their conclusion is that cell lysing releses significant P into solution.

Thank you Jatin Srivastava , Frank Krikowa, Greg Mccullough for your valuable suggestions.

@Frank Krikowa:

1. Can we consider filtered reactive phosphorous to be orthophosphate?

2. If we use destructive method, cell bound phosphorous fraction may release, so how do we account for orthophosphate concentration?