Field Test for Microlevel Determination of Cationic Surfactants in Aqueous Solution Wolfgang Geyer Rohm and Haas Company, Research Division, 5000 Richmond Street, Phdadelphia, Pa. 19137
Numerous procedures for the measurement of cationic surfactants (quaternary ammonium compounds) in aqueous solution have been described (1-5). In general, a colored complex with an anionic dye is formed which is extracted into an organic solvent to separate it from excess dye. The color intensity of the organic phase is measured spectrophotometrically or, alternately, by changing the pH, the anion is extracted back into water (following the initial separation), and then the color intensity is' measured. The method described here was developed to simplify the apparatus and procedure and to eliminate the need for an organic solvent.
30 ml SYRINGE
INLET COVER
EXPERIMENTAL Reagents. All chemicals are reagent grade, used without further purification. Apparatus. A filtration apparatus (Figure 1) is assembled from a plastic 30-ml syringe, (Dolbey Medical Supply Co., Yeadon, P a . ) which is attached-without plunger-to the inlet of a Millipore 5-p Aerosol field monitor (Millipore Co., Bedford, Mass., Catalog No. MAWG 037A0, 5 - p ) . Procedure. Add two drops of 50% NaOH and 10 drops (-0.5 rnl) of 0.15% aqueous methyl orange solution to 25 ml of sample solution in a 2-02 plastic screw-capped bottle. Shake vigorously, then pour the mixture into the open syringe barrel. Allow the solution to pass through the filter by gravity flow. Switch the syringe from the inlet to the outlet opening of the monitor assembly. Suck the filter dry with the syringe. Carefully remove the top cover of the monitor assembly and wash the retained precipitate twice with 5-ml portions of t a p water to remove excess reagent, again using the syringe to pull the liquid through the filter. Finally, detach the spacer and transfer the filter, without the support, to a 1-02 screw-capped vial containing 5 ml 2N HC1 to dissolve the precipitate. Compare the red color of the aqueous solution with a series of standards. Reference standards for visual comparison are prepared by analyzing solutions containing 2, 4, 6, 8. and 10 ppm Hyarnine 3500, respectively, by the described procedure.
RESULTS AND DISCUSSION This procedure has served successfully as a field test with swimming pool and cooling tower water containing 0-10 ppm Hyamine 3500. Accuracy is fl ppm. Proteinaceous material, which ordinarily interferes with the determination of active bactericide in sanitizing solutions, can be removed by filtration of the sample through a 0.22-p ( 1 ) R . E. Keller, Anal. Chem.. 35, 1753-4 (1963) (2) A 0 Gettler and I Sunshine, Ana/. Chem.. 23, 779-81 (1951) (3) R Mitchell and E. 6. Clark, R o c . SOC.Exp. Bioi. Med.. 81 (105-9) 1952;abstracted in Fresenius' Z. Anal. Chem., 141, 313 (1954). 14) M E. Auerbach, ind. Eng. Chem.. Anal. Ed., 15, 492 (1943). ( 5 ) H . D. Held, "Kuhlwasser," Vulkan Verlag Essen (German ed.) 1970, p 400
SPACER
5p
FILTER
SUPPORT
MAT
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OUTLET COVER
Figure 1. Filtration assembly
Millipore filter in a Swinny syringe adapter (6). The procedure, as described, is based on Hyamine 3500. an alkyl (C12-C16) dimethylbenzylammonium chloride (Rohm and Haas Co., Independence Mall West, Philadelphia, Pa. 19105) added to swimming pool or cooling tower water a t 0-10 ppm. Higher concentrations were measured after appropriate dilution. Maximum quaternary compound content is 250 pg/25 ml of solution, as visual comparison of the developed color is difficult a t high absorbances. Linearity of response and possible interference with typical field samples was checked spectrophotometrically. Beer's law was closely followed for the 0-10 ppm range a t 510 nm . The procedure applies, with corresponding calibration, to similar compounds, such as Hvarnine 1622. Hyamine 2389, etc. The aqueous reference stnnda-rds appear to be stable indefinitely if the filter disk is removed from the vial after color development. Received for review October 23, 1973. Accepted March 14. 1974. (6) Unpublished communications
ANALYTICAL CHEMISTRY, VOL. 46, NO. 9. AUGUST 1974
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