given in Table I. T h e precision of sample packing is illustrated in Table 11. Table I11 shows t h a t t h e average difference between t h e fluorescence x-ray estimations and chemical analyses of aluminum in t h e 14 samples, with more than 4.3% aluminum, is 3.8% of the amount found, and the maximum difference is 7.8%. The average difference of silicon in the 12 samples, m-ith more than 1.6y0 silicon, is 2.6% of the amount found, and the maximum difference is 6.3%. For the 12 samples containing more than 0.12% iron, the average iron difference is 4.475 of the amount found and the maximum difference is 10.9%. The lower limit of detection of each element is around 0.2%. It is concluded, therefore, that the present method, having a 5 to 11% variation, is sufficiently accurate for the routine analysis of flotation and leaching samples. I n analyzing samples containing less than 6y0 aluminum or silicon, the precision could be improved either by increasing the counting time from 40 to 100 seconds, or by using the fixed count system. Judging from the
published literature (I), the precision might be further improved by: using a suitable internal standard, briquetting the sample into a wafer or pelletizing it in borax or glass, and/or vigorous control of sample grinding. However, any one of these steps will lower the rapidity of the present method.
(5) Conley, J. E., Brown, R. A., Caervenyak, E. J., Anderberg, R. C., Hardiner, H. J., Green, S. J., U. S. Bur. Mines, Bull. No. 465, (1947). (6) Engelhardt, V. W., Geol. Rundschau 43. 568-72 (195.51. (7)-iohns, D., Grim, R.E., Bradley, W. F., J . Sediment. Petrol. 24, 242-51 (1954). (8) Kellogg, H. H., Trans. A I M E 173, 343 (1947). (9) TI-.. Xorplco Re&. 3 . S o . \ - , Parrish. ~-~~~~~~ 2-5, 24-36, (liarch-September 19i6). (10) Reese, IC X., Cundiff, IT. H., Ind. Eng. Chem. 47,1672-80 (19.55). (11) Runke, S.hl., Howe, E . C.! Kennedy: J. S.. Kenworthv. H.. U. S.Bur. Mine:. Repi. Invest. 4440 (1940). (12) Rimke, S. 31.. O’lIeara, R. G.. Am. Inst. .Tfz%ing J f e t . Engrs y o . 1698 (1944). (13) Scott, R . h.,Pittsburgh Conference on Analytical Chemistry and Applied Spectrometry, Pittsburgh, Pa., March 1957. (14) Shapiro, L., Brannock, IT. IT . U. S. Geol. Survey Bull. 1036-C (1956) (15) Tingle, ITr. H.. Matochn, C. K.. A X L L .CHCXI30, 494 (1958).
e.
\ - - - - I
ACKNOWLEDGMENT
~
The Triter is indebted to D. R. Llaneval and H. A. McKinstry for helpful suggestions and cooperation. H e also wishes to thank the Mineral Conservation Section, Pennsylvania State University, for making this work possible. LITERATURE CITED
(1) Adler, I., Axelrod, J. M., ANAL. CHEX27, 1002-3 (1955).
(2) Archibald, F. R.,Jackscn, C. P., Trans. A I M E 159. 227-40 (1941). (3) Black, R.H., A ~ A LCHEM. . 25, 713-8 ( I 953). (4) Brindley, G. I\*., “S-Ray Identification and Crystal Structures of Clay lIinerals,” pp. 32, 86, 306, Mineralogical Soc., London, 1951.
RECEIYED for review August 25, 1958 Accepted lfaich 31, 1959. Contribution No. 59-18, Mineral Conservation Series, College of Mineral Indiistries.
UIt raviolet Spectrophotometric Determination of Phthalic Acid Application to Analysis of Naphthalene Oxidation Products W. P. FASSINGER and C.
E. GONTER
Research and Developmenf Deparfrnent, Piffsburgh Coke & Chemical
The acidity of solutions containing oxidation products of naphthalene cannot b e attributed solely to phthalic and maleic acids. Phthalic acid in 0.1 M hydrochloric acid can b e determined spectrophotometrically with little or no interference from maleic acid a t a wave length of 274 mp. The acids are precipitated as their barium salts in alcohol to separate them from naphthoquinones and other compounds present which interfere at this wave length. The expected precision of the . method is to less than i ~ l . 5 ~ 0The accuracy is to 1 1 . 5 % of the amount present for concentrations up to 4 grams per liter.
D
laboratory studies of the catalytic oxidation of naphtlialene, it had been assumed that the total acidity of the solutions could be attributed solely to phthalic and maleic URIKG
1324
ANALYTICAL CHEMISTRY
Co., Neville
Island, Pittsburgh
acids. The solutions \{-ere titrated with standard sodium hydroxide solution to a p H of 8.5. The maleic acid was determined by a polarographic method. The phthalic acid concentration was then determined by difference. It became evident as work progressed that this assumption was incorrect, and that a more specific method was necessary for determining phthalic acid in aqueous solutions containing the oxidation products of naphthalene. Previous work showed that phthalic acid could be determined spectrophotometrically a t a wave length of 274 mp with little or no interference from maleic acid in the expected concentration ranges. However, 1,4-naphthoquinone, which is a major constituent in the solutions, and other naphthalene oxidation products which could be present in the solutions absorb strongly between 270 and 300 mp. It was therefore necessary to separate phthalic
25, Pa.
acid and 1,4-naphthoquinone before the spectrophotometric method could be used. According to work done by Jlilas and Walsh (I) on catalytic oxidations and by Warshowsky, Elving, and Mandel (3) on the determination of maleic and fumaric acids, maleic and fumaric acids can be quantitatively precipitated as barium salts in ethyl alcohol. Although no supporting evidence could be found in the literature, it was felt that barium phthalate would also be insoluble under the same conditions. lJ4-Naphthoquinone, which is fairly soluble in alcohol, would remain in solution. REAGENTS A N D APPARATUS
Barium Hydroxide Solution, 0 . 3 5 5 . Dissolve 60 grams of barium hydroxide, c.P., in 200 ml. of carbonate-free distilled water. Heat if necessary. Dilute t o 1 liter with carbonate-free
distilled water, a n d mix thoroughly. Filter before using. Barium Chloride Solution, 0.01M. Dissolve 2.08 grams of barium chloride, c.P., in 200 ml. of carbonatefree distilled water. Dilute t o 1 liter with carbonate-free distilled water. hlix thoroughly. Hydrochloric Acid Solution. Dilute 10 11x1. of concentrated hydrochloric acid, c . P . , t o 1 liter with distilled water. Mix thoroughly. Phthalic Acid Standard Solution. Accurately weigh 0.2200 gram of recrystallized phthalic acid into a 100ml. volumetric flask, add about 50 ml. of distilled rvater, h f a t t o dissolve, cool, and dilute t o volume with distilled water. Mix thoioughly. Spectrophotometer. Beckman Model D U , equipped with a photomultiplier a n d 1.0-cm. silica cells. PROCEDURE
Pipet a suitable aliquot of the sample solution containing from 10 to 15 mg. of phthalic acid iiit o a 250-1111. beaker. Add sufficient diqtilled water t o make the total volume 20 nil. and add a few drops of phenolphthalein indicator solution. Add barium hydroxide solution drop!%-ise \\-ith stirring until a faint pink color is visible. Then add 10 ml. of barium chloride solution. Add 100 ml. of absolute ethyl alcohol (c.P.) and stir vigorously n i t h a stirring rod. Allon the solution to stand 1 hour to ensure complete precipitation of the phthalates. Filter the solution with suction through a Gooch crucible fitted with a glass fiber filter pad. Use ethyl alcohol to transfer and n-ash the precipitate. Place the cruciblr on a clean suction flask and dissolve the precipitate b y pouring warm hydrochloric acid solution through the crucible. Quantitatively transfer the acid solution into a 250nil. volumetric flask, dilute to volume, and mix thoroughly. Use hydrochloric acid solution to transfer and dilute. Determine the absorbance of the solution on a spectrophotometer a t 274 mp in 1-em. cells against a blank of hydrochloric acid solution. Determine the concentration of the phthalic acid from a calibration curve prepared from solutions of recrystallized phthalic acid treated in the above manner, EXPERIMENTAL
The absorptivity (specific cxtinction coefficient) of recrystallized phthalic acid plus an equivalent amount of barium hydroxide in 0.1M hydrochloric acid solution was determined a t 274 mp on a spectrophotometer, using a slit width of 0.4 mm. All absorptivity values were calculated as follows: Absorptivity
=
log Io/I
concn. in grams Der liter X ca1 lengih The average of the values obtained over a concentration range of 0.02 to 0.09
mg. per ml. was 7.72. This value agrees well with that of 7.77 found by Shreve and Heether (2) for potassium acid phthalate in 0.1M hydrochloric acid at 276 mp. The method depends upon precipitation of barium phthalate and its complete separation from the naphthoquinones. T o determine the extent of the separation, synthetic solutions were prepared from aqueous solutions containing approximately 2 grams of phthalic acid per liter, 2 grams of maleic acid per liter, and an acetone solution containing 1 gram of 1,4-naphthoquinone ppr liter. The synthetic solutions were prepared so that the concentrations of 1,4-naphthoquinone and maleic acid corresponded to the average of the concentrations expected in the samples. Phthalic acid concentration was varied over the expected range. An excess of barium hydroxide was added to 20-ml. portions of the sample solutions, followed by three volumes of absolute ethyl alcohol. When the alcohol was added, a white gelatinous precipitate formed. The solution was filtered with difficulty through paper. The precipitate was dissolved in 0.1M hydrochloric acid solution and an absorption curve run. Examination of the curve indicated that all of the 1,4naphthoquinone had been removed. However, the phthalic acid n-as not quantitatively recovered in these experiments. At times, upon addition of the barium hydroxide, reduction and polymerization products of the l,+i-naphthoquinone formed which were insoluble to some extent in the ethyl alcohol, but were soluble in the hydrochloric acid solution. These products interfered when the concentration of the phthalic acid was determined spectrophotometrically. T o eliminate the reduction and polymerization, the solutions were neutralized to a phenolphthalein end point, and a solution of barium chloride was added to give the excess barium ions necessary to precipitate the phthalic and maleic acids completely. The absorptivity of a hydrochloric acid solution of recrystallized maleic acid was determined at 274 mp; a value of 0.57 was obtained. The concentration of maleic acid in the samples was not expected to exceed 0.1 mg. per ml. I n the final dilution, it should not be more than 0.004 mg. per ml., which concentration would give a calculated absorbance of 0.002. This value is considered to be within experimental error. Filtration with suction through Gooch crucibles, fitted with glass fiber filter pads and a small amount of asbestos to effect a seal, was most efficient and least time-consuming. Before the method was applied to samples, i t was again evaluated on
synthetic mixtures. The procedure was identical to that described. Approximately 95% recovery was realized for all concentrations of phthalic acid used. As the error appeared consistent, the procedure was used on solutions containing phthalic acid only. The absorptivity values were calculated and found t o be lower than those calculated from the original standardization-Le., 7.38. By applying this lower value, the calculation of the results shown in Table I were in good agreement with the theoretical values.
Table I.
Analysis of Synthetic Mixtures
Phthalic Acid, Present 0.0266 0.0440 0,0616 0.0880
Afg./Ml.
Found 0 0266 0,0448 0.0614 0.0857
70
Recovery 100.4 101.8 99.7 97.4
A series of samples Tvas run using both the detailed spectrophotometric technique above and the polarographictitration technique (Table 11). Data shon-ing the precision of the niethod are given in Table 111.
Table II.
Comparative Results
(Grams of phthalic acid per liter)
2
Spectrophotometric XIethod 'Av.) 2 09 4.14
8
1 98
Polarographic Titration Method 2.07 4.18 2.39
8 9 10
2.13
2.02
Sample 1
Table 111.
2.01
1.66
2.00
1.68
Precision of Method
(Each sample aliquot 5 ml. per 250 ml.) Gr:ims Phthalic Sample Absorbance Acid/Liter 6 0.318 2.08 0.320 2.10 Av. 2.09 i 0.01 7 0.316 2.07 0.316 2.07 Av. 2.07 i 0.00 8 0.322 2.11 0.328 2.15 Av. 2.13 i 0.03 9 0.304 1.99 0.309 2.03 Av. 2.01 =c' 0.03 10 0.254 1.66 0.253 1.66 Av. 1.66 i 0.00
VOL. 3 1 , NO. 8, A U G U S T 1 9 5 9
1325
PRECISION A N D ACCURACY
The data obtained indicate the pccted standard deviation between duplicate determinations is less than 1.5% of the amount of phthalic acid present i n the I and Ir and recovery data supplied by the
organic laboratory shovr- that the accuracy Of the method iS within 1 . 5 7
LITERATURE CITED
(1) Milas, S . A., Walsh, IT. L., J . Chen?.Sot. 57, 1390 (1935).
-4iit.
t
2, Shreve, 0. D., Heether, 41. R , . ~ N A L .CHEM. 23, 441 (1951). 3 1 Warshowsky, B., Elving, P. J., Ilandel, J., Ibrd., 19, 161 (1947).
RECEIVED for review Xovember 10, 1958. Iccepted March ,6, 1959. Division of dnalytical Chemistry, 134th Meeting, ACP Chicago, Ill., September 1958.
Ultraviolet Absorption Spectra of Phthalic Anhydride and Related Substances Analytical Method for Naphthalene and 1,4-Naphthoquinone HANS
PETERS
Research laboratory, Reichhold Chemie AG, Hamburg, Germany
b Ultraviolet absorption spectra of phthalic anhydride and related substances are described. Changes in materials, and, in particular, the reaction kinetics of photochemical changes of naphthoquinone have been examined. A spectrophotometric method of analysis for naphthalene and naphthoquinone has also been developed. Naphthalene can b e determined more accurately b y using methanol as a solvent and b y measuring the absorbance of the suitable absorption maximum at 31 1 mp after 17 hours. Owing to ester formation, phthalic anhydride makes practically no contribution to the absorption after this period. The naphthoquinone content can b e calculated b y measuring absorbance at 347 mp immediately after dissolving the sample to b e analyzed. To avoid serious errors in analysis caused b y photochemical changes in the naphthoquinones, the substance must be stored in the dark and work done in red light.
T
quantitative determinations of phthalic anhydride and related substances. such as maleic anhydride, benzoic acid, naphthalene, and 1,4naphthoquinonr. are difficult when only conventional methods. such as ~ 0 1 1 1 metric analysis. gravimetry, and oxidimetry, are used. 1.4-Saplithoquinone interferes in almost all methods and in some very considtrably. -4 number of publications describe polarographic ( 2 , 4, 9) and spectrophotometric (1, 3, 5 6 , 8.14, 16) determinations. Optical methods, however, usually record only the spectra of thesr bodies and are very often concerned just with the detection of (he isomeric phthalic acids in resins and polyesters. I n the determination of the compoHE
1326
ANALYTICAL CHEMISTRY
nents of crude phthalic anhj-dride iron. a nianufacturing process by optical methodc, alloaance must be made for changes taking place before and durinz analysis. -in analytical method I. described here for phthalic anhydride, naphthalene, and I ,4-naplithocliiinoiie and particular consideration 1- given to changps in these substancps. In developing the method, special importance nap attached to the accuracj- of determination of 1,4-naplithoquinone and naphthalene.
All solvents were filtered through a sintered-glass funnel (G. 3) from Schott & Genossen (pore size, 15 to 40 mw). EXPERIMENTAL
Figures 1 3 show t h e absorption spectra of phthalic anhydride, maleic anhydride, benzoic acid, naphthalene, and 1 - 4 naphthoquinone deterrninpd iinmediately after dissolving in methanol, carbon tetrachloride, and 1,4-dioxane. Brigg's logarithm of the molar absorptivity in liters per mole em. n-as APPARATUS A N D MATERIALS chosen as ordinat,e and the n-ave length in millimicrons as abscissa. The Spectrophotometer. T h e absorptransmittancies of methanolic solutions tion nieasurements were made in of both dicarboxylic acid anhydricles a Carl Zeiss quartz ultraviolet spectron-err expected to be affect'ecl by ester, photometer, Model P M Q 11. Slit or rather half-ester, formation. The widths of 0.003 t o 1.5 mm. were used. Ultraviolet Lamp. Photochemical spectra for phthalic anhydride and reactions ere carried out with a maleic anhydride in Figure 1 are ncPhilips ultraviolet lamp (HPR 125 cordingly indicated by broken lines. IT), This is a high-pressure mercury After 17 hours the sprctruni of lamp n i t h an internal reflector and phthalic anhydride had changed fundashort wive length cutoff of its radiation iiirnt,ally (Figure l, curve P-411). As of about 308 mp. Reference Materials. PHTHALIC maleic anhydride in methanol solut.ion has no interest anal!-tically, the correASHTDRIDE, technical (Bayer), rcsponding change in this spectriiiii n-as crystallized twice from carbon tetrachloride. not examined in detail. ~ I A L EASHYDRIDE, IC technical (ReichThe absorption maxima of the soluhold), recrystallized twice from carbon tions of all five substances in the three tetrachloride. sol\-ents occur a t about' the same wave RESZOIC ACID, analysis grade (E. lengt,h. The absorption range of naphMer&). thoquinone extends farthest into the PUREKAPHTHALEKE (Russian procilong w v e length portion of the ultrauct), recrystallized twice from carbon violet.. tetrachloride and sublimed once. Changes in Spectra of Naphtho~,~-S.IPHTHOQUISONE, technical (Schuchhard), distilled with steam once quinone under Short-Wave Light. and sublimed twice. Esperinients carried out in rooms of Solvents. ~~IETHAX analytical OL. differing light intensity revealed that,, and chromatographical 'grade' (E. under the influence of short-n-ave Merck). light, the absorption spectra of napliCARBOS TETRACHLORIDE, analytical thoquinone in methanol solution. carand chromatographical grade (E. bon tetrachloride, or dioxane change Mer&). considerably. E r e n solid naphtho~ , ~ - D I O X A Sfor E , ultraviolet cpectrnquinone undergoes chemical changes, photometry (E. Nerck). Ultraviolet Absorption.
to
