to nine a t 75", four a t 110", and three a t 150" C. At 150' C., however, a later and previously overlooked peak is detected. When very large samples were pyrolyzed, additional peaks of very small size were detected. These have been disregarded, however, in the preparation of the graphs, as being more likely to confuse than to elucidate the problem. The observation of Janak ( 3 ) that the critical factor in reproducibility is the linear velocity of the carrier gas along the pyrolysis unit is of interest here, but was not examined in this study. By plotting the retention times on a horizontal logarithmic scale, besides gaining compactness, one can establish a visual pattern for the pyrolyzates of each barbiturate which would be recognizable by another investigator using the same stationary phase under somewhat different chromatographic conditions. Obviously, it is essential for any one desiring to use this method for the identification of barbiturates t o
establish his own standards. The representation offered in the accompanying graphs may, however, serve tentatively t o identify a barbiturate and may aid in the selection of the appropriate standard barbiturate to be pyrolyzed to confirm the identification. The close correspondence between the pyrolysis chromatograms of secobarbital and thiamylal points up the fact that their structures differ only in that the latter has a sulfur atom substituted for the usual oxygen atom a t the 2 position. A similar relationship existing between pentobarbital and thiopental is reflected in the chromatograms also, though somewhat less markedly. These observations indicate the possible application of pyrolytic gas chromatography not only to identification but also to structure studies. Its value for quantitative determination should receive attention. The possible effects of metabolites and other physiological materials also remain to be studied.
ACKNOWLEDGMENT
The authors gratefully acknowledge the technical assistance of H. R. Harvey; and further, thank cooperating pharmaceutical supply houses for furnishing the pure compounds used in this study. LITERATURE CITED
(1j Davison, W. H. T., Slaney, S., Wragg, A. L., Chem. & Ind. (London) 1954,
1356.
(2) Janak, J., Natuie 185, 684 (1960). (3) Janak, J., Coll. Czechoslov. Chem. Commun. 2 5 , 1780 (1960). (4) Parker, K. U., Kirk, P. L., ANAL. CHEM.33, 1378 (1961). (5) Strassburger, J., Brauer, G. M., Tryon, M., Forziati, A. F., Ihid., 32, 454 (1960j. RECEIVED for review December 18, 1961. Accepted April 17, 1962. California h-
sociation of Criminalists, Fall Meeting 1960, Berkeley, Calif. Work supported by grants from the Sational Institutes of Health, U. S. Public Health Service (RG-4372 and RG-5802), and from the Research Committee, University of California.
Qua Iita tive Gas Chroma t o g ra phic A n a lysis by Means of Retention Volume Constants CHARLES MERRITT, Jr., and J. T. WALSH Pioneering Research Division, Quartermaster Research and Engineering Center,
,A method for the functional group classification and subsequent qualitative identification o f chromatographic peaks from retention volume data alone i s described. The method employs two columns having different liquid phases. When appropriate liquid phases are employed, the ratio o f isothermal retention volumes, or the difference between programmed temperature retention volumes, o f compounds within an homologous series is constant. Different constants are found for the various homologous series. From criteria established from this behavior, the functionality of a given compound can b e determined. The method can b e applied to chromatograms obtained either isothermally or with programmed temperature and with either packed or capillary columns. In this study, criteria are established for the identification of members of homologous series of normal alkanes, alkyl benzenes, alcohols, aldehydes, ketones, ethers, esters, thiaalkanes and thiols.
T
HE INABILITY of gas chromatography by itself t o provide adequate qualitative data has impaired its usefulness. -4uliiliary chemical (21) or in-
U. S. Army,
strumental (1, %, 6 , 7 , 9, 10, 16) methods have been required to identify peaks obtained from unknown mixtures particularly when such mixtures consist of several components having different functionality. This situation has been due largely to the fact that retention volume data on a single column lack sufficient specificity to permit unambiguous identification. The difficulty of collecting eluted chromatographic peaks, particularly from complex mixtures or of small amounts of a component, has limited the application of subsequent instrumental analysis. The determination of compound type by means of functional group analysis (21) is limited by sample size. Furthermore, functional group analysis cannot be readily adapted to the detection of inert types of compounds such as aliphatic hydrocarbons or ethers. It is highly desirable, therefore, to have available the means for characterization of functionality of eluted components from retention volume data alone. The possibility of using data from two or more columns having different liquid phases has been reported previously (3, 6, 11-15, 19, %3), but the use of such data has been generally neglected. The purpose of this investigation is to
Natick, Mass.
shorn that retention volume data from appropriately chosen columns can be used in a systematic way to provide a method for the functional group classification and subsequent qualitative identification of chromatographic peaks. I n this study criteria have been established for the identification of members of homologous series of normal alkanes, alkyl benzenes, alcohols, aldehydes, ketones, ethers, esters, thiaalkanes, and thiols. The establishment of criteria for isomeric compounds is currently being studied and nil1 be the subject of a subsequent paper. EXPERIMENTAL
Apparatus and Procedure. Conventional gas chromatography apparatus \vas used throughout this study. The packed columns were either the stainlws steel coil type or the glass U-type. Twenty per cent b y weight of the liquid phases used were coated on 60-80 mesh firebrick. T h e thermal conductivity detectors used were four-element bridges (tungsten filaments) operated a t 200 m a . from a 12-volt source. The ionization detectors used with packed columns employed either radium-226 or strontium-90 as the radioactive source. Capillary columns were 100-foot stainless steel capillaries coated from 5% VOL. 34, NO. 8, J U L Y 1962
903
I
olkoner
,
,'
,
I
W1
CW-4000
3
oidehvdes
2
6
8
IO
2 4 6 8 ' . " ' ' ' ' '
I O , /
CARBON
d
k'. 3
4
i
2 '
4
6 7 1 0
4
5 , a , IO
NUMBER
Figure 2. Isothermal ietention behavior of various homologous series of oxygen-containing compounds on different columns (arbitrary ordinate scales)
______
4
6
8
10
12
6
8
10
C A R B O N NUMBER
Figure 1 . Isothermal retention behavior of homologous series of hydrocarbons on different columns (temperature: 1 2 5 " C.)
by volume solutions of the liquid phase. (The authors have found that some commercially coated capillary columns do not give the desired behavior and consider that freshly coated columns prepared in the laboratory give best results.) The detector used with the capillary columns n-as a radiumtype argon detector. Most of the data reported here were obtained with a single, laboratory-built apparatus by replacing columns. A series of experiments performed on two different commercial gas chromatographs showed that variation of instrument design had no effect on the evaluation of the retention volume constants. I n particular, for example, the retention volunie ratios for alcohols, aldehydes, and ketones were the same within the established limits of precision when a Carbonau column R B P used in one instrument and a &@'oxydipropionitrile column was used in the other. I n later stages of the study, a dual column instrument was developed which made it possible to obtain t u o chromatograms from a single sample injection and to present each chromatogram on separate channels of Y dual channel recorder. The design anid construction of a dual column gas chromatograph employing packed columns and thermal conductivity detectors, together with the niodificatioiis of a commercial gas chromatographic instrument for dual column operation employing either packed or capillary columns with argon ionization detectors is described elsewhere ( I ? ) . Isothermal retention volume data were obtained for packed columns operated at 125" C. and with a flow rate of 75 ml. per minute. Retention volume data for prograninied tempernture operation of both packed and capillary columns were taken for columns programmed manually from 30 O to 150" C. a t a rate of 7" C. per minute. T o obtain reproducible retention volume data, i t is necessary, of course, to achieve reproducible temperature programs. A temperature variation of = k l . O o C. throughout the range of the 904
ANALYTICAL CHEMISTRY
program is adequate and can be obtained easily (20). Although all data presented in this study refer to the operating conditions stated above, i t should be noted that other values for the operating parameters, such as temperature, heating rate, flow rate, column loading, may be employed when convenient n ithout requiring extensive experimental work to obtain the necessary calibration data. Retention volume data from the literature may be used directly for establishing the experimental conditions for isothermal operation of columns. When it is desirable to employ a temperature program, the Habgood and Harris (8) method of data conversion may be used. Although the literature data will suffice generally to determine whether a given set of operating parameters Rill meet the necessary criteria for establishing a set of retention volume constants, the application of the method will probably require each operator to determine his own values for k' or A V R because of the difficulties associated with the techniques of preparing reproducible column packings. I n this ~ o r k for , simplicity of calculation, the retention volumes are expressed as the distance in centimeters of the center of the peak from the start of the chromatogram (air peak). The retention volumes used for evaluation of the retention volume constants described below were all determined experimentally in replicate for each compound. The average values of retention volunie constants were calculated from the average value of the retention volumes for a t least five members of each homologous series. The average deviation of the measurement of retention volumes was about 0.1 cm. This precision is about as good as one's ability to measure the distance on the chart paper-Le., to about 1 mm. Subsequently, the precision of the retention volume constants is of the same order, and it may be concluded that errors in retention volume constants are mainly the accidental errors of measurement of retention volume.
Carbowax 20-M Carbowax 4000 (Temperature: 125" C.)
-
RESULTS AND DISCUSSION
Isothermal Retention Volume Ratios. T h e fact t h a t the ratio of iqothermal retention volumes of compounds n ithin a given homologous series of t n o columns having different liquid phases is constant has been implied in previous reports. For euample, Desty and Whyman (6) have recommended that the data be treated by plotting the elution time of a component on one column against the elution time of a component on the other. The functionality is then determined from the slope of the line. Another method. suggested by Lewis, Patton, and Kaye ( I d ) , consists of plotting in a corresponding way the logarithms of the elution times, in which case the intercept characterizes the compound type. A detailed study in this laboratory of the isothermal retention volumes of the members of various homologous series on a variety of liquid phases has revealed that only certain combinations provide suitable graphs-e.g., see Table 11. Furthermore, many combinations of column pairs give slopes or intercepts that lie close together, making a definitive characterization difficult. I n any event, the preparation of graphs is unnecessary since the ratio of isothermal retention volumes n-ill be a constant vharacteristic of the functionality of the compound when suitable column pairs are used. Once the values of the constants are determined, identification of compounds as individuals can be made readily by interpolation on the usual log retention volume us. carbon number graphs (18). The criterion that the ratio of the isothermal retention volumes be conqtant is that the slopes of the log retention volume vs. carbon number plots for both columns be equal. Typical log retention volume us. carbon number plots for the homologous series of normal aliphatic hydrocarbons and alkyl benzenes on Carbowas 20-31 and Carbo\\-a\; 4000 columns are shown in Figure 1 .
JVlien the slopes are parallel, the difference in the logarithms of the retention volumes is constant, t h a t is A log
‘VR = k
(1)
l h i s leads t o the fact that the log of the ratio of the retention volumes anti, correspondingly, the ratio of the retention volumes will also be (nonitant. log ~ R ( c W - 2 o M ) / v R ( c w - 4 0 0 ~ ~k
(2) V X (CW-20M)/T7~(CW-4000) antilog tL
=
9’ ( 3 )
’Lhe isothermal retention volume ratio is designated as k’. \Vhen suitable liquid phases employed on the columns are chosen, the required parallel relationship of the slopes of the log retention volume us. carbon number plots may be found for nearly all functional group type compounds. The data for some homologous series of osygen-containing compounds on Carbonax 20-hI and Carboltau 4000 columns are plotted in Figure 2. The values of the retention volume ratios (k’) vary sufficiently to enable easy characterization of the compound type. Fur example, ketones may be distinguished readily from aldehydes by their respective retention volume ratios, 1.4 and 2.3. The isothermal retention volume ratios for a number of homologous series on Carboaax 20-31 and Carbowax 4000 columns are tabulated i n Table I. It may be noted here, also, that the functionality of inert type clompounds, such as hydrocarbons and ethers, may be easily determined. This cannot be done readily by means of functional group reagents or by most :iuuiliary physical methods. .4 number of combinations of column pails were evaluated to see if they would provide the expected behavior. Eight column substrates, all used in the same amount on firebrick and operated a t the same temperature and flocv rate for the same length of column, were compared in all possi tile combinations using the solutes of Table I. Two criteria were chosen for satisfactory performance. First, the values for the retention volume ratios for each homologous series of compounds should have a sufficiently wide separation to enablr easy characterization of the compound type. Secondly, the average deviation of the constants should be small. A column pair was considered to provide valid functionality constants cc hen the average deviation of the retention volume ratios calculated for several members of a n homologous series is no greater than the average deviation of the retention volumes from which they are calculated. On this basis, since the average deviation of retention volumes obtained was usually about 0.1 cm.. and never greater than 0.2 cm., a difference of 0.2 or more in the value of
the retention volume constants was considered sufficient to enable characterization. The results are summarized in Table 11. The two column pairs which proved most satisfactory were Carbowax 20-M and Carbowax 4000, and fl,fl’-oxydipropionitrile (OPN) and Carbowax 4000. Several of the other column pairs gave constant values of the retention volume ratio for the various homologous series of compounds, but the values obtained under conditions used in this study were too close to permit definitive characterization. The pairs, Carbowax 4000 and Silicone 703, and Carbowax 4000 and Silicone SF-96, deserve special consideration since the constants obtained, although close, had a very small deviation. These column pairs might prove particularly useful if different column lengths were employed. The combinations marked S G failed t o show a parallel relationship of the log retention volumecarbon number plots and thus failed to yield constant values of the retention volume ratios for the various homologous series. The column pair, Carbowax 20-31 and Pilicone SF-96, gave (17) good values of the constants under somewhat different operating conditions. I n addition to the column pairs evaluated in this study, the data of Desty and Whyman (6) and Lewis, Patton, and Kaye (14) show that tricresyl phosphate-Cenco Hyvac oil and n-hexatriacontane-benzyldiphenyl as column pairs also provide a constant A log VR. From the intercepts of their log V R us. log V Rgraphs, however, the corresponding values of the isothermal retention volume ratios for some of the homologous series on these column pairs would be too close for definitive functional group characterization. T h e values of the “retention index” increments described by Kovats and Wehrli (IS,62) and calculated from retention volume data on Apiezon L and Emulphor 0 (a polyethylene glycol) columns fail to provide either the required precision or the extent of numerical separation needed to distinguish important functional group types. Consideration of the various sub-
Table 1.
Isothermal Retention Volume Ratios CK-20M and CR-4000 columns at 125” C.
Compound Type Methyl ketones Acetates Aldehydes Alcohols Alkyl benzene8 Alkanes Dialkyl ethers Thiols
Compounds Used Average in k’ Devia- Evalua(;Iv. ) tion tion 1 . 4 0.1 c3-C~ 1.9 2.3
3.5 3.7
0.1 0.1 0.2 0.1
1.4 4.8
0.2 0.2
5.5
0.2
c3-c,
C*-C* C,-C, Ce-ClO CrC12
Cd-Clz Cs-Cg
strate combinations R hich have been investigated indicates that the desired behavior is obtained on polar columns of differing degree, but not on combinations of nonpolar or polar-nonpolar columns. Programmed Temperature Retention Volume Differences. T h e fact t h a t isothermal rhromatograms of homologous series of compounds give constant values of retention volume ratios suggested t h a t a similar relationship could be developed t o yield a similar type of functional group retention volume constant for programmed temperature chromatograms. Because it is the retention volume and not the log of the retention volume which is linear with carbon number for an homologous series for programmed temperature chromatograms, i t can be seen immediately that if a suitably chosen column pair provides parallel slopes, the difference in retention volume Kill be constant. The values for the retention volume difference, A V R , thus enable one to distinguish the functional group type of compounds eluted from a temperature programmed column. The retention volumecarbon number graphs of data for several oxygencontaining functional group types on P,P’-ouy~lipropionitrile and Carbowax 4000 columns are shown in Figure 3. 811 shon- the necessary parallel relationship. The values of the retention
Table II. Selection of Column Pairs for Isothermal ( 1 25” C.) Retention Volume Ratiov
cw-
CW-2OM Rp-400 Sq OPN Too close Too close K G CW-4000 X Very good Too close NG CWSOM X Too close NG Reoplex-400 X NG Squalane X Silicone-703 Silicone SF-96 Apiezon-M OPK = PIP’-oxydipropionitrile; CW = Carbowax; OPN 4000 X Good
5-703
SF-96 Too close Close Close Fair Too close Too close Fair Too close NG X Too close NG
X
Rp
=
Ap-M NG NG NG NG
Too close Too close Tooclose
Reoplex, etc.
VOL 34, NO. 8, JULY 1962
905
CARBON
NUMBER
Figure 3. Programmed temperature retention behavior of various homologous series on different columns
..--.-p,p'-oxydipropionitrile
-
Carbowax 4000 Temperature programmed from 150' C. at 7' C. per minute
30'
C. to
volume difference which enable their characterization are also indicated. The behavior of various combinations of column pairs (see Table 11) under programmed temperature conditions was also investigated. The combination of ovydipropionitrile and Carbowax 4000 showed the desired parallel relationship of the retention volume us. carbon number graphs for every homologous series studied. A number of other column pairs m-ere satisfactory for some of the homologous series, Table 111. I n addition, the data of Dal STogare and Langlois (4) indicate that the column pair, silicone rubber gum and Estynox acetylated butyl ricinoleate, mill provide a constant programmed temperature retention volume difference
Table 111.
RSH AV.:l
8
I , , ( , , 2
4
6
4
CARBON
Figure 4.
8
8
NUMBER
Graph showing distinction
of compounds having same retention volume constant
Compound Types Found to Give Constant Programmed Temperaturea Retention Volume Differences on Various Column Pairs
OPN and CW-4000 RP-400 and CW-4000 alkanes alkanes alkyl benzenes alkyl benzenes alcohols alcohols aldehydes aldehydes ketones ketones esters esters ethers thiols thiaalkanes 30" to 150" C. a t 7" C. per minute. Table IV.
RP-400 and OPX alkyl benzenes alcohols aldehydes ketones esters
RP-400 and C W-20 ?\I alcohol esters
Programmed Temperaturea Retention Volume Differences
OPN and CW-4000 Columns A~~~~~~ A V R(av.), deviation, cm. cm. -0.4 0.2 0.05 1.4 1.8 0.1 1.9 0.1
Compound Type Alkanes Dialkyl ethers Thiols Alcohols Thiaalkanes Alkyl benzenes Acetates Aldehydes Methyl ketones 30" C. to 150" C. a t
906
for certain homologous series, but data are given only for n-alcohols, methyl n-ketones and methyl n-esters. The programmed temperature retention volume differences for p$'oxydipropionitrile-Carbowax 4000 and Reoplex 40C-Carbowax 4000 column pairs are tabulated in Table IV. For some compound types the elution times on a particular column pair may be reversed when compared to other compound types. For example, normal alkanes are retained longer on Carbowax than on p,p'-oxydipropionitrile, rvhereas for most other functional group types the reverse is usually the case. I n calculating the retention volume difference, this behavior is indicated by assigning a negative value to the retention volume constant. As with isothermal retention volume ratios, the AVB values also differ enough to
2.1 2.2 2.8
0.1
0.1 0.1 0.1
3.5 4.3 0.3 7" C. per minute.
ANALYTICAL CHEMISTRY
RP-400 and CW-4000 Coiumns Average AVR(av.), deviation 1.4 0.3 ... ... ... ... 2.3 0.2 , . .
, . .
4.2 3.1
0.1 0.1
2.9
0.2
3.2
0.2
Compounds Evaluated CS-CI,
cB-c1* C4-Cs c1-c7 c2-cs C,C1, cs-c, G-Cs c3-c 9
permit characterization of the functional group type. The average deviation of the values is quite satisfactory, but in some cases the values of the constants for certain functional group types appear to be rather close. For example, the thiols and alcohols on OPS-Carbowax 4000 differ on the average only by 0.1 cm , and appear to fall within the same range. This difficulty can be readily resolved, however, from consideration of the individual retention volumecarbon number plots of the data as seen in Figure 4. Since the pair of retention volumes found on the tn o columns will intersect the retention volume-carbon number plot only at an integral carbon number for the appropriate compound, the compound can be identified as an individual. I n this case, for example, the retention volumes for n-butanol intersect the graphs for normal alcohols a t 4. The right-hand side of the figure shon s that the pair of retention volumes does not J ield an integral number on the plots for the thiol series. Although use of the retention volumecarbon number graph obviates the problem of close values of the retention volume constants without additional evperimental data, it is also possible to distinguish the functionality by using another column pair. For evample, acetates and ketones have the values 3.1 and 3.2, respectively on the Reoplex 400-Carbom ax 4000 column pair. 1 hey are readily distinguished on OPSCarbowax 4000, however, by the values 2.8 and 4.3. I n this case, data for only one additional column are needed. Effect of Column Length. Because the retention volume constants, either isothermal or programmed temperature, gave values in some cases t h a t i\ere rather close to one another, a study \vas made of the effect of column length on t h e value of t h e constants. Table V shoms the effect of lengthening one of the columns on the value of the isothermal retention volume ratio. I n this case, when a 12-foot ovydipropionitrile column is used I\ ith a 6-foot Carbowax 4000 column, a better spread of the values for the constants is obtained. Similar results were obtained for the programmed temperature-retention 1-olume constant when the column lengths m r e increased. Hidden Peaks. Another questioii 1%-hicharises is Ti-hether a compound eluted n i t h the same retention volume as another compound on one of the columns can be identified. Table VI gives a n evample of a bituntion for both isothermal and programnled temperature conditions. But! 1 benzene and heptenal are eluted n ~ t hthe same retention volume a t 125" C. from Carbowax 4000 but have different retention rolunies on Carbowax 20-11.
Capillary Column Programmed Temperature Retention Volume Differences. T h e most difficult problem
Table V. Change in Isothermal Retention Volume Constants with Column Length
6-Foot OPN/ 6-Foot
in qualitative analysis encountered b y t h e gas chromatographer is t h e identification of peaks eluted from capillary columns. Small sample size employed on capillary columns does not permit the use of chemical reagent to detect functionality nor ran enough material be collected upon elution to afford analysis by auxiliary physical methods. The extension of the concept of retention volume constants to capillary column ionization detection systems greatly enhances the usefulness of such systems. A study of the programmed temper-
12-Foot OPN/ 6-Foot
Compound Type CW-4000 CW-4000 Alkanes 0.8 1.7 Thiols 1.4 5.1 Alkyl benzenes 1.6 6.4 Thiaalkanes 1.7 6.0 Acetates 2.0 8.1 Alcohols 2.2 8.6 Aldehydes 2.8 11.7 hlethyl ketones 3.1 12.3 (Temperature: 125' C.)
Table VI.
Identification
of Hidden Components
ISOTHERMAL V R VR (CW-4000) (CW-2Olf) Iz' 2 1 cm. 7.8 3.7 2 1 4 5 2.3
Butylbenzene Heptanal
PROGRAVMED
Type Alkyl benzene Aldehyde
TEMPERATURE V R
VIR(OPN) (CW-4000) 9 8 8 3 7 7 8 3
Dimnylether Dodecane
Table VII. Programmed Temperature Retention Volume Differences
100-Foot stainless steel capillary columns coated irith OPN and CW-4000 (30" C t o 150" C. a t 7 " per minute)
Compound T) pc Alkane. Dialkyl ethers Aldehydes Alkyl acetates Ketones .41kyl henzenes Thiaallxtnes A41cohols
-1VR
(AT.).
Cm. -3 0 -0 0 1 2
6 i
4 1
2 2 2 4 -3 5
Compounds Evaluated C6FC12 c6-c12 C1-C3 CrCs C&*
cs-cio c3-ci c2-CG
The fwt that two components are eluted simultaneously on the Carbowax 4000 column is, of course, revealed b y the a p p e x m c e of an extra peak on the chromatogram from the Carbowax 20-11 column. Calculation of the rctention volunie ratio then identifies the compound types, and subsequent identification is made in the usual n a y from the log retrntion volume vs. carbon number plots. Similarly, for programmed temperature operation, diamy1 etlicr and dodecane elute from the Carbon ox 4000 column with the same retention x olume. Retention volumes are different, however, on OPK. I n this case, calculation of the retention volume difference identifies the functional grouli type of the compound.
AVR
1 5 -0 6
Type Ether Hydrocarbon
ature retention volume-carbon number plots on 100-foot stainless steel capillary columns coated m-ith Carbon ax 4000 and P,p'-oxydipropionitrile for a number of homologous series showed t h a t parallel slopes nere obtained (see Figure 5 ) . The programmed temperature retention rolunie differences are summarized in Table T'II. The retention volume differences are sufficiently well separated to permit characterization of the compound type. I n spite of the excellent separability and high sensitivity, capillary columnionization detector gas chromatographs have found only slight utility in the analysiq of multicomponent, heterofunctional mixtures because of the inXow, ability to identifj- peaks.
through the use of retention volume constants, qualitative data can be obtained conveniently. ACKNOWLEDGMENT
The authors are indebted to Robert SV. Slater for his contributions to the experimental work. LITERATURE CITED
(1) Anderson, D. M. W.,Duncan, J . L., Chem. & Ind. 1958, 1662. (2) Bellis, H. E., Slowinski, E. J., Jr., J. Chem. Phys. 25, 794 (1956). (3) Brown, I., iVature 188, 1021 (1960). (4) Dal Kogare, S., Langlois, W.E., ANAL. CHEM.32, 767 (1960). (5) Desty, D. H., Whyman, B. H. F., Zbzd., 29, 320 (1957). (6) Drew, C. M., RlcXesby, J. R., Smith, S. R., Gordon, -4.S., Zbid., 28, 979 (1956). ( 7 ) Gohlke, R. S., Ibzd., 31, 535, (1959). (8) Habgood, H. R., Harris, W.E., Ibid., 32, 450 (1960). (9) Heaton, IT. B., Kentmorth, J. T., Ibzd., 31, 349 (1959). (10) Holmes, J. C., Morrell, F. A , , A p p l . S p d r y . 1 1 , 86 (1957). (11) James, A . T., Research (London) 8 , 8 (1955). (12) James, A. T., Xartin, A. J. P., Brit. Med. Bull. 10, 170 (1954). (13) Kovats, E., Helv. Chzm. Acta 41, 1915 (1958). (14) Lewis, J. S., Patton, H. W., Kaye, \v. I., ANAL. CHEM. 28, 1372 (1956). (15) .Littlewood, A. B., Phillips, C. S. G., Price, D. T., J . Chem. SOC.1955, 1484. (16) McCreadie, S. IT. S.,Killiams, A. F., J . A p p l . Chem. (London) 7, 47 (1957). (17) Rlerritt, C., Jr., Kalsh, J. T., ANAL CHEJI.34, 908 (1962). (18) Pecsok, R. L., "Principles and Practice of Gas Chromatography," pp. 137-8, Wiley, Sew York, 1959. (19) Pierotti, G. J., Deal, C. H., Derr, E. L.. Porter. P. E..J . Am. Chem. SOC.78, 2989 (1956). (20) Sullivan, J. H., Kalsh, J. T., 'Llerritt, C., Jr., ANAL.CHEM.31, 1826 (1959). (21) K'alsh, J. T., RIerritt, C., Jr., Zbid., 32, 1378 (1960). (22) Wehrli, h.,Kovats, E., Heli,. Chim. Acta, 42, 2709 (1959). RECEIVEDfor reviex October 5, 1961. Accepted May 14, 19G2.
Correction Flame Photometry Using Oxycya nogen Flame I n this article by J. W. Robinson [ANAL,CHEM.33, 1226 (1961)j, some of the wavelengths quoted in Table I,
CASBOU
hLhrBEQ
Figure 5. Programmed temperature retention behavior of various homologous series on capillary columns
______
-
B,p '-oxydipropionitrile
Carbowax 4 0 0 0 Temperature programmed from 150' C. at 7 ' C. per minute
30'
C.
to
pages 1228-9, are incorrect. They are listed below : Wavelength Correct Element Quoted Wavelength Ba 4534 4934 Ga 4300 4033 Au 4837 5837 4994 Delete Mg 4536 4358 Hg 2922 2929 Pt 3282 3383 Ag 2183 2138 Zn VOL. 34, NO. 8, JULY 1962
907
