600 Analyst, Jzcne, 1982, Vol. 107, PP. 600-605

Gas - Liquid Chromatographic Separation of Toluidine, Chloroaniline and Dichloroaniline Isomers on Various Stationary Phases Including Heteroaromatic Corn pounds

Aoi Ono Defiartment of Chemistry, Faculty of Education, Niigata University, Niigata, 960-21, Japan

It is difficult to separate toluidine, chloroaniline and dichloroaniline isomers using the normal liquid stationary phases an a non-alkali-treated support. However, toluidine isomers were completely resolved on caffeine, theo- bromine, theophylline, xanthine and hypoxanthine, and chloroaniline isomers were effectively separated on picolinic acid, quinolinic acid, isonicotinic acid, orotic acid, 3,5-diaminobenzoic acid, theobromine, xanthine, uracil and a mixed stationary phase of melamine and barbituric acid. Further, six dichloroaniline isomers were also effectively resolved on nicotinic acid, iso- nicotinic acid, picolinic acid, creatine, hydroxy-L-proline, caffeine, hydantoin and mixed stationary phases consisting of nicotinamide and p-aminobenzoic acid and of silicone KF-54 and sodium hydroxide. These effective separations were obtained on non-alkali-treated supports.

Keywords : Gas - liquid chromatogyafihic separation ; toluidine, chloroaniline and dichloroaniline isomer separation ; heteroaromatic stationary phases

Various liquid stationary phases have previously been investigated for the analyses of toluidine and chloro- and dichloroaniline isomers.1-7 However, there have been few systematic studies on the resolution of these isomers. Therefore, this study was undertaken.

This paper reports the results obtained using heteroaromatic amphoteric compounds (nicotinic acid, isonicotinic acid and picolinic acid), an aromatic amphoteric compound (p-aminobenzoic acid), purine derivatives and aromatic and aliphatic amines as stationary phases for the separation of toluidine and chloro- and dichloroaniline isomers.

Experimental Stationary Phases

The compounds used as stationary phases were obtained from Nakarai Chemical Co. (Kyoto, Japan) as guaranteed-grade materials and silicone KF-54 from Shinetsu Chemical Co. (Tokyo, Japan) as a pure-grade substance, and were used after purifrcation by recrystal- lisation or chromatography. The purities of these compounds were confirmed by thin-layer chromatography (TLC) and nuclear magnetic resonance (NMR) spectroscopy.

Samples

Japan), were used after purification by recrystallisation or distillation. confinned by TLC and NMR spectroscopy.

The samples, obtained as guaranteed-grade materials from Tokyo Kasei Kogyo Co. (Tokyo, Their purities were

Apparatus

ionisation detector was used. A Shimadzu (Kyoto, Japan) Model GC-5A gas chromatograph equipped with a flame-

Chromatographic Procedure The separation column was a 2.25m x 3mm i.d. stainless-steel U-tube packed with

acid-washed firebrick C,, (Johns-Manville, Denver, CO , USA) (60-80-mesh) support coated with 20% m/m of the stationary phase. The column and injector temperatures were 140 and 270 "C, respectively. Nitrogen was used as the carrier gas at a flow-rate of 25 ml min-l.

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ON0 601 Results and Discussion

Although in gas - liquid chromatographic analyses amines are strongly adsorbed by interacting with the acidic parts of a support,8-10 the C,, supports used in this work were not treated with an alkali, in order to ascertain the activity of the stationary liquids.

It has been reportedll that chloroaniline isomers were effectively completely separated on lH-benzotriazole and N-ethylurea and toluidine isomers were also Completely resolved on lH-benzotriazole, carbazole and melamine. Further, all of these separations were effectively obtained on non-alkali-treated supports.

Separation of Chloroaniline Isomers As shown in Tables I and 11, the aromatic and heteroaromatic amphoteric compounds

picolinic acid, quinolinic acid, isonicotinic acid, orotic acid, 3,5-diaminobenzoic acid and uracil completely separated all three chloroaniline isomers. In addition, thymine, uracil, orotic acid and cytosine, which have amino and imino groups, were found to be effective for the separation of these chloroaniline isomers. Further, succinamide was as effective as succinimide.ll Based on this result, caffeine, theobromine, theophylline, xanthine, hypo- xanthine and adenine were examined, and as shown they provided nearly complete resolutions. On the other hand, a mixed stationary phase column of melamine and barbituric acid (15% each) also separated the isomers fairly completely.

TABLE I RELATIVE RETENTIONS OF CHLOROANII.INE ISOMERS

Stationary phase Picolinic acid . . .. p-Aminohippuric acid . . Isonicotinic acid . . .. Orotic acid .. .. 3,6-Diaminobenzoic acid Cytosine . . .. .. Caffeine . . .. .. Theobromine . . .. Theophylline . . .. Xanthine . . .. .. Hypoxanthine . . .. Adenine . . . . .. Thymine . . .. . . Succinamide . . .. Isonicotinic acid + sodium

hydroxide . . .. Melamine + barbituric acid Uracil . . .. . .

Quinolinic acid . . .. . . . . . . .. .. .. . . . . . . . . .. .. .. . . . . .. .. ..

Relative retention A

f , Retention time o-Chloro- m-Chloro- B-Chloro- of o-chloro-

aniline 1.00 1.00 1.00 1.00 1 .oo 1 .oo 1 .oo 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00

aniline 3.15 2.80 2.30 2.42 3.52 2.24 2.74 2.47 2.73 2.08 2.63 2.38 2.16 2.94 2.42

aniline 4.40 3.90 2.30 3.29 6.71 2.73 2.96 2.87 3.35 2.27 3.46 3.71 2.63 3.67 2.67

anilinelmin 2.00 1.00 2.30 3.10 2.10 2.10 2.30 1.70 6.00 2.60 6.30 2.40 1.90 1.80 1.20

1.00 1.81 2.12 5.20 1.00 3.13 5.06 1.60 1.00 1.43 1.87 2.30

Ratio of relative retention of

p-isomer to that of m-isomer

1.40 1.39 1 .oo 1.36 1.91 1.22 1.08 1.16 1.23 1.09 1.32 1.56 1.22 1.25 1.10

1.17 1.62 1.31

Separation of Toluidine Isomers As shown in Tables I and 11, the aromatic and heteroaromatic amphoteric compounds

picolinic acid, quinolinic acid, $-aminohippuric acid, isonicotinic acid and thymine resolved well all of the toluidine isomers. Caffeine, theophylline, theobromine, xanthine, hypo- xanthine and adenine were also examined, and were found to give nearly complete base-line separations, except for adenine.

A mixed stationary phase consisting of 15% isonicotinic acid and 3% sodium hydroxide and also one consisting of melamine and barbituric acid (15% each) gave an excellent separa- tion of these isomers.

Comparing the separation of chloroanilines with that of toluidines, although aromatic and heteroaromatic amphoteric substances give nearly complete separations of chloroanilines, iiot all provided complete separations of toluidines, although the separations were appreciable. Caffeine, theobromine, theophylline, hypoxanthine and xanthine provided nearly complete

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602

Stationary phase Picolinic acid . . .. fi-Aminohippuric acid . . Isonicotinic acid . . ,. Orotic acid .. .. 3,5-Diaminobenzoic acid Cytosine .. .. Caffeine . . .. .. Theobromine . . .. Theophylline . . .. Xanthine . . .. .. Hypoxanthine . . . . Adenine . . .. . . Thymine . . .. .. Succinamide . . . . Isonicotinic acid + sodium

hydroxide . . .. Melamine + barbituric acid Uracil . . .. ..

Quinolinic acid . . ..

ONO: GLC SEPARATION OF TOLUIDINE,

TABLE I1 RELATIVE RETENTIONS OF TOLUIDINE ISOMERS

Analyst, Vol. 107

Relative retention

o-Toluidine . . 1.00 . . 1.00 . . 1.00 . . 1.00 . . 1.00 .. 1.00 . . 1.00 . . 1.00 . . 1.00 . . 1.00 .. 1.00 . . 1.00 . . 1.00 . . 1.00 . . 1.00

. . 1.00 . . 1.00

. . 1.00

1

m-Toluidine p-Toluidine 1.75 2.29 1.56 2.12 1.20 1.36 1.60 2.14 1.53 1.53 1.33 1.33 1.36 1.36 1.50 1.80 1.63 2.00 1.29 1.41 1.86 2.55 1.41 1.59 1.50 1.71 1.56 1.89 1.00 1 .oo 1.45 1.62 2.78 4.79 1.43 1.65

Retention time of

o-toluidinel min 5.20 2.50 2.50 7.80 7.60 2.40 3.60 2.00 9.30 2.40

15.20 4.60 3.40 3.90 0.60

8.90 10.80 4.60

Ratio of relative retention of p-isomer to

that of rn-isomer 1.31 1.36 1.13 1.34 1 .oo 1.00 1 .oo 1.20 1.23 1.09 1.37 1.13 1.14 1.21 1.00

1.12 1.72 1.12

separations of both chloroanilines and toluidines. In general, the resolution of polar com- pounds on a mixed stationary phase of polar substances is difficult12-14 but, as described above, mixed stationary phases consisting of isonicotinic acid and sodium hydroxide and of melamine and barbituric acid gave good separations.

In the separation of toluidine isomers, the theoretical plate numbers (with m-toluidine) of the stationary phases used were 4 720 (caffeine), 2 900 (theobromine), 3 900 (theophylline) and 8 600 (xanthine), and these stationary phases provided base-line separations. Theo- bromine gave the best separation with the lowest theoretical plate number.

In addition, in the separation of chloroaniline isomers, the theoretical plate numbers (with m-chloroaniline) of the stationary phases were 2 500 (picolinic acid), 9 800 (caffeine), 7 700 (theobromine), 13000 (theophylline), 8 900 (hypoxanthine) and 4300 (uracil). These stationary phases also gave base-line separations and picolinic acid provided the best separa- tion with the lowest theoretical plate number.

Separation of Dichloroaniline Isomers As shown in Tables I11 and IV, isonicotinic acid, picolinic acid, hydantoin, uracil, creatine,

thymine, hydroxy-L-proline, caffeine, theophylline, theobromine, acetylurea and mixed stationary phases consisting of silicone KF-54 and 3% sodium hydroxide and of nicotinamide and fi-aminobenzoic acid (15% each) effectively separated all six isomers.

Nicotinic acid,ls which effectively separated these isomers, is a heteroaromatic amphoteric compound, and the heteroaromatic and aliphatic amphoteric compounds isonicotinic acid, picolinic acid, creatine and hydroxy-L-proline showed fairly effective separations. Further, m- and p-aminobenzoic acid and 3,5-diaminobenzoic acid, which are amphoteric compounds, were examined. They provided fairly good separations but could not resolve 2,4- and 2,3- dichloroanilines.

The basic compounds used as stationary phases listed in Tables I11 and IV were used in order to neutralise the acidic parts of a support. From the above results, it can be concluded that the stronger basicity of a pyridine is more effective than the weaker basicity of an aniline in the separation of dichloroaniline isomers on the amphoteric derivatives of pyridine or aniline.

The hydrogen bonding interaction between dichloroanilines and quinolinic acid may be stronger than that between dichloroanilines and nicotinic acid, isonicotinic acid or picolinic acid; on this basis, quinolinic acid may be unable to separate all of the dichloroaniline isomers.

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603 JMne, 1982 CHLOROANILINE AND DICHLOROANILINE ISOMERS

TABLE I11 RELATIVE RETENTIONS OF DICHLOROANILINE ISOMERS ON VARIOUS STATIONARY PHASES

Stationary phase Nicotinicacid .. .. Picolinic acid . . . . Isonicotinic acid . . . . Quinolinic acid . . . . 9-Aminohippuric acid . . SIB-Diaminohenzoic acid . . 9-Aminobenzoic acid . . m-Aminobenzoic acid . . Hydantoin .. .. .. Uracil . . . . . ltl-Benzotriazole . . . . Creatine .. .. .. Benzimidamle .. .. Carbazole .. . . . , Thymine .. .. .. L-Cystine .. . . . . Hydroxy-L-proline . . Hypoxanthine . . .. Caffeine .. .. .. Theophylline . , . . Theobromine . . . . Adenine .. . . .. Xanthine .. .. . . Succinimide . . .. Nicotinarnide . . .. Phthalimide .. .. Isatoic anhydride . . Benzoguanamine . . . . Melamine .. . . . . Acetylurea . . . . . . Barbituric acid Guanidine phosphatk N-Ethylurea . . . . Imidazole .. . . .. Cvtosine .. .. .. Melamine + m-aminobenzoic acid Melamine + o-aminobenzoic acid Silicone KF-54 Silicone KF-54 + sodium* hydroxide . . Nicotinamide + p-aminobenzoic acid . . Melamine + barbituric acid . . . .

Relative retention* r

2,5-Dichloro- 2,4-Dichloro- 2,3-Dichloro- 3,5-Dichloro- 3,4-Dichloro- of 2,6-dichloro- aniline aniline aniline aniline aniline anilinelmin

A , Retention time

2.77 2.85 2.56 2.86 3.04 2.81 2.74 2.86 2.56 2.80 2.88 3.48 2.81 2.37 3.13 1.72 3.53 3.13 2.89 2.85 3.27 2.73 3.02 3.00 3.17 2.82 3.00 1.29 2.88 3.40 2.43 2.92 3.00 3.25 3.14 2.67 3.33 1.69 1.44 2.68 2.54

3.89 3.82 3.28 4.14 3.04 3.15 2.74 2.86 3.19 3.53 4.00 3.68 4.31 3.27 4.07 2.07 3.75 4.13 3.11 3.25 4.13 3.40 3.57 3.42 4.33 4.00 3.00 3.00 3.56 4.60 2.93 3.50 4.33 5.25 3.57 2.67 4.50 1.69 3.47 2.95 3.00

4.31 4.06 3.50 4.14 3.24 3.15 3.13 2.86 3.50 3.73 4.00 4.00 4.31 3.27 4.27 2.07 4.14 4.13 3.58 3.50 4.32 3.40 3.57 3.58 4.33 4.00 3.99 3.00 3.56 5.00 2.93 3.50 4.33 5.25 3.57 2.93 4.50 1.94 3.80 3.12 3.00

7.89 8.79 6.28 8.57 6.96 7.00 6.03 6.00 6.69 7.00 7.75 7.44 8.00 6.13 9.73 4.30 9.81 8.60 7.37 7.30 6.68 6.80 4.90 8.00 9.00 8.82 3.99 6.00 7.00 9.60 5.71 8.00 8.17

10.00 8.07 6.00 9.83 2.53 7.20 6.68 6.46

10.89 12.30 8.61

12.14 8.04 8.08 7.91 7.00 8.56 9.07

11.50 10.24 11.38 8.67

12.67 5.00

10.42 10.60 9.15 8.70

12.78 8.77 9.67 9.66

12.17 11.82 3.99 7.53 8.50

13.40 7.29

10.83 12.00 13.75

8.71 6.93

11.83 3.10 9.20 7.85 9.00

0.90 1.65 1.80 0.70 2.50 2.60 3.10 0.70 1.60 1.50 0.80 2.50 1.60 3.00 1.50 1.60 3.60 1.50 1.90 2.00 2.20 1.50 4.20 1.20 0.60 2.20 1.50 1.70 1.60 0.50 1.40 1.20 0.60 0.40 2.80 1.50 0.60 1.30 1.50 4.10 1.20

* The relative retention is the ratio of two retention times (2,6-di&loroaniline = 1.00) and is based on adjusted retention times.

The heteroaromatic amphoteric compounds hydantoin, uracil and thymine also provided fairly good separations of all of the isomers; on the other hand, 1H-benzotriazole, benzi- midazole, carbazole, phthalimide and barbituric acid also gave fairly good resolutions but they could not separate all of the isomers. The amphoteric compound thymine provided fairly good resolutions but neither the acidic barbituric acid nor the basic cytosine could separate the 2,4- and 2,3-isomers.

Caffeine, theophylline and theobromine effectively separated all of the dichloroanilines but hypoxanthine, xanthine and adenine could not resolve all of the isomers. Xanthine, hypo- xanthine, caffeine, theophylline and theobromine could resolve all of the nitroxylene isomers.17 Caffeine, theophylline and theobromine gave a fairly complete separation of xylenol isomers,18 but could not resolve all of the xylidine isomers.19

On the xanthine derivatives, the better the separation of the 2,4- and 2,5-dichloroanilines, the poorer was the separation of the 2,4- and 2,3-isomers.

Acetylurea and N-ethylurea, having imino, amino and carbonyl groups, provided effective separations and acetylurea resolved all of these isomers. Although it is difficult to resolve polar compounds on a mixed stationary phase c o l ~ m n , ~ ~ - ~ ~ the mixed stationary phases consisting of nicotinamide and 9-aminobenzoic acid and of silicone KF-54 and 3% sodium hydroxide resolve all of the isomers. Although the degree of basicity of the stationary phase is important in the resolution of these isomers, it is important to obtain symmetrical peaks in the gas-chromatographic analyses of aniline derivatives.

The fairly complete separations on nicotinic acid, picolinic acid, isonicotinic acid, creatine, uracil, caffeine, theophylline and theobromine were obtained at temperatures below the melting-points of these compounds and the resolution of dichloroaniline isomers on them

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604 Artalyst, Vol. I07 ON0 : GLC SEPARATION O F TOLUIDINE,

TABLE IV SEPARATION FACTORS OF DICHLOROANILINE ISOMERS ON VARIOUS STATIONARY PHASES

Separation factor*

Stationary phase Nicotinicacid .. .. .. Picolinic acid . . . . . . . . Isonicotinicacid .. , . .. Quinolinicacid .. .. .. p-Aminohippuric acid . . . . 3,5-Diaminobenzoic acid . . . . p-Aminobenmic acid .. .. m-Aminobenzoic acid . . . . Hydantoin . . . . . . . . Uracil . . .. .. .. IH-Benzotriajdle .. .. .. Creatine . . . . . . . . Benzimidazole .. .. .. Carbazole . . . . . . . . Thymine . . . . . . . . L-Cystine . . , . . . . . Hydroxy-L-proline . . . . . . Hypoxanthine .. .. .. Caffeine . . . . - . . . Thwphylline . . . . . . . . Theobromine . . . . . . . . Adenine . . . . . . . . Xanthine . . . . . . . . Succinimide . . . . . . . . Nicotinamide .. .. .. Phthalimide . . . . . . . . Isatoicanhydride . . . . .. Benzoguanamine .. .. .. Melamine . . . - . . . . Acetylurea . . . . . . . . Barbituric acid .. .. Guanidine phosphate' . . . . N-Ethylurea . . . . . . . . Imidazole . . . . . . . . Cytosine Melamine + &mh%er&~ acid: : Melamine + 0-aminobenzoic acid . . Silicone KF-54 Silicone KF-54 + d u r n h&oxidi Nicotinamide + fi-+o@zoic acid Melamine + barbitunc acld . .

..

..

..

..

..

..

i,6-Dichloro- 2,4-Dichloro- aniline to aniline to 2,6-isomer 2,b-isomer

2.77 2.85 2.56 2.86 3.04 2.81 2.74 2.86 2.56 2.80 2.88 3.48 2.81 2.37 3.13 1.72 3.53 3.13 2.89 2.85 3.27 2.73 3.02 3.00 3.17 2.82 3.00 1.29 2.88 3.40 2.43 2.92 3.00 3.26 3.14 2.67 3.33 1.69 1.40 2.68 2.54

Ratio of the adjusted retention times of two adjacent peaks.lK

I 1

0 4 8 12 16 20 Retention time/min

Fig. 1. Separation of dichloro- aniline isomers by the column coated with 20% caffeine on C,,, 60-80 mesh, a t 140 "C. Peaks: 1 = sol- vent; 2 = 2,8dichloroaniline; 3 = 2,5-dichloroaniline; 4 = 2,4- dichloroaniline; 5 = 2,3-dichloro- aniline ; 6 = 3,5-dichloroaniline : and 7 = 3.4-dichloroaniline.

1.40 1.34 1.28 1.45 1.00 1.12 1.00 1.00 1.25 1.26 1.39 1.06 1.53 1.38 1.30 1.20 1.06 1.32 1.08 1.14 1.26 1.25 1.18 1.14 1.37 1.42 1.00 2.33 1.24 1.35 1.21 1.20 1.44 1.62 1.14 1.00 1.36 1.00 2.41 1.10 1.18

2,3-Dichlom- aniline to 2,4-isomer

1.11 1.06 1.07 1.00 1.07 1.00 1.14 1.00 1.10 1.06 1.00 1.09 1.00 1.00 1.05 1.00 1.10 1.00 1.15 1.08 1.05 1.00 1.00 1.05 1.00 1.00 1.33 1.00 1.00 1.09 1.00 1.00 1.00 1.00 1.00 1.10 1.00 1.16 1.10 1.06 1.00

3,5-Dichloro- aniline to 2 ,%-isomer

1.83 2.16 1.79 2.07 2.16 2.22 1.93 2.10 1.91 1.88 1.94 1.86 1.86 1.87 2.28 2.08 2.37 2.08 2.06 2.09 1.66 2.00 1.37 2.23 2.08 2.20 1.00 2.00 1.96 1.92 1.95 2.29 1.89 1.90 2.26 2.05 2.18 1.30 1.89 2.14 2.15

3,C-DichloA aniline to 3,5-iwmer

1.38 1.39 1.37 1.42 1.16 1.15 1.31 1.17 1.28 1.29 1.48 1.38 1.42 1.41 1.30 1.16 1.07 1.23 1.24 1.19 1.91 1.29 1.97 1.21 1.35 1.34 1.00 1.26 1.21 1.40 1.28 1.35 1.47 1.38 1.08 1.16 1.20 1.23 1.28 1.18 1.39

I 1 1

0 2 4 6 8 10 Retention time/min

Fig. 2. Separation of dichloroaniline isomers by the column coated with 20% nicotinic acid on C,,, 60-80 mesh, a t 140 "C. Peaks: 1 = solvent; 2 = 2,6-dichloroani- line: 3 = 2,!3-dichloroaniline; 4 = 2,4- dichloroaniline ; 5 = 2,3-dichloroaniline : 6 = 3,5-dichloroaniline; and 7 = 3,4- dichloroaniline.

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June, 1982 CHLOROANILINE AND DICHLOROANILINE ISOMERS 605 seems to be due to adsorption on to the stationary phase. On the other hand, nearly sym- metrical peaks were obtained on these compounds. This result may be due to the heavy load of the stationary phase (20% m/m).20

In general, better peaks and shorter retentions were obtained for the dichloroanilines than for the xylidines on these compounds. The theoretical plate numbers with 2,4-dichloro- aniline isomers on various stationary phases are 4 870 (theobromine) , 2 920 (nicotinic acid) , 4800 (hydantoin) , 2860 (thymine), 9860 (caffeine), 7220 (hypoxanthine) and 4990 (acetyl- urea); caffeine gave a high plate number and fairly good resolution, and thymine gave fairly good resolution at a low theoretical plate number. The fairly good separations of dichloro- anilines on caffeine and nicotinic acid are shown in Figs. 1 and 2, respectively.

Conclusions

Organic arnphoteric compounds are effective in the resolution of toluidine, chloroanilinf and dichloroaniline isomers and the control of their basicity is important for dichloroanilines Fairly good separations of toluidine, chloroaniline and dichloroaniline isomers were obtained on non-alkali-treated supports.

1. 2. 3. 4. 5. 6. 7. 8. 9.

10.

11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

References Henkel, H. G., J . Gas Chromatogr., 1965, 3, 320. Bombaugh, K. J., Anal. Chem., 1965, 37, 72. Pertsova, N. V., Memova, M. M., and Dobychin, S. L., Tr. Gos. Inst. PriRZ. Khim., 1969, 62, 171. Snegova, A. D., Motsarev, G. V., and Treger, Yu. A., Zh. Anal. Khim., 1970, 25, 1423. James, A. T., Anal. Chem., 1956, 28, 1964. Fitzgerald, J . S . , Aust. J . AppZ. Sci., 1961, 12, 51. Funaoka, W., Kojima, T., and Igaki, H., Anal. Chem., 1964, 36, 2214. James, A. T., Martin, A. J . P., and Smith, G. H., Biochem. J . , 1952, 52, 238. Nelson, J., and Milun, A., Chem. Ind. (London), 1960, 663. Link, W. E., Morrissette, R. A., Cooper, A. D., and Amullin, C. F., J . Am. Oil Chem. SOC., 1960,

Ono, A., AnaZyst, 1981, 106, 906. Ono, A., J . Chromatogr., 1979, 180, 170. Ono, A., J . Chromatogr., 1980, 193, 300. Ono, A,, and Masuda, Y. , J . Chromatogr., 1980, 197, 251. Ettre, L. S., J . Chvomatogv., 1979, 165, 235. Ono, A., J . Chromatogr. Sci., in the press. Ono, A., J . Chromatogr. Sci., 1981, 19, 448. Ono, A., Chromatographia, 1980, 13, 752. Ono, A., Chromatographia, 1981, 14, 692. Martire, D. E., in Purnell, J. H., Editor, “Progress in Gas Chromatography,” Interscience, New

Received July 20th, 1981 Accepted December 14th, 1981

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York, 1968, p. 93.

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