Table I. Absorbance Data-0.05 to 1.00 ppm Chloride in Ethylene Glycol c1-, Abs Av Net abs (485 m d abs (abs-blank) ppm Blank 0.318 0.319 ... 0.05 0.10 0.20 0.30
0.50 0.70 1.00
0.320 0.361 0.364 0.416 0.415 0.513 0.501 0.590 0.594 0.771 0.774 0.946 0.951 1.22 1.22
0.363
0.044
0.416
0.097
0.507
0.188
0.592
0.273
0.773
0.454
0.949
0.636
1.22
0.901
Table 11. Absorbance Data-0.5 to 10.0 ppm Chloride in Ethylene Glycol Cl-, Abs Av Net abs ppm (485 m d abs (abs-blank) Blank 0.031 0.032 ... 0.5 1.0 2.0 3.0 5.0 7.0 10.0
0.033 0.071 0.072 0.118 0.122 0.211 0.210 0.290 0.290 0.460 0.462 0.656 0.656 0.966 0.968
ABSORBANCE DATA
Absorbance data for 0.05 to 1.00 ppm and for 0.5 to 10.0 ppm inorganic chloride in ethylene glycol are given in Table I and Table 11, respectively.
0.072
0.040
DISCUSSION
0.120
0.088
0.211
0.179
0.290
0.258
0.461
0.429
0.656
0.624
0.967
0.935
Utsumi (2) states that the analytical procedure is not specific for chloride. Bromide, iodide, cyanide, sulfide, thiosulfate, bromate, iodate, and nitrite react in the same way with mercuric thiocyanate as chloride and will interfere. Ferrocyanide and ferricyanide can interfere. The sensitivity and accuracy of the colorimetric method for chloride developed by Iwasaki, Utsumi, and Ozawa ( I ) has been greatly improved by the use of mercuric acetate and/or hydrochloric acid to regulate the amount of reagent blank in order to obtain maximum sensitivity for inorganic chloride. Furthermore, the sample of alcohol or glycol is used for the reference solution, thus balancing any variations in the absorbance at 485 mp that the sample may have. The principle here illustrated for determining inorganic chloride in water soluble alcohols and glycols should with modifications be applicable to other analytical problems concerning trace amounts of inorganic chloride. For chloride in aqueous solutions, sulfuric acid should not be used to prepare the ferric iron reagent as the development of the color is retarded by the presence of large amounts of sulfate ion.
of 0.30-0.32 absorbance unit by the dropwise addition of 0.1M mercuric acetate or 0.1N hydrochloric acid to the ferric iron reagent solution and then determine the value to the third decimal place. Preparation of Calibration Curves. Prepare a series of standard solutions of inorganic chloride in redistilled, chloride-free methanol (assumed to be in ethylene glycol with a density of 1.115) as follows: STOCKSOLUTION.Dissolve 1.838 grams of sodium chloride in 10 ml of water and dilute the solution to 1000 ml with redistilled methanol. This solution is equivalent to 1000 ppm chloride in ethylene glycol. STANDARD SOLUTION 1. Dilute 10.0 ml of the stock solution to 1000 ml with redistilled methanol. Concentration: Equivalent to 10 ppm chloride in ethylene glycol. STANDARD SOLUTION 2. Dilute 100.0 ml of standard solution 1 to 1000 ml with redistilled methanol. Concentration: Equivalent to 1.O ppm chloride in ethylene glycol. Properly dilute aliquots of standard solutions 1 and 2 with redistilled methanol to obtain other standard solutions of desired chloride concentrations. Obtain net absorbance data (absorbance minus reagent blank) in the desired ranges according to the procedures. Prepare calibration curves by plotting net absorbance us. ppm chloride in ethylene glycol. Procedure (0.05 to 1.0 ppm Inorganic Chloride). Place two 50-ml portions of a sample of ethylene glycol in respective 100-ml beakers. Add 10.0 ml of 0.1% mercuric acetate 278
solution to the portion to be used as a reference solution. Add 10.0 ml of mercuric thiocyanate solution to the other portion. Add 2.0 ml of ferric iron solution to the contents of each of the beakers. Stir each solution well and let the color develop for 15 minutes. Fill a IO-cm absorbance cell with the reference solution. Fill another 10-cm cell with the other solution and read the absorbance at 485 mp. Subtract the reagent blank from the absorbance to obtain the net absorbance and read the number of ppm inorganic chloride in the sample from the suitable calibration curve. Procedure (0.5-10.0 ppm Inorganic Chloride). Proceed as described in Procedure (0.05-1 .O ppm inorganic chloride) and let the color develop for 5 minutes. Fill a 1.0-cm absorbance cell with the reference solution. Fill another 1.0-cm cell with the other solution and read the absorbance at 485 mp. Subtract the reagent blank (one tenth of the figure used in the other procedure) from the absorbance to obtain the net absorbance and read the number of ppm inorganic chloride in the sample from the suitable calibration curve.
RECEIVED for review July 28, 1970. Accepted October 26, 1970. (2) S. Utsumi, Bull. Chem. Soc. Jap., Pure Chem. Sect., 73,835-8 (1952).
Correct ion Rapid Method of Determining First-Order Rate Constants from Experimental Data In this article by R. 0. Wale [ANAL.CHEM.,42, 1843 (1970)l there is an error in the caption for Figure 2. It should read as follows: The theoretical r f ( r ) function whenf(r) = 0.1 exp (-0.lt) exp ( - t ) demonstrating one maximum.. .
ANALYTICAL CHEMISTRY, VOL. 43, NO. 2, FEBRUARY 1971
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