tissues. For repeated (15 times) 10minute counts a t high voltage tap 7 of a series of 11 different blood samples of varying degrees of color, the average standard error was 1.7%. At high voltage tap 11, a value of 1.87, was obtained for a similar series. The adequate sensitivity of the liquid scintillation method, together with the ease of manipulation and counting of large numbers of samples, makes it suitable for routine counting of tissues.
The scintillator bead method of Steinberg may be useful (IS). The sensitivity, S, of the liquid scintillation method for 60-minute counting times for sample and background, absolute efficiences of 20 and 5% for carbon-14 and tritium in tissues, carbon-14 and tritium background of 30 and 70 c./m., respectively, and channel limits of 10 to 100 were calculated from the formula, S = Ex/2.2 p p c .
where 2 is obtained from the equation 1.96 (60 x
ACKNOWLEDGMENT
+ 120 B ) 1’2/60 = 0.05 z
The author thanks C. N. Rice of this laboratory for his advice during this investigation.
where E is absolute counting efficiency, z is sample c./m., and B is background
c./m. Absolute sensitivity values of 123 =k 6 ppc. and 6 i 2 =!= 34 p p c . , were obtained for carbon-14 and tritium, respectively. Because the efficiency figures used are the lowest observed, the sensitivity of the method is higher than these values for many of the
LITERATURE CITED
(1) AgranoE, B. W., Nucleonics 15, 106
(1957). (2) Arnold, J. R., Science 119, 155 (1954). (3) .Aronoff, S.$, “Techniques of Radiobiochemstry, pp. 35-64, Iowa State College Press, Ames, Iowa, 1956.
(4)Eisenberg, F., Jr., “Liquid Scintillation Counting,” p. 123, Pergamon Press, New York, 1958. (5) Freedman, A. J., Anderson, E., Nucleonics 10, No. 8, 57 (1952). (6) Funt, B. L., Hetherington, A, Science 125, 986 (1957). (7) Haves, F. N., Roger, B. S., Langham, ‘8. If.,Nucleonics 14, No. 8 , 58 (1952). (8) Herberg, R. J., Science 128, 199 (1958). (9) Kinard, F. E., Rev. Scz. Znstr. 28, 293 (1957). (IO) Kinnory, D. S., Kanabrocki, E. L., Greco, J., Veatch, R. L., Kaplan, E., Oester, y; T “Li uid Scintillation Counting p.” 223, %ergamon Press, New Yori(,1958. (11) Passmann, J. hi., Radin, K. S., Cooper, J. A. D., ASAL. CHEM. 28, 484 (1956). (12) Passmann, J. M., Radin, N. S., Cooper, J. A. D., Cancer Research 17, 1077 (1957). (13) Steinberg, D., Nature 182,740 (1958). (14) Vaughan, M., Steinberg, D., Logan, J., Science 126, 446 (1957). (15) White, C. G., Helf, S., iVucleonics 14, No. 10, 46 (1956).
RECEIVEDfor review March 23, 1959. *4ccepted October 23, 1959.
Determination of Platinum, Sulfur, and Chlorine in Platinum Reforming Catalysts ANNE
L. CONRAD
and JEAN
K. EVANS
Research Department, The Standard Oil
b A new method for the determination of platinum in petroleum conversion catalysts utilizes the volatility of platinum chloride a t induction furnace temperatures, Evolved gases are absorbed in acid and the platinum is determined colorimetrically using p-nitrosodimethylaniline. Total time for a determination is approximately 2 hours. Reproducibility with the standard fusion methods was within f 0.005%. Modifications are also included for the determinations of sulfur and chlorine in catalysts by induction furnace methods where volatile platinum causes interference. By trapping the volatile platinum in hot formic acid, standard titrations of both sulfur and chlorine can b e performed. HE analysis of petroleum conversion T c a t a l g sts for less than 1% platinum usually requires a tedious fusion procedure bo obtain complete solution of the aluminum base sample. The problem becomes very time-consuming with used catalysts, where two or three fusions may be required to put the last trace of sparingly soluble catalyst into solution. I n addition, some separation from ex7
46
e
ANALYTICAL CHEMISTRY
Co. (Ohio), Cleveland, Ohio traneous elements is usually required. I n seeking a more rapid procedure for obtaining soluble platinum salts from the catalysts, the possibility of volatilizing platinum appeared practical and vias investigated. I n 1940 Seath and Beamish (11) noted that platinum salts were volatile at high temperatures. Later, Beamish and McBryde (3) studied the volatility of platinum chloride using the U-tube chlorination of samples. I n both cases volatility TTas considered detrimental to the analytical method. Other analysts ( l a , 15, 16) have used sealed tube and wet chlorination methods to obtain rapid solution of platinum salts without losing platinum. Platinum has been recovered by volatilization of platinum chloride (9). When a n induction furnace was used ior burning reforming catalysts, the volatility of platinum was again observed. Attempts to determine sulfur dioxide iodometrically following the Leco procedure (4) failed. Excessively high titrations led to the conclusion that some interfering element was consuming iodate. Spectrographic examination of the sulfur-absorbing solution showed that platinum was present. Similarly, attempts to titrate chloride
in a n absorbing solution after an induction furnace burning always gave low results. Because platinum was found in the solution, it n a s concluded that some form of covalent platinum chloride was being evolved, rendering a bound chloride unavailable for titration. It v a s also believed that any long, hightemperature drying of the catalysts would result in loss of platinum if any chloride were present in the sample. On these bases, attempts were made to obtain the complete volatilization of all platinum in the sample. Spectrographic examination of the initial fusion mixtures showed that this was not the case. Although some platinum had been evolved, considerable amounts remained behind in the crucible. As evidence existed that platinum chloride TI as the volatile constituent, more chloride was assumed to be needed to ensure the complete volatilization of platinum. The addition of a chloride salt to the fusion mixture before burning proved satisfactory. Sodium, potassiuni, barium, and aluminum chlorides were tested. I n all cases spectrographic checks showed that all the platinum had been evolved from the fusion mixture; aluminum chloride was preferred be-
Table 1. Effect of Iron on Repeatability of Platinum Measurements
06d
yo Platinum
0
z
C6-
Iron
LI:
a
0
g
c4-
a c2-
O
I
8-
?
h
0
4
k
I R O N REMOVED
8
IC
15
I4
;1
I8
20
Iron
present 0.294 0.337 0.508 0.381 0.335 0.306
removed 0,380 0.3iB 0,359 0,375 0.390 0.389
TIME - D A Y S
Figure
I.
Effect of excess iron on color development
0
A
0
cause it left no solid deposits along the combustion tube n-alls.
Sample 1 Sample 2 Sample 3
Procedure. Dry the ground catalyst sample for 1 hour a t 110' C., and weigh immediately into a ceramic crucible (Leco IH-13) containing 2 EXPERIMENTAL scoops of C.P. aluminum Chloride. Equipment. 1 high-temperature For most catalysts 0.10 gram of sample induction furnace, Leco RIodel X-519 is sufficient. Mix the sample and (Laboratory Equipment Corp.), was aluminum chloride with aglass stirring used, hut other suitable models are rod and add 3 additional scoops of available. Attachments required for aluminum chloride (total approxithis furnace include: mately 1 gram), 1 scoop of AIundum, and 3 scoops of iron chip accelerator. Ignitor supplied for combustion of orCover the crucible with a porous lid. ganic materials, Leco 5-519-5 Inlet-gas mashing, drying, and control Set up the induction furnace with the system, Leco 1150 ignitor in place and the special heating Inverted Lshaped glass extension on top mantle (300" C.) on the exhaust from of combustion tube and connected to the combustion tube. Connect the exabsorber haust to a gas-washing bottle conHeating mantle for glass extension, taining 100 ml. of ion exchange purified special model from Brisco Mfg. Co. water and 10 ml. of concentrated hydroCeramic crucibles, Leco IH-10-855,and porous covers, Leco X-519-8 chloric acid. Connect the exit from Absorber or gas-washing bottle, Harthe gas-mashing bottle to a sodium shaw 5060 (Harshaw Scientific Division, hydroxide scrubber to prevent the Harahaw Chemical Co.) escape of obnoxious fumes. Burn the sample follom-ing induction furnace X spectrophotometer, Beckman procedures. Intense white-hot burning Model B, n-as used but other spectroshould persist for several minutes. photometers IT ith adequate sensitivity Wash the absorbing solution into a and resolution at 525 mp are equally 250-ml. beaker and reduce the volume satisfactory. Reagents. IROS CHIP ACCELER- to approximately 50 ml. by boiling. Filter into a 100-ml. volumetric flask TOR, ayailable in pure form from through a No. 42 Whatman paper. Leco. S o . 501-77. Make up to volume m-ith ion exchange RR ALUISDUJI,90-mesh, refractory purified water and pipet a suitable grain, S o r t o n Co. aliquot containing 0.025 to 0.150 mg. STAKDARD PLhTINUM SOLUTIOK. of platinum into a separatory funnel. Dissolve 1 gram of 99.9% pure platAdd 2 ml. of concentrated hydrochloric inum n-ire (American Platinum acid, 15 ml. of C.P. chloroform, and Works) in 50 ml. of aqua regia with gentle heating. ETraporate the solu10 ml. of 6% aqueous cupferron solution in that order. Extract imtion almost t o dryness and treat with mediately for 30 seconds, shaking vigthree successive 10-ml. portions of 1 orously and relieving pressure several to 1 hydrochloric acid, each time times. Draw off the lower layer which evaporating almost to dryness. Transfer the final material to a 100-ml. volucontains the chloroform solution of metric flask. add 4 ml. of concentrated iron-cupferron complex. Add 15 ml. of chloroform and extract vigorously for 15 hydrochloric acid, and dilute the solution t o volume. This stock solution conseconds to remove excess cupferron. Draw off the lower layer and discard, tains 10 ing. of platinum per ml. PreAdd 2 drops of concentrated hydropare final dilutions containing from chloric acid and repeat the extraction 0.0005 to 0.003 mg. per nil. daily for calibration curves. n i t h 15 ml. of chloroform. COLOR REAGEKTSOLUTIOK. DisBefore mixing the reagents, adjust solve 0.5% p - nitrosodimethylaniline the p H of the sample solution and the (Distillation Products Industries, No. dilution water to 2.2, using sodium hydroxide and hydrochloric acid. This 188) in fresh absolute ethyl alcohol. BUFFERSOLUTION. Combine 50 ml. p H adjustment is very critical to color of 4 M sodium acetate and 53 ml. of development, as emphasized by Yoe 4 M hydrochloric acid. (17). At no tinie during the color de-
velopment should the p H vary by more than 10.05 unit. Transfer the sample solution to a 50-ml. volumetric flask, add 1 ml. of p H 2.2 buffer solution and 1 ml. of 0.5% p-nitrosodimethylaniline solution. Immerse the flask in boiling water for exactly 20 minutes, then remove and immediately cool in a 20" C. bath for 5 0.2 minutes. Heating and cooling periods must be rigidly controlled. Dilute to volume with ion exchange w t e r a t a pH of 2.2. Alcohol was not used in the final solution because sensitivity was not required. Read the absorbance a t 525 mk and calculate the platinum concentration. Prepare a blank including the burning procedure through color development and correct all sample values. For calibration, prepare the final dilutions of the standard platinum solution so that they contain 0.0005 to 0.003 mg. of platinum per ml. Develop and read color as described above. DISCUSSION
The evolution of platinum chloride by induction furnace burning separates platinum rapidly from other catalytic constituents, Considerable amounts of iron accelerator, however, were evolved during the burning. The presence of excess chloride probably increased the volatility of iron. Thus, it was necessary to add a large excess of chloride to guarantee the complete evolution of platinum. Three times the theoretical amount of chloride, added as aluminum chloride, was needed in the fusion mixture. With this amount of excess chloride, all platinum could be evolved as platinum chloride and absorbed in dilute acid solution, Approximately */z hour is required for this procedure. Several colorimetric platinum methods are available in the literature ( I , 2 , 8, 10). The stannous chloride method was tried without success. The presence of too much iron or the nature of the volatile platinum species prevented color formation. The colorimetric method proposed by Yoe (17) using p-nitrosodimethylaniline proved most satisfactory. However, the volatile iron from the accelerator was present in sufficient quantities to interfere. Initial experiments performed n-ithout removing iron showed that the color intensity due to iron p-nitrosodimethVOL. 32, NO. 1, J A N U A R Y 1960
47
Table II. Platinum Determination by Induction Furnace Platinum -4dded Found Known Blends 0,423 0.425 0.207 0,213
Table IV. Chlorine by Induction Furnace in Presence of Platinum 76 Chlorine NBS Sample Known Found KO.89, lead-barium glass 0.051 0.050
0.051 S o . 93, borosilicate glass 0.036 0.034
0.036
0.104
0,104
No. 89, +2% PtO?
% Platinum Fusion
X-ray Typical Samples 0,364 0.363 0.359 0.358 0.368 0.367 0.390 0.394 0,750 0.756
Induction furnace 0.370 0.359 0.366 0.389 0.751
S o . 93,
Sample S B S S o . 79 PtCl,, theor. 0 13%S
+
Catalyst 1 2 3 4
%S
-
48
ANALYTICAL CHEMISTRY
3
Found
4
0.125 0.133 0.26 0.26 0.02 0.03 0.08 0.10 0.02 0.03
5
\ lnniline increased steadily Iyith time. Figure 1 compares the absorbances obtained with excess iron present and with iron removed. The latter values show negligible increases within the first few liours. The actual platinum values obtained in the presence of excess iron n ere very erratic (Table I), but gave excellent repeatability after the iron had hccn removed. -4rapid procedure for the removal of iron was required. For this purpose the entire absorbing solution is first evaporated with acid. Most of the iron is thus converted to ferric chloride and the remaining traces of iron oxides can be filtered from the solution. The sample or a n aliquot containing 0.025 to 0.150 mg. of platinum is extracted with chloroform and aqueous cupferron solution (6). Precipitation r i t h cupferron alone gave a voluminous, difficult-to-filter solid which may contain coprecipitated platinum. The solubility of the iron cupferron complex in chloroform simplifies the separation, permitting simultaneous precipitation and extraction of the iron in one step. Although platinum forms no cupferron complex, the presence of excess reagent must be avoided to prevent coloration of the aqueous layer. Several immediate \lashings of the water layer with chloroform are required.
0.052 0.035 0 035 0.036
+ 4% PtO?
yc Chlorine Acid Typical Oxygen Samples flask evolution 1 0.28 0.31 0.30 9
Table 111. Sulfur by Induction Furnace in Presence of Platinum
0.050 0.050
6
0.82
0.87 1.50 1.44 1.03 1.09 0.382 0.312 0.315
Induction
0.32 0.33 0.88 0.96 1.40 1.39 1.19 0.389 0.316
RESULTS
To check the accuracy of the procedure, pure platinum wire was dissolved and added quantitatively to an alumina catalyst containing no platinum. Concentrations of platinum ranged from 0.1 to 0.45%. Table I1 shon s that recovery of platinum after a n induction furnace burning n as &0.005~0,.Table I1 also shows the results obtained on typical catalyst samples compared to those obtained by the classical basic fusion and by x-ray methods. Average differences were less than *0.005%. Modification for Sulfur Determination. T h e volatile platinum interferes with the published iodometric titration of sulfur by induction furnace methods (4). Excessively high titrations combined with spectrographic verification of the presence of platinum indicated that platinum would have to be removed before the sulfur could be titrated quantitatively. For this purpose, the evolved gases !\-ere passed through a hot solution of formic acid (6, 7 , lS, 14). This solution rapidly reduces platinum salts to platinum black. Sulfur dioxide is not retained by hot formic acid and can be determined accurately by iodometric titration in the adjacent absorber. The formic acid trap consisted of a 250-ml. Erlenmeyer flask, complete with glass inlet adaptor and a 125mm. condenser obtained from Kontes Glassware Co. (K-61700, K-18150, and K-45725, respectively). This trap is inserted betneen the exit of the combustion tube and the sulfur titrator.
One hundred milliliters of concentrated formic acid are placed in the trap and kept boiling on a hot plate during the burning of the catalyst sample. Gases eyolved from the induction furnace combustion tube are carried by a stream of oxygen through the hot forniic acid, where platinum is reduced to platinum black. The unabsorbed gases, including all of the sulfur dioxide, are carried on into the sulfur titrator, where the iodometric titration can be conducted without interference. Table I11 shon s the repeatability of values obtained on both typical samples and on Kational Bureau of Standards (XBS) KO.i 9 fluorspar to nhich platinum had been added. JIaxinium deviations were found to be SZ 0.02% sulfur. Modification for Chlorine Determination. Formic acid may also be used to eliminate platinum interference in chlorine determinations. Here excess standardized silver nitrate may be added to the formic acid trap and the chloride precipitated as silver chloride a t the same time that platinum is precipitated as platinum black. The excess of silver nitrate can be titrated for the determination of chlorine content. Considerable care should be taken to prevent the decomposition of silver nitrate in hot formic acid. Excessiyeljlong heating periods should be avoided and the flask should be shielded from light during the procedure. To check the accuracy of this procedure two XBS samples \\ ere checked both with and without added platinum. Results are shown in Table IV, where average deviations from the knox-n concentrations were 0.0047,. Results on typical catalyst samples are also shown in Table IV. Here results are also compared to those obtained by other conventional methods of analysis. By use of the above procedure both sulfur and chlorine may be determined simultaneously on one burning. Platinum, however, in the useful concentration ranges is difficult to determine simultaneously n ith either sulfur or chlorine. If higher concentrations of platinum are involved, it might be possible to filter and n-eigh the platinum black precipitated in the formic acid. I n typical catalysts the amount of platinum black formed is too minute for gravimetric weighing, but fusion and colorimetric measurements might be possible. ACKNOWLEDGMENT
The authors are indebted to R. E . Farrell and Ruth Zuback, Sohio Process and Product Development Laboratory, for the cooperative testing of these samples and to the Standard Oil Co. (Ohio) for permission to publish this \To&.
LITERATURE CITED
G. H., .44sa~.CHEXI.25, 1622 i 1953). ( 2 j Ai;&, A y e k , G. H., Meyer, A. S., Jr., Ibid., (1) hyers,
23, 299 (1951). ( 3 ) RPami' Beamish, F. E., McBryde, W.A., I b i d . , 25, 1613 L.2) I V 1 3 (1953). (lYdr3 J. ( 4 ) Conrad, A . L., Evans, J. K., Gaylor, V. F., Ibid.,31, 422 (1959). IT. ( 5 ) Furman. Furman, K. H.. H., Mason. Mason, i\-. B., B.. Pekola, J. S.,Ibid., 21, 1325 (1949). ( 6 ) Gilchrist, R.,J . Research A'atl. B u r . Standards 20, 745 (1938).
( 7 ) Gilchrist, R., Kichers, E., J . Am. Chem. Sac. 57, 2565 (1935). ( 8 ) Gordon, C. L., Schlecht, K. G , Wichers, E., Bur. Standards J . Research 6 , 421 (1931). ( 9 ) Xixon, TI-. S.(to Cniversal Oil Products Co.), U. s. Patent 2,828,200 (?riarch 25, 1958). (10) Ryan, D. E., Analyst 76, 167 (1951). ( 1 1 ) Seath, J., Beamish, F. E., IND.ESG. CHEII., A s a ~ ED. . 12, 169 (1940). ( 1 2 ) Smith, 31. E., A s . 4 ~ . CHEM. 30, 912 (1958).
( 1 3 ) Swisher, Ll. C., I N D Esc. . CHEJI., ANAL. ED. 1 1 , 162 (1937). ( 1 4 ) Vonossi, R., A n d e s asoc. guim. Arg. 38. 117 11950). (15) 'Westland, k. D.. Bemnish, F. E., ASAL. CHEX 30, 414 (1958). ( 1 6 ) Wichers, E., Pchlecht, JY. G.,
Gordon, C. L., Bur. Standards J . Research 6 , 421 (1931). ( 1 7 ) Yoe, J. H., Kirkland, J. J., i 2 s . 4 ~ . CHEW26, 1335-40 (1954). RECEIVEDfor review June 15, 1959. Accepted September 25, 19-59.
Volumetric Determination of Isophthalic and Other Dicarboxylic Acids in Modified Alkyd Resins G. G. ESPOSITO and M.
H. SWANN
Coating and Chemical laboratory, Aberdeen Proving Ground, Md.
b A volumetric method involving nonaqueous titration was developed for general application to the determination of single dicarboxylic acids in all types of modified alkyd resins. Gravimetric methods are unsuitable for measuring isophthalic acid and are rarely adaptable to modified alkyd resins of any type. The volumetric method is more rapid than the ultraviolet method and requires no special equipment.
A
of dicarboxylic ncids are used in the manufacture of alkyd resins, polyesters, and plasticizers and riiinierous analytical mc.thods are availnlile for detecting and measuring these acids. M?th the exreption of the chlorinatrd a i d liydrogc~natedphthalates and possibl) azelaic and maleic acids (j),all of thcse acids can be separated as their dipotassium salts by saponification in anhydrous medium. This technique is the first step in most of the analytical procedures. Calculation of phthalic anhydride from the \\-eight of the precipitated salts ( 2 ) was the fastest and most popular method for a number of years but \Tas unsuitable for alkyds modified n ith polystyrene, vinyl chloride-acetate, epoxy, and other resins. The introduction of isophthalic acid resulted in high yields by the gravimetric method due to coprecipitation of alkali and fatty acid soaps with the salts. This acid must be determined spectrophotometrically (8). A certain amount of potassium carbonate always precipitates with the dipotassium salts, so that even in the analysis of pure phthalate alkyds, a correction by titration with acid has to be applied. Other volumetric methods ( 3 , 6) have been proposed for o-phthalic anhjdride in alkyd KUMBEE
resins but are subject to error from the coprecipitated carbonate and free alkali. Recent methods (1, 4) provide for the rapid identification of dicarboxylic acids in alkyds and, for those containing single acids, the volumetric procedure described in this paper is rapid and generally applicable. I t s time-saving features include the elimination of the need for drying, m-eighing, and cooling filtration crucibles and the subsequent application of instrumental measurement. The acids are measured by nonaqueous titration in ethylene glycolethyl alcohol medium. I n Table I, the values resulting from the analysis of a variety of modified alkyds by gravimetric and volumetric methods are compared to the values obtained by the ultraviolet procedure ( 7 ) . Volumetric and spectrophotometric ( 8 ) analyses on five isophthalic alkyds are compared in Table 11. EXPERIMENTAL
Reagents. Potassium hydroside in methanol, 0 . 2 s . Dissolve 6.5 grams of potassium hydroxide in 100 ml. of absolute methanol, filter, and dilute t o 500 ml. with methanol. Hydrochloric acid in ethyl alcohol, 1.0s. Dilute 10 ml. of concentrated hydrochloric acid t o 120 ml. with absolute ethyl alcohol. Hydrochloric acid in ethyl alcohol, 0.024N. Dilute 1 ml. of concentrated hydrochloric acid to 500 ml. with absolute ethyl alcohol. Table 1.
m-Cresol Purple indicator. Dissolve 0.025 gram of m-Cresol Purple in 100 ml. of absolute ethyl alcohol. Isolation of Dipotassium Salts. ISOPHTHALIC ACID. -4 sample containing 0.05 to 0.15 gram of isophthalic acid is weighed into a 1-liter Erlenmeyer flask a n d dissolved in 50 ml. of benzene. Two hundred milliliters of 0.5N alcoholic potassium hydroxide (made with absolute ethyl alcohol and filtered) are added and t h e sample is refluxed in a water bath for I'/z hours. Benzene (270 ml.) is added and the sample is cooled to room temprmture and allowed to stand for 1 1 2 hour. It is then filtered through a fritted-glass crucible of coarse porosity, prc,ferably one prepared with a mat of filtering asbestos. The prwipitatcd salt is transferred and washed with about 150 ml. of 2 to 1 benzenr-ethyl alcohol mixture and air is drawn through the crucible for about 1 minute. It is then reserved for nonaqueous titration. I n the cas? of isophthalic acid only, it is advantageous to warm the crucible for about 15 minutes in an oven a t 105' C. just before dissolving the salts. Table II.
Analysis of lsophthalic Alkyds
Isophthalic Acid, 7 Ultraviolet Volumetric 19.0 59.8 36.7 27.6 19.9
19.0; 59.6; 35.9: 27.4: 19.9:
19.3 59.8 36.2 37.8 20.1
Analysis of Some Modified Alkyds
Type of XIodification
Ultraviolet
Found, 7G Gravimetric
Volumetric
Styrenated alkyd Epoxy ester modified alkyd Poly(vinylto!uene) alkyd
19 9 25 7 20 0
23 6 ; 24 8 28 7; 30 8 22 7 ; 23 1
1') 6 ; 19 7 25 7 ; 26 0 19 7 : I n 9
VOL. 32, NO. 1, JANUARY 1960
49
