Table II.
Temperature Coefficients Chemical Shifts
of
Compound c.p.s./"C.a Tetramethylsilane (by def.) 0 Cyclohexane f0.008 Acetone -0.046 1,1, I-Trichloroethane -0.020 p-Dioxane -0.026 Dichloromethane -0.038 Chloroform -0.052 a Positive sign indicates a downfield shift. I n this solution, the chloroform resonance is shifted from about 4 c.p.s. downfield from its normal position in exclusively highly chlorinated solvents because of hydrogen bonding to the acetone and the p-dioxane. For the same reason, the dichloromethane line is shifted about 1 c.p.s. downfield. The line positions vary somewhat with temperature. The temperature coefficients are shown in Table 11. Calibration cahecks based on these
line positions should be made nithin a few degrees of 37" C. DISCUSSION
K i t h the above measured positions of the various resonance lines, this solution can be used a t any time to check the scales of an KLCIR spectrometer. K i t h the A-60, the lines provide several check positions (to test for linearity) in the 1000-, 500-, 250-, and 100-c.p 5 . sneep nidths The 50-c.p.s. w e e p nidth scale can be calibrated by setting the CJ cloheaane reqonance line near 6 = 0 on the rhart and observing the po4tion of the acetone line. The observed separation should be 126.72 85.98 = 40.74 c.p.9. An alternative method nould be to set the acetone line near S = 0 and observe the position of the 1,1.l-trichloroethane line. This ceparation should h 163.84 - 126.72 = 37.12 c.p.s. As received, our -1-60 wai considerahh in error a t each weep width.
Adjustments are nom- made frequently to minimize the errors. The reference sample also provides a means for checking the accuracy of the sweep-offset potentiometer. By offsetting each of the resonance lines successively so that they appear near 0 c.p.s. on the chart, the sveep offset readings can be compared with the true off set's. ACKNOWLEDGMENT
The u.;e of a mixture of solutes for calibration v a s suggested by D. P. Stevenson of t'hese laborat'ories. LITERATURE CITED
(1) Arnold, J. T., Packard, 11. E., J . Chem. Phys. 19, 1608 11951). ( 2 ) Chamberlain, K.F.. Saunders, R. K.,
Humble Oil and Refining Co., private cmrnrnunication, *4ugust 1962. J. L. JUNGNICKEL
Shell Development Co. Emeryville, Calif.
Controlled-Potential Coulometric Determination of Hydrazine SIR: -4 precise and accurate determination of hydrazine in acidified solutions of ammonia was necesary to establish the conversion of ammonia to hydrazine by the fis-ion energy of uranium, a process under study by Aerojet-General Sucleonics ( 3 ) . The applicability of controlled-potential coulometric titrimetry to this type of sample seemed promising based on the data and interpretation presented by Karp and Meites (2) for the electrooxidation of hydrazine. The investigation resulted in a simple procedure in which hydrazine is determined directly in sulfuric acid solutions of ammonium sulfate. The fission gaqe.;. iodine and bromine, present a t concentrations niuch lower than the hydrazine, do not interfere with the procedure. The method is precise. accuratc and should he suitable for diver.-(, h\-tli,nzine-contaiiiing *ample>. EXPERIMENTAL
Apparatus. -4 controlled-potentia1 coulometer designed and constructed in this laboratory (1) vias used. cell n-a.4 constructed from a 50-ml. centrifuge tube flattened on the bottom and cut off a t a length of inches. -4 1-inch aide arm of 7-mm. diameter borosilicate glass tubing was placed on the side of the vessel 1/2 inch above the bottom and a t a n angle of 45' above horizontal. The stirrer is a Kel-F coated magnetic stirring bar 7/8 inch in length and inch in diameter rotated approximately 800 r.1i.m. The analytical electrode is a 0.056-inch diameter platinum wire spiralled about 6 times to a diameter of just under I inch. 1986
ANALYTICAL CHEMISTRY
The auxiliary electrode separator is a 9-nim. diameter borosilicate glass tube n i t h a fine-porosity frit end and a qel of submicron Sil, Cahot Corp ) in 0.5M sulfuric acid wed as a plug to decrease the flow rate of electrolyte out of the electrode. The electrolvte in the auxiliary electrode compartment is 0 5M wlfuric acid and the auxiliary electrode is a platinum wire heliu. The reference electrode is a Beckman reference electrode Model 39270 tip--ealed to the end of G-mm. diameter borosilicate glass tubing and connected nith a length of Tygon tubing to a mercury-mercuroua sulfate--0 5M bulfuric acid rfference cell. The analytical electrode i, po+itioned l 16 inch above the magnetic stirring bar and the auxiliaIy and reference electrode.: are po-itioned inch aboLe the analytical electrode n-ith the tip of the reference electrode a \ c h e as posiible to the gap between the auxiliary and analytical electrode.. -4 Teflon block is u,ed to hold the electrodes in position and to act as a stop for the cell so that the po4tioning is reproducible. Reagents. X hydrazine stock solution \vas prepared from reagent grade hydrazine sulfate (J. T. Baker Chemical Co., S o . 1-2177) t o contain 3.532 nig. per ml. of hydrazine in 0.05M sulfuric acid. T h e hydrazine sulfate was used as a primary standard. All h> drazine solutions used were dilutions of this stock solution. Other reagents were prepared from analytical grade materials. Procedure for Conditioning the Platinum Analytical Electrode. Pipet 5.0 nil. of 1 . O M sulfuric acid into the cell, po-ition the cell on the electrode astigated, The relative dant1:wl deviat,ion of the method is 0.09%, independent of concentration lei-el, bahed on 24 analyse; over the linear range of concentration and the method is not biased compared
to electrical calibration of the coulometer. Conditioning the platinum analytical electrode prior to analysis of each sample and adding the sample to the cell after the potentiostat was connected to form a n oxide coating on the anode were found to be very important factors governing the bias and precision. K i t h no surface renewal treatment, the oxide coating apparently changes from sample to sample, introducing an increasingly negative bias and imprecision. Changing the oxidation potential from +0.2 to 0.6 did not change the analysia value. Varying the sulfuric acid electrolyte concentration from 0.5 to 1.531 did not significantly change the results. .Immonium sulfate equal to 1.OX in the original sample solution (O.lJ1 ammonium sulfate in the cell) had no effect. I n testing for possible catalytic effects, the f i 4 o n gase., iodine and bromine, in trace quantities ( 5 X 1 O - * X in the cell) gave no detectable biah. Uranium dioxide, being filtered from the qample, was not considered to be a problem and was not inieitigated. If any carried through the filtration step, it would di+ solve as uranium(1V) which would coulometrically oxidize to gib e a quantitatire interference. S o other >ample component would b t e.rpected to interfere.
-1mercury pool analytical electrode with sodium hydroxide electrolyte was investigated. A negative bias of 2% with 1.8 mg. of hydrazine in the cell was observed. Because this negative bias increased with lesser amounts of hydrazine, it is believed due to the reaction of hydrazine with atmospheric oxygen in the baiic electrolyte. Because air-free sample5 are difficult to obtain. this approach was abandoned in favor of the platinum electrode procedure with the sulfuric acid electrolyte
+
LITERATURE CITED
(1) Booman, G. I,.> Holbrook, W. B., A 4 S CHEW ~ ~ ~ .35, 1793 (1963). ( 2 ) Karp, S., Meites, L., J . ;Ins. Chem. SOC.
84,906 (1962j. (3) Pearson. R. L.. Standerfer. F. R.. Snvder. 'H. J.. Watanabe. ' H. T.. Carpenter, L. G., Miller, R.' I., U. S; Air Force Rept. ASD-TR-7-840 A ( V I ) . 1962. Available from Defense, Document Center, Alexandria, Va. 1
,
GLEVYL ROOKAS WAYYEB. HOLBROOK Phillips Petroleum Co. -4tomic Energy Division Idaho Falls, Idaho Work done under Contract S T ( 10-1)-205 to Idaho Operations Office, U. 9. Atomic Energy Commission. Work sponsored by the Aeronautical Systems Division, Airforce Systems Command, U. S.-4ir Force.
Determination of Acetaldehyde by Colorimetry SIR: A spot te*t for qualitative determination of acetz ldehyde has been knonn for many years ( 2 , s ) . It is based upon the reaction of s cetaldehyde with sodium nitroprusside and a secondary aliphatic amine, yielding a blue. watersoluble product. The chemistry of the reaction is not known. This communication reports a q iantitative colorimetric method ba.etl 3n a modification of the reaction. Tlii., modification, in which acetic acid 1. added t o the system, give< a pink color insi ead of blue, n ith a maximum ab.orptiori at 575 mp. The method detects acetaldehyde in concentration> as lon as 1 p.p.m.
a Lumetron Photoelectric Colorimeter, Model 402E (Photovolt Corp.) n i t h a 5-em. cell and 550-mp g1n.s filter. Distilled water was used to set 100%
Table I.
Interfering aldehyde Formaldehyde
EXPERIMENTAL
Calibration. Standards n-ere prepared in 100-1111. volumetric flasks so t h a t on dilution to vclume they would contain from 0 to 40 p.p.m. of acetaldehyde. I n addition, each flask contained 3.0 nil. of 2OY0 (v./v.) morpholine solution, 2 5 ml. of 10% (v./v.) acetic acid sol Ition, and 1.5 ml. of freshly prepared 2'7, (w./v.) sodium nitroprusside solution. After dilution to volume, the standrtrds mere allowed to stand 3 hours for c d o r development. At the end of this period, per cent transmittance data were obtained using
Propionaldehyde
transmittance. K h e n the logarithm of the per cent transmittance mas plotted as a function of the acetaldehyde concentration. n qtraight line
Interference in Acetaldehyde Analysis
Reniarls Interferes by enhancing color formation, yielding high results when its concentration is above 10 p.p.m. Present in quantities over 500 p.p.m., color inhibition and low results occur. Interferes by enhancing color formation, giving high results. At 10-p.p.m. propionaldehyde, 30 p .p.m. acetaldehyde is analyzed as 33 p.p.m. while at 500 p.p.m. propionaldehyde, the analysis would be 40 p.p.m.
Interfering aldehyde Crotonaldehyde
Tiglaldehyde Acrolein
Glyoxal
Remarks enhancement and high results becomeserious between 100 and 500 p.p.m. crotonaldehyde. S o interference up to 500 p.p.m. Serious color enhancenient, leading to high results if present in greater than 500p.p.m. concentration. Color inhibition, giving low results, begins between 10 and 50 p.p.m. At 500 p.p.m., serious color enhancement is noted. Color
VOL. 35, NO. 12, NOVEMBER 1963
1987
