subjected to repeated injections of massive amounts of deionized and natural waters, continues to be stable after six months. No changes have been observed during this period in the retention times, peak areas, and peak shapes of indole and o-phenylphenol for the same operating conditions. This fact indicates that any chemical interaction that exists between the column and water is weak and reversible. The constancy of the retention times also indicates that butanediol succinate has not been hydrolyzed from the column with water during this period. The temperature of the column was a critical, but easily adjusted, parameter in this study. We have observed that as the degree of separation of indole and o-phenylphenol from water increased, the symmetry of the peak improved, and the peak height gradually increased. This separation was governed only by the temperature of the column; the flow of nitrogen was maintained at a constant rate of 120 ml/min, and a 1-m column was employed throughout this study.
The ghosting phenomenon which has been mentioned by others (4) was never observed during this study. The previous study recommended in their procedure (4) to inject 1-pl samples of water between analyses to ensure cleanliness of column, syringe, and detector. We have found no need for these injections in our study. This method has been successfully employed for the quantitative determination of indole and o-phenylphenol in our relatively unpolluted water samples. If the degree of pollution becomes excessive, quite likely a new column and other operating conditions might be required. However, if indole and ophenylphenol are separated from other components and from water, no deleterious effects will be observed. The excellent precision and accuracy of this method have ensured the continued use of this technique in our laboratories.
RECEIVED for review March 29, 1968. Accepted May 21, 1968.
Gas Chromatographic Determination of Nitric Oxide on Treated Molecular Sieve Russell N. Dietz Brookhaven National Laboratory, Upton, N . Y. 11973
RECENT STUDIES required the determination of NO, NzO, NOZ, and air (02and N2) from one experimental flow system; CO, 02,and COzfrom another; and 02,O s ,CO, and COzfrom a third. A photometric analyzer was acquired to determine the O8 and NO2, for Os cannot be determined by gas chromatography and NOz only with subambient procedures ( I ) . Needed, then, was a column which could satisfactorily separate the other components in a single chromatogram. The column packing for the separation of inorganic gases has typically been molecular sieve, but the problem with NO determinations on this material has been extreme tailing of the peak making quantitative evaluation difficult. Trowel1 ( I ) eliminated the tailing on molecular sieve 13X by using only a very short activation period of 5 minutes at 250 "C; however, this gave a:very short column life-about 1 month. Subambient temperature techniques have been tried with moderate success, but tailing of the NO peak was not completely eliminated and warming to room temperature or above ( 2 ) or the use of a precut column (3) was necessary to analyze for NzO and COZ. Most recently, a new type of column packing-microporous polymer beads-has successfully been used to separate NO and NzO as well as C 0 2( 4 ) at room temperature. However, O2and Nz were represented as one peak on the chromatogram and the NO peak was not well resolved from that of air. Further investigation of these materials by Hollis and Hayes ( 5 ) showed that at - 78 "C,N2, 02, and argon are separated as (1) J. M. Trowell, ANAL.CHEM., 37, 1152-4 (1965). (2) D. H. Szulczewski and T. Higuchi, ibid., 29, 1541-3 (1957). (3) L. Maruillet and M. Trenchant, Methodes Phys. Anal. (Jan./ June), 37-9 (1956), Chem. Abstr., 18377~. (4) 0. L.Hollis, ANAL.CHEM., 38,309-16 (1966). (5) 0. L. Hollis and W. V. Hayes, "Gas Chromatography 1966," A. B. Littewood, ed., Elsevier Publishing Co., London, 1967, p 57.
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ANALYTICAL CHEMISTRY
well as CO and NO in that order. But at ambient temperature the separation of each of the above is poor. An extremely long (18-foot or more) and narrow (0.10-inch) column results in only slightly better separation with a sacrifice in the limit of detectability. To eliminate subambient temperatures and still analyze for all the aforementioned gases, one is forced to turn to a temperature-programmed, molecular sieve column. Preliminary investigation showed excellent results for each gas with the exception of tailing of the NO peak. EXPERIMENTAL
Apparatus. An F & M chromatograph, Model 810, (Hewlett-Packard) with a 6-foot by '/(-inch 0.d. stainless steel dual column containing molecular sieve SA (Linde) and a thermal conductivity detector, was used with ultrahigh purity helium (Matheson). The detector was operated at 100 "C and a bridge current of 230 ma. A 5-cc sample was injected at ambient conditions using a gas sampling valve. The initial column temperature of 60 "C was maintained for 4 minutes after which the temperature was increased to 250 "C at the constant rate of 30 "C per minute. The upper limit temperature was held for 8 minutes to ensure the elution of the last component, COZ, prior to automatic cooling to the initial column temperature. The helium flow rate was 25 cc per minute at a delivery pressure of 40 psig. Pretreatment. The sample column containing molecular sieve SA was placed in the chromatograph and heated to 300 "C under vacuum (1 p ) for 20 hours to remove H2O and fully activate the material. A positive pressure of helium was then introduced at 300 "C to minimize the possibility of 02-adsorption and the flow was switched to a low flow rate of NO taking care to exclude Oz. This exclusion of 0 2 was necessary to prevent the premature formation of NO2. After the column was sufficiently saturated with NO at 300 "C (about 1 hour), the temperature was lowered to 20 "C while
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Figure 2. Separation of inorganic gases and CH4
Figure 1. Separation of NO and N 2 0 Sample volume, 0.8 cc: 49.8 % NO, 49.8 % NzO, 0.4
Sample volume, 5 cc; approximately 1
of each component in C 0 2
N2
maintaining the NO flow rate. Following saturation of the sieve at 20 "C (about 0.5 hour), the column was flushed with He to remove excess NO, again taking care to exclude Oz to prevent the premature formation of NOZ. After flushing with He for about 0.5 hour, 0 2 was introduced to convert the remaining, more tightly held, NO into permanently bound NOs. The O2 flow was maintained for 0.5 hour at 25 "C and then raised to 100 "C for another 0.5 hour to ensure complete conversion to NO2. RESULTS AND DISCUSSION
A resulting chromatogram from this treated sieve for 0.4 cc each of NO and NzO shows absolutely no tailing of the NO peak (Figure 1) and no loss in resolution of the components of a sample containing 1% each of H2, 0 2 , Nz, CH4, and CO in C 0 2(Figure 2). A full chromatogram is obtained in slightly over 18 minutes. Several variations of the procedure for pretreatment indicated that without the initial evacuation-Le., activation by He only at 300 "C-the final column still produced some tailing of the NO peak. Furthermore, a positive pressure of He was introduced after evacuation to eliminate any possibility 'of localized heating from the rapid adsorption of NO. Other variations of pretreatment such as precooling the column to 20 "C before admission of the NO or maintaining the O2flow only
at 25 "C were not tried and may or may not improve the results. Tailing of the NO peak on untreated sieve probably occurs by a strong interaction of adsorbed NO with certain sites on the sieve. NO remains on these sites during the pretreatment flushing with He at 20 "C and is then converted to the permanently bound NO2 molecule when the column is flushed with 02.Thus, these strongly adsorbing NO sites are permanently eliminated without damaging the remaining structure of the sieve, and tailing of the NO peak no longer occurs. Calibration of the chromatograph was accomplished with the use of pure gases and known-concentration gas mixtures with sample loops of calibrated volumes ranging from 0.2 to 5 cc. Theoretically, the peak area should be directly proportional to the component volume in the sample; in practice, peak area divided by the component volume was not a constant number, F, but varied slightly in a linear manner with the logarithm of A . For esch component gas, peak areas were divided by the corresponding volume to obtain F, which was plotted us. the logarithm of A . The data were fitted by leastmean-square analysis to Equation 1 and the results
F = alog A
+b
(1)
appear in Table I. For an unknown sample, then, the volume of the component gas in cubic centimeters is obtained from
Table I. Calibration Constants and Precision F = a log A b Concentration, per cent = (100A)/V F a
+
Component a b
H 2
0 2
Nz
-8.30 158.4 1.8
26.7 5012 0.8 4 1.9
74.1 4900 0.7 8 3.6
Rel. std. dev. of F, Limit of detection, ppmb 100 Retention time, min. 1.1 A = peak area, cm* (height X half-height width) V = sampler volume, cc F = calibration factor defined by Equation 1 above When using a 5-cc sample loop.
NO 340.4 3975 1.5 12 5.1
CH4 0 4465 1.5 12 5.2
(1) (2)
co
NO
coz
169.9 4585 0.5 6 7.8
- 777.
- 1738.
7160 12.0 25 14.1
9510 0.5 4 15.6
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VOL. 40, NO. 10, AUGUST 1968
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AIF where F is defined by Equation 1. The concentration in per cent is then Concentration, per cent = (100 A)/VF
(2) where V is the volume of the sample loop in cubic centimeters. As shown in Table I, the relative standard deviation of F for each component is less than 2% except for NzO which was 1 2 x . The large error associated with NzO is related to the irreproducibility of the peak heights. Note that NO and CH4 cannot be independently determined because their retention times and peak widths are essentially identical. And as long as the component volumes of NzO and COzare no greater than about 0.5 cc each, quantitative separation is obtained. The gases which we have been analyzing in our experiments sometimes contain 1 to 150 ppm NO2 which is determined photometrically to within 1 ppm. The subambient method that Trowell developed for the determination of NO2 ( I ) was
shown to be successful in a flowing system but we soon found that many of our experimental conditions yielded NO2 concentrations in the range of 5 to 20 ppm which were difficult to determine with great accuracy by the subambient technique. Although the NOz does not elute as a peak on our chromatograph, because it is strongly and irreversibly adsorbed on the sieve, it has not interfered with chromatographic analysis of the other components. And after 12 months of use, the column still retains its original characteristics and calibration to within 2%. ACKNOWLEDGMENT
The author is grateful to T. P. Schreiner for assistance with the calibration. RECEIVED for review December 1, 1967. Accepted May 21, 1968. Work supported by the U. S. Atomic Energy Commission.
Pinacolyl Pyridinium Bromide as a New Color Reagent for Basic Amines Anthony Wu and Walter T. Smith, Jr. Department of Chemistry, University of Kentucky, Lexington, Ky. 40506
IN THE COURSE of studying the possible rearrangement of a-bromopitacolone in base, we were able to isolate a quaternary salt of a-bromopinacolone and pyridine which possesses a unique chemical feature in its reaction with basic amines. This crystalline salt, pinacolyl pyridinium bromide, is readily prepared by the reaction of a-bromopinacolone with pyridine in petroleum ether solvent. This material reacts with a variety of basic compounds, including amines, organometallic compounds, and inorganic bases to give a yellow color. Table I lists a number of amines which gave a positive test. A negative test is given by weak bases such as m-chloroaniline, o-chloroaniline, 2,4,6-collidine, N,N-dimethylaniline, 2,4lutidine, 2,6-lutidine, pyridine, and pyrrole. The pKb’s, ~~~
.20
~
Table 1. Comparison of Amine Basicity (pKb) and Absorbance of Colored Product Formed with Pinacolyl Pyridinium Bromide No. Amine PKb A 47.0 1. Allylamine 2. 2-Aminoethanol 4.56 45.5 3. Benzylamine 4.63 28.0 4. n-Butylamine 3.39 63.0 5. sec-Butylamine 3.44 62.4 6. t-Butylamine 3.55 66.0 7. Cyclohexylamine 3.36 60.6 8. Diethylamine 3.02 63.0 61.5 9. Dibutylamine 10. Morpholine 5.60 13.5 11. Phenethylamine 4.17 48.5 58.3 12. n-Hexylamine 13. n-Propylamine 3.41 64.2 14. Triethylamine 3.24 52.0 15.3 15. Tributylamine 16. Tri-n-propylamine 3.30 15.5 1578
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ANALYTICAL CHEMISTRY
01 2
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8
PK Figure 1. Plot of pKb of amines listed in Table I us. absorbance of color formed with pinacolyl pyridinium bromide. where available for these amines which gave a negative test, fall in the range 8.7-11.4. The amines which we have found to give a positive test all have pKb’s of 5.6 or lower. In fact, the intensity of the color appears to be directly related to the basicity of the amine. From a plot of absorbance us. pKb (Figure 1) it can be seen that absorbance is inversely proportional to the pKb of the amine. The major exception to this relationship is in the trialkyl amines and is probably caused by steric factors which come into play in this reaction but which would not be important in simple protonation of the amine. It should be noted that the pKb values used are for water and may not necessarily be linear in the 95% ethanol
