I would like to use Stannous Chloride method for the measurement of SRP in water and sediment sample of freshwater lakes. Form the previous study I got that the SRP level gone bellow the 0.2 mg/l. I am thinking about concentrate such kinds of samples by boiling more volume of water. Please let me if this procedure is valid or not.
Yes, the procedure is valid. Soluble reactive phosphorus exists in the form of various types of orthophosphates. P in the extract is determined spectrometer after developing molybdenum blue color. The intensity of color varies with P concentration in the extract. The orthophosphate ion in the acid molybdate solution from phosphomolybdate complex is reduced by stannous chloride to produce molybdenum blue color.
Dr. Adhurya, if you have ICP in your laboratory , then you may go for ICP measurements as the P concentration of your sample seems to be low , otherwise you have to concentrate the sample as you are doing.
As I recall in APHA's 'Standard Methods for Water and Wastewater' you can use a liquisd-liquid extraction with Butyl Alcohol. The LOQ or MDL is about 0.2 0r 0.02 ppb.
Thank you Dr. Tarafdar and Dr. Neagle for your kind suggestion. I have another query. During boiling off the water for concentrating the sample, if there are any chance of the conversion of other form of P to SRP due to heat?
No idea! Though it is possible, particularly if nucleic acids denature (from bacteria) and you get ortho-phosphate.
It may be, because microbial biomass P are susceptible to temperature but you can control it very well by putting blank ( only water) in the similar condition and then adjust the blank values.
Mr.Sagar,I do not recommend concentration of lake water samples by boiling. Now more sensitive colorimetric methods based on the same molybdate blue colour principle with modifications and improvements are available.You may try the following methods.
Watanabe FS and Olsen SR 1965.Test of an ascorbic method for determinig phosphorus in water and NaHCO3 extracts from soil. Soil Sci.Soc.Am.Proc(J)29:677-678.
A modified single solution method for the determination of phosphate in natural waters. Murphy J. and Riley JP ( 1962) Anal.Chim.Acta, 27: 31-36.This is one of the common methods used to estimate reactive P in lake waters.
Subba Rao A , Sammi Reddy K and Takkar PN ( 1997) Malachite green method compared to ascorbic acid for estimating small amounts of phosphorus in water, 0.01M calcium chloride and Olsen soil extracts.Commun. Soil Sci.Plant Anal. 28:589-601.
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