Table II. Effect of Removal of Sodium Ion by Ion Exchange Resin
Sample A B
Meq. Sulfate After resin Before resin 0.1105 0.1111 0.1105 0,1038 0.1038 0.1038 Av. 0.1072
0.1074 0,1068 0.1068
n . inno
0 . io06
0.1006 0.1037
deviation of the Thorin titration alone, as determined by triplicate titrations on 21 samples, is 0.4% of the mean, or 0.0006 meq. of sulfur trioxide. The use of acid or neutral peroxide for the total sulfur oxide absorber
solution would simplify the procedure by eliminating the ion exchange step, However, it is preferred that the peroxide be destroyed in order to prevent deleterious effects upon the organic ion exchange resin. The presence of caustic is necessary to prevent stripping of sulfur dioxide by high concentrations of carbon dioxide. The presence of sodium in the solution caused significant interference, thus substantiating the necessity for its removal by the resin (Table 11). ACKNOWLEDGMENT
The author is pleased to acknowledge the assistance of C. C. Graf in the initial phases of the work. Appreciation is expressed to the Shell Oil Co. for permission to publish this paper.
LITERATURE CITED
(1) American Petroleum Institute, “Man:
ual on Disposal of Refinery Wastes Method 774-54, Vol. 5, 1st ed., 1954. (2) Zbid., Method 775-54, Vol. 5, 1st ed.,
1954. (3) Corbet>t,P. F., J. Znst. Fuel 24, 24751 (1951). (4) Corbett, P. F., J . SOC.Chem. Znd. 67, 227 (1948). (5) Flint, D:, Zbid., 67, 2 (1948). (6) Fritz, J. S., Freeland, M. Q., ANAL. CHEM.26, 1593 (1954). (7) Fritz, J. S., Yamamura, S. S., Zbid., 27, 1461 (1955). (8) Los Angeles ilir Pollution Control District Method, 1956. (9) McCombie, H. R., private communi-
cation, Shell Chemical Corp., P.O. Box 431, Pittsburg, Calif. RECEIVED for review September 13, 1957. Accepted hlay 9,1958.
indirect Flame Spectrophotometric Determination of Sulfate Sulfur W.
M. SHAW
University o f Tennessee Agricultural Experiment Sfation, Knoxville, Tenn.
,A study was made of the flame spectral emission properties of barium with the objective of applying the barium emission to indirect flame spectrophotometric determination of sulfate in waters and oxidized biological materials. The barium emission intensities were measured in oxyhydrogen flame with the Beckman DU spectrophotometer and photomultiplier attachment using the 51 5-mp band head for peak emission, and the 522-mp for cation background correction. Iron, aluminum, and phosphate were eliminated by precipitation in ammonium acetate solution buffered a t p H 4. Calcium, strontium, and manganese gave spectral interferences. Sulfate determinations in waters containing a wide range of cation and phosphate concentrations carried out b y the gravimetric and flame spectrophotometric methods showed satisfactory agreement.
T
determination of sulfate is of widespread interest and application: agriculturally, in irrigation waters, soils, crops, and feeds; industrially, in boiler feed waters; biochemically, in oxidation products of certain amino acids; and medicinally, in blood serum for the detection of renal deficiency. The procedures for the determination of sulfate may be grouped into three classes: gravimetric (17 ) , titrimetric HE
1682
ANALYTICAL CHEMISTRY
(H),and turbidimetric (8). Each has its o m quantitative adaptation, and serves particular requirements of speed and convenience. The accuracies attributed to these methods by the American Public Health Association ( 2 ) are: gravimetric, t o 1 2 % ; turbidimetric and titrimetric, to *lo%. NeJv colorimetric (5) and titrimetric (16, 18) methods hare recently appeared in print. These methods, although of high precision and accuracy, h a r e no direct bearing on this study. The objective vias to develop a flame photometric procedure for the determination of sulfate sulfur. This procedure should be faster than the gravimetric procedure, and more accurate than the simpler titrimetric and turbidimetric procedures, and, a t the same time, eliminate sulfate and phosphate as interferences with the accurate flame photometric determinations of calcium (4). which until recently ( 1 ) hal-e received scant recognition. The procedure should have a wide range of application, including the determination of sulfate in rain n-ater, soil extracts, lysimeter leachings, irrigation waters, and sea water, and total sulfur in ashed plant and biological materials. It was the aim to carry out the sulfate determination on sample preparations used for the determination of other elements. The method is based on the reaction of sulfate ion with barium chloride, re-
sulting in the precipitation of barium sulfate. The barium chloride must be added in standard quantities, because the sulfate determination is based upon the difference between the barium added and the residual barium after precipitation. The rcsidual barium is determined by its flame emission intensity as compared with barium standards. ANALYTICAL PROBLEMS
The analytical problems are essentially those of flame spectrophotometric determination of barium in complex miutures. These map be resolved into t h e follon-ing parts: 1. Spectrophotometric adjustments for barium emission, including selection of wave length, fuel combination, and suitable barium concentration range. 2. Extent of barium emission interferences from extraneous cations and anions. 3. Methods of correcting for interfering ions or removal, where corrections are not feasible. 4. Practical procedure for the flame photometric determination. 5. Testing for analytical accuracy on substances selected for wide range of sulfate content and interfering elements, using gravimetric determinations as reference. CHEMICALS AND EXPERIMENTAL PROCEDURE
Stock solutions were prepared from analytical grade chemicals of the cations
sodium, potassium, calcium, strontium, magnesium, manganese, and aluminum as chlorides in concentrations, so that 1 ml. nas equivalent to 1 mg. of the metal. The barium chloride solution v, as prepared in 0.0625N concentration, so that 1 ml. was equivalent to 1 mg. of sulfate sulfur. All quantitative expressions with respect to barium, as mg. of barium, actually designate the sulfur equivalent of the barium concentrations or quantities; the actual barium quantities are 4.29 times as great. Thc sulfate solution was prepared from ammonium sulfate in 0.03125.V concentration; 1 ml. was equivalent to 0.5 mg. of sulfur. The phosphate solution n as prepared from ammonium dihydrogen phosphate; 1 ml. was equivalent t o 1 mg. of phosphorus. The ferric ion 1% as as 0 . 5 5 ferric chloride hexahydrate, dissolved in 0.5N hydrochloric acid; 1 ml. was equivalent to 9.3 mg. of iron and had a potential acidity of l K . Interferences with barium emission n-ere estimated by mixing various cations with a standard addition of barium, and comparing the emission intensities of the mixtures 15-ith that of barium standards. These emission readings were made in conjunction with a barium calibration curve, so that any departure expressed in emission units could be translated into milligrams of barium. I n the phosphate and aluminum precipitation studies, the accuracy of the technique was judged by the recovery of added barium. The salt concentration was equal in all comparisons. The instrument used was the Beckman JIodel DU spectrophotometer supplied with photomultiplier and oxyhydrogen burner. The burner grill was surrounded by a bell-shaped duct which led to an exhaust fan and the fumes were carried away t o the outside Selection of Emission Band H e a d and Instrumental Adjustments. I n a comprehensiye bibliography on spectroscopy and flame photometry through 1933, Mavrodineanu (2.3) cites only five reference. on barium. The flame spectrogram given by Katanabe and Kendall (31) shows prominent band peaks a t 488. 516. 533.6, and 873 mp. Determination of sulfate as an example of anion analysis by Rame photometry is mentioned (3%). Certain spectral properties of barium in relation to those of other elements are shown in Figure 1. The 515-mp n-ave length nas preferred to that of 489 mp because it produces a greater photocurrent, and because its emission difference b r h e e n 515 and 522 nip is greater than the corresponding difference between 489 and 494 m p . The band peak of 553.6 mp cannot be used because of interference by the strong calcium emission band head a t 554 mp. The band head 873 mp used in earlier studies (19, SO) was not investigated because its use would preclude the use of the photomultiplier. For all flame work re-
-
-L,
470
480
490
............ K ..............Mg
h 530 54'
500 510 520 WAVE LENGTH MH
-
Figure 1. Barium emission between wave lengths of 470 and 540 my Background radiations of 1000 mg./l. of elements and Mn
ported, the instrunient was adjusted as follovvs : Selector switch Slit width, mm. Spectrophotometer sensitivity, turns from counterclockwise position Photomultiplier sensitivity Wave length, nip For band-peak measurement For background 01 pressure, p.5.i. H, pressure, p.s.i.
0 1 0.03-0.05
0 5-1.0 4 515 522 15 2
INTERFERENCES WITH BARIUM FLAME EMISSION
Interference constitutes the most serious problem in flamc photometry as an analytical tool. It is essential to investigate the extent and nature of interference from associated elements. IONSLIKELY TO INTERFERE. The constituents of natural waters (10) that are likely to interfere with barium emission are the cations: sodium, potassium, calcium, strontium, and magnesium; and the anions: bicarbonate, nitrate, and silicate. Salt and acid extracts of soils may contain appreciable concentrations of aluminum, iron, and manganese. The phosphate ion is an important constituent of plant ash. I n the preparation of the sample there may be introduced chloride, perchlorate, acetate, and hydrogen ions. TYPESOF INTERFERENCES. Gilbert, Haws, and Beckman (16) presented a
Na, K, Ca, Mg,
general discussion of flame emission interferences. Several types of interferences are depicted in Figure 1. With reference to barium band head 515 mp, sodium, potassium, and magnesium show continuum interferences, calcium and manganese shox spectral interferences, and aluminum shows radiation interference. GROUPTREATMENT FOR IXTERFERINQ IONS.The bicarbonate, nitrate, and silicates can be largely eliminated through evaporation to dryness in the presence of hydrochloric acid. The iron(III), aluminum, and phosphate ions may be eliminated through special methods for their joint precipitation. The remaining cations cannot be easily eliminated and will be investigated for interference. CORRECTIONS FOR CATIONINTERFEREWE. Margoshes and T'allee (22) set forth two methods of correction: the direct method, by which the net emission is obtained by the difference of emission reading a t the band head minus that a t the nearest trough, and the indirect method, by which the net emission is obtained by subtracting from the total emission reading the background readings on the same band head. The test that has been used to differentiate between continuum and spectral interferences is that which compares the emissions of the extraneous cations a t the band head and a t the adjacent VOL. 30, NO. 10, OCTOBER 1958
1683
-t
O
t
I
I
40
20
U T K U CWNTRATION
I
-
60
I
eo
I
100
mg.11.
Figure 3. Effects of increasing concentrations of iron, manganese, and aluminum on barium emission intensity at band head of 51 5 mp 200
400 CATION No.
600
CONCENTRATION K 0
Ca
d
Mp v
800
I000
- mg./l. Sr
0
Figure 2. Effects of increasing concentrations of sodium, potassium, magnesium, and strontium on emission intensity at band head 5 15 mp A. In presence of Ba (5 mg./100 ml.) 6. Cation background in absence of Ba
CORRECTIOXS FOR h I I X E D C.4TIOSS DIRECTAND INDIRECT METHODS.
BY
The results on barium recoveries in the presence of mixed cations in concentrations up to 2000 mg. per liter (Table IV) show good agreement between the direct and indirect methods. Again, the presence of 600 mg. of calcium per liter shows a slight negative effect by the direct method, and a significantly high recovery by both methods in the presence of potassium. EFFECT OF MIXEDCATIOKCONCENTRATIOKS ON NET BARITAX E&fISSION. I n the data presented in Table T', both the mixed cations and the barium concentrations were varied, testing the reliability of the direct method a t different levels of barium concentration. A solution of 100 mg. of barium per liter was aspirated, and the instrument ad-
trough. The results of this test, given METHODS.Table I11 gives the barium in Table I, show that calcium, stronrecoveries in the presence of individual tium, and manganese have pronounced cations in concentrations of 100 to 1000 spectral interference with barium a t mg. per liter. A comparison of the 515 mp>and the direct method of backdata in the last two columns shows a ground correction in the presence of high fair agreement in barium recoveries after concentrations of cations may be used correction by both methods. The two when solutions of low sulfate content exceptions are the loiv recovery in the are concentrated for greater accuracy. presence of 1000 mg. of calcium per liter INDIRECT CORRECTIOK.Curves givin the direct column, and the generally ing background radiation on 515 mp us. high recoveries by both methods in the cation concentrations were prepared. presence of potassium. I n the upper half of Figure 2 are given the radiation enhancements due to cations in the gresence of barium: the lower half s h b w the cation background Table I. Emission Intensities of Interfering Cations at Barium Band Head 51 5 and above the flame background in the ah522 Mp sence of barium. The curves differ ac: to both magnitude and regularity of Interfering Cation Concn., Emission in T-Scale Divisions 4t515mp At522mp At 515-522= mp effects; the background effects are proCation hIg./L. portional to cation concentration; in the Na 1000 10 5 10 5 0 K 1000 16 0 16 0 0 radiation curves, the enhancements are Ca 1000 9 5 13 0 -3 5 proportionately greater at the low catCa 500 5 0 7 0 -2 0 ion concentrations. The radiation efIIg 1000 4 0 3 0 1 0 fects of aluminum, iron(III), and manSr 1000 10 0 13 0 -3 0 Sr 500 5 0 7 0 -2 0 ganese up to 100 mg. per liter are shown Tvln 1000 43 0 60 0 -17 0 in Figure 3. Mn 500 21 0 30 0 -9 0 To test the applicability of backa In 100-ml. solution, each division of difference reading = about 0.2 mg. Ba. ground correction curves, mixtures uf sodium, potassium, calcium, and msgnesium were prepared to contain different proportions of these elements, and Table II. Barium Recoveries after Indirect Correction for Cation Background by Two Sets of Correction Curves including 5 mg. of barium (Table 11). The uncorrected barium recoverieq n-ere Cations, in Addition Ba Recovery, 1Ig. 1 to 2 mg. in excess of the true value. t o 5 X g . of Ba, S e t Emission" in n!Ig./1oo Ml. T s ~ ~ i ~ on ~ ~ ~ . cnCorrected by Curves Fig. 3 After corrections by curves A , the reSa K Ca Mg 515 M p corr. A B sults were 0.6 to 1.0 mg. low; and, after 4 2 5 1 7 1 60 71 20 20 100 corrections by curves B, the results 4 0 5 3 6 6 10 67 60 20 10 were 0.1 to 0.4 mg. high. The indirect 4 4 5 4 6 4 20 64 10 60 10 correction by curves B yielded results 10 10 20 60 60 6 0 42 5 2 much closer to the true value. r e t emission here denotes total emisslon, mlnus flame background. In other inCORRECTIOXS FOR IKDIVIDUAL C A T stances net emission denotes emission on 515 minus that on 522 mp. 10x3 BY DIRECT AND INDIRECT 0
1684
ANALYTICAL CHEMISTRY
justed t o give 1 0 0 ~ oreading on T-dial a t 515 mp; a net reading (on 515 522 mp) of 52 divisions was obtained. The inclusions of 40, 60, and 80 nig. of mixed cations per 100 ml. did not significantly alter the average net barium emission of the corresponding barium concentrations. Based on 1 gram of material, these cation concentrations represent a range of 4 to 8% of the sample. The net emission on 515 mp obtained by the direct method of correction offers the simplest and quickest method for determining barium concentrations in the pwsence of mixed cations u p t o 800 iiig. per liter including sodium, potassium, calcium, and magnesium in the proportions of 25 : 37.5 :25 : 12.5, respectively. OTHER METHODSOF BACKGROUND CORRECTION.Strickland and Maloney (SO) precipitated sulfate as barium sulfate in blood serum after removal of phosphate. They obtained barium emission on 873 mp, minus the reading with solution that had no barium added. The objections are that this procedure requires two separations and tn-0 sets of solutions. ChoTv and Thompson (9), in their analysis of sea n-ater, found t h a t sulfate and magnesium ions seriously depressed the emission intensity of calcium, and that these interferences could not be corrected by the method of line-minusbackground einisqions. They resorted t o the standard addition technique. The disadvantage lies in the multiplication of the number of tests required. Workers in the ceramic industries (12)25) and in rock analysis (19,20)fayor coinpeiisating standards for correcting for interference. This method is practiml only n hen a large number of samples of nearly the same composition are undergoing analysis (11 ) . Anion Interference. There are fexv d a t a available on anion interferences 11 ith barium cniission, b u t a relationship somewhat analogous t o t h a t of calcium TT ould be expected. Bicarbonate, nitrate, a n d silicate interfeiences (33) can be eliminated by evaporation n i t h hydrochloric acid. T h e phosphate ion has been shoivn to interfere n i t h calcium ( 4 , 1 9 . I t s effect on barium emission is shown in Figure 4. The disturbing effect of calcium and magnesium on the barium emission pattern, resulting from increasing additions of phosphate, is evident. Mitchell and Robertson (24) found aluminum severely depresses calcium emission. Margoshes and Vallee (22) consider the action of aluminum in the flame as that of a n anion. For its chemical separation aluminum may be joined with phosphate. Fieldes and coworkers ( I S ) , working with ammonium acetate extractions cf soils, removed the phosphate and sesquioxides by precipitation n ith ammonium hydroxide. Shaw and T-eal
Table 111.
Barium Recoveries after Corrections for Individual Cation Background by Direct and Indirect Methods
Emission in T-Scale Div., Wave Length, AIM 515 522 Diff. 57 0 30 0 27 0 59 5 32 0 27 5 62 0 35 0 27 0 66 0 40 0 26 0 fiO 0 32 0 28 0 34.0 29.0 63.0 40.0 28.5 68.5 28.5 77.0 48.5 27.0 57.0 30.0 27.0 59.0 32.0 26.0 64.0 38.0 22.5 69.5 47.0 56 0 29 0 27 0 57 0 30 0 27 0 57 5 30 5 27 0 59.0 31.5 27 5
Cations, in Addition to 5 RIg. of Ba, PIIg./lOO MI. Na 10 20 50 100
K _-
10 _.
20
50
100 Ca
10
20 50
100 10 20 50
Mg
100
un corr. 5 10 5 35 5 60 6 00 5 40
%70
6.25 7.10 5.10 5,30
5.80 6.35 5 00 5 10 5 15 5 30
Ba Recoveries, 3Ig. Corrected by Methods Direct Indirect" 5 10 4 98 5 15 3 11 5 10 5 00 4 90 4 80 5 25 5 24 5.38 5.35 5.30 5.45 5.30 5.50 5.10 -1.98 5.10 5.06 4.90 5.20 4.20 5.15 5 10 4 95 5 10 5 00 5 10 4 90 5.20 4 80
a By subtracting from uncorrected column the cation concentrations expressed in mg./l., multiplied by the factors of 0.012 for Na and Ca; 0.016 for K ; and 0.005 for hlg. These individual products or their sum denote the Ba correction expressed as mg. of Ba.
Table IV.
Barium Recoveries after Correction for M i x e d Cations by Direct and Indirect Methods
Cations, in Addition to 5 1Ig. of Ba, M g Na 100 10 10
10
/loo
K 20 60
10
10
Table V.
111.
Ca 20 20 60 20
Mg
60 10 20 60
Emission in T-Scale Div., a t Knve Length, M 515 522 Diff. 26 5 50 5 77 45 5 27 5 73 44 5 25 5 70 26 5 39 5 66
p
Ba Recoyeries, 11g. Corrected by Methods corr. Direct Indirect 5 10 5 12 7 10 5 30 5 36 6 70 4 90 5 39 6 40 5 10 5 21 6 00
cn-
Net Emissions (515 - 522 Mp) a t Various Barium Concentrations, as Influenced by M i x e d Cation Concentrations
Ba Concn., Mg./lOO RI1. 1 0
2.0 4.0 6.0 8.0 Weighted av., 100 mg./1.
Net Emissions" at Total Extraneous Cation Concentrations*, Mg./lOO hI1. 60 80 Av. 0 40 . 5 03 5 22 5.08 5.15 -i _25_ 9.93 9.85 10.25 9.?$ 9.88 20.60 20.60 20.45 20.70 20.59 31.00 30.78 31.00 31.62 31.10 41.60 41.47 41.88 42.50 41.86 51.59 51.26 51.62 52.43 51.72 ~
~~~
]Freighted, v!. Net Emission for 100 XIg./L. 51.50 49.65 51.48
51.83 52.33 51.36
Net emissions represent averages of 4 readings in scale division on -1 consecutive days. Cations were in mixtures of S a , K, Ca, and Mg in proportion of 25:37.5:25: 12.5% of total in order given. On basis of 1-gram sample, total cation concn. = 4 to 8%. a
(27) adopted a similar but simplified step in their flame photometric determination of calcium and magnesiuni. The effect of aluminum u p t o 100 nig. per liter on the emission intensity of barium is shou-n in Figure 3. EFFECT OF IXTRODUCED ANI OB^. I n the proposed method, the solution medium is composed of 0 . 1 S ammonium chloride, 0 . 2 s acetic acid, and ammonium hydroxide to give a pH of 4. I variable concentration of the perchlorate ion may be expected from the wet ashing of organic materials. Figure 5 shon-s that the increasing concentration
of chloride ion, vhile the acetate ion remained a t 0.2.1', caused a continuous decrease in the barium emission intensity. An increasing concentration of the acetate ion, while the chloride ion remained a t O . l S , caused a continuous increase in the emission intensity. I n the buffer solution, the perchlorate ion in concentrations up to 0.1Y sho\Ted no effect on barium emission. It is essential that dilutions, when necessary, be made with the dilute buffer mixture rather than with water, and t h a t any concentrations required should be done prior to addition of the buffer solution. VOL. 30, NO. 10, OCTOBER 1958
1685
CIO.-ION 0
x
5 Mq.Ea
0
SMpBo+lOMgCa 1 5 M g E a t IOMg C o t ZOMq K
CONCENTRATION
- NORMAL
02
04
06
08
I
I
1
I
C,Oq
A CzH92
6
20 -
I
0
I 2
I 4
PO,-P CONCENTRATION
VARIABLES AFFECTING REMOVAL OF IRON(III), ALUMINUM, AND PHOSPHATE FROM SOLUTIONS CONTAINING BARIUM
Many analytical samples may be devoid of or contain only negligible concentrations of iron, aluminum, and phosphate; in such instances, the step for their removal mag be omitted. Hon-ever, in consideration of the wide range of materials that may be analyzed by the procedure, provisions for their removal must be incorporated in the procedure. PRELIMISARY ISVESTIGATIOKS. The generally accepted method for the joint removal of iron(III), aluminum, and phosphate from the earth alkalies and alkalies is that developed by Blum (6) for the separation of aluminum. Various modifications of the basic acetate method have been used for removal of phosphate from solutions of biological products ( 1 4 , and, conversely, by the addition of phosphate, for the removal of iron and aluminum ( 3 ) . The characteristics of the acetate method are p H 5 to 5.4 and prolonged heating for complete precipitation ( 7 ) . Stadie and Ross (29) pointed out the difficulties attending the acetate method, and proposed an alternative method of precipitation of phosphate by the addition of iron(II1) and neutralization in the cold with ammonia to pH 8. The precipitations with ammonia mere investigated first for their appli-
Table VI.
Fixed Constituents, Mg./50 MI. 2.5 Ba 5.0 Po4-P
+ 2.5 Ba '+ 5.0 PO4-P 2.5 Ba + 5.0 POI-P 1686
I
I
I 6
to
8
- Mg./50MI.
I
I
38
2
4 C z i l j O z bNO C!-ION
cability to the separation of iron(III), aluminum, and phosphate from standard additions of barium. The variables of iron-phosphate ratios and p H in the range of 5 to 8 were investigated. The data are omitted to save space. The results shov that the precipitations of iron(II1) and phosphate both in the hot and cold in the p H range of 6.5 to 7.5, there was a coprecipitation of a high percentage of the barium content. There \vas apparently no coprecipitation of barium a t pH 5 to 6, but the low buffer capacity of the solution made it difficult to maintain a stable pH. PRECIPITATIOS OF PHOSPHATE] ALUMINUM, .4ND IRON(II1) B Y A LfODIFIED BASIC ilCETATE hfETHOD. Work was directed toward determining the effects of certain variables on the precipitation of aluminum and phosphate. Synthetic mixtures were prepared. generally containing 5 mg. of barium, 5 mg. of phosphate, and mixtures of aluminum and phosphate. The acetic acid-ammonium acetate buffers of p H 4, 5, and 6 were used. EFFECTS O F I" 9 K D IRON(III)PHOSPHATE RATIOON PHOSPHATE PRCCIPITATIOX. The data of Table VI show the doniinant role of pH in preventing barium coprecipitation by the ferric phosphate precipitate. At p H 6, the increasing additions of iron, up to an iron-phosphorus ratio of 18 t o 1, effected some increase in the barium re-
I 6 CONCENTRATKW
I
I B
. NWMM.
IO
covery, and attained a maximum of 70%. At pH 5, the maximum barium recovery was 92y0 which was attained at the iron-phosphorus ratio of 11 t o 1. At p H 4, the barium recovery was 1 0 0 ~ o when the iron-phosphorus ratio mas 11 to 1 or greater. The analysis of the phosphorus content of the filtrates from precipitation at p H 4 showed that the iron-phosphorus gravimetric ratio of 2 to 1 was inadequate for the complete phosphate precipitation; the ratio of 4 to 1 leaves about 0.04 mg. of phosphorus in 100 ml. of solution, and a t the ratio of 9 to 1, that value is 0.01 mg. It appears that R quantity of iron at least four times the gravimetric value of the phosphorus content is necessary for complete precipitation of the phosphate. Determinations by the thiocyanate method ($8) showed an average iron content of 0.2 mg. per 100 1111. PRECIPITATIOX OF A L ~ M I X C M AND . ALLXINUM AND PHOSPHATE,AT PH 4, AS AFFECTEDBY IROX(III)CONCEKTRATIOS. I n the absence of ferric iron, aluminum remains entirply in solution (series -4, Table VII). Series B shows the effect of aluminum on emission intensity of barium. Series C shons that the minimum quantity of ferric iron required for the complete precipitation of 5 mg. of aluminum is about 50 mg. At iron-aluminum ratios of 6 to 1 or less, the precipitate 17-as dispersed, diffi-
Recovery of Added Barium after Precipitation of Phosphate with Ferric Chloride, as Influenced by pH and Fe/P Ratio Ba Added, Mg. 0 9 3 18.6 27.9 37.2 46.5 55.8 74.4 93.0 __-__ 0 1.9
Precipitation Medium 0,Z.V NH4C1,0.2N HCzH10z
+ NH40H to pH 6 0.1N N&Cl, 0.2N HCzH302 + ",OH to pH5 0.1N NHdCl, 0.2X HCzHsOz + NHaOH to pH 4
ANALYTICAL CHEMISTRY
PeIP ntio - -,- R ------
5.6 7.4 9.3 11.2 14.9 Ba Recovery, ' &- of Addition at Fe(II1) Variables _ .? 66 72 50 72 44 54 3.i
18.6 i5
34
26
44
48
68
76
76
84
92
92
92
46
76
88
96
98
99
100
100
100
cult to filter, and yielded colloidal iron in the filtrate. The precipitations in ratios of 10 to 1 and greater formed more flocculent precipitates and nearly waterclear filtrates. The presence of 4 mg. of phosphate phosphorus, in addition to 5 mg. of aluminum, required a somewhat larger excess of iron than for aluminum done (series D, Table VII). Assuming the presence of 2.5 to 5.0 mg. of phosphate phosphorus, a quantity that may be contained in 1 gram of plant material, an addition of 6 ml. of 0.5N ferric chloride should be sufficient. Insufficient quantity of ferric chloride can easily be detected by the buff colored precipitate and the colloidal appearance of the suspension after a few minutes’ standing. I n doubtful cases more ferric chloride may be added without harm. Other methods were examined (df, 34) and found unsuitable for the joint removal of aluminum and phosphate.
Table VII.
Effect of Iron(lll) Concentration Recovery of Added Bo after Precipitation of Aluminum Phosphate a t pH 4 Barium Recovery, 70
Added,
Mg./50 hI1.
Remarks
A1 0 1 2 3 4 6
100 79 64 52 43 40
All A1 remained in solution
0 0.2 0.4 0.6 0.8 1.0
100 94 90 86 81 76
All in solution
94 94 96 100 100
Filtrate clear but colore$ brownish yellow of Fe ppt. dispersed very slow fil-tration Nearly water clear, goo& filtration
Fe 18.6 27.9 37.2 46.5 55.8 65.1
Fe/Al
Mg. Ratio 3.7 5 6 7.4 9.3 11.2 13.2
100
+
FLAME
SPECTROPHOTOMETRIC PROCEDURE FOR SULFATE SULFUR
Reagents. A. Standard hydrochloric acid, 1N. B. Ammonium hydroxide, lN, standardize against A. C. Buffer solution, 2N acetate. Dilute and partially neutralize required acetic acid to p H 4 by the glass electrode, dilute with distilled water to 1 liter. D. Ferric chloride solution. 1X solution of ferric chloride hexahydrate, dissolved in 0.5N hydrochloric acid. E. Standard barium chloride solution, 0.0625iY solution of barium chloride dihydrate, dried in a desiccator. Store in a cool dark place; 1 ml. is equivalent to 1 mg. of sulfur. F. Buffer mixture, chloride-acetate solution, 100 ml. of reagent A. Neutralize with ammonia, add 100 ml. of C, and dilute with distilled water to 1 liter (for dilution purposes). Preparation of Analytical Sample. Use a water sample or soil extract of sufficient volume t o contain 2 t o 8 mg. of sulfate sulfur. Acidify with hydrochloric acid and evaporate to dryness. If the rcsidue shons presence of organic matter, add 5 ml. of 15% hydrogen peroxide, cover, and evaporate to drlness, Remove the beakers from hot plate, add 5 ml. of reagent A, and heat to boiling in covered beakers. Transfer t o 150-ml. beakers, dilute to about 100 ml. with water; heat to near boiling. Add dropiTise, by pipetting, while stirring, 10 ml. or more of reagent E, the volume being golerned by the expected sulfate content and calculated to give a residual barium of 2 to 8 mg. Digest precipitate on hot plate until volumr is reduced to about 60 nil. REMOVAL OF PHOSPHATE AKD ALCMIXCRI. To samples of natural waters and ammonium acetate-soil extracts, add the following reagents: 10 ml. of C, 0.5 ml. of D, 4.5 ml. of A, and 10 ml. of
Fe/(Al P) Mg. Ratio 0 37.2 44.6 59 5 74 4
n
0
B; to acid-soil extracts and plant ash solutions, add 10 ml. of C, 5 ml. of D, and 10 ml. of B. Boil gently on a hot plate in covered beakers for 30 minutes and until the volume is reduced to about 80 ml. Remove from hot plate and examine precipitate after settling. It should be a dark red color, well flocculated, and settled nearly clear. If this is not the case, add 2 to 3 ml. more of reagent D, and a corresponding volume of reagent B ; digest on hot plate, as before. Remove and rinse the cover glass, and transfer the suspension into a 100-ml. volumetric flask, rinsing the beaker ti\-ice with water. Place in a cooling water bath for 10 minutes. Fill to the mark with water; mix and filter on 12.5-cm. dry folded filter, and collect any desired portion of the filtrate in a small borosilicate flask. Store in a dark cool place until ready for analysis. Preparation of Barium Standards. Transfer into 100-ml. volumetric flasks 0, 2.5, 5 , 7 . 5 , and 10 ml. of barium chloride standard A. These correspond to concentrations in sulfur equivalents of 0, 25, 50, 7 5 , and 100 mg. per liter. Add 10 ml. each of reagents A, B, and C. Fill to the mark with water and mix. Filter if not perfectly clear; keep in a cool dark place. CALIBR.4TION O F ST.4NDARDB. n-arm up the instrument for about 15 minutes; adjust dark current to zero. Light the burner and aspirate nater for a minute or two. Aspirate the 100 nig. per liter standard, locate the 515-mp peak, set the T-dial on 100, and manipulate the slit and sensitivity knob within the limits given until the ammeter is balanced. Check the dark current before
80 92 93 100 100
Filtrates water clear
and after this reading. If not in balance, adjust dark current, and repeat adjustment for standard reading. TOTALEMISSIONCURVE. Alternately, obtain emission readings with the 100 mg. per liter standard and the blank, with water rinsings between readings, until constant readings are established. Plot on graph paper. The points should trace a straight line. Similar curves can be established with maximum standards of 200 or more mg. per liter if needed. NET EMISSIONCURVE. Each point on this curve is the difference between two emission readings. For the first reading, obtain emission readings for the 100 mg. per liter standard on 515 mp; for the second, gently turn the wave length dial to 522 mp and obtain reading in that position. Alternately get emissions on 515 and on 522 mp until constant readings are obtained. Subtract the 522 reading from that on 515 mp, and designate the difference as net emission for 100 mg. per liter standard. Similarly obtain nPt readings for the remaining standards. The net emissions vs. concentrations should trace a straight line. Total and net bariuni calibration curves are given in Figure 6, READINGOF VXKSOWNS.While the instrument is n arming up, place unknowns and standards in 5-mL beakers with cover glasses, and allow 15 to 30 minutes for temperature equilibration. Read unknowns entirely on 515-mp wave length if correction for background is to be made by the indirect method, or on both 515 and 522 mp, if correction is t o be made by the direct method. Frequently check with standard nearVOL. 30, NO. 10, OCTOBER 1958
* 1687
est the concentration of last reading on 515 mp. If standard does not check, readjust by using the sensitivity h o b , and repeat the last pair of readings. Find the milligrams of barium corresponding t o the net emission on the
calibration curve. Subtract the milligrams of barium thus found from the milligrams of barium taken for the precipitation, and denote that difference as the milligrams of sulfate sulfur inthealiquot.
ANALYSIS
OF
WATERS, SOIL LEACHINGS, AND SEA WATER
The Procedure for the flame Photometric determination of sulfates was applied to rain waters, lysimeter leach-
i
30
9n
Bo
Figure 6.
C o n c o n t r o l l o n - Mg./I.
Barium emission vs. concentratim
0 Total emission on 51 5
tnp mp readings
0 Net emission of 51 5-22
Table VIII.
Flame Photometric and Gravimetric Determinations of Sulfate Sulfur in Waters
so4-s Source Rain water from lysimeter rain gage, 1956, by quarters
No. 1
2
3
4
Lysimeter leachings from Hartsells sandy loam, 1956
Lysimeter leachings from heavily limed Hartsells sandy loam, 1956 Tap water, Knoxville, May 1957
101
102 103 104 105 106 110b 624 628 631
Synthetic sea water prepared from reagent chemicals (8)
1
2
Ca 2.5 3.1
2.8 4.0 14 29 94 43 41 54 18
40 82 41 27.5
Constituents, Mg./L. K Na 0.2 0.3 N.D. 0.4 1.9 N.D. 3.3 N.D. 0.4 0.7 3.9 N.D. 2.2 1.6 N.D. 1.4 3.6 N.D. 8.2 1.6 N.D. 14.0 25.2 N.D. 10.4 N.D. 20.4 10.4 N.D. 20.0 3.4 N.D. 5.8 0.7 1.8 ~. 0.7 2.4 30.0 2.0 4.3 1.6 N.D. Mg
P
N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. 32
N.D.
Calculated Values for Undiluted Sample 800 2,540 767 21,126 N.D.
n
and S04-S, 1770 mg./l.
Volume Used per Test," hll. 1000 1000 1000 1000 500 500 500 500 500 500 500 500 500 500 1000
4(100)c lO(100) lO(200) 20(200) 30( 500 ) 40(500) 50(500)
Gravimetric Std. Mg./1. dev. 1.8
1.6 1.4 2.2
12.53 11.47 11.60 11.00 10.13 10.27 8.40 9.47 9.47 9.33 8.03
0.23 0.23 0.40 0.72 0.23 0.23
...
...
... 1753 ... ... ... ...
0.40
0.23 0.23 0.23 0.23
... 19.2
...
...
... ...
Flame Photometric Std. Mg./l. dev. 2.2 2.0 1.6 2.0 12.40 11.20 11.27 11.53 9.93 10.20 8.47 10.2
0.00 0.00
9 8 8 17
0.40
10.0
1760 1720 1732 1697 1566 1656 li19
0.12 0.23 0.50 0.20 0.25 0.00 0.00 0.07
41.8
10.0
10.9 46.1 151.1 35.3 67.1
" In each instance final volume of test solution was 100 ml.
* Received heavy application of KH,H2P04.
Figures in parentheses refer to Ba concentration of standards by which instrument sensitivitL-was adjusted to give readings of 100 on T dial. e
1688
ANALYTICAL CHEMISTRY
ings, city water, and synthetic sea water in varying dilutions. Both the flame photometric and gravimetric determinations n ere performed on at least three independent samples, and the averages are given in Table VIII. The major constituents of the samples are given to show concentration of extraneous ions. I n rain water, the quantity of sulfur in the aliquot was only about 1 mg.; in lysimeter leachings, it m-as about 5 mg.; in sea water, it was from 3.5 t o 44 mg. The total concentrations of extraneous cations in the analytical samples of sea water were from 1000 to 12,600 mg. per liter. The flame photometric sulfur determinations show good agreement with those obtained gravimetrically, for each type of water represented. The sea water yielded most consistent results when 10 nil. was taken per determination, although satisfactory results were obtained also with 20 and 40 ml. of water per 100-ml. final volume. It is believed that the comparative analytical values and the corresponding standard deviations shown in Table VIII sufficiently demonstrate the satisfactory accuracy and precision of flame photometric results, as compared with their gravimetric equivalents, without a n y additional statistical analysis. The determination of total sulfur in biological materials by the spectrophoto-
Analyses,‘’ 2nd ed., Kiley,
metric method will be presented in a subsequent publicat,ion. LITERATURE CITED
(1) Adams, F., Rouse, R. D., Soil Sci. 83, 305 (1957). (2) Am. Pub. Health Aksoc., Inc., New
York, “Standard Methods for the Examination of Water, Sewage, and Industrial Wastes,” 10th ed., 1955. (3) Assoc. Offic. Agr. Chemists, “hlethods of Analysis,” p. 100, 1955. (4) Baker, G. L., Johnson, L. H., ASAL. CHEY.26, 465 (1954). (5) Bertolacini, R. J., Barney, J. E., Ibid., 29, 281 (1957).
(6) Blum, ‘ifT. J., .4m. Chem. SOC.38, 1282 (1916).
( 7 ) Britton, H. T. S., “Hydrogen Ions,” 4th ed., Vol. 11, p. 152, Van Nostrand Kew York, 1956. (8) Chemin, L., Yien, C. H., Soil Sci. SOC.Am. Proc. 15, 149 (1950). (9) Chow, T. J., Thompson, T. G., ANAL. CHEM.27, 910 (1955). (10) Clarke, F. W., U. S. Geol. Survey Bull. 491 (1911). (11) Dean, J. .4., Thompson, Clarice, ANAL.CHEM.27, 42 (1955). (12) Diamond, J. J., Ibid., 28, 328 (1956). (13) Fieldes, M., King, P. J. T., Richardson, J. P., Swindale, L. D., Soil Sci. 72, 219 (1951). (14) Fiske, C. H., J. Biol. Chem. 51, 55 (1922). (15) Fritz, J. S., Yamamura, S. S., Richard, hl. J., ANAL.CHEM.29, 158 (1957). (16) Gilbert. P. I.. Haws. R. C.. Beck‘ man, A. d.,Ibid.; 22, 772 (1950). (17) Hillebrand, F. W., Lundell, G. E. F.,
Bright, H. A., Hoffman, J. I., “Applied
(20) Hortsman, E. L., I I (1956). (21) Kolthoff, I. hI., Stenger, V. A,, hloskovitz, B., J . Am. Chem. SOC.56, 812 ( 1 934) (22) Uargoshes, M.,Vallee, B. L., +$SAL. CHEJI. 28, 180 (1956). (23) Mavrodineanu, R., A p p l . Speclroscopy 10, 51, 137 (1956). (24) hlitchell, R. L., Robertson, I. h l . , J . SOC.Chem. Ind. Trans. (London) 55, 269T (1936). (25) Roy, N., k i . 4 ~ .CHEJI.28,34 (1956). (26) Schroeder, W.C., ISD.ESG.CHEJI., A N A L . ED. 5,403 (1933). ( 2 i ) Shaw, W.hl., S-eal, N. C., Scil Scz. Soc. Bm. Proc. 20, 328 (1956). (28) Snell, F. D., Snell, C. T., “Colorimetric Methods of Analyses,’’ Vol. 11, 3rd ed., p. 307, Van Xostrand, Kew York, 1949. (29) Stadie, K m . C., Ross, E. C., J . Biol. Chem. 65, 735 (1925). (30) Strickland, R. D., hlaloney, C. hl., Am. J . Clin. Pathol. 24, 1100 (1954). (31) Watanabe, H., Kendall, K. K., Jr., Appl. Spectroscopy 9, 132 (1955). (32) Keichselbaum, T. E., F-arnep, P. L.. hlararaf. H. W.,ASAL. CHEJI.23, 68h (195T). ‘ (33) \Vest, P. W., Folse, P., Montgomery, D., Ibid., 22, 667 (1950). (34) Willard, H. H., Tang Y. K., IXD. EXG.CH EJ~..,ANAL. ED.9,’$57 (1937). \ - - - - I
RECEIVED for review Xovember 6, 1957. Accepted April 29,1958.
Determination of Silicon, Germanium, and Tin in Their Volatile Organo Compounds MICHAEL P. BROWN and GERALD W. A. FOWLES Chemistry Department, Southampton University, Southampton, England
b A rapid dry combustion method of analysis has been developed for the determination of silicon, germanium, and tin in their volatile organo compounds. Some 13 compounds have been analyzed b y this procedure, with an average error of 0.370;.An analysis could normally be completed in 3 to 4 hours.
D
are encountered whenever volatile organo compounds of silicon, germanium, and tin, such as hexamethyldisilane, hexamethyldigermane, and hexamethyldistannane compounds are analyzed by the standard techniques available for organo compounds of these elements. I n general, the available methods may be classified according to the type of approach used, IFFICULTIES
such as wet oxidation, fusion, and dry combustion. W e t Oxidation. I n this method, which is t h e most commonly used, t h e organo compound is completely oxidized-for example, by a mixture of fuming nitric and sulfuric acids, ignited, and weighed as t h e oxide. Although this method is useful for t h e analysis of nonvolatile organosilicon ( 2 ) and organogernianium (4, 7) compounds. it is unreliable for volatile compounds because material can easily be lost \\-hen the sample is introduced. There is also a strong tendency for organosilicon compounds to form the carbide instead of the oxide, because of incomplete oxidation before or during evaporation of the acids. With germanium compounds-e.g., ethylger-
nianiuni derivatives-complete oxidation is obtained only after prolonged treatment with the acids ( 6 ) , often refluxing for a veek or more. Moreover, if the solution is evaporated too soon, volatile germanium compounds are formed and lost from the solution. Although organotin compounds are on the n hole more easily oxidized, analysis of volatile substances by this method (3, 8) is still experimentally difficult. Fusion. Oxidation by fusion procedures with sodium peroxide in Parrtype bombs has been extensively carried out v i t h organosilicon compounds (1, 9, 12) only. For volatile substances, this method is the most reliable but requires about 24 hours for completion. VOL. 30,
NO. 10,
OCTOBER 1958
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