According to the results shown in Table I, any of the three types of cell could be used with equal reliability in electroanalytical experiments. There are, however, some practical advantages and disadvantages of each type. There are two methods by which the mercury level can be adjusted to give a planar configuration. One is simply a visual observation, from the side or from above. The other is to measure transition times a t a given current and to adjust the mercury level until a minimum transition time is obtained, which should correspond to the minimum, uncurved area. The first method is very easy to apply using the cell shown in Figure 2, where the )observation can be made from the side. With the other two cells, the observation must be made from above and can be complicated by refraction in the solu-
( 2 ) Delahay, P., LIattax, C. C., J . A m . Chem. SOC.7 6 , 874 (1954). (3) Lingane, J. J., J . Eleclroanal. Chem. 1, 379 (1960). (?) Lingane, J. J., Ibzd., 2, 46 (1961). ( a ) hleites, L., “Polarographic Tech-
tion. The second method can be applied in all three cells, but is more time consuming, more tedious, and less precise. From this standpoint, then, the cell shown in Figure 2 is the easiest to use. The cells shown in Figures 2 and 3 allow linear diffusion in the solution for cathodic processes and in the mercury for anodic processes. The cell in Figure 1 does not allow linear diffusion in the mercury for anodic processes. The cells in Figures 1 and 3 are relatively easy to fabricate while the fabrication of the cell shown in Figure 2 is more difficult because of the platinum-to-glass seal.
niques,” 1st ed., p. 270, Interscience, New York, 1955. (6) Nicholson, AI. M., Karchmer, J. H., ANAL.CHEM.27, 1095 (1955). (7) Ramaley, L., Brubaker, R. L., Enke, C. G., Ibzd., 35, 1068 (1963). (8) Reilley, C. N., Everett, G. W., Johns, R. H.. Ibid.. 27. 483 (1955). (9) Strehlt, C’. A:, Cooke, JIr. D., Ibid., 2 5 . 1691 (19j3). (10) ‘Yon Stackelberg, AI., Pilgram, M., Toome, T.’., Z. Electrochem. 57, 342 (1953).
Investigation supported in part by Public Health Service Predoctoral Fellonship (No. 1-F1-GLI-28, 705-01) from the National Institute of General RIedical Sciences and in part by the U. S. Atomic Energy Commission (A. E. C. document NO. COO-256-53).
LITERATURE CITED
(1) Bruckenstein, S., Rouse, T. O., ANAL. CHEM.36, 2039 (1964).
A KWIC Index to X-Ray Diffraction Powder Data F. W.
Matthews and L. Thomson, Canadian Industries Limited, Central Research Laboratory, McMasterville, Quebec, Canada
the use of a T permuted title program (KWIC), which is available in the standard “softHIS PAPER DESCRIBES
ware” package for most data processing computers. The work described made use of a KWIC program written for an 11311 1401, 8K, 4 tape machine. It is available from the authors. The ICKIC program is a development of Luhn ( 2 ) and has been widely used for information retrieval purposese.g., the *\merican Chemical Society publication, Chemical Titles. Through these programs orderly arranged lists of diffraction data for each of the five strongest lines of the X-ray diffraction patterns can be provided, as ne11 as lists by chemical name, empirical chemical formula, and structural fragment. These lists are generated from
I
two single line entries for each compound. A KWIC program usually provides a field of six or more characters (alphabetic or numeric) to be used for a serial number for identification of an item and a field of 60 t o 70 characters for the “title” entry to be permuted. See Figure 1. The program recognizes each entry between blank spaces in the title as a “word.” Words may contain any combination of letters, numbers or punctuation marks. A record is made for each word in the “title” and the resulting records are sorted bringing each “word” to the center column of the page. A list of words for which a record should not be made, whenever they appear in a title, may be appended to the program as a ‘ h o n significant word
6
Figure 1 .
666
e
ANALYTICAL CHEMISTRY
’\
list.” The computer will omit entries under these words. The sort sequence in the example shown is alphabetic followed by numeric characters. Punctuation marks precede both. “Words” longer than twenty characters are not indexed in the program used. As much of the title is included after the word as can be printed on the same line. The remainder is printed a t the beginning of the line. This is referred to as the “wrap-around” feature. An asterisk denotes the beginning of a title. In adapting the KWIC program for listing x-ray diffraction data, a number of conventions were adopted to improve the usefulness and completeness of the entries. The first line of the title consists of the chemical name and the five strongest “d” spacings of the diffraction
Sample input form for key punching
X - R A Y DATA INDEX HTI-PLIC PCIC 5.734 4.76E 4.78P ~ G A L L I L PC h L C A I C E G ? A P k l T t 4.80J A L L P I h A T E b E X 4 t-YCdPTE 8.6OA *Af‘IhC V d L t k I C AClU..15.4A 4.871 I h C h E CAHkCXYLIC v C I C 6.eCC C.27C 4.896 !4.92t +GALLIIIIJ C t - L C S I C E G R A P h l T t A h Y C d l P Y A I C I h E 8.2LJ 5.581 5.25Ji5.07J
3.980
3.2CC 4.360 4.211 4.630
3.93E 4.3jH
2 . ,LI4P 1.59E 1 . 2 3 G *CALL I 2.861 2 . 7 2 J 4.051 3.42J +CHLCHC ANTHdAClr 3.43A 3.284 2.14C 1.24C 4 0 1 t T H Y L G I CXC l t r K 3.29A 2.13G
13-823 12-0c1 12-008 13-876 13-818
12-004 13-82 1
CHEMICAL NAME INDEX
MOLECULAR FORMULA INDEX
CHEMICAL STRUCTURE INDEX
+Ih bA*3.2ZA~2.11G*l.f~lE *GA 3E*3.28Ae2.14C*l.L4C * C . 4 H . t ) hH2 211e4.051,3.42J ,4.89Fq4.63U*3.43A ~ C 1 4 H . 6 LIZ CL +C.Gh.4/ QMC,
[email protected] 4AG3 2.MOA12.75A*2.43A,2*35A Figure 2.
E
L3.18C L3.35C CCH /C..5HllN02 C C H /C.15H.7CLC4 CCH/2 /C..BH.604 I , 52
6.42Gv4.2 4.92693.9 15.4A 4 . 8 7 1 1 4 6.800vb.270 5.73&*4*7bt13. 4.32E9
Samples of sections from x-ray data index, printed
pattern along with their relative intensities. A second title entry gives the molecular formula, the structural formula for organic compounds and the “d” spacings. I n this second entry the “d” spacings are linked by commas creating a “word” of more than twenty spaces, which is not permuted. Xlternately the chemical name could be used in place of the five “d” spacings if this is considered to be more significant. If a “d” spacing greater than 9.99 occurs,
it is entered in the second line of the title as a “word.” This provides for correct numerical sequencing of the “d” spacings in the x-ray data index. I n the x-ray data index the compounds are listed under each of the five “d” spacings. Through the KWIC program these are arranged in numerical sequence with respect to the “d” spacings of the other compounds in the index. Within each entry the “d” spacings for the five strongest lines are
12-003 12-004 13-876
13-818 13-82 3 12-207
by computer
listed in descending numerical sequence. This ordering provides for a more efficient search than lists which do not retain this sequence of “d” values-e.g., the Fink Index ( 1 ) . The relative intensities of the five strongest lines of the diffraction pattern are indicated by letters of the alphabet (see Table I). A logarithmic table may be used for indicating the relative intensity in place of the linear one given on page 668. VOL. 38, NO. 4, APRIL 1966
667
Table 1.
A B C D E F G H
100 90 80
TO
60 50 40 30
I J L
20 5 0
The chemical name index provides an entry for each “word” used to name the compound. K h e n useful indexing entries will result, the usual chemical
name has been fragmented into chemically significant syllables. Control of the list is accomplished by use of blanks and punctuation symbols as well as the ‘[stop list.” The chemical formula index consists of a molecular formula index and an index by chemical fragment for organic compounds. These are stylized to provide for proper sequencing by the computer sort. The method described is illustrated Tvith the first twenty-five patterns of the twelfth set of the ASTM index, extracts from which are shown in Figure 2. Figure 1 shows the input form for three of the entries. This form is designed to
facilitate accurate punching by the key-punch operator. The method has been used for laboratory files of x-ray diffraction data and has proved to be both econoinical to prepare and efficient to use. LITERATURE CITED
(1) Fink Index, X-Ray Diffraction Data File, American Society for Testing and llaterials, 1916 Race St., Philadelphia,
Pa. (2964).
( 2 ) Luhn, H. P., “Keyword-in-context Index for Technical Literature (KR’IC Index),” IBM ildvanced System De-
velopment Division, Yorktown Heights, N. Y. (1959).
Heat Treatment of Molecular Sieves for Direct Separation of Argon and Oxygen at Room Temperature by Gas Chromatography Britt-Marie Karlsson, Chemical Laboratories, AGA Aktiebolag, Lidingo, Sweden RAPID
and simple method for the
A determination of oxygen and argon
mixtures a t room temperature on specially treated molecular sieves has been developed a t this laboratory. =it the 5th International Symposium on Gas Chromatography in Brighton it was indicated that we had succeeded in separating small quantities of argon and oxygen on a thermistor instrument using a %meter Xolecular Sieve 5.1 column a t room temperature. Since then we have given this subject closer study. .As the difference in retention time between argon and oxygen a t room temperature is negligible on niolecular sieves, experiments were made to diminish the influence of the sieves on argon, employing a method siniilar to that proposed by James and Martin for GLC (a), which consists of reducing the carrier’s influence on the sample by admixing a compound of the same nature as the sample in the stationary phase. EXPERIMENTAL
The molecular sieves were heated in air or helium purge with a humidity of 100 p.p.m. at 450’ C. for periods varying from 5 to 24 hours. This gave a poor separation, whereas treatment with argon under the same conditions gave good results after only 5 hours a t 450’ C. and slow cooling. These analyses were carried out on the helium ionization chromatograph described by Berry ( I ) , working with millimicroliter quantities ml.) (Figure 1). With our thermistor instrument (Fractometer 116 E, Perkin-Elmer), only small quantities could be separated, but after treatment over a period of 30 hours good separation was obtained even with the Fractoineter 116 E (Figures 2 and 3). The best results were obtained with Molecular Sieve 5A, but, surprisingly, the results with 13X were nearly as good (Figure 4).
668
ANALYTICAL CHEMISTRY
X special study on the effect of humidity in the air, helium, and argon used during the heat treatment of the sieves has been made a t humidity levels a t 100 p.p.m. and 10 p.p.m. At a humidity degree of 100 p.p.m., only argon gave good resolution. At 10 p.p.m. H20, however, even heliumtreated molecular sieves gave good separation of argon and oxygen, although after a few weeks a deterioration in the resolution occurred, whereas the argon-treated sieves still give the same
resolution after having been in use for 6 months. The gases employed were of high purity and with a carbon dioxide content below 0.5 p.p.m. The heat treatment discussed consists of heating the molecular sieves in argon to a temperature of 45@-500’ C., followed by slow cooling over a period of 8 hours. The results obtained a t temperatures below 400” C. have not been satisfactory, nor were any better results obtained at temperatures above 500’ C.
I
30-
20 -
I
.-E C
8
2
\ s
c
t
t
a
lo-
L!
v)
fi I
I
5
---
i s
i 2
I
I
0
I*c Figure 1.
Chromatogram of air
Tritium detektor at 650 volts; flow rate, 90 mi. He/minute; temperature, 23’ c.; column, 2.2m 5A, Analabs, Inc. (70- to 80-mesh); Sample volume, 21 6 X 1 0-6 ml. paper feed, 1 inch to */6 inch/minute Peak number
1 2 3
Compound Ar 0 2
Nz
Sensitivity
1/10 1 /30 1 /30
