Colorimetric Method for Determining a Surface-Active Agent GUY R. WALLIN’, Cannon Mills,Kannapolis, N . C. NTIL Jones (3) developed his methylene blue method, there was no easy way to determine surface-active agents. Basic fuchsin is a better reagent, however, because its insolubility in chloroform simplifiesthe extraction and makes it possible to use plain chloroform as a blank, with a consequent saving in time. Basic fuchsin reacts with a variety of sulfated and sulfonated materials, such as alkyl aryl sulfonates, the dioctyl ester of sodium sulfosuccinic acid, and sulfonated petroleums, forming a chloroform-soluble, fluorescent, magenta-colored complex.
90
80
70
u60 V
Z
2 50 Z
2
5 40
5 cy n W
30
90
10
base. The acid groups of cotton are able to convert the base of the magenta-colored state. The nitrates of alkali metals react with basic fuchsin to produce a magenta-colored chloroform-soluble complex on the acid side, as do the surface-active agents. Potassium iodide, iodine, potassium bromide, and calcium chloride also form magenta-colored chloroform-soluble complexes with basic fuchsin. Basic fuchsin also reacts with sodium pentachlorophenate quantitatively to produce a rcd chloroform-soluble compound, preferably at an alkaline pH. All these reactions will occui 11 ith methylene blue; however, with methylene blue, alkalics produce a red chloroform-soluble complex which turns blue upon being filtered through cotton. It is generally believed that the addition of electrolytes to a cdloid electrolyte (basic fuchsin) causcs a salting out of the colloidal electrolyte. The fact that nitrates and calcium and sodium chloride form chloroform-soluble %omplexes” with basic fuchsin would seem to contradict the salting out mechanism. As basic fuchsin is insoluble in chloroform, the aggregated fuchsin should also be insoluble. S o information other than an abridged spectrophotometric curve has been obtained with regard to the chloroform-soluble complex formed by basic fuchsin with dodecylbenzene sodium wlfate. An abridged spectrophotomctric curve obtained with a LeitzRouy photometer is shown in Figure 1. This curve was prepared from the extract resulting from the reaction between dodecylbenzene sodium sulfate, manufactured by the Monsanto Chemical Company, which is approximately 40% active niaterial; the balance is sodium sulfate (4). This curve shows an absorption band from 480 to 535 nip which is the green region of the bpectrum; therefore, for colorimetric determinations a filter covering this region is necw3ary. Basic fuchsin has an absorption band at 520 to 550 nip. ,4 calibration curve was PI epared with a Klett-Summerson colorimeter, using a green filtei with a mean transmittance of 520 mp. A spectrophotometric curve was also prepared with the compound used above. In thi. instance Beer’s law holds good up to 1 mg. PROCEDURE
400
480 560 WAVE LENGTH, MILLIMICRONS
640
Figure 1. Absorption of Colored Extract
Basic fuchsin has been used as an analytical reagent by others, but not for surface-active groups. It has been used in Schiff’s reagent (6) and for determining bromine ( 2 ) . Other uses of basic fuchsin are described by Rlellan (4). EXPERIMENTAL
+
Reagents. Reagents used are 0.1% basic fuchsin, conccntrated hydrochloric acid, and chloroform, U.S.P. Analysis of Solutions. Place a sample containing approximately 0.5 mg. of active agent in a 125-m1. separatory funnel and dilute to 20 ml. with distilled water. Add sufficient concentrated hydrochloric acid to obtain a H of 1.2 as determined by a meter or other suitable means. Ad%2 ml. of 0.1% basic fuchsin, mix, extract with 20 ml. of chloroform, and allow to separate. Draw off the chloroform layer into a 100-ml. volumetric flask through a funnel nearly full of absorbent cotton. The cotton removes water-soluble dye. Repeat the extraction until clcar,
-
The reaction appears to be RSOB BF RS03BF, whew RSOI is the anion of a sulfonated compound and BF is the catioti of basic fuchsin. The RSOI group seems to react with a component of basic fuchsin, as a blue component is noted in the water layer if an excessive amount of m t t i n g agent is added. Basic fuchsin is composed of rosaniline and pararosaniline. It is not believed that both components take part in the reaction, but thib has not been definitely established. Basic fuchsin also reacts with alkalies, to form a brown fluorescent chloroform-soluble complex which turns red upon being filtered through cotton. The brown color is probably due to the formation of a pseudo-
* Present address, 604 Chandler St.,
Table I. Amount in Solution, Mg.
1.0
1.0 0.5 0.5
Recoveries
.4niount Recovered, hIg. 1,05 1 .05
0
.io
0 51
Recovery.
%
105 105 100 102
Amount on Material,
Ms. 1.0 1.0 0.5 0.5
High Point, N. C.
616
0.99 0.99
0.80 0 52
99 99 100 104
V O L U M E 2 2 , NO. 4, A P R I L 1 9 5 0 generally three times. Wash the cotton filter with chlorolorin, and make up to volume with chloroform. Transfer the solution to a photoelectric colorimeter and read, having previously sei the instrument to zero with chloroform. Analysis of Textile Material. Take a piece of material that i h expected to have no more than 0.5 mg. of surface-active material present and place in I) 125-ml. separatory funnel. Extract with 100 ml. of hot isopropyl alcohol which has been heated on a steam bath. Extract with 20 ml. of boiling water to free absorbed alcohol, and compress material with a stirring rod as much as possible. Place the extract in a dye beaker in a steam bath and drive off all alcohol, as determined by odor and cessation of bubbling, but do not allow the evtract to go to dryness. The residuc should be 20 ml. or less. Transfer to a separatory funnel and proceed ELS n-ith solutions. SUMRI 4RY
At an acid p1-I basic fuchsin nil1 react quantitatively with dodecylbenzene sodium sulfate, giving a chloroform-soluble magenta-colored extract which may be measured in a photoelectric colorimclter. The method is accurate and simple. The method is norispccific, as side reactions nith groups other than the sulfite group can occur; however, there is no interference from sodium sulfate, which does not precipitatc basic fuchsin or form a chloroform-soluble complev I\ ith ba5ic fuchsin. Sodium sulfate does not react with methylene blue. Thcx fact that b u i c fuchsin is not a specific reagent for suifacc-
617 :ic*tivt. :igcwt,s is not believed to hinder its use.
Although this nicthotl \vas actually calibrated for only one compound, the :ruthor has made numerous calibrations wit'h the methylene blur method, and found that side reactions did not interfere other than to produce a deviation from I3ecr's lam, making it necessary t o plot a curve. lIaximum accuracy cannot be achieved with readings that are caither very high or very low. With instruments giving a reading i n per cent transmittancy, the minimum error will occur at 36.8y0 transmittancy ( 6 ) . Ayres shows that greatest accuracy is obtainable over the transmittancy range of 20 t o 60% for photometric analysis (1). A small experimental error is magnified more on a percentage basis in the lower concentration rapgcs t,h:iri in the higher ones. LITERATURE CITED
( I ) Ayres, G. H., ANAL.CHEM.,21, 652-7 (1949). (2) Gutzeit, G., Hela. C h i m Acta, 12, 713 (1929). (3) Jones, J. H., J . Assoc. Ofic. &r. Chemists, 28, 399-409 (l!l45). ( 4 ) >fellan, Ibert, "Organic Reagents in Inorganic Analysis." Philadelphia, Blakiston Co., 1941. ( 5 ) Schiff, H., Ann., 140, 93 (1866). (6) Tmyman, F., and Lothian, G . I?., I'roc. P h y s . SOC.(Lomfori),45, 643 (1933). Its(.t~vr:uFebruary 24, 1949
Kelly Tube for Sedimentation Analysis S. C. SANE, 11. K. SHIRPURKIR, V. 1.. DESIEPANDE,
AND
hl. S. 'I'EL4NG
Laxntinurayan Institute of Technology, "Vagpur University, .Vagp[ir, Indin
AY'EKS (1-3, j,6,9,10) dealingwith improvements in thetechIr)nique of sedimentation analysis with the Kelly tube include elaborate calculations of the correction factor to be included i i i the original Kelly equation ( 4 ) to account for the progressive increase in the liquid level in the settling tube due to the recession of the liquid from the capillary side arm. The present paper describes a. practical device for maintaining the liquid level in the settling tube constant so as to retain the validity of the original equation. The uncertain errors caused by ordinary methods of measuring the angle of inclination of the capillary side arm of the Kelly tube in the working position of the apparatus
W Figure 1.
Constant-Level Device
after it is placed in a theinlosttitic bath have been one of the niiijor drawbacks of Kelly's apparatus ( 7 , 8 ) . Because the sign of tlic angle of inclination is directly utilized in calculating the distribution of the particle size, the need for a precision determination of the angle cannot be overemphasized. The constant-level device is further useful in the precision determination of the angle of inclination of the capil1ar.v side arm. CONSTANT-LEVEL DEVICE
In Figure 1, test tube B with a side hole, H , a t M is firmly clamped a t a predetermined height to receive the overflow and hence to function as a self-operating constant-level arrangement. The amount of overflow and the consequent loss of solid particles from the suspension (which is usually dilute) are very insignificant; a recession of 10 cm. in the capillary (usin Kelly's dimensions for the apparatus) is equivalent to 0.3 ml., wkich may correspond to the total recession a t the end of an experiment. A t the commencement of the experiment, a little excess of the suspension is poured into the settling tube, t o ensure that AI has been reached. Because the suspension is turbid, it is not possible to observe whether or not the excess has entered B , but this can be ascertained by inserting a narrow glass tube and emptying B by applying suction. The volume displaced by the immersed portion of B must be taken into consideration, while calculating the volume of the suspension under investigation. The self-adjusting constant-level device eliminates the pcrsonal error of the observer in noting the initial level, particularly with turbid suspensions, The extreme importance of niaintaining the level constant is appreciated if it is realized that a difference of 0.1 mm. in the level at M will cause a difference of O.l/sin b = 3.82 mm. in the horizontal portion of the capillary, i f Lb is 1.5". Alternative arrangement can bc made to maintain the liquid level constant-e.g., a side tube, C (shown in Figure l), may be joined a t M to permit the overflow. Such devices demand very accurate glass blowing for joining the tube in a required position The device suggested in Figure 1 using test tube R can be easily constructed and readily assemhletl.
