a 1986 a 368100001
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8/21/2019 A 1986 a 368100001
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January 2 8, 1986
Inthe late 1950s, wehad been carrying out workat theDepartmentofOceanography, UniversityofLiverpool, on the cycle of phosphate in the sea.Our work was held back by the lack of a suitable
method for determination of the very low levelspresent ( < 1-16OMgl~).Photometric methods de-
pending on the formation ofphosphomolybdenumblue complexes had been in use since the 1920s.However, the intensity of the colour that was oh-.tamed with a given amount of phosphate verymuch depended on thereductant used to reduce
the intermediate phosphomolybdic acid.1
Tin (II) chloride had been used forthis purpose,
as it gave a very intense blue colour and hence avery high sensitivity. It had the disadvantages thatthe colour was only stable for a very few minutesand that in seawater the formation of the colourwas delayed and its intensity decreased by thepresence of the major ionsof the seawater. We setabout trying to find a reducing agent free fromthese defects.
Aftertesting a numberof compounds, we foundthat ascorbic acid (vitamin C ) was satisfactory and
allowed the analysis to be carried out with a singlereagent rather than by adding the reducing agentafter the acid molybdate as had been donebefore.
2It had the disadvantage that the colour
development required 12 hours, leading to thepossibility that organic phosphorus compoundsmight be hydrolysed and their phosphorus includ-ed in the analysis. Ascorbic acid had been used a sa reductant in the analysis before,
3but thecondi-
tions employed were not optimal, and maximumcolour w as not, therefore, developed.
We decided, therefore, to se e if the rate ofcol-our development could be increased. I had readthat the incorporation of bismuth in the reagentdid speed up the reaction.
4When we tried this, we
found that this w as the case but that hydrolysis ofthe bismuth led to a turbidity that made thetechnique useless for the determination of lowlevels ofphosphate. Consideration of the periodictable suggested that it might be worthwhile substi-tuting antimony—its immediate neighbour inGroup Va—for bismuth. Immediate success wasachieved when this w as done, colour developmentbeing complete in two to three minutes. Onceformed, the colour, which was due to a complexcontaining antimony, phosphorus, and osolybde-num, was stable for many days. Furthermore, thetechnique gave a sensitivity slightly superior tothat obtained with tin (II) chloride, was free frominterference from most other elements, and w as
- not affected by seawater salts.I suppose that the reason this paper has been so
extensively cited i s that itprovides a simple, highlyreproducible technique for the determination ofmicrogram amountsofphosphate. Almost 25 yearslater, the method is still basically the recommend-
ed standard procedure for the analysis offresh andpotablewaters,5’6 as well as seawater.7’8 Althoughit was originally developed for the analysis ofphosphate in natural waters, it has been widelyadopted in many other fields, including, for examSpIe, botany, zoology, biochemistry, geochemistry,metallurgy, and clinical medicine. Indeed, kits forthedetermination are available commercially for
use in physiological investigations and water anal-• ysis.
This W e e k ’s Citation C la s s ic ® ~[ Murphy J & Riley I P.Amodified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta 27:31-6, 1962.
[Department of Oceanography. University of Liverpool, Englandi
This paper presents a simple and reproduciblephotometric procedure for the determination ofparts per billion concentrations of phosphate innatural waters. It is adaptable tomany other typesof sample because of its freedom from interele-ment interferences. [The sow indicates that thispaper ha s been cited in over 1.520 publications,making it the most-cited paper ever published inthis journal.]
James Murphy and John P . RileyDepartment of Oceanography
University of LiverpoolLiverpool 169 38X
England
I. BurtonI D & Riley I P. The determination of soluble phosphaie an d tOtal phosphorus insea waters and of totalphosphorus inmarine muds. Mikrochinr. Acm 9:1350-7, 1956.
2. Murphy I& Riley IP. A single solution method (or the determination of soluble phosphate insea water.
J. Ma,. Biol. ,
4
sxn. UK 37:9-14. t958. (Cited 60 times.(3. Greenfleld L I & Kelber F A. Inorganic phosphate measurement in seawater. Bull. Ma,. Sci. Gulf Caribb. 4 :323-35. 1954.
4. lean M. etude du d o s age du phosphore et de l’arsenic dans es aciers par cotorim4trie.Anal. Chim. Ado 14:172-82. 1956.
5. Her Majes*y’e Stationery Office. Methods foe the examination of waters and assodated materials: phosphorus in waters, effluents and sewages. London: HMSO. 1981. 31 p.
6. American Public Health Association. Standard methods for th e examination of water and oastewater.Washington, DC: American Public Health Association, 1984.
7. KoroleffK. Determination of nutrients. (Grasshoff K, Ehrhardi M& Kremling K. eds.( Methods of seawater analysis. Weinheim. FRG: Vertag Chemie, 1983 . 419 p .
8, Parsonu IR. Make Y & Lelil C M.A manaal of chemical and biological methods for seawater analysis.Oxford: Pergamon Press. 1984. t73 p.
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