.
V O L U M E 2 6 , N O . 8, A U G U S T 1 9 5 4
Table 111. Analyses of Mixtures of Arsenic and Silicon P.P.M. Si02 1.0 1.0
P.P.M. SiOn 1.1 1.0 0.8 3 .. 52 3 3.1
P.P.LM.As 3.0
1.0
5.0 8.0
3.0 3.0 3.0
3 .0 6.0 9.0
P.P.M. -49 2.6 5.1 8.4 2.7
6.1
9.2
I
I00 -
;.%"
+ W 0
A5 measured
a w X
0 75
-
*I
X I
in
o Organic Phase o
Aqueous Phase
-
Y
m
W
/
5O-
I
/
0
m > 0 J
5
8
25-
* Appatent"over 100%'kextraction 01
0
5
I I IO 15 % E t OH IN AQUEOUS PHASE
J
1383 containing 17% alcohol were extracted for 2 minutes with 20 ml. of isoamyl acetate and the absorbances of the extracts measured a t 323 mp against an isoamyl acetate blank, Beer's law was obeyed and an absorbance index for molybdoarsenic acid in isoamyl acetate was determined. Mixtures of silicate and arsenate were made up from the stock solutions and the color developed according to the standard procedure. h procedure similar to that described for analysis of silicate and phosphate mixtures was used to analyze the silicate and arsenate mixtures.
Results are summarized in Table 111.
SUMMARY AND CONCLUSION
A means of separating the heteropoly molybdo- acids of arsenic, silicon, and phosphorus by means of solvent extraction has been devised. The technique has been successfully tested for the spectrophotometric analysis of artificial mixtures of silicon and phosphorus and silicon and arsenic. While a mixture of all three elements was not analyzed, it neems entirely possible to determine arsenic, silicon, and phosphorus in one sample. The sum of all three heteropoly acids. which have identical spectra in the near ultraviolet region, could be determined on one sample. Then aliquots of this sample could be treated to remove phosphorus, and then arsenic, selectively, into isoamyl acetate in which medium these two elements can be individually determined. Finally the silica could be determined by correcting the absorbance in the aqueous phase for the contribution of arsenic and phosphorus.
20
Figure 3. Effect of Ethyl Alcohol Concentration on Extraction of Molybdoarsenic Acid by Amyl Acetate
ACKNOWLEDGRIEKT
The authors are indebted to the U. S. Atomic Energy Commission and the Xlallinckrodt Chemical Works, St. Louis, Mo., for partial support of this work.
Beer's law was checked in the aqueous phase by making up 3 , 5, 8, 10, and 15 p.p.m. of arsenic according to the standard
procedure. The absorbances of these solutions, when plotted 'gainst gave a straight line which did not go through zero, but crossed the zero absorbence a t a concentration of 1.5 p.p,m. of arsenic. Il'hen 20-ml. aliquots of these solutions
LITERATURE CITED
A., and Rogers, L. B., AKAL.CHEM., 26, 1278 (1954). (2) Hure, J., and Ortis, T., BUZZ SOC. chim. France, 1949, 834. (3) Wadelin, Coe, and Mellon, M. G.. ANAL. CHEX.,25, 1668 (1953). (1) DeSesa,
K E C E I IED for review February 25, 1954.
.Iccepted l l a y 12, 1954.
Analysis of Phosphate Mixtures by Filter Paper Chromatography JOAN CROWTHER D e p a r t m e n t o f Chemistry, O n t a r i o Research Foundation, Toronto, C a n a d a
PRE
VIOUS papers ( 10,1 1 ) from these laboratories described a technique for separating and determining phosphate anions by means of filter paper chromatography. Because a number of laboratories are now using this technique, and the methods of these laboratories have been greatly improved in accuracy and convenience, an up-to-date description appeared in order. Various methods exist for the analysis of phosphate mixtures but they do not have as wide a range of usefulness as the method under consideration. Bell's ( 3 , 4)procedure is not as accurate; the mixture cannot be more than 25% pyroposphate and trimetaphosphate can be determined only by difference. The method of Raistrick, Harris, and Lowe (9) will not tolerate more than 4% orthophosphate while the various x-ray methods, such as the one developed by Raistrick ( 8 ) , are limited to crystalline mixtures. As compared with these methods, the chromatographic procedure permits the direct determination of more species of phosphate anions, with as good or better accuracy. +
MATERIALS
Orthophosphate, KIHPO~, reagent grade. Pyrophosphate, Na,P,O?, supplied by Albright and Wilson, Birmingham, England. Tetrametaphoqphate, ( S L L P O ~ ) ~ . ~ H supplied I ? O , bj- rllbright and Wilson. Filter paper chromatographic tests showed that these materials were not contaminated by other phosphates ( 10 ) and that the amounts of phosphorus present were in accordance with the formulas. Trimetaphosphate, ( NaPO3)3.H2O, supplied by Albright and Wilson. Although no other phosphates ( 10 ) were present in this material, the water content was lower than indicated by the formula, corresponding in fact to 0.94%. Triphosphate, NajP,010.6H,0, supplied by Albright and Wilson. In the triphosphate sample (according to the chromatographic analysis), 2.3 and 1.5% of the phosphorus were present a8 pyrophosphate and orthophosphate, respectively.
1384
ANALYTICAL CHEMISTRY
Although it was undesirable to determine the impurities in the triphasphate sample by the analytical procedure that was being evaluated, no other course appessed practical. Attempts were made to prepare pure anhydrous sodium triphosphate, but some pyro- and orthophosphate were always present. However, i t can he shown that this chromatographic analysis of the "pure" triphmphate sample is consistent with the analyses obtained in this laboratory of phosphate mixtures containing this material.
100,
Figure 2.
C h r o m a t o g r a p h i c T a n k with S t a n d and T r o u g h Assembly
concentration of the solution sliould be approximately 0.25 atomic weight of phosphorus per litrr. Once the solution has been applied and the spots have dried, the chromatogram is placed in the jar in the position indicated by Figure 3, and the solvent flom commences. CONDITIONS FOR SEPARATING VARIOUS MIXTURES bo
THEORETICAL %P AS
TRIPHOSPHATE
Figure 1. Comparison of Theoretioal and Measured Percentages of Phosphorus Found as Triphosphate
Assuming that the material on hand urns pure iVaaP3010.6Hs0, mixtures of tx-, pyro-, and orthophosphate were prepared in which the percentage of phosphorus present as triphosphate was varied from 4.2 to 70.3%. In Figure 1, the percentage of triphosphate phosphorus found by the analysis is platted against that calculated on the above assumption. If the assumption of purity were correct, the points should fall along the diagonal shown in broken line. However, they are everywhere below this line and fall on another line consistent with the author's analysis of the material itself. Therefore, it was concluded t h a t the percentage of the total phosphorus present in the form of tri-, pyro-, and orthophosphate was 96.2, 2.3 and 1.5'%, respectively. Alternative hypotheses considered appeared unlikely on chemical 5nd other grounds.
The length of time which the chromatogram is run, the solvent, and the type of filter paper used depend upon the components of the phosphate mixture. This information is summarized in Tshle I, hut an explanation may be of value. Running Time. T h e length of time which a chromatogram is run is determined by experience and is the time required to separate the components of the mixture. Ihwever, with acid solvents (pH 1.5 to 2.0), the condensed phosphates ma." hydrolyze if the run is longer than 48 hours. Solvent. Many solvent mixtures have been studied (6, fl), b u t in general i t is found that a single phase dcohol-water-acid (or base) system is superior. The selection.of a, suitshle solvent,. however, is largely an empirical proposition.
-
POLYTHENE
COLLAR
THREE ROD ASSE
SOLVENT TROUGH
,
-
CHROMATOGRAM SPACING , ROD
PROCEDURE
Apparatus. The a p r a t u s congists of a well insulated box containing glass jar8 inside dimensions 12 X 7 X 18inches) with typical stand and t,rough assemblies as shown in Figure 2. Each jar is fitted with a plate glass lid sealed on with petrolatum. The trough is filled with the solvent mixture (hereafter referred to as the solvent). T o help keep the jar saturated with the vapor
~
~
~~~~~
sides of the tank. "This step, which was suggested by Mortimer ( 7 ) has proved very effective. Preparation of Chromatogram. The phosphate solutions are spotted on the chrcmatogrsms along the starting 1inq (Figure 3) with B microDiDet. This startinp line is annroxlmatels 14 inches from t6e-hottom of the c h r h a t o g r a m ' d u t is below the spacing rod as indicated in Figure 3. Considerable care is required in applying the phosphate solution to the chromatomam. Between 60 and 90 Y of DhosDhorus must he anDlied to %e rimer for Quantitative results, hut the chromatograms must
F i g u r e 3.
Position of C h m m a t a g r a r n
In acid media, the solvent tertiary butyl alcohol @0ml.)-water (20 mi.)-formic acid ( 5 ml.), gives excellent resolution hut is too. ~10wto permit the separation of phosphates having. more than four phosphorus atoms per molecule. Thus, for phosphates of' higher molecular weight, a less viscous hut also less efficient. alcohol must be used. Using the solvent isopropyl alcohol (SO ml.)-wateter (20 m1.)-formic acid ( 5 mL), phosphates with six or less phosphorus atoms per molecule are believed to he separated and determined. With this solvent, however, the resolution is. incomplete, and a faint streak of phosphates exists between thecomponents. This situation is undesirable, hut as yet no remedy has been found. Owing to this streaking, Ohe standrwd deviation, is increased from 0.8 to 2%.
V O L U M E 26, NO. 8, A U G U S T 1 9 5 4 Table I . Procedure S O .
l b
Possiblr Phosphate Componentsa Ortho-, pyro-. tri-, H.P.C
1385
Chromatographic Separations on Filter Paper Filter Paper Cclileicher and Schuell 589 orange ribbon
Soli-ent terf-Butyl alcohol (80 inl.)-water (20 nil.)-formic acid ( 5 nil ) terf-Butyl alcohol (80 ml.)-water (20 ml )-formic arid ( 5 ml )
Running Time, Hours 30
2h
Ortho-, pyro-. tri-, trimeta-. tetra-, tetrameta-, H.P.C
Sclileicher a n d Schuell 589 black ribbon
3d
Ortho-, pyro-, tri-, trimeta-. tetra-, tetrameta-, penta-, hexa-, H.P.C Pyro-, tri-. tetra-, penta-, hexa-, septa-. octa-. nona-, 1I.P.C
Schleicher and Schuell 589 orange ribbon
Isopropyl alcohol (80 nil.)-water (20 ml.)-formic acid ( 5 ml.)
48
Srhleicher and Schuell 589 black ribbon
(a) kit-Butyl alcohol (80 ml.1-water (20 ml.1-formic acid ( 5 ml.) ( b ) n-Propyl alcohol 160 nil.)-water (20 h-con,centrated a m m o n i u m hydroxide (20 ml.)
16
4'1 e /
30-40
Remarks Yery clear band.
Tery cli3ar band? h l t danger of o v w loading thin f i l t p r
paper chroinatogram Bands joined hy streak of p l m pliatrs
Bands joined b>streak of phus]>hate?
48
turw to identify conipoiients hdorc, :tn analysis is attempted. I11 Table I the conditions under l\-liii'h various combin:itions of phosphates can be separated iire summarized. F o r exaiiipk, using Procedure 1, ortho, pyro, tri, or any conihination of these t,hree can be separated a n d d e t,er mi n e d . Any other phosphates present i i i the mixture will rrmain as a group on or near thr starting l i n ~ and can be drtermined otily :IS a group. 1'11E4TMENT O F DEVELOPED CARO.MATOGRARI S
General. Once the rhromatogram has been run as indiwted above, the procedure c o n k t s of identifying the phosphate bands on the chromatogram, cutting out the bands, eluting the phosphates from thtb paper, and colorimctrically drtrrmining the amount of plioy,horus in each band by x niodificat.ion of the Bo16z and 1Iello11( 5 ) procedure. Identification of Bands on Chromatogram. T h e p h o s phate bands are identified on thr chromatogram by. spray. ing ivith an avid m01yhd:~tesolution and heating the chromatogram to form the phosphomol~-bdatecomplex. By exposing the dried chromatogram to ultraviolrt light for approximately 1 minute the complex is rrduced to form a blue color ( 2 ) . This method is much simpler and more sensitive than the use of hydrogen sulfide gas as the reduct'ant (11).
a Listed in order in which they occur on chromatograin-first found closest t o bottom of cliroiiiatograitl. .%I1 components named need not be present. .4ny or all sperified conlimnrnts can he determined under t h e w conditions, b u t if a phosphate is not named, i t cannot be detprinined. b If procedure is carefully followed, resulting chromatograms x i l l slio!Y clean-cut bands of phosphatri w i t h no background. C H . P . refers to any higher polyphosphate groups which. under these conditions. would remain on or rlose tu starting line of chromatogram. With Procedure 2 H . P . refers t o all phosphates having more than four phosphorlip atoms per molecule while in Procedure 4 H.P. refers t o all phosphates having more t h a n nine phosphorus atoins per molecule. H . P . , therefore, deals with t h e polyphosphates which, if present, cannot be separated under specified conditions, a n d must be treated a s a group. d Procedures not yet fully developed because of lack of pure samples of tetra-, penta-, hexa-. septa-, octa-, and alcohol nonaphosphates. I n specified basic solvent, pyro- and triphosphate are not separated from each other; thus such a mixture is successively chromatographed in two solvents t o overcome this difficulty. Initial run in acid solvent separates pyro- from triphosphate. Chromatogram is then removed from tank. dried, and re-run in n-propyl alcohol-waterammonia solvent. Since pyro- and triphosphate have same R f values in this basic solrent they remain separated, f If any or all of ortho-, trimeta-, and tetrametaphosphates are present in this phosphate mixture they will have r u n off bottom of t h e chromatogram b y end of run. This difficulty can he overcome by using chrdmatogram which is longer t h a n 14 inches or b y decreasing running time. If latter step is taken some of polyphosphates listed will not he separated. .In alternative method would be t o use Procedure 2 in conjunction with Procedure 4 . .-
In basic media the solvent n-propyl alcohol (60 nil.)-water (20 ml.)-concentrated ammonium hydroxide (20 nil. ), provides the best resolution, and is believed to permit the separation of phosphates having nine or less phosphorus atoms per molecule. .4gain, however, the streaking between bands is present and the standard deviation for such an analysis is only 2%. Filter Paper. Finding or preparing suitable filter paper for quantitative chromatography was one of the greatrst difficulties encountered. To summarize the problem, briefly, an examination of earlier techniques shorved that they could be materially improved if (1) the phosphorus blank on the paper could be rrduced or made more uniform and (2) if the impurities in the paper tending to complex with condensed phosphate anions could he decreased. Both factors required a purer paper. Efforts were made to achieve this by ( a ) an investigation of washing techniques and ( b ) t>estinglots of paper submitted by various filt'er paper companies in an effort to meet the requirements, which are much more exacting than t,hose ordinarily met in filter paper chromatography. Under (a) some 50 methods were invrstigated. Even the most painstaking gave results which were largely unpredictable although occasionally good. Cnder ( b ) the papers first meeting the requirements were Schleicher and Schuell, S o . 589 Black and Xo. 589 Orange Ribbon. Two lots of each type have been satisfactory. The black and orange ribbon papers, although similar in purity, differ chromatographically. The black paper permits comparatively rapid resolution of the phosphate components, but care must be taken to avoid overloading-i.e., streaking. With orange paper, the resolution is much slower, but the danger from overloading is considerably decreased. Thus orange paper is used wherever feasible, as it is much easier to handle. General. Thus the type of paper, running time, and solvent are selected by considering the components of the phosphate mixture. Qualitative chromatograms are run on unknown mix-
Colorimetric Determination of Phosphorus. The deterniinntion of the amount of phosphorus in the bands is simple. The bands are cut out, and the phosphate is eluted by soaking t h e paper in 25.00 ml. of O.1N ammonium hydroxide. After 1 hour or more, a 20.00-ml. aliquot of this solution is pipetted int,o a 50.00-ml. volumetric flask. If, however, more than 50 */ of phosphorus are expected, a 10.00-ml. aliquot is removed. To this aliquot then, 5 ml. of 10N sulfuric acid are added, and the solution is heated in a hath at 100" C. for 30 minutes. This heating period is required to hydrolyze the cyclic and polyphosphatrs quantitatively to orthophosphate. To the cooled hydrolyzed solution, 1 ml. of 12.5% ammonium molybdate is added, the flask is shaken, and then 1 ml. of 0.6% hydrazine hydrochloride is added. The volume is then adjusted to 50.00 ml.;and the flask is placed in a bath a t 100" C. for exactly 10 minutes. The flask is then cooled rapidly by placing it in a bath of cold water. The absorbance of the solution is then measured on R Reckman spectrophotometer a t 830 mp, using distilled water as the reference solution. This colorimetric analysis i p also carried out on blanks. The filter paper blanks are approximately equal in area to the bands of phosphates. In addition, a solvent blank is run on 20.00 ml. of 0.1N ammonium hydroxide. The filter paper and solvent blanks have similar absorbances (reference solution ie distilled mater) and this value is subtracted from the values obtained for the phosphate bands. The blanks then are the effective reference solution, but it is felt that the use of distilled water is a check on errors in the blanks which would be revealed by a more than slight variation from day to day. From the absorbances, the amount of phosphorus present is calculated using the calibration curve. This straight line relationship was determined by using standard solutions of KHoPOI, ?iarP&,, and
ANALYTICAL CHEMISTRY
1386
._
Table 11. Analytical Results for Mixtures of Pjro-, Tri-, and Orthophosphates
teimined chromatographically
in the normal way, but it i? newssary to determine the % % L7c %b 70 % % % c"r c70 Ch % total phosphorus by analyzing P as P a * P as P as P a s P as P a ? P aP '8 f' aP as P a, ortho- pvrotriortho- pyrotri- ortho- p i l o tilortho- psrotria dilute solution of the detergent, since the foaming in conCalcd. cornposition 7.1 2>3 ti7.i 20.2 75.7 4.1 317 424 2.58 78ti 5.5 15.9 centrated solutions makes ac. i ~ ineasured . curate volume measurements coniposition 7.1 24 0 G8.0 20.0 75.6 4 . 8 31.9 41.i 2ii 3 78 6 5 . 3 16.1 impossible. 9 detergent may Individual 1 7.7 24.6 G7.8 19 1 7 6 . 8 4.1 31 fl 41.8 27.2 78.3 4.8 16 7 be encountered in which some analytiqal 2 7.7 24.6 67.7 20.9 74.; 4 . 7 31.5 41.1 37.1 78.0 6.1 15.8 coniposi3 6.5 2 4 . 8 68.0 20 0 75.a 4.5 31.9 42.2 2S.8 77.6 6 . 4 16.11 of the interfering chemicals tiom 4 6.9 2 5 8 07.3 20.8 75.8 3.4 320 42.t 254 78.3 4.8 17.0 5 6.8 24.8 ti8 4 19.4 74.7 5 8 33 0 40 5 26.3 78.4 5,2 16.3 nwntioned in the following 6 7.1 24.7 68.2 20.0 76.5 3.5 3 2 1 41, 2G.1 8 0 . 6 4 , s 1 4 . 8 section are present. If so, this method of -analysis would hP unsuitatlle without modificaTable 111. Analytical Results f o r a Mixture of Poly- anti tion. Cyclic Phosphates The main weakness of this analytical method is the effect of c70 5 c C ' Vc P as P a$ polyvalent cations on the filter paper chromatograms. I n mod,'C P as P aP as TriTetraerate quantities-e.g., up to 1.5% magnesium-interference is OrthoPyroTrimetametanot evident, but as the concentration of these cations increases Cali,dcouiposition 19 9 20 l 13.0 25.2 19.8 the chromatograms become streaked owing to the formation of 20.2 13.4 24.9 1'3.8 A v . measured 19.8 complexes. It is possible that a cation exchange column could composition au = 0 . 7 3 = o.(i2 = 0.60 = 0.42 = 0.78 be used to remove these ions. Citric acid and glycerol also tend 19.9 15.3 24.6 19.1 Individual 1 21.0 20 8 16.1 25.0 18.8 analytical 2 19.4 to complex with condensed phosphates, and the resultant prod15.0 24.8 20.0 l,ompositions 3 19.3 20.8 uct fails to form the reduced blue phosphomolybdate complcx. 4 20.1 20.8 14.3 25.6 19.3 15.6 24.2 20.(i 5 20.4 19.2 The colorimetric determination of phosphorus has an appre25.0 20 o 6 18.3 19.9 15.9 ciable tolerance for many ions as indicated by Boltz and Mellon a u = Standard deviation ( 1 ) based on sis determinations (6). The interfering tendencies of silicates are important when (3011sidering the analysis of detergent mixtures. Fortunately siliEXPERIMENTAL AYD DISCUSSION cates do not affect the chromatographic separation of phosphates and the colorimetric determination of phosphorus tolerates a t Four standard solutions containing ortho-, pyro-, and triphosleast, 1000 parts per million of silicate. One silicate, S a i O . SiOy. phntc were prepared and analyzed six t,imes over a number of SH,O, has a R , value similar to orthophosphate, but the l a t h is days. The results of thcae determinations and their averages still quantitatively recovered. The presence of soap in the deare shorn in Table 11. Siniilarly a solution containing ortho-, tergent interferes with the analyses but this difficulty is e n d > pyro-, tri-, trimeta-, and tetrnmetaphosphate was analyzed six surmounted by an alcohol extraction. times over a number of day$. The individual determinations in hlthough polyvalent cations interfere, this chromatographic chronological order, their avmtgw, and standard deviations ( 1 ) analytical procedure has much to recommend it. An operator arc $holm in Table 111. can make 30 to 40 determinations per day. Components (up The *tatistical analyses of all results for ortho-, pyro-, and trito four phosphorus atoms per molecule) are direct,ly determined phosphate indicat,ed that there was no variation in precision and with equal accuracy, xvhile longer chain polyphosphatee do not in110 significant departure from the calculated distribution of terfere since they can be grouped together. The distribution of phosphorus. The average standard deviation is 0.83 based on phosphorus among the components (up to four phosphorus 75 degrees of freedom. In addition, no difference is noticed beatoms per molecule) does not affect, the accuracy, and the standtwwn analyses carried out' on different days. However, the ard deviation of the procedure (0.83 based on i 5 degrees of analyses of about 20 chromatograms are normally required for freedom) compares favorably with the accuracy of other procea11 operator to attain this degree of precision. durw for phosphate mixtures. The analyses of the solution which also contained trimetaand trtrametaphosphate (Table 111) are in accordance with ACKNOWLEDGiMENT the calculated distribution of phosphorus. The author is indebted to D. B. DeLury for the statistical analSolutions of phosphate glasses have been analyzed by this chro?$is of the experimental results and to .$. E. R. Westman for matographic procedure, and results have been obtained on band$ hi3 advice and direction in this st,udy. occupying positions which might logically be ascribed to tetra-, penta-, hexa-, septa-, octa-, and nonaphosphates as well as to thc LITERATURE CITED phosphates of lower molecular weight. This does not mean that (1) d m . SOC. Testing Materials, "A.S.T.AI. llanual on Quality all phosphate glass solutions can be analyzed. The composition of Control of Materials," Spec. Tech. Pub. 15C (January 1951). such solutions varies with the molar sodium to phosphorus ratio, ( 2 ) Bandursky, R. S.,and Axelrod, B., J . B i d . Chem., 193, 405 arid complete analysis is only possible when this ratio is greater (1951). (3) Bell, R. K., d l v a ~ CHEM., . 24, 1997 (1952). t,han 1.5 roughly. As the sodium to phosphorus ratio decreases to (4) Bell, R. S . , IND.EXG.CHEX,ANAL.ED., 19, 97 (1947). 1.0 the percentage of phosphates with nine or less phosphate (5) Boltz. D. F., and Mellon, AI. G., Ibid., 19, 873 (1947). atoms per molecule decreases until none is present. The pre(6) Hanes, C. S., and Isherwood, F. A. Nature, 164, 1107 (1919). cision of these glass analyses is i 2 % , but the accuracy is un(7) Mortimer, D. C., National Research Council, Ottawa, Canada, private communication. known. Pure samples of phosphates, with four or more phos(5) Raistrick, B., Sci. J . R o y . CoZZ., 19, 9 (1945). phorus atoms per molecule, have not as yet been obtained, and (9) Raistrick, B., Harris, F. J., and Lowe, E. J., Analyst, 76, 230 hence i t is impossible t o prepare standard solutions to test the (1951). accuracy. (10) \Testman, A . E. R., and Scott, A. E., A-ature, 168, 710 (1951). (11) Westman, ii. E. R., Scott, il. E., and Pedley, Joan, Chemistry A number of household detergent mixtures have been analyzed in Can., 4 , 189 (1952). by this method, and as yet no excessive difficulties have been RECEIVED for review December 7, 1953. Accepted May 28, 1954. encountered. The per cent distribution of phosphorus is deSolution 1
Solution 2
-
Solution '3
~~~
Solution 4
