August, 1924
INDUSTRIAL A N D ENGINEERING CHEMISTRY
797
Spectrophotometric Analysis Applied to Chromotrope IOBlB2 By W.D.Appel and W. R. Brode BUREAW 08 STANDARDS, WASHINGTON, D. C.
T
The data presented indicate that spectrophotometric measurements tested by comparative dyeHE spectroscope and, ing and by titanous chloride in recent Years, the of solutions of chromotrope /OB may be used fo determine color spectrophotometer strength and that such determinations agree uery well with practical ~ ~ i h t i o n .The ir&~mation obtained has been studied have been used by many dyeing tests for strength. The measurements cannot be franslated into dye-testing terms of hue (“shade”) and brightness for smaller to determine whether specworkers for the study of the tral transmissive values for relationship between Color uariations in the quality of the dye. Quantitafiue spectrophotometric measurements of reasonably pure chromotrope IOB. a-naphsolutions of CbomotroPe and constitution of dyes thylamine-aZ0-H acid, and a-naphthylamine-azo-l-naphthoE3,6,8- 10B can be translated into and for the identification of There have aPtrisu[fonic acid are gioen. ordinary comparative dyeing terms of strength and peared references to the use of the spectrophotometric quality. method for the evaluation of commercial dyes14but very few MATERIALS data have been published to indicate the value of the method compared with the methods in Use. It Was thought The commercial samples of chromotrope 10B represented that a comparison of analyses of a simple dye by this method experimental batches of the color.8 The results of comparaby titanous chloride titration and by the ordinary practical tive dyeing tests were furnished with the samples. dyeing test would be of interest. The standard sample of chromotrope 10B was prepared in The titanous chloride titration method has shown a marked the laboratory from carefully purified chromotropic acid and gain in favor for the determination of the strength Of dyes.6 a-naphthylamine of correctmelting point.^ After coupling It can never entirely displace the practical dyeing test, how- in the usual way, the disodium salt of the dye was purified by ever, because it tells nothing about the quality of dyes-i. e., crystallization from water. The disodium salt of a-naphthyltheir hue (“shade”) and brightness on the fiber. The spec- amine-azo-~acid was prepared in way, from retrophotometric method, on the other hand, a t least has the crystallized H aoid. The sample of the trisopossibility of not only giving the strength of dyes but also dium salt of ~-~~phthylamine-azo-l-naphthol-3,6,8-tr~~~~fon~c their variations in quality. Since under standard conditions acidlo was redissolved, filtered, and precipitated to make certhe spectral transmission of pure substances in solution is tain of its purity. These standards should contain sodium characteristic for each chemical entity16the subsidiary dyes &loride and moisture as their chief impurities. which exist as impurities in commercial dyes and are the CHEMICALANALYSES OF THE STANDARD DYES cause of variations in hue and brightness on the fiber might --Naphthylamineor-Naphthylaminebe expected to show up in spectrophotometric measurements azo-chromotropic a-Naphthylamineazo-1 OH-3,6,8Acid azo-H Acid sulfonic Acid of solutions of the dyes. % % % Chrornotrope 10B is the simple azo dye, a-naphthylamine- Insoluble in water None None None 4.22 2.60 15.03 azo-chromotropic acid.’ Refined a-naphthylamine is used in NaCl Moisture 4 45 9.29 2.790 the manufacture of dyes and is a fairly pure product. The Dye by difference 91.3 88.1 82.2a 91.7 88.5 80.3 subsidiary dyes in chromotrope 10B would be formed from 91.0 88.1 82.6a a-naphthylamine and the impurities in the chromotropic a High results indicate the presence of about 1 per cent of naphtholacid used. The two likely impurities are H acid and a-naph- trisulfonic acid in this dye. NazSOa was not found. thol-3,6,8-trisulfonic acid depending on which of the two commercial processes was used in the manufacture of the chroPROCEDURE motropic acid. Solutions of the laboratory preparations in a phosphate The spectral transmittancy in the visible range has been buffer solution, pH 6.75, were measured with the Konigmeasured for solutions of relatively pure samples of chromoMartens spectrophotometerlll using a heterogeneous light trope 10B, a-naphthylamine-azo-H acid, and a-naphthylamine-azo-l-naphthol-3,6,8-trisulfonic acid in three different source in concentration 1 cg. per liter and 1or 2 cm. thickness solvents. Solutions of a series of commercial samples of for wave lengths 460 to 670 mp a t intervals of 10 m p chromotrope 10B representing considerable variation in Note -The buffer solution was made up t o be 0.01 molal with respect to monophosphate and t o disodium phosphate and its p H value determined hue and brightness by the dyeing test have been measured in sodium colorimetrically. The ordinary C. P. quality salts are not to be relied upon the same way in one solvent. All these samples have been with respect to their pH value, and the buffer solutions made from them
gpcls
1 Received March 31, 1924. Presented before the Division of Dye Chemistry a t the 67th Meeting of the American Chemical Society, Washington, D. C., April 21 t o 26, 1924. 2 Published by permission of the Director, U. S. Bureau of Standards. a Watson, “Colour in Relation t o Chemical Constitution,” Longmans, Green & Co., 1918; Formanek and Grandmougin, “Untersuchung und Nachweis organischer Farbstoffe auf spektroskopischen Wege,” Springer, Berlin, 1908, 1911, 1913; Kayser, “Handbuch der Spectroscopie,” Vol. 111, Hirzel, Leipzig, 1905; Holmes, THISJOURNAL, 15, 833 (1923). 4 Holmes, Colov T y a d e J., 13, 6 (1923); Mathewson, J. Assoc. Oficial Agu. Chem., 2, 164 (1916); THISJOURNAL, 12, 833 (1920); Wales, Am. D y e s k f Reporter, 12, 751, 791, 855, 863 (1923). 6 Calcott and English, THISJOURNAL, 15, 1042 (1923). 6 Watson, Kayser, lac. c i f . 7 Colour Index No. 90, 1923; Schultz, Farbstofftabellen, No. 114, 1914.
should be tested.
Additional measurements were made with homogeneous source (Hg and He lines). Measurements on the standard sample of chromotrope 10B were made by two different observers12 a t different times on the Konig-Martens spectrophotometer. All three of the standard dyes were also measured on a 8 Obtained from the Newport Co., Carrollville, Wis., through the courtesy of Ivan Gubelmann, chemical director. 9 Lee and Jones, THISJOURNAL, 14, 961 (1922). 10 Supplied by the Newport Company. 11 Gibson and others, BUY.Standards, Sci. Paper No 440,18, 121 (1922). 1 2 The authors are indebted t o M. K . Frehufer for a determination of the absorption spectrum of the standard sample of chromotrope 10B.
INDUSTRIAL A N D .ENGINEERING CHEMISTRY
798
Vol. 16, No. 8
TABLEI Sample 183 182 181 184 176 179 177 175 Cg. sample per liter 1.487 1.988 1.666 1.392 1.845 1.462 1.821 1.848 Wave length peak, mg 540 539 540 541 542 541 541 541 1.45 1.455 1.43 1.43 1.43 1.40 1.45 1.50 Value peak 14.46 14.33 14.91 14 45 14.35 14.31 Sum values 460 t o 600 14.43 14.03 ( A ) Chromotrope 10B. B) a-Naphthylamine-azo-H acid. )C) a-Naphthylamine-azo-l-naphthol-3,6,8-trisulfonic acid. Numbered samples measured in the concentration given and thickness 5 cm. The purified samples A, B,and C liter and thickness 1 or 2 cm. and the values multiplied by 2.5 or 1.25,respectively.
Keuffel & Esser Model B color analyzer, the results rtgrecing with those made on the Konig-Martens instrument. Solutions of the standard dyes.in 0.1 N hydrochloric acid and 0.1 N caustic soda solution in concentration 0.5 cg. per liter and thickness 5 cm. were measured on the Keuffel & Esser spectrophotometer. Solutions of the commercial samples were measured with the Keuffel & Esser spectrophotometer in concentration 0.5 cg. per liter of pure dye on the basis of the titanous chloride titrations and in thickness 5 em. It was found best to set the instrument for transmittancy and read the wave length for that transmittancy value. From these basic values curves were drawn. The data presented with this report were obtained from the curves. Titanous chloride titration of these dyes was carried out by the indirect method.I3 One-tenth normal titanous chloride solution was used and the excess determined by titration with 0.05 N ferric alum. The end point was determined electrometrically by the galvanometer swing method.I3 The average of duplicate titrations was used. Individual titrations agreed to within 0.4 per cent.
EXPERIMENTAL D.4T.4 I n Table I are given the data needed for estimating the strength of the commercial products. The values of the 18
(A)
C
...
535 1.125 11.22
measured in concentration: 1 cg. per
Note.-The transmittancy of a dye solution is the quantity obtained from actual measurements on a solution of given thickness and concentration a t any wave length-i. e., the ratio of the light transmitted by the solution to chat transmitted by the solvent. It is used in the form of its negative logarithm because this quantity is, on the basis of Beer's law, directly proportional to the product of concentration and thickness, computations being thus greatly simplified. Curves plotted with this quantity as ordinate also represent the absorption more nearly as it appeaps to the eye. See Gibson and others" for spectrophotometric nomenclature. See Troland'4 for standards and nomenclature of colorimetry.
Only the sum of the values for wave lengths 460 to 600 taken a t intervals of 10 mp and the values at the peak of the band are given in this table. Assuming that Beer's law holds over the range in concentration at which these measurements were made,15it is a simple matter to calculate the percentage of dye in the samples from the formula Percentage purity =
A W X B
where A is the value of -loglo transmittancy for the sample, W is the weight of the sample in centigrams per liter of the solution measured, and B is the value of -log10 transmittancy for the pure dye, 1 cg. per liter, calculated for the same thickness in which the sample was measured. These values are J . Obtical SOC.A m . , 6, 527 (1922). Beer's law often fails in that -logla transmittancy is not strictly proportional to concentration. See Holmes, THISJOURNAL, 16, 35 (1924). 14
LENGTH3
a-Naphthylamine-azo-chromotropic acid.
B 548 1.40 14.24
negative logarithm of the transmittancy of the dyes were obtained directly from the curves.
WAVE
FIG.1
a,2nd observer
...
538 1.457 14.70
16
Lee and Jones, THISJOURNAL, 14,46 (1922).
WAVE
A
178 1.786 543 1.54 15.28
LENGTH
FIG.2
0
1st
observer.
( B ) a-Naphthylamine-azo-H acid (C) a-Naphthylamine-azo-l-naphthol-3,6,8-trisulfonic acid Solvent: Phosphate solution, p H 6.75 Measured: Concentration, 1 cg. per liter; temp., 25' C.; thickness-(A) 1st observer, 1 cm.; 2nd observer, 2 cm ; ( B ) 1 cm ; (C)2 cm. Plotted: 3.3X values for unit concentration and thickness
(A)
or-Naphthylamine-azo-chromotropic acid
( B ) a-Naphthylamine-azo-H acid ( C ) a-Naphthylamine-azo-l-naphthol-3,6,8-trisulfonic acid Solvent: 0.1 N HCl Measured: Concentration, 0.5cg. per liter; thickness, 5 cm.; temp., 25O C. Plotted: 1.2X observed values = 3 X values for unit concentration and thickness A', B', C ' : Same as above but solvent 0.1N NaOH
INDUSTRIAL A N D ENGINEERING CHEMISTRY
August, 1924
799
compared with similar data from the titanous chloride titrations and practical dyeing tests in Table 11.
from them show. Sample 178 stands out as being somewhat different from the rest. The data indicate that it is contaminated with a-naphthylamine-azo-H acid and therefore T A B L E 11-ANALYTICAL RESULTS FOR COMMERCIAL S A M P L E S ------PERCENTAGE PURITY-that it should dye a bluer hue than the other samples. This Spectrophotometer Dyeing Test Average it does do. It may be said, then, that the measurements do Peak 460 t o 600 Sample “Shade” Dyeing TiCls not offer a criterion for predicting the variations in hue of 67.0 66,1 183 YY Bri 66 67.2 182 Y 50 50.3 51.8 51.0 dyeings of these dyes for a range of from YY to BB but that 69.8 59.0 181 Y 60 60.0 wider variations than this begin to be evident in the trans70.7 184 OK (std.) 72 71.9 71.8 176 B 57 54.2 67.2 53.2 gg:: mission of the solutions. There is a slight shift in the ab179 BD DD DD 60 68.4 177 BB 60 54.6 53.9 53.5 sorption peak from the yellower dyeing to the bluer dyeing 51.7 175 BBD 52 54.1 52.0 members of the series, but the shift cannot be directly trans178 BBB 66 56.0 59.2 58.2 Y = yellow, B = blue, Bri = bright, D = dull. lated into dyeing hue. The “shade” gradings are for unchromed dyeings. Piirified chromotrope I1 shows good agreement between measurements of 10B would be graded YYY Bri compared with 184. a-Naphthylamine-azo-H acid dyes much bluer red. a-Na~hthylamine-azo-l-na~hthol-3,6,8-tridye content by the spectrophotometric method and titanous sulfonic acid dyes very much yellower and brighter red. chloride titration method. With the yellower dyeing and preIn Table I11 are given the actual transmittancy values sumably purer samples, 181,182,183, and 184, both methods obtained from the curves multiplied by a factor for each dye agree quite wel.1 with the dyeing method of testing strength. which will convert the measurement at the peak of the ab- The measurements of the bluer and duller samples show sorption band to the value shown by the laboratory standard greater variations from the dyeing values, which for these chromotrope 10B. I n this table, then, the variations in the samples may themselves have a rather large factor of error. 7
TABLE 111-VALUES
FOR -LOG10
TRANSMITTANCY AT DIFFERENT WAVE LENGTHS FOR PHOSPHATE BUFFERSOLUTION
COMMERCIAL AND P U R I F I l D SAMPLES IN
A
Sample Wave length m p
183
182
181
184
176
460 470 480 490 500 510 520 530 540 550 560 570 580 590 600
0.87 0.49 0.65 0.56 1.09 1.33 1.52 1.68 1.75 1.70 1.62 1.48 1.29 0.98 0.60 540 1.75
0.38 0.49 0.65 0.86 1.08 1.31 1.52 1.66 1.75 1.69 1.60 1.48 1.28 0.99 0.64 539 1.75
0.37 0.51 0.68 0.87 1.08 1.32 1.51 1.69 1.75 1.71 1.62 1.48 1.28 0.97 0.60 540 1.75
0.31 0.47 0.66 0.87 1.10 1.32 1.52 1.66 1.75 1.71 1.61 1.48 1.29 1.01 0.64 541 1.75
0.38 0.39 0.41 0.38 0.38 0.35 0.55 0.49 0.54 0.54 0.53 0.54 0.71 0.70 0.71 0.64 0.71 0.70 0.89 0.89 0.90 0.83 0.90 0.88 1.10 1.10 1.11 1.05 1.09 1.12 1.31 1.26 1.32 1.32 1.32 1.32 1.51 1.53 1.45 1.52 1.52 1.54 1.68 1.66 1.66 1.63 1.70 1.68 1.75 1.74 1.75 1.75 1.75 1.75 1.69 1.69 1.72 1.69 1.70 1.69 1.59 1.59 1.57 1.63 1.58 1.60 1.44 1.51 1.46 1.46 1.48 1.47 1.27 1.26 1.34 1.29 1.26 1.28 1.00 1.00 1.06 1.01 0.99 0.99 0.64 0.66 0.63 0.65 0.66 0.64 542 541 541 541 543 539 1.70 1.78 1.75 1.75 1.75 1.75 (C)a-Naphthylamine-azo-l..naphthol-3,6,8-trisulFonic acid.
,
Wsve length peak Value peak ( A ) Chromotrope 10B.
( B ) a-Naphthylamine-azo-H acid.
179
177
175
178
B 0.38 0.46 0.55 0.71 0.91 1.16 1.39 1.59 1.73 1.75 1.72 1.62 1.49 1.27 1.03. 548 1.75
c 0.54 0.67 0.84 1.05 1.30 1.48 1.63 1.74 1.74 L65 1.50 1.28 1.00 0.66 0.35 535 1.75
A quantitative estimation of small to moderate amounts of a-naphthylamine-azo-H acid or a-naphthylamine-azo-lnaphthol-3,6,&trisulfonic acid in mixtures with chromotrope 10B does not appear to be practicable from spectrophotometric measurements of solutions of the mixtures in the solvents used. Of course, the use of other solvents or a preliminary separation of the components of the mixture by immiscible solvents’6 might be found efficacious. It should be distinctly understood that precision is claimed The dye content of the samples calculated frokn measureonly for measurements of the laboratory preparations in ments a t one wave length at the peak of the absorption band phosphate solution. Each point on these curves is the aver- is as satisfactory as that obtained by averaging measurements age of from six to ten settings of the spectrophotometer. at a series of wave lengths over the whole band. (Equally Even so, the absolute accuracy of the measurements is not satisfactory results are obtained by using measurements a t high, as can be seen from Fig. 1, Curve A , where careful wave length 538 m,u for all the samples.) measurements of solutions of the standard dye dissolved at With respect to the application of the spectrophotometric different times and measured by different observers are re- method to commercial work, the writers’ results lead to the corded. The error may be introduced by the effect of a general conclusion that the method is a satisfactory one for number of different factors on the color of the very dilute the routine testing of the strength of successive batches of solutions used. More particularly the time factor with re- dye by the manufacturer or of successive purchases by the spect to the solution reaching a state of chemical or physical consumer, and that large deviations in quality from the equilibrium may be mentioned as contributing to this error. chosen standard may be detected by the method. However, Considering the rather large error involved in practical it is not probable that the method will be extensively used for dyeing tests, it was not thought worth while to strive for either of ”these purposes, because, like the titanous chloride great precision in the spectrophotometric measurements of titration, it does not clearly indicate the small variations in the commercial samples. This must be borne in mind in quality which the manufacturer must know in mixing batches considering the results of the work. to give his standard product and which may be of great Although the commercial samples were-chosen to represent importance to the user of dyes. a rather wide range of variation in the hue of dyeings (Table ACRNOWLED GMENT 11, Column 2), the spectrophotometric data for transmission The authors wish to acknowledge the cooperation of the of solutions of the dyes do not show such variation (Table 111). This cannot be taken to mean that the spectrophoto- Colorimetry Section, Bureau of Standards, and their inmetric method is not sensitive, but simply that the solutions debtedness to K. s. Gibson of that section for valuable advice. of the dyes may not show the variation which dyeings made l6 Mathewson, THISJOURNAL, 5 , 26 (1913).
shape of the curves of the commercial dyes from the standard may be easily seen. Such variations might be expected to indicate the viriations in the quality of the dye. Fig. 1 shows the transmittancy curves for the standard samples in phosphate buffer solution, Fig. 2 in 0.1 N hydrochloric acid and in 0.1 N caustic soda. DISCUSSION OF RESULTS
