Photocolorimetric Method for Determination of Quaternary Ammonium Salts E. L. COLICHRIANl, Turco Products, Inc., Research Laboratories, Los .Ingeles, Calif, solution. above.
ETHODS for the estimation of high molecular weight quaternary ammonium compounds are reviewed by DuBois (3). Recently an argentometric method using eosin or dichlorofluorescein as an indicator has been proposed (4). Auerbach’s method for all quaternary ammonium salts offers great sensitivity and selectivity in the presence of common inorganic and organic impurities (1) a n d permits determination of very small concentrations of quaternary ammonium salts. Reported difficulties in clarifying the extracting solvent led -2uerbach t o substitute benzene for ethylene dichloride in a revised method (g), which is somewhat longer than the original procedure and cannot be so widely applied to all types of quaternary salts because of the loss in solvent power effected by the substitution. Either of the Auerbach methods will yield good results if extreme care and precision of method are followed. Unfortunately, the somelvhat tedious operations cannot always be controlled precisely-time and rapidity of shaking play too great a role in determining the extent to M hich the results can be reproduced. I n order to preserve the high inherent selectivity of Auerbach’s method and yet eliminate the uncertainties mentioned above, a modification is proposed. Sensitivity is lower, preventing quantitative evaluations of concentrations of the order of 0 to 20 p.p.m., but for the higher ranges is entirely adequate for routine commercial analyses. The method consists of forming the n-ell-known quatqnary ammonium-bromophenol blue salt (1) in carbonate solution in the presence of an excess but definite critical concentration of dye. The color intensity of the solution is measured directly without extracting the colored complex with an organic solvent (as is done in the Auerbaoh method). A photoelectric colorimeter with the proper filter is used to record the color density. Carried out in this manner, the difficulties associated with the use of organic solvents in extraction of color are avoided. Color intensity differences recorded by the instrument are sufficient for establishing satisfactory “photelometric” calibration curves.
Once calibration curves have been established for a given quaternary salt, the above procedure can be used to determine unknown concentrations. For quaternary solutions above 500 p.p.m., simple aliquot dilutions yield solutions that can be analyzed by this method. DISCUSSIOS AND RESULTS
I n Table I are s h o m the results of a determination of the concentrations of dilute solutions of octadecenyl dimethyl et,hyl ammonium bromide and octadecenyl dimethyl benzyl ammonium chloride by the method given here, compared w-ith values obt’ained by DuBois’ argehtometric method ( 4 ) . Actually, these dilute solutions were obtained by aliquot dilutions, once a l.OOno solution was accurately prepared and standardized by DuBois’ method. In calculating unknown concentrations of quaternaries in the range 100 to 500 p.p.m,, results were found to be reproducible t o about *2%. In the range 50 to 100 p.p.m., reproducibility of 5 to 7% \vas possible, and around 7 to 10% in the range 25 to 50 p.p.m. Concentrations below this amount should not be determined without first deriving a t,hird calibration curve in which only a very small excess of dye is employed. I n this way sensitivity of the method can be increased, so that concentrations of the order of 10, 20, and 25 p.p.m. can be determined with something more than semiquantitative accuracy. An excess of the dye is of necessity always present along with the dye-quaternary complex. This factor prevents the method from being as sensitive as Auerbach’s, because of the decrease in light transmission effected by this arrangement. Table I.
Determination of Dilute Concentrations of Quaternary .4mmonium Salts
Quaternary Salt
METHOD
Prepare a calibration curve for the quaternary salt in the range 0 to 500 p.p.m. by the following procedure: To 50.00 ml. of distilled water, 1.00 ml. of 10% sodium carbonate, and 1.00 ml. of standard quaternary salt solution (between 0 and 500 p.p.m.), add precisely 2.00 4..of 0.040% bromophenol blue solution. Record the color densities of the resulting quaternary-dye solutions after exactly 5 minutes with a photoelectric colorimeter employing a red filter-e.g., Central Scientific So. 87309D, wave length 645 millimicrons. -4 Cenco-Sheard-Sanford photelometer, Type B2, was employed in this investigation. The reference (or blank) solution, set a t 100% transmission, is the same as the above except that the 2.00 ml. of dye are replaced with distilled water, to compensate for any color+hat might be due to a highly colored quaternary salt. A plot of p.p.m. of quaternary salt added us. color densities, on a semilogarithmic scale, yields the desired calibration curve. In the range 0 to 100 p.p.m., the calibration curves prepared by the above method have excessively steep slopes, and thus will not yield as accurate results as in the range 100 to 500 p.p.m. To eliminate this difficulty, the following proportions of reactants should be used in the lower range of concentrations: T o 50.00 ml. of distilled water, 1.00 ml. of 10% sodium carbonate solution, and 4.00 ml. of standard quaternary salt solution (between 0 and 100 p.p.m.), add precisely 1.00 ml. of 0.04070 bromophenol blue
Otherwise, the procedure is the same as that employed
Octadecenyl dimethyl ethyl ammonium bromide ‘Octadecenyl dimethyl benzyl ammonium chloride
Concentration DuBois method Above method P.p.m. P.p.m. 394 400 255 250 122 125 400 410 250 257 125 121
Deviation
% -1.5 +2.0 -2.4 +2.5 +2.8 -3.2
The addl Lion of very small quantities of triethylamine, triet,hanolamine, ethylamine, phenylenediamine, diethanolamine, and oleyldimsthylamine had no effect on the light transmission or on the results of the quantitative determination of the twb salts cited above. - t seems probable that selectivity of the bromophenol blue reagent is analogous to that found in Auerbach’s method. Tinted concentrated quaternary antiseptic solutions (1 t o loyo)when diluted to the range 100 to 500 p.p.m. did not appreciably affect the results. The commercial product Cepacol (250 p.p.m. of cetylpyridinium chloride), colored a deep yellow, produced only a very slight deviation in the amount of light transmission. This deviation was u-ithin the limits of error of the method. This is to be expected, since the colorimet,ric blank employed tends to compensate for colored quaternary salts.
1 Present address, Department of Chemistry, University of Southern California, Los Angeles, Calif.
430
JUNE 1947
431
The procedure presented here oficrs grvater simplicity, rapidity, and reproduction than previous methods employing dyes such as bromophenol blue. dccuracy and sensitivity are satisfactory for routine control determinations of quaternarv ammonium compounds.
LITERATURE CITED
(1) (2) (3) (4)
-iuerba&, M . E., ISD. ESG. CHEII., SAL. ED.. 15, 492 (194.7). ~ t ~ i d16, . , 739 (1944). DuBois, A. S.,Am. Dyeslii,fl R c p t r . 34, '245 (1945). DuBois, A . S.,IXD.Esc;. CHEM.,- ~ s . \ L . ED.,17, 744 11945).
Nomograph for Flash Vaporization AIELVIK SORU', .Yord & Co., Znc.,Keyport, X. J . flash vaporizatiori problemr;, \y]iei,e multicomponent teriis involv,2c{,tedious trial-and-eryor solutionq irc,(l, If one desires t o evaluate the entire flash vaporization c u r ~ cof per cent distilled us. liquid temperature, the time required for thc' calculations is out of proportion to their value. Several attempt> have been made to reduce the burden of the calculations in these problems, notably b y Gilbert (a). This paper presents a nomographic method which further simplifies the calculations.
where Z F ~ xi, , and Y, represent the mole fractions of component i in the feed, h u i d , and rapor, respectively. If t'he equilibrium between liquid and vapor is represented as y, = Iiix; and the fraction vaporized as T' r = -F
FXFi = I
XF L
?Jt
LZt f T'yt
(2)
Present addresp, T a y n e 1-nirersity. Detroit, 3lich.
loo
LL
f
d 250'-
-
K a Q053, h 5
Figure 1. h-ornograph
0.0700
a
0.09,
y,'Ki = TZi
(5) 6,
(7)
Equation 7 states the fact that the mole fractions must always add up to 1. These cquntions arc essentially the same as those presented by Dodge ( 1 ) . The solution o € the flash vaporization equatiom rcquires trial and error. If the feed composition and the flash vaporization temperature and pressure are known (thus fixing the values of the equilibrium constants), it is necessary to assume a value for the frnction vaporized, T , in order t o detrrmine the vapor composition from Equation 5 . Thcn, the sum of nll the vapor mole fractions, Zy, must be compared with unity, in accordance with Equation 7'. If a check is not thus obtained, new values of r must be assumed and recalculations made until the required check is obtained. The tion may then be determined from
0%
XF
+ (1 - r) /Xt
xy, = 1
,080
EKhMPLE:
T
ZI =
(1)
and
(4)
the equations for a flash vaporization may be written as
Consider a multicomponent mixture which is to be flash-vaporized. Let the number of moles of feed be called F , and the number of moles of liquid residue and of vapor be called L and T', respectively. Then, by material balances, we have
F = L + T '
(3)
The nature of the flash vaporization equations makes the elimination of trial snd error impractical when there :ire many components. When the number of components is small, a nomographic solution without trial and error is feasible, but as the number of components increases, such a solution becomes too univieldly. However, it is poqsible, by means of a nomograph, to rably the numerical computations e trial-and-error process, and thereby he problem considerably. Such a represented by Figure 1, wGch is a plot of Equation 5 . Inorder to solve a flash vaporization problem with this chart, the following procedure is used: Assume a value of the fraction vaporized, r, and find the curve corresponding t o that value. At the appropriate value of K for a given component, follow a vertical line to this r curve, and then go horizontally over to the center pivot line. This locates a pivot roint, which when connected by means of a straightedge t o the value of the feed concentration, ZF, determines a line intersecting the vapor composition axis at the appropriate value of the vapor concentration. This procedure is indicated in the figure. Thus, a value of y for each component is obtained, and a check made t o determine whether they all add up to unity. The
