that recommended by the manufacturer with the following exception: The solvent used was a 60% (v/v) solution of 1,4-dioxane in demineralized, deionized (DMDI) water to form a solution containing 100 mg of Amadec-F per ml of solution. This corresponds to 1.0 mM each of total acetate and the lanthanum complexan chelate. This solvent gave considerably more sensitive results than the 60% (v/v) isopropanol, diethyl ether, methanol, ethanol, acetonitrile, or acetone solutions recommended by the manufacturer. The most sensitive and reproducible results were obtained when 1 ml of the Amadec-F concentrate was added t o 4 ml of the fluoride standard. The calibration was carried out using matched (*0.5% T) I-cm i.d. cuvettes and read a t 620 nm against an unexposed reagent as the 100% T reference. The preliminary experimental data showed that after a color development time of 30 min, the depth of color became stable and remained so for 16 hr, thus confirming the observations of Yamamura et al. (1962). Further experimental work showed that solutions higher in fluoride content stabilize in shorter times after exposure as originally noted by Belcher and West (1961a). As examples, the % T decreased hyperbolically from 84 to 65 over 28.5 min a t 10 ppm fluoride, from 57 to 26.4 over a 24.5-min period a t 30 ppm fluoride, and from 28 to 10 over a 21-min period a t 60 ppm fluoride. Thus, a minimum color development time of 30 min was selected for use. When equivalent pairs of exposed reagent were subjected to light stability tests, no difference was noted. The rate and degree of color change as measured by % T decrease were the same for light shielded samples as for those exposed to laboratory light levels. This indicated that diffuse light (indirect natural light or fluorescent) has no effect on the stability of the exposed fluoride reagent. In adapting this procedure to the analysis of airborne HF, 4 ml of DMDI water were drawn into properly preconditioned (about 150 ppm H F for 8 hr) 50-ml polypropylene syringes and used as the absorbing medium. Sample gas (46 ml prepared by the permeation tube technique to cover the range of 0.1-100 ppm HF) was drawn into vertically oriented syringes at the rate of 2 ml/sec. Following gentle hand shaking for 2 min, the resulting solutions were expelled into cuvettes and 1 ml of the AmadecF concentrate was added followed by thorough mixing. The fluoride concentration was plotted against the Yo T after the 30-min color development time had elapsed. The data so obtained show Beer’s law to be followed over the range of 1-35 ppm fluoride (corresponding to 97-20% T ) . The lower detection limit was 0.3 ppm fluoride. The upper reliable limit of calibration was 70 ppm fluoride. The relative analysis error for triplicate analysis of nine equally spaced points over this range was consistently below 1.52%. As an alternate t o the permeation tube technique, calibration with standard XaF solution may be used. To ten 25-1111 volumetric flasks, add graduated amounts (1 ml, 2 ml, 3 ml. , 10 ml) of 6.417 x lO-5M NaF solution. Dilute each flask to the mark with DMDI water. Add 1 ml of the Amadec-F test reagent to 4 ml of the calibration solution in a clean 1-cm cuvette and mix well by pouring back and forth into another clean cuvette. The first point is equivalent to 5 ppm H F in air as measured with a 46-ml syringe air sample. The last point is equivalent to 50 ppm. Calibration points should be determined in triplicate. The relative analysis error which may be expected over the 5-50 ppm range is between 1.4 and 2.06%. Any syringes not used for calibrations or ambient air sampling for a period of 8 hr should be reconditioned prior to use. 588
Environmental Science & Technology
This adaptation of the lanthanum-alizarin-complexan method to the syringe-sampling procedure for airborne fluoride provides a greatly extended useful range with a fivefold increase in sensitivity over the ferric sulfosalicylate fluoride bleaching method used by Meador and Bethea (1970).
Acknowledgment The assistance of R. M. Garvert in the preliminary fluoride experiments is appreciated. Literature Cited Belcher, R., West, T. S., Talanta 8,853 (1961a). Belcher, R., West, T. S., ibid., 8, 863 (1961b). Burdick and Jackson Laboratories, Inc., Reagent Sheet BJ-12F, Muskegon, Mich., 1966. Burdick and Jackson Laboratories. Inc.. “Quantitative Colorimetric Determination of Fluoride’ with ‘Amadec-F,” revision of 1-23-67, Muskegon, Mich., 1967. Gully, A. J., Bethea, R. M., Graham, R. R., Meador, M. C., Rept CR-1388, p p 37-9, 129-30, Nat. Aeronaut. Space Adminis., Washington, D.C., 1969. Meador. M . C., Bethea, R . M., Enuiron. Sci. Technol., 4, 853 (1970). C . S . Environmental Protection Agency, Fed. Regist., 36 (841, 8189 (1971). Yamamura, S. S., Wade. M . A., Sikes, J . H., A d . Chem.. 34, 1308 (1962).
Receiued for reuieu Decem her 26, 1973. Accepted March 8, 1974.
Further Development of a Generalized Kinetic Mechanism for Photochemical Smog- Addendum T. A. Hecht, J. H. Seinfeld, and M. C. Dodge
For those readers who might wish to reproduce the simulations reported in the article which appeared in Environmental Science a n d Technology, Vol. 8 , No. 4, pages 327-39, we present here some additional data. In carrying out chemical analyses of reactants and products, large volumes of gas were drawn from the chamber during an experiment. Removal of such large samples for analysis was necessary to obtain accurate determinations of contaminant concentrations. A volume of clean air, equal in volume to the amount of gas removed for sampling, was added to the chamber to maintain the total chamber pressure a t 1 atm. To determine the amount of dilution, ethane, a hydrocarbon which is virtually unreactive in photochemical smog. was added to the reactant mix as a tracer gas. If ethane is assumed to be chemically inert, its loss from the chamber can be attributed entirely to sampling and dilution, carried out a t an average rate given by - d c / d t = k c . The “rate constant” for the reaction is then k = [2.3 log(c,/cr)]/(tf - t o ) , where o and f denote the beginning and ending times of the irradiation. The average dilution rate constants for the experiments used for validation were: EPA r u n
306 314 345 318 325 329 459
/:
x 104 (min-1) 7.5 8.5 7.5 8.2 8.5 8.9 4.8
EPA run
307 333 348 349 352 457
i;
x 104 (min-1) 9.5 10.0 7.9 9.3 9.5 6.9
