Spectrophotometric Determination of Tin with Phenylfluorone SIR: Until recently there were no photometric methods of high sensitivity available for the determination of tin. Luke (4) has developed a method using phenylfluorone, because tin interferes with the determination of germanium with this reagent (6). It was desired to analyze pure tin samples below the concentration range reported by Luke. Some modifications allowed the use of phenylfluorone t o analyze samples with as little tin as 0.02 y per nil. A fluorometric method for the determination of tin with flavonol has been developed by Coyle and White ( g ) , which is also reported t o be sensitive to about 0.02 y per ml.
.300L 0
4 00 1.0
2.0
3.0
4.0
5.0
Figure 1 . Tin phenylfluorone
determination with
EXPERIMENTAL WORK
The general method for preparing standard tin solutions and samples for analysis was similar to that of Luke. However, the following modifications TI ere necessary. A Bcckman Model DU spectrophotometer equipped with 5-cm. absorption path cells was used for all photometric measurements. The procedure developed by Luke called for the addition of 1 ml. of 37, hydrogen peroxide solution, 10 ml. of a pH 5 buffer, 1nil. of gum arabic solution, and 10 ml. of phenylfluorone solution shortly before photometric measurenients were performed. This procedure n as unsatisfactory for the small amounts of tin present during this research. For samples in the lower range (as little as 0.02 y), satisfactory results were obtained by using 0.5 ml. of 3y0 hydrogen peroxide solution, diluting with 10 nil. of hydrochloric acid (1 t o 9), and then rciducing to a volume of about 5 ml. by boiling. This procedure destroyed the excess peroxide which was added to cnsure oxidation of tin to the stannic forin. Failure to destroy excess peroxide gave erratic results, apparently because of the oxidation of phenylfluorone. Gum arabic also gave erratic results in this laboratory. After the solution had cooled, 5 nil. of buffer solution was added, and the solutions 1% ere diluted to about 19.5 ml. with deionized water. The pH of the solution was adjusted to 3.5 with a fern drops of 4N hydrochloric acid and Accutint indicator paper Nos. 50 and 60. The volume was adjusted to 20 ml., then 5 ml. of 10 y per ml. phenylfluorone reagent was added. Absorbances a t 510 mp were determined, using water as a reference solution. Measurements were made 10 minutes after the addition of the phenylfluorone, as the color had completely deyeloped within this time. Measurements made after 30 minutes mere also satisfactory, but appreciable fading had
occurred after I hour. Measurement with a pH meter after the phenylfluorone addition indicated the pH of the solutions was 3.8 f 0.1. RESULTS A N D DISCUSSION
Because this analysis was developed for solutions which originated from pure tin samples, there was no concern with interfering metals. Luke and Campbell (4, 5 ) hare discussed interfering metals and their removal. I n this laboratory the amount of peroxide added was not found t o be critical. The added perouide was varied from 0.1 to 1.0 ml. without significant change in absorbance. Figure 1 shows the results nbtained n-ith solutions of known tin content. Although the calibration was macle a t 510 mp as recommended by Luke, subsequent measurements of the absorption curves a t pH 3.8 (Figure 2) indicates that 530 mp is the optimum wave length. The difference in the absorption of the phenylfluorone reagent and the test solution is a t a maximum and this wave length is not located on the steep shoulder of the phenylfluorone curve. For a filter photometer the 540-mp band should be used. The calibration curve for this type instrument may not be linear, as a wide band of radiant energy will cause deviation from Bouguer-Beer's law unless the absorption curve is essentially flat over the x-ave lengths used. Preparation of a Ringbom (1, 7 ) plot indicated that maximum precision occurs between 20 and 65% transmittancy, which corresponds to the concentration range 2.4 to 13 y per 25 ml. of solution. From the Ringbom plot it was found that the relative photometric error per 1% absolute photometric error over
5 00
6 00
WAVE LENGTH ,mp
6.0
MlCIiOGRAMS OF TIN
Figure 2. Absorption spectra of phenylfluorone _ _ _ _ _ 50 y of phenylfluorone in 25 ml. of 20% methanol-water solution buffered a t p H 3.8 50 y of phenylfluorone 6 y of tin in 25 ml. a t 20% methonol-water solution buffered a t p H 3.8 Tin complex (by difference)
+
.. . . . .
1.000 7 - 1
,
600
.d'I
a cc m ,400
2
,/'
,200
4 00
'. 5 00 WAVE LENGTH, mp
600
Figure 3. Absorption spectra of phenylfluorone
--_-_
50 y of phenylfluorone in 25 ml. of 20% methanol, 4 . 8 X l O - ' M with HCI -5 0 y of phenylfluorone in 25 ml. of methanol, 4.8 X 1 0 - 4 M with HCl
this concentration range is 2.7%. To increase the precision a t lower concentrations, the trace analysis method of Reilley and Crawford ( 6 ) was incestigated. A solution slightly more concentrated than the most concentrated test solution was inserted into the light path with the transmittancy dial set a t 0%. The instrument was balanced by the dark current control. Then with the transmittancy dial set a t 100% the instrument was balanced with the sensitivity control while EL phenylfluorone blank was in the light path. To determine the limit to which the instrument could be extended, successively smaller concentrations were used to set the 0% transmittancy. This VOL. 31, NO. 8, AUGUST 1 9 5 9
1441
fluorone molecules. If this interpretation is correct, considerable dimerization orcurs in 20% methanol-water solution at p H 3.8 and a phenylfluorone concentration of 2 X 10-470. Howcver, R-hen pure methanol is used as solvent with the same phenylfluorone concentration, a single absorption peak is observed, as shon-n in Figurr 3. At lower acid concentrations the absorption curves are fhifted to longer n'are lengths. Neutral solutions exhibit single peaks with both methanol and 20% methanol-water as solvent. The fact that the binodal curve is favored by increased acid concentration and by aqueous solutions and that these peaks occur a t concentrations as low as 2 x 10-4 y per ml. would not be expected in the light of the explanation previously given.
limit was found to be about 2 y per 25 ml. The absorption spectra of phenylfluorone and of its tin complex (Figure 2 ) are interesting, in that the curve for the reagent itself shows two maxima, one a t 460 mp and another at 490 mp, while for the tin complex there is a single maximum around 530 mp. These curves n-ere obtained in 20% niethanolwater solution a t a p H of 3.8 and phenylfluorone concentration of 2 x Hillebrant and Hoste (3) h a w determined the absorption spectruni of 3 X 10+yOphenylfluorone in benzyl alcohol A single peak at 475 nip is observed. However, when the absorption spectrum of 0.015yc phenylfluorone is measured with a 0.012% solution as reference, two maxima arc observed, one a t 460 and the other a t 490 nip. Hillebrant and Hoste suggest that this is caused by dimerization of the phenyl-
of Ordnance Research, U. S. A m y , for sponsorship of research on adsorption, in the course of which the development of a sensitive method for tin analysis became necessary. They also thank John A. Dean for valuable discussions.
ACKNOWLEDGMENT
Thc authors are grateful to the Office
LITERATURE CITED
(1) dvres. G. H.. ANAL.CHEY. 2 1 , 65.3 j19i9).' ( 2 ) Coyle, C. F., White, C. E., Ibid., 29, 1-186 (1957).
( 3 ) Hillebrant, A,, Hoste, J., Anal. C ~ ~ I I L . - 4 c l ~18, 569 (1958). (4) Luke, C. L., ASAL. CHESI. 28, 1276 (1906). (5j Intke, C. L., Campbeil, ?If. E., Ibid , 28, 1273 (1956). iU) Reillel-, C. Y., Craxford, C. >I., Ibid., 27, 716 (1955). ( 7 ) Ringborn, A, Z. anal. Chem. 115, 332 j 1!)30'l
ROYL. BEXSETT HILTONA. 3JiITH
Department of Chemistry The University of Tennessee Knoxville, Tenn.
Determination of Acetylene in Ethylene Oxide
Infrared Analysis of Monochloropropene Mixtures H. 1. SPELL, The Dow Chemical Co., Freeport, Tex.
1 Raze ~k~~ Componenf Name Formula
-
1
No.1
-__
-1
,
2
~
1
j
3
Accuracy
0-100
CaH,CI,
propeie
t r r n s - l -Chloro 1-propene
CaHsCl
' X orv
7c
6.1. Pfs.
f0.5
10.18
I
,
Slit
(mm) LA or
cis- 1 -Chloro-
Av 0.250 0.051
0.1
100 0.1
100 0.1
8.48
0.180 0.045
100 0.1
Instrument: Perkin-Elmer Model 12C, NaCl prism Somple Phase: Solution in carbon disulfide Cell Windows: NaCl Absorbonce Measuremenf: Colculotion:
Base line---
Inverse m a t r i x _ -
0.540 0.065 0.020 0.002
Point-_LC
2 3 4 Moteriol Purity:
0.022 1.280 0.090
14.60~ 0.042 0.002 1.720
0.004
0.022
7c
%
X or v 6.1. Pfs.
13.65 13.413.8
AY
,
Concn. mm Hg lengfh
mm
0.760 0.0667
'
760 100
Insfrument: Perkin-Elmer Model 1 12, NaCl prism Sample Phase: Vapor Cell Windows: NaCl Absorbance Measurement: Colculation:
1
Bore line _ X Point-
Inverse matrix--G r a p hica I X
Successive approx.-
Mafrix:
13.65~ 100 p . p m b y weight gives on absorbance o f 0.402.
Maferiol Purify: Reference compounds 99 +7cpure. contained < 2 p . p m acetylene.
Graphical___
1
Range
Relative Absorbance'-Analyticol ComponentlX
Successive approx.--x
Relotive Absorbancesa-Analytical Mafrix: Componenfli 10.18~ 12.53~
Component Nome Formula
100
1 .oo 0.178
propene
No.1
Accuracy
___. _I-.
14.60
1 -propene
CS-90
H. 1. SPELL, The Dow Chemical Co., Freeport, Tex.
Concn. mg/ml length mm
~ ~ _ _-~ _ r t 0 . 5 12.53 0.450 0.082
I 0-30
1
CS-89
8.48~ 0.040 0.003 0.015 1.690
Reference compounds 99 +% pure
Ethylene oxide
Commenfs: The Beer's l a w line i s curved so that a t ieost three points have to b e established from synthetic blends to cover the concentration range of 0-200 p . p m Lower limit of detection i s 2 p.p.m. This analysis may b e performed with a 10-meter cell loaded to 300 mm. Hg pressure. The accuracy i s f0.5 p.p.m. Absorbance is measured using the same base line points as for the meter cell run.
Relative absorbances are given as the slope of the Beer's l a w concentration curves used expressed in terms o f absorbance per 100yG of constituent.
a Relative absorbances are given as the slope o f the Beer's taw concentration curves used expressed in terms o f absorbance per 10070 of constituent.
These d a t a represent standard publication and submission is open t o anyone in accordance with regulations of ANALYTICAL CHExiaTRY. T h e Coblenta Society is acting only a s a n aid t o t h e journal
To standardize procedure. ANALYTICAL CHEmaTRY requests t h a t material h e sent in quintuplicate to t h e chairman of t h e review committee: Robert C. Wilkerson, Celanese Corg. of America, Post Office Box 8, Clarkrvood, T r x .
a
1442
ANALYTICAL CHEMISTRY
