for a sufficient lengt'h of time to give the required length of tape feed. In the I B I I coding system all digits must have an odd number of holes in the talle. An even number of holes cannot be handled by the computer. parity checking auxiliary attachment was added to the punrh to indicate when an even number of holes was punched due to some difficulty in the converter rnechankm so that repair could be accwmplished in a minimum of time. This is especially important when considerable time elapses bet'ween the t'ape punching and the actual computer comput at ion. Sample information, such as column niimher and sample number, is written on each end of the tape for identification purposes. The computer program requires the effluent volume of each peak and the identification of the amino acid responsible. This information is obtained from the analog record (chart) and is ent,ered in the appropriat'e place on a line of an 80-column work sheet along with such items as column num-
ber, run number, tape start time, tot'al solids, and size of sample. This information is punched from the work sheet into a punch card which is fed into the computer memory to be used when called upon by the comput'ation program. The elect,roniccomput,ations are made a t the U.S. Department of Agriculture Research Service, Biometrics Division, Beltsville, LId. Information about the machine language program can be obtained from that organization if required. Performance. T h e instrumentation described has been in use for about 2 years, operating from 5 to 7 days per week. T h e percentage of lost time due to breakdown of components has been less t h a n 1%. T h e calculated d a t a have been demonstrated to have a n accuracy equal to, or better t h a n , t h a t obtained by the manual calculation from t h e corresponding analog chart. The higher accuracy results can probably he accounted for through the fact that all data points are employed in the computer calculation of peak areas while only selected points are used in the manual system. Use of this procedure
has eliminated the need for one professional chemist per year on the project. ACKNOWLEDGMENT
The authors gratefully acknowledge the help of the Datex Corp., Ilonrovia, Calif., who manufactured the equipment used. I n addition, they acknowledge the help of several engineers from the Leeds and Korthrup Co., Philadelphia, Pa., and of engineers from the International Business Machine Co., Philadelphia, Pa., in instruction in the basic electronics necessary for the final dwigning of the equipment. In addition, it is known that several other electronic manufacturers can assemble suitable equipment for use in t'his application; the United States Government cannot recommend any one of these instruments over another. LITERATURE CITED
(1) Moore,
S., private communication (1962). ( 2 ) Spackman, D. H., Stein, R. H., hloore, S., ANAL.CHEM.30, 1190-1206
(1958).
Apparatus for Quantitative Determination of Fluorine in a Mixture of Oxygen and Fluorine Stanley W. Comer, Air Force Rocket Propulsion laborafory, Research & Technology Division, Air Force Systems Command, Edwards, Calif. ~ T N T H E S I Sof fluoroxi compounds involves the analysis of mixtures of oxygen and fluorine. The apparatus described in this article was designed and built to determine the amount of fluorine in a mixture of oxygen and fluorine. THE
R B
A
B
STIRRINC 0 & R
EXPERIMENTAL
The apparatus is shown in Figure 1. Pressure d h i n the apparatus does not differ greatly from at'mospheric pressure; therefore, vacuum stopcocks are not, used. The stopcocks are lubricated with Kel-F No. 90 grease (Minnesota Mining & Manufacturing Co., St. Paul 6, Ninn.). To perform an analysis. the apparatus is filled with gascous oxygen and fluorine. Mercury is added to react with the fluorine. As a result of the reaction, pressure in the apparatus is reduced. After completion of the reaction, Kel-F polymer oil is added to restore atmospheric pressure in t'he api)aratus. The volume of oil plus t'he voliime of mercury equals the volume of fluorine in the sample. Opcration of the apparatus is as follows. Part .4 is connected to part B , and the apparatus is put into a constant temllerature water bath which isq)laced over a magnetic stirring motor. Kel-F oil (or concentrated sulfuric acid) is carefully poured into the manometer. Tube B is connected to a vacuum manifold which has a pressure gauge
C
PART A
Figure 1 .
PART B
MANOMETER
Fluorine analyzer
calibrated in millimeters of Hg. The manometer is isolated from the manifold by t i m i n g the three-way stopcock S I to the position which connects the manifold to the reaction flask. K h e n a pressure of 1 mm. or less is reached, stopcock S3 is closed. .A mixture of gaseous O2 and F2 is allowed to enter through tube .-I until the pressure in the apparatus is approximately 20 mm. above atmospheric pressure. Stopcock SI is closed and the temperature is allowed to stabilize for ten minutes. After the temperature has stabilized, excess pressure is relieved through stopcock S2. An excess amount of reagent grade mercury is slowly added through tube R. If mercury is added t'oo rapidly, gas may escape as stopcock S2is opened. The reaction between fluorine and mercury is complete when fresh mercury exposed by the stirring bar does not become discolored. Atmospheric pressure is restored in
the alqxiratus by adding Kel-F oi through tube R. Tube R i h initially filled iyith oil to a mark near the t o p of the reservoir. The amount of oil delivered is obtained by refilling the reservoir to the mark with oil from a buret. I t may be necessary to refill the reservoir several times. After adding a volume of oil equal to the estimated volume of fluorine in the sample minus the volume of mercury, stopcock SBis slon-ly turned to connect the reaction flask to the manometer. The volume of oil to be added or subtracted (arithmetically) from the amount, already in the flask is determined by the relative position of the t,wo nienihci in thc manonwtel~.which is calibrated in millilitcrs of oil. If the initial and final trniperatures and the barometric pressiire have not changed, the vohime of Kel-F oil plus the volume of mercury is equal to the volume of fluorine in the sample. RESULTS A N D DISCUSSION
A mixture of fluorine and oxygen was made by adding. fluorine to a large volume of oxygen until the mixture contained approximately 30y0 (by volume) fluorine as determined by pressure gauge readings. Results of analysis of the mixture by the procedure described in this article are given in Table I , Tests 1, 2 , and 3. Temperature of the water bath is givrn in VOL. 3 6 , NO. 8, JULY 1964
1693
column 2. Atmospheric pressure a t the time of analysis is shown in column 3, and the volume of mercury, in column 4 . The volume of oil. column 5 . added to the volume of mercury gives the volume of fluorine, column 6, in the sample. Volume % Fz is given in column 7 . Results of analysis of a second mixture of 02 and F2 are given in Table I, Tests 4 and 5. A precision of *0.3% is indicated by data-in Table I.
Table I.
Temp., Test
O
c.
Volume
70FQin Mixture of Fz and 02
Atm. press., mm. Hg
1-01. Hg, ml
1
27.0
681
25
2 3
28 0 26 0
68 1
25 25 25 25
4 5
24.7 21 2
681 679 678
I-01.
Yol.
oil, nil
FP,ml
66 66 67
91 91 92
90
115
90
115
Fz, R 27 2 27 2 27 5 34 4 34 4
A Chromatographic Method for Determination of Trace Impurities in Grade-A Helium AI Purer and C. A. Seitz, Helium Research Center, Bureau of Mines, Amarillo, Texas
method is defor the determination of neon, hydrogen, oxygen, nitrogen, and met,hane in helium with a sensitivity of 1.2, 28.0, 1.2, 1.0, and 1.6, p.p.m. per division, respectively, using a 1-mv. recorder which has a 100-division full scale. This method is suited for the analysis of helium a t the point of use, giving one analysis every 5 minutes and using approximat,ely 200 cc. of sample. Two systems have been used previously for the analysis of Grade-l helium. The first method, involving concentration of trace impurities in G r a d e d helium by freezing them at liquid helium temperature ( 2 ) followed by mass spectrometer analysis, though good for analyzing standards, requires equipment not normally available. Thermal conductivity methods have also been used to analyze Grade-A helium, but the indicated impurity is CHROMATOGRAPHIC
A' scribed
V
expressed only in terms of total parts per million nitrogen equivalent. The two original 5-02. sample loops of the Beckman GC-2Ai chromatograph were changed to 8 and 16 cc. to give the needed range of sensitivity. Letting one sample have about twice the volume of the other permitted a high and low sensitivity. EXPERIMENTAL
h chromatographic column 13 feet long by 3/,6-1nch i d . , filled with 30- to 60-mesh 13X Linde Molecular Sieve maintained a t 40" C., was used. These conditions gave good resolution for neon, hydrogen, oxygen, nitrogen, and methane with retention times of 41, 46,
70, 97, and 130 seconds, respectively. A 22-foot column !\a> usrd for better reqolution of neon and hydrogen in ipecial case>. I t i+ deyirable to uqe a constant IToltage tianbformer to regulate the 110 volt, a c . to the chromatograph and recorder. Before purifying the helium carrier (already below 25 1i.p.m. total impurity) negative peaks were often obtained bec$se the-carrier gas contained approximately the same type and concentration of impurities as thP sample. The purifier used was a liquid nitrogen-cooled charcoal trap built by -1.D. Little, Inc., for purification of helium ahead of the -1. D. Little-Collins helium cryostat. Subsequrntly, a somewhat simpler but effective purification system
I
5. C.
Fltxibla tubb ' Contomr of W r t U 4
eorritr lnlaf
u7
T I M E , minutes
Figure 1. tograph
1694
Sample and carrier-gas flow to chroma-
ANALYTICAL CHEMISTRY
Figure helium
2.
Chromatographic
scans
of
Grade-A
