V O L U M E 25, NO. 6, J U N E 1 9 5 3
909
taining hydrochloric acid or acetic acid, but sulfuric acid, in the concentrations used, prevented complete precipitation. The iron in a solution containing as little as 5 p.p.m. can be ~uccessfullydetermined by means of the new reagent. While neocupferron has been employed in the analysis of iron in solutions of the same order of dilution ( 5 ) ,cupferron would not be useful a t such low iron concentrations. The presence of relatively large concentrations of calcium, manganese, nickel, cobalt, zinc, chromium, mercurous, aluminum, cadmium, or trivalent arsenic ions does not interfere with the quantitative iron determination as carried out in solutions containing 6 to 10% (by volume) of hydrochloric acid. The presence of copper in a concentration higher than that of the iron does ammonium interfere, even if the precipitate is washed q-ith 6 hydroxide ( 5 ) .
This new reagent exhibits many of the characteristics of cupferron, but is much more sensitive in the determination of iron
(6). LITERATURE CITED
Baudisch, O., Chem. Ztg., 33, 1298 (1909). Baudisch, O.,Ibid., 35,1141 (1911). Noyes, W.A., Jr., “Organic Syntheses,” Collective Vol. 11, 2n$ ed., p. 108, New York, John Wiley & Sons, 1944. (4) Schulman, S., O T ~Chem., . 14,385 (1949). (5) Smith, G.F., Cupferron and Xeocupferron,” pp. 17-20, Columbus, Ohio, G. Frederick Smith Chemical Co., 1938.
i.
RECEIVED for review October 7, 1952. Accepted March 20, 1953. A portion of a thesis submitted b y R. E. Fulmer in partial fulfillment of the requirements for the degree of doctor of philosophy, Department of Chernistry, University of Cincinnati, June 1952.
Quantitative Estimation of Amine-Cadmium Halide Complexes By Titration in Nonaqueous Solvents LEO LEV1 AM) CHARLES G. FARMILO Food and Drug Laboratories, Department of National Health and Welfare, Ottawa, Canada
No generally applicable titrimetric procedure for the quantitative estimation of amine-cadmium halide complexes has as yet been reported. It is the purpose of this paper to describe a method which permits such determinations. The complexes are dissolved or suspended in a small volume of glacial acetic acid, reacted with excess mercuric acetate and, after being diluted with p-dioxane, are titrated by means of perchloric acid. The experimental data indicate that the neutralization process takes place in accordance with the general scheme: [Organic . Excess CHsCOOH--t base-cadmium halide complex] HdCzHs0z)z -. acetate of organic base Cd(CHaC00)z [HgX1]
-
+ + HCldO -4cetate of organic base + Cd(CHBC00)z dioxane perchlorate of organic base + Cd(ClO4)z+ CH&OOH. +
The method is as accurate as conventional aqueous acid-base titrations and a precision of &O.Sl% is obtained when using crystal violet as the indicator. Complexes of the type studied are frequently prepared by the forensic chemist as microcrystalline amine derivatives and the method described should prove of particular value in the identification and characterization of medicinally important nitrogenous bases.
T
WENTY-FIVE years ago Conant, Hall, and Werner ( 4 , 5 ,I O ) showed that many organic compounds which exhibit little or no basic properties in water behave as relatively strong bases in glacial acetic acid and can be accurately determined in this solvent by titration with perchloric acid. The pioneer investigations of these workers were followed by intensive theoretical and applied studies of others and as a result nonaqueous titrimetry with perchloric acid has become a widely accepted method for assaying many classes of chemical substances. Strong and weak organic bases ( 1 , 3, 9, 1.4, 19, 21, S I ) , amino alcohols (19), alkylene oxides ( S ) , amino acids and
polypeptides ( I 11, 20, SO), oxazolines (19),tertiary aliphatic and aromatic amines in the presence of primary and secondary amines ( I , 9, 12, 3 2 ) , basic nitrogen compounds in refined aromatic and aliphatic hydrocarbons ( 3 3 ) and in hydrogenated coal oils (SJ), sulfonamides ( S I ), antihistamines (I@, vitamins and related compounds ( 17 , 22, 24), salts of aniinefi, basic heterocyclic nitrogen and quaternary ammonium compounds (1,8, dd), alkali metal salts (15, 16, 21, as), and salts of organic and inorganic acids (2, 3, 19, 21, 23, S I ) have all been determined by titration with perchloric acid in nonaqueous systems. It is the purpose of this paper to show that the method also permits the quantitative estimation of complexes of organic bases with metal halides. Such compounds are of particular interest to the forensic chemist concerned with the identification and characterization of drugs because, under suitable conditions, the complexes are obtained as microcrystalline precipitates whose characteristic habits may readily be recognized and studied under the microscope. REAGENTS AND SOLUTIONS
Perchloric acid 0.05 21‘ in dioxane, prepared by dissolving a p proximately 4.2 ml. of perchloric acid 70 to 72%- A.C.S. grade in 1 liter of dioxane. Standardization against N.B.S. potassium acid phthalate was performed in accordance with the procedure given by Seaman and Allen ( 2 7 ) . Dioxane, British Drug Houses, certified chemical grade. Glacial acetic acid, A.C.S. grade. Mercuric acetate solutions, made up by dissolving 3 and 6 grams, respectively, of mercuric acetate C.P. in 100 ml. of hot glacial acetic acid and allowing to come to room temperature. Crystal violet indicator solution, prepared by dissolving 0.1 gram of dye (Difco Biological Stain Commission approved sample) in 100 ml. of glacial acetic acid. ANALYTICAL PROCEDURES
Amines and Amine Salts. The organic bases were analyzed in accordance with the procedure given by Fritz (9) and the salts m-ere determined by the method of Pifer and Wollish ( 2 2 ) . Metal Halides. These compounds were analyzed following essentially the procedure given by Pifer and Wollish for the titration of inorganic salts ( 2 3 ) . The accurately weighed sample was dissolved in 0.1 ml. of water, 5 ml. of 3% solution of mercuric acetate in glacial acetic acid were added and, after being diluted
ANALYTICAL CHEMISTRY
910 Table I.
Determination of Amines and Salts by Titration with Perchloric dcid %
Gram Equivalent HCIOI Mole
HClOI Useda, MI.
E n d Point Color
Rpcovery
0.0988 0.1033 0.1002
9.04 9.34 9.10
Light green
99.94 98.78 99.23
Antipyrine
0.0777 0.0804 0.0694
8.61 8.98 7.73
Light green
98,5l 99.27 99.01
Brucine
0.1805 0.1762 0.1086
9.65 9,46 5.82
Blue-green
99 62 100.1 99.94
1
Choline chloride
0.0573 0.0481 0.0607
8.59 7.17 9.06
Green-blue
98.87 98.32 98.44
1
Blue-green
98.85 99.39 99.0;
Blue-green
98.53 99.02 98.86
1
Compound
Molecular Formula of Free Ba-e CH3-C
Aminopyrine
CH,
\J
Weight of Sample, Gram
f
-N
C-
1
0
/
Cinchonine
0.1305 0.1076 0.0896
8.01 6.64
Karcotine
0.1165 0.1039 0.0877
5.96 5.32 4.47
Blue-green
99.88 100.0 99.53
1
Nicotine
0.0338 0.0355 0.0397
8.65 9.05 10.19
Light green
98.00 97.65 98.30
2
Cocaine. " 2 1
5.52
Blue-green
Quinine. HC1
0,0990
Stovaine
a
Normality of HCiO, = 0.04726.
0.1050 0.0786
7.64 8.14 6.06
Blue-green
101.8 101.2 101.5
99. 04 99.48 98.94
1
V O L U M E 25, N O . 6, J U N E 1 9 5 3 with 60 ml. of dioxane, the mixture u-as titrated with perchloric acid to a blue-green end point using 3 drops of crystal violet as indicator. Amine-Metal Halide Complexes. A sample of the dry and finely powdered compound-prepared in accordance with the procedure referred t o in column 2 of Table 111-was weighed out accurately into a 250-ml. Erlenmeyer flask and shaken with 4 ml. of glacial acetic acid followed by 2 ml. of the 6% mercuric acetate solution. To the mixture 60 ml. of dioxane and 3 drops of crystal violet indicator were added, and titration was carried out with 0.05 N perchloric acid in dioxane, using a microburet calibrated to 0.01 ml. for measuring the volume of titrant consumed. EXPERIMENTAL RESULTS AND DISCUSSION
In Table I are reported the results obtained 011 nitrogenous bases and their salts which were used to prepare the amine-metal halide complexes. The position of the nitrogen atoms affected by the titration is indicated by means of an arrow in the structural formulas shown in column 2. A4minopyrineand antipyrine were found to use only one equivalent of perchloric acid per mole in spite of the difference in nitrogen content and fundamental structural resemblance of the ring system. Since amido nitrogen is not affected by perchloric acid one may assume that it is the adjacent weakly basic pyrazolone ring nitrogen in antipyrine which is titrated. Similarly only one of the nitrogen atoms in aminopyrine is dliciently basic to react n-ith perchloric acid. Brucine was found to consume only one equivalent of perchloric acid per mole which observation is in line with the classical researches of Perkin, Robinson, and \Tieland ( I S ) who showed that but one of the twn nitrogen atoms of this molecule is basic in character (see molecular formula shown in Table I). Cinchonine, nicotine, and quinine used two equivalents of perchloric acid per mole which finding is in accordance with the diacidic character of these bases. Observations of similar nature were made by Auerbach ( 1 ) who used titration with perchloric acid to advantage for differentiating the weakly basic quinoline ring nitrogen from a strongly basic tertiarj- amino nitrogen in a side chain of the same molecule. This author found the method a valuable means for assaying the A-P-nitrogen [from "acetous perchloric titration,'' a term originally proposed by Toennies and Callan (SO)] of a compound containing several nitrogens of different types of linkages. The results on the t,hree cadmium halides that w r e used for preparing the metallic amine conipleses are shown in Table 11. Cadmium acetate was found to be titrat'able by the same general procedure without mercuric acetate being present in the system. Two equivalents of perchloric acid per mole of salt were also used up in this titration and it appears that the halides are converted to cadmium acetate which is subsequently titrated. I t was not possible to determine the salts in pure glacial acetic acid because of unsatisfactory end points in this solvent ( 2 5 ) . *4lso,the compounds dissolved rather sluggishly in glacial acetic acid and the use of 0.1 ml. of water for effecting their solubilization prior to reaction with the mercuric acetate reagent shortened the time of analysis considerably. h volume of about 5 ml. of glacial acetic acid was found to be necessary to keep the syst'em homogeneous throughout the analysis. The results of application of the titrimetric method to the amine-metal halide complexes are presented in Table 111. Inspection of these data and comparison with those recorded in Table I shows that in each case the amount of perchloric acid consumed by the amine-metal halide complex equals the sum of the equivalents used up by the corresponding amine plus the metal halide. It is therefore reasonable to assume that the complex is split during the process of analysis, and that addition of t'he mercuric acetate solution-a reagent first advocated by Pifer and FVollish for the nonaqueous titration of halide acid salts of organic bases ( 2 8 ) and of inorganic salts containing acidic halide anions (2S)-to the glacial acetic acid solution of any of the amine-cadmium halide complexes investigated generates an equivalent amount of the acetate of the organic base plus the acetate of the metal, both of which are subsequently titrated
911
ith perchloric acid. The mercuric salt of the halide acid which is formed simultaneously as well as the excess mercuric acetate added to the system do not react with perchloric acid because of their low degree of ionization ( 6 2 ) . The titrations may therefore be visualized as proceeding in accordance with either of the following schemes:
TI
A
+ CHBCOOH + z Hg(CH3COO)t --++ CHSCOO- + Cd'+ + BCHaCOO- + n HgS? + Cd + 3CHzCOO- + 3HC104 --+ 3CHaCOOH + B S HCIO, + Cd(C104)Z
B K CdX, BSH+ B S H $-
(1)
++
(2)
B
+ + + + + + 2 B S H + + C d + + + 4CH3COO- + 4HCIO*+ 4CHdCOOH + 2BS.HCIO4 + Cd(CIO4)A ( B S ) ? . C d X , 2CHaCOOH Hg(CH,C00)2 + 2B?;H+ 2CHaCOOCd-+ 2CHaCOOHgX,
(1)
(2)
C
+ + 1' 2Hg(CH?C00)2+ + C d + + + 2CHaCOO- + 1'IZHyIJ ( 1 ) B S ? H ? + ++ Cd-+ + 4CHZCOO- + 4HC104 + 4CH3COOH + BS,.SHCIO, + Cd(CI0,)~ ( 2 )
BS2H.CdI3 CHiCOOH BSZH2+++ 2CHICOO-
D
+
(BNH)*.CdL 2Hg(CH,COO)? 2BPiH+ 2CH3COOCd++
+ + + PCH3COO- + BHgI? ( 1 ) + Cd + 4CHaCOO- + 4HCIO4 + 4CHaCOOH + 2BS.HCIOd + Cd(CIO4)g ( 2 )
2BNH
++
Table 11. Determination of C a d m i u m Halides hy T i t r a t i o n w i t h Perchloric .kcid Weight of Saniple, Gram
HC10, Useda,
0.0495 0 0423 0.0515
9.21 7.88 9 51
Cadmium bromide C d B n . 4H?O
0.0734 0.0688 0.0548
9 04 8 51 7 34
Cadmium Iodide CdIn
0.0787 0.0813 0. 075.5
9.04 9.31 8.69
Compound Cadmium chloride CdClz. 21/2 Hn0
a
1\11.
70 of
Theory 100.2 99.75 99.50
Found. Equiv./ZIole 2 . 005 1.995 1,990
99.70
2.002 2.010 1,994
94.80 98.95 99.45
1.996 1,979 1.989
100.1 100.5
Xormality of HClOd = 0.04719.
.\I1 complexes of the type B S . C d X , and (BS)2.CdX2, respectively. as well as those of the general formula (BNH)2.Cd14were obtained from bases having only one titratable nitrogen (see Table I ) whereas those of the general formula BS2H.CdIS\%ere prepared from bases containing tn o titratable nitrogens-e.g., cinchonine, nicotine, and quinine. If only one of these nitrogens reacts with the glacial acetic acid present t o form the amine acetate, further interaction with the titrant takes place during the neutralization until the fully protonated base has been generated. Thus titration of the quinine cadmium iodide complex may be represented as follows:
E
+
BK2H.CdI3 l1/*Hg(CH3COO)2+ BNzH' CH&OOC d + + 2CHaCOO-
+ + + + 1'/2HgI2 + 3CH&OO- + 4HC104 * BS2H2++ + 3CH3COOH + 4C104BSzHl+ + Cd + 4ClO4- + BS~.~HCIO +ICd(CIO4)z
BNzH
(1)
+
+
(2)
++
(3)
Neutralization of this complex involves therefore the simultaneous titration of both anions and cations and this phenomenon also occurs when the free base is treated similarly. 4 s far as the
912
ANALYTICAL CHEMISTRY
curic iodide was observed only after several hours. Addition of dioxane to the cholineWeight of HC106 G r a m Equiv. c a d in i u m chloride-mercuric Used" E n d Point $Z HClOd/Mole Predicted Sample, MI. ' Color Recovery of Compound Equivalence acetate system caused formaCompound Gram 2.972 3 0.0851 8.97 Light green 90.07 Arninopyrine.CdIi tion of a precipitate which re2.964 0.0797 98.80 8.38 dissolved during the titration. 2.950 98.33 10.41 0.0995 The corresponding systems of 3.005 3 0.0490 9.66 Green-blue 100.2 Choline.CdClr 2.979 0.0514 10.05 99.30 all other amine-metal halide 2.987 99.57 0.0422 8.27 complexes remained clear on 4 10.09 Light green 3.972 99,30 0.0993 (Aminopyrine)2.CdIi 4,003 100.1 0.1005 dilution with this solvent. 10.29 3.981 8.42 99.52 0.0827 The color changes occurring 4 7.81 Green-blue 98.75 3.950 (Antipyrine),.CdIr 0.0693 a t the end points were easily 99.05 3.962 0.0842 9.52 3.975 0.0730 99.38 8.28 recognized and good reproduci4 8.21 Green-blue 100.4 4.016 (Antipyrine),.CdCl, 0.0540 bility was obtained in all cases. 101.0 4.039 7.51 0.0491 100.0 4.002 8.91 0.0588 However, when a 0.01 N per4 7,55 Green-blue 99.78 3.991 0.0579 chloric acid solution was used (Antipyrine), .CdBrz 99.02 3.961 7.88 0.0609 for the titration, the end points 99.15 3.966 0.0494 6.40 could no longer be located with 3.970 4 8.41 Light blue 99.25 0.0788 Cinchonine.H.Cd1a 3.996 99.90 8.81 0.0820 sufficient precision and poten3.962 0.0691 99.05 7.36 tiometric titrations should be 4 7.83 Light green 98.90 3.956 0.0613 Nicotine.H.CdI8 3.924 98.10 carried out when using a titrant 0.0551 6.98 98.45 3.938 7.45 0.0586 of this concentration. Titra4 3.989 0.0799 8.25 Light blue 99.73 Quinine.H.CdIa tion of the cadmium iodides of 4.007 100.2 0.0855 8.87 99.28 3.971 0.0713 7.33 cinchonine, nicotine, and qui4 98.35 7.59 Light green 3.934 0.0988 (Aminopyrine.H),.CdId nine was a c c o m p a n i e d by 3.968 7.77 99.20 0.1003 3.925 98.13 0.1121 8.59 formation of a precipitate, and 4 7.29 Blue-green 100.3 4.011 0.1210 (Brucine.H),.CdIa this phenomenon was also ob3.982 0.1481 8.86 99.55 served during titration of the 3.996 7.85 99.90 0.1308 corresponding free bases. Ap 3.955 4 6.86 Blue-green 98.88 0.1006 (Cocaine.H)l.CdId 3.966 99.15 0.1231 8.42 parently these amines form 3.997 99.93 7.35 0.1066 perchlorates which are but 4 5,96 Blue-green 99.20 3.968 0.1027 (P';arcotine.H),,CdI~ 3.995 99.87 5.48 0.0938 slightly soluble in the solvent 3.975 99.38 0.1171 6.81 system used. I n the case of 4 9,36 Blue-green 99.90 3.996 0.1208 (Stovaine. H h C d I I cinchonine-cadmium iodide the 98.95 3.958 0.1018 7.81 99.35 3.974 8.87 0.1151 precipitate was p a r t i c u l a r I y a Xorniality of HCIO4 = 0.04719. voluminous and was found to vary with the amount of mercuric acetate present. Apparently the reagent reacts in this instance not only with the metal authors are aware this special feature accompanying the nonhalide but also with the amine and during titration with peraqueous titration of amines for which the number of titratable chloric acid a highly insoluble mercury-containing amine pernitrogens exceeds the number of acetate groups the molecule chlorate is formed. In accordance with this interpretation, can hold, has never been reported. If, on the other hand, the titration of the complex was accompanied by a haziness only number of moles of acetic acid with which the amine interacts exwhen the amount of mercuric acetate added to the system w a ~ ceeds the number of titratable nitrogens present-e.g., nicotine but slightly above the amount required to precipitate the iodine acetate-the excess acetic acid, behaving like a solvent, will not as mercuric iodide. affect the course of the titration. Kone of the complexes exhibited basic character when dissolved It was not necessary and in many cases was even impossible in water. Those of the type B.CdX2 and B2.CdX2were very to solubilize the complexes in the small amount of glacial acetic slightly, and those of the type BH.CdX3 and (BH),.CdX, quite acid used and its addition to the system could always be folstrongly, acidic. Duqu6nois (6) utilized this property by titratlowed by immediate addition of the mercuric acetate reagent. A ing the compounds he had prepared with a base (alcoholic potaE precipitate of red mercuric iodide formed when the amine-cadsium hydroxide) using ethyl alcohol as solvent and bromophenol mium iodides were treated in this manner but this precipitate blue or methyl red as indicator. Since the results he obtained redissolved readily on addition of the dioxane. X o distinct end were found to express the correct percentage of hydrogen iodide points could be detected when the titrations were carried out in present in the sample, it would appear that the general formulas glacial acetic acid alone and the use of dioxane as reaction medium B.HI.CdI2 and (B.HI)2.Cd12instead of B.H.CdIaand (B.H)%.Cd14 was found to reduce appreciably the range over which the various respectively would account more appropriately for the acid-base color changes of the indicator occurred (86). (Information relationships shown by these compounds. KO titrimetric proconcerning the use of organic solvents to increase the sensitivity cedure has as yet been reported for the cadmium halide complexes of a reaction was obtained from C. Pifer and E. Wollish when visitof aminopyrine, antipyrine, and choline chloride. With the ing their laboratories a t Hoffmann-LaRoche, Inc., Nutley, N. J.) exception of (aminopyrine .H)*.CdI,titration of these compounds It was imperative, hoffever, to add this solvent.only after Reacin both ethyl alcohol and acetone by means of alkali proved imtion 1 in A, B, C, D, and E had gone to completion. Irreversible practical and as far as we could determine the analyses here reprecipitate formation or permanent discoloration of the system ported constitute the only direct method presently known for occurred in some cases if this rule was not followed. Furthermore, their quantitative assay. all operations should be carried out a t room temperature since Experimental work is in progress to apply the method of analysome of the compounds were noted to decompose on heating. The sis to complexes of amines with other metals-e.g., mercury, cadmium iodides of cinchonine, nicotine, and quinine reacted very arsenic, zinc, lead, etc.-and promising results are being obtained. slowly with the mercuric acetate reagent and formation of red,merTable 111. Determination of Amindadmiurn Halide Complexes by Titration with Perchloric Acid
913
V O L U M E 25, NO. 6, J U N E 1 9 5 3 The method is rapid and simple and affords stoichiometric results without necessitating the use of elaborate and costly equipment. It should prove of particular value to the forensic chemist concerned with the microchemical identification of dangerous drugs because it enables him to titrate directly those complex compounds which he is so often called upon to prepare and characterize. ACKNOWLEDGMENT
The authors are indebted to L. I. Pugsley for many constructive criticisms and helpful suggestions. LITERATURE CITED
.luerbach, &I. E., Drug Standards, 19,127 (1951). Beckett, A. H., Camp, R. M., and Martin, H. W,, J . Pharm. and Pharmacol., 4, 399 (1952). Blumrich, K. G., and Bandel, G., Angew. Chem., 54,374 (1941). Conant, J. B., and Hall, N. F., J . Am. Chem. SOC.,49, 3047 (1927).
Conant, J. B., and Werner, T. H., Ibid., 52, 4436 (1930). Duquhois, P., Anal. Chim. Acta, 1, 50 (1947). Duquhois, P., J . pharm. chim., 26, 353 (1937). Ekeblad, P., J . Pharm. and Pharmaeol., 4 , 636 (1952). Frita, J. S., ANAL.CHEX,22, 578, 1028 (1950). Hall, N. F., and Werner, T. H., J . Am. Chem. Soc., 50, 2367 f 1928).
Harria, L. J., J . Bid. Chem., 84, 296 (1929); Biochem. J., 29, 2820 (1935).
Haslam, J., and Hearn, P. F., Analyst, 69, 141 (1944). Henry, Th. A,, “The Plant Alkaloids,” 3rd ed., pp. 511-23, London, J. & A. Churchill, Ltd., 1939.
(14) (15) (16) (17) (18)
Herd, R. L., J . Am. Pharm. Assoc., Sci. Ed., 31, 9 (1942). Higuchi, T., and Concha, J., Ibid., 40, 173 (1951). Higuchi, T., and Concha, J., Science, 113, 210 (1951). Kahane, E., Bull. SOC. chim. France, 18,92 (1951). Kleckner, L. J., and Osol, A., J . Am. Pharm. Assoc., Sci. Ed., 41,
573 (1952). (19) Markunas, P. C., and Riddick, J. A., AXAL. CHEX..23, 337 (1951); 24, 312 (1952). (20) Nadeau, G. F., and Branchen, L. E., J . Am. Chem. SOC.,57, 1383 (1935). (21) Palit, S.R., ANAL.CHEM.,18, 246 (1946). (22) Pifer, C. W., and Wollish, E. G., Ibid., 24, 300 (1952). (23) Pifer, C. W.,and Wollish, E. G., Ihid., p. 519. (24) Pifer, C. W., and Wollish, E. G., J . Am. Pharm. ASSGC., Sci. Ed., 40. 609 11952). (25) Pifer; C. W., Wollish, E. G., and Schmall, AI., A s ~ L .CHEM., 25, 310 (1953). (26) Schuyten, AI. C., Acad. roy Belg. classe sci., 32, 866 (1896) (27) Seaman, W., and Allen. E., ANAL.CREM.,23, 592 (1951). (28) Seaman, W., Hugonet, J. J., and Leibmann, W., Ibid., 21, 411 (1949). (29) Souchay, P., Bull. soc. chim. France, (5), 7,797,809,835 11940). (30) Toennies, G., and Callan, T. P., J . Bid. Chem., 125, 259 (1933). (31) Tomicek, O., Collection Czechoslov. Chem. Commzms., 13, 116 (1948). (32) Wagner, C. D., Brown, R. H., and Peters, E. D., J . Am. Chem. Soc., 69, 2609 (1947). (33) Wilson, H. K,,J . SOC.Chem. I n d . (London), 67, 237 (194% (34) Wittmann, G., Angew. Chem., A60, 330 (1948). RECEIVED for review October 30, 1962. Accepted March 13, 1963 Presented before the Division of Analytical Chemistry at the 122nd IIeeting of the AMERICANCEEMICAL SOCIETY, Atlantic City, K,J.
Refractometric Analysis of Flowing Solutions HARRY SVENSSON Laboratories of LKB-Produkter Fabrihaktiebolag; Stockholm, Sweden This work was initiated in the course of the design of two new types of recording refractometers in order to elucidate clearly the special problems inherent in the refractometry of flowing solutions. The conditions under which errors in the refractivity-volume curve are significant are given quantitatively where possible, and some information regarding the suitability of different cell constructions and different methods of recording is gained. Moreover, the refractive properties of two specific types of cells are analyzed and compared with each other. The analysis includes sensitivity, optical and volumetric resolving powers, light-transmitting capacity, and range of linear response. A cell described long ago by Hallwachs is found to have, under specified constructional and operational conditions, a linear range corresponding to the refractivity increment of 30% sucrose with an error less than 10-5. The results should interest not only chemists using refractometry as an analytical tool, but also instrument manufacturers and scientists who wish to build their own instruments.
for flowing solutions can serve as a means for keeping the concentration at a desired, constant value ( 1 1 ) . FACTORS AFFECTING USEFULNESS OF RECORDIhG REFRACTOMETERS
Optical Resolving Power. This concept may be defined a3 the reciprocal of the least difference in refractivity that can be detected v,-ith certainty by the instrument:
.
R, = l / A n
(1)
The requirements to be met by the optical resolving power can be found by considering the refractivities of the components (in distillation) or the specific refractive increments of the components (in chromatography and other cases where a solvent is transporting the components), and by deciding how small an admixture of one component in another or in the solvent is to be detected. If in a chromatographic fractionation the least specific refractive increment is 0.001 (for a 1% concentration increase) and if that component is to be detected down to a coilcentration of O.Ol%, then a resolving poiyer of lo5will be neceamry. If the optical reqolving power is written as follon.4: ds
R
ECORDING refractometers have recently found application in chromatographic analysis and a number of instruments for
that purpose h a r e been dexribed (3,4,7 , 9 , H , 14-16). T h a t is, however, not the only field where such instruments can be used. Fractional distillation is another example where a recording refractometer can serve as an aid in the subdivision of the effluent into fractions. Moreover, in the production of chemicals on a large firale by continuously operating methods, a refractometer
where X is the numerical value of the directly recorded qualitywhether this is an angular deflection, a linear di~plncement,an electric current, a number of interference fringei, etc.-then it appears as the ratio between the Tensitivity :
S = dX/dn
(3)
