The recommended number of selected points, about 10 to 15, is conveniently small for routine runs. In general, suitable number and spacing of points may vary in different applications. The number and spacing of points can be established easily by repeated reduction of one data curve with different selected points. Such checks should be made periodically.
The computer program is written in BASIC language and has been used with the General Electric time-sharing computer. The program listing is available from the author.
RECEIVED for review June 9, 1969. Accepted October 8, 1969. ~~
Complete Gas Chromatographic Analysis of Homo- and Copolymers of PoIya mide Resins Sadao Mori and Motohisa Furusawa Laboratory of Chemistry, Faculty of Engineering, Yamanashi University, Kofu, Japan
Tsugio Takeuchi Department of Synthetic Chemistry, Faculty of Engineering, Nagoya University, Nagoya, Japan
A TECHNIQUE FOR THE DETERMINATION OF COPOLYAMIDES has been developed (1). However, the method does not resolve the components of the w-amino acid-type polyamides and the procedure requires extraction treatment and ion-exchange separation. A number of publications have appeared on the gas chromatography of the a-amino acids in their N-trifluoroacetyl methyl ester form (2-4). The fatty and aromatic amines have also been separated as their N-trifluoroacetyl derivatives (5, 6), and some of the w-amino alkanoic acids (C3, Cs, C,, C9,and CI1)as N-trifluoroacetyl methyl esters (7). The method described in this paper gives qualitative and quantitative results for the gas chromatographic determination of all components recovered from the hydrolyzed copolyamides-ie., diamines, dibasic acids, and w-amino alkanoic acids. The hydrolysis product of the copolyamide with 6N HC1 is esterified with HC1-methanol, followed by trifluoroacetylation with trifluoroacetyl anhydride, and then gas-chromatographed. The components were identified by comparing their retention times with standard reagents. A second hydrolyzate was blended with the appropriate internal standards of homologs and followed by the same procedure. Reproducibility and repeatability of the method are better than those of earlier techniques. The method is applicable to all types of copolyamides resulting from the copolymerization of diamine-dibasic acid (DADB) with DADB, DADB with w-amino acid, and w-amino acid with w-amino acid. EXPERIMENTAL
Reagents. All diamines, dibasic acids, and some w-amino alkanoic acids (C2, CS,Cq, Cj, and Cg) were commercial products of reagent grade, used without further purification. The 7-aminocaprylic (c,), K-aminoundecanoic (CII),and X-aminolauric (C,,) acids were obtained from corresponding com(1) A . A ~ ~ ~ ~ , A N A L . C H 1116(1968). EM.,~O, (2) P. A. Cruickshank and J. C. Sheehan, ibid., 36, 1191 (1964). (3) S. Makisumi and H. A. Saroff, J. Gas Chromatog., 3,21 (1965). 39, 1194 (1967). (4) G . E. Pollock, ANAL.CHEM., (5) R. A. Morrissette and W. E. Link, J . Gas Chromatog., 3, 67 (1965). (6) R. A. Dove, ANAL.CHEM., 39, 1188 (1967). (7) E. P. Usova, Zh. Anal. Khim., 22, 304 (1967). 138
mercial polymers by acid hydrolysis. Trifluoroacetic anhydride, methylene chloride, and 2,2-dimethoxypropane were obtained from the Tokyo Chemical Co. The esterification reagent, anhydrous methanol-hydrogen chloride (5 was prepared at this laboratory. Apparatus. A dual thermal conductivity detector gas chromatograph (Shimadzu Model GC4ATPF) with a linear temperature programmer was used. The column was a 2 meter x 3 mm i.d. stainless steel tube packed with 80- to 100-mesh Celite 545 coated with 5% (w./w.) neopentyl glycol succinate polyester. The column was conditioned at 240 "C for 24 hours. The injection port and the detector oven were maintained at 220" and 260 "C, respectively. A helium flow rate of 80 ml per minute and a detector current of 120 mA were maintained. Isothermal temperature was maintained at 200 and 220 "C, or programmed from 140 to 220 "C at a rate of 4 "C per minute. Procedure. A 0.1-gram sample of copolyamide was weighed into a glass tube and 10 ml of 6N hydrochloric acid were added. The tube was then sealed and placed in an oven at 130 f 5 "C for a prescribed length of time. The tube was shaken at 1-hour intervals. The hydrolyzate was transferred to a 30-ml evaporation vessel and evaporated to dryness on a steam bath. The hydrolysis residue was divided; one portion was blended with 0.01 gram of each appropriate internal standard, and the other was used for qualitative analysis. T o both residues, 40 ml of anhydrous 5 x hydrogen chloride in methanol and 1 ml of 2,2-dimethoxypropane were added. The reaction mixtures were refluxed in an oil bath for 3 hours. After the reaction, the methanol and the 2,2-dimethoxypropane were removed under reduced pressure and the residues of diamine dihydrochlorides, dibasic acid methyl esters, and w-amino alkanoic acid methyl ester hydrochlorides were dried in vacuo. To these reaction products, 1.0 ml of trifluoroacetic anhydride and 1.O ml of methylene chloride were added, and the resulting solutions were stored at room temperature for 30 minutes to 2 hours until complete dissolution. Approximately 10 ~1 of the final solutions were chromatographed. The components of the copolyamide were identified by comparing these retention times and separation temperatures with the derivatives of known diamines, dibasic acids, and w-amino alkanoic acids. The schematic describing the procedure is shown in Figure 1. Calibration. Each diamine, dibasic acid, and w-amino alkanoic acid composing the copolymer components was
ANALYTICAL CHEMISTRY, VOL. 42, NO. 1, JANUARY 1970
x),
SAMPLE
*1
B N - H C I , 130
'C
Table I. Retention Times and Separation Temperature for Derivatives
HYDROLY zAT E ____-
1
EVAPORATE
Programmed RetenSepara- Isothermal tion tion retention time, temp., time, "C minutes minutes
H Y D R 0 LYZ 4 T E,DRY
,
DIVIDED
',
v
i
ESTERIFY , W I T H HCI-METHANOL
+
01A M I N E 2 H C I , D I E S T E R S , W-AMINO
1
4ClD
EVAPORATE
-
GAS
amine Trimethylcncdianii~ie(C,)
-
TO
A N A LY S I S
1
0 U A N T I T AT1 V E
ANALYSIS
A N A L Y S Id
Figure 1. Schematic of qualitative and quantitative determination of copolyamides separately weighed out ( 5 to 25 mg) into a 10-rnl capacity vial, and blended with 10 mg of appropriate internal standards of homologs which were diamine, dibasic acid, and w-amino alkanoic acid having a different retention time, and then carried through the procedure. The peak area of each component was ratioed with the corresponding internal standard and plotted with respect to the weight of the diamine, the dibasic acid, and the a-amino acid, respectively. RESULTS AND DISCUSSION
Gas chromatograms of di-N-trifluoroacetylated diamines, dibasic acid dimethyl esters, and N-trifluoroacetylated amino alkanoic acid methyl esters were obtained showing symmetrical peaks without tailing. No potassium hydroxide or alkali addition on the solid support of gas chromatographic column DEGREES 152
164
176
188
CENTIGRADE 200
~ ~ . .
212
3
6
9
12
,
15
IE
21
N-Trifltioroacetylated amino acid mcthyl cster Glycine (C?) &Alanine (CJ y-AInino-if-btityric acid (C,) 8-Amino-ri-valeric acid (C,) eAmino-rr-caproic acid ( ( 2 6 ) 7-Amino-//-caprylic acid (CS)
K-Amino-11-undecaiioic acid (Cld
A-Amino-rz-lauric acid (C12) Dibasic acid dimethyl ester Succinic acid (C,) Glutaric acid (C5) Adipic acid (C,) Pimelic acid (Ci) Suberic acid (CS) Azelaic acid (C,) Sebacic acid (Go) Dodecanoic acid (C12)
212.0 219.6 220.0
15.5
20.6 33.7
3.1 4.0 6.8 9.7 12.7 16.7
152.4 156.0 167.2 178.8 190.8 206.8
(Sep. temp. 200 "C) 0.7 0.9 1.6 2.4 3.3 6.2
22.5
220.0
14.8
24.7 1.7 2.6 3.8 5.2 6.8 8.7 10.6 14.8
20.8 146.8 150.4 155.2 160.8 167.2 175.8 182.8 199.2
Table 11. Analyses of Synthetic Mixtures and Copolyamide of 6,66 Synthetic mixture
220
Concentration, mg Added Found&
Rel. error,
%
Hexamethylenediamine Adipic acid t-Aminocaproic acid
10.0 10.0 30.0
9.91 10.40 29.60
Hexamethylenediamine Adipic acid e-Aminocaproic acid
15.0 15.0 20.0
15.08 14.52 20.35
+o. 5b
Hexamethylenediamine Adipic acid e-Aminocaproic acid
20.0 20.0
19.92 19.64 10.30
-0.4 -1.8 +3.0
mean
11.9
10.0
-0.9 +4.0
-1.3 -3.2 +1.8
i
I I
0
(Sep. temp. 220 "C) 4.2 5.3 6.6 8.1 9.9 12.9
(C,?)
~
CHROMA TDGRAPHY
QUALITATIVE
18.0 19.9 Pentainethylenediamine (CJ 21 . 5 Hexamethylenediamine (C,) 23.0 Heptamethylenediamine (C,) 24.9 27.9 Octamethylenediamine (C,) Nonamethyletiediainine (C,) 30.8 Decamethylenediamine (Clo) 35.8 Dodecamethyleiiedianiine 49.2
Tetramctliylenedianiiiie (Ca)
THOSE S P E C I F I E D FOR Q U A L I T A T I V E
ANHYDRIDE CHLORIDE
T R I F LUO R O A C E T I C AND METHYLENE
~
ESTERIFY WITH H C I- W E T H A N O L
IDENTICAL
DIAMINE 2TFA, DIESTERS, w-AMINO ACID ESTER T F L
-
Di-N-trifluoroacetylated di-
I
ESTER H C I
D I A M I N E ZHCI, DIESTERS, W_ - A.M A C I D E S T E R HCI,DRY -I N O
I I
Derivative
THE INTERNAL STANDARD
24
27
Blended polyamide 6/66, Added Found3t0
30
MI N U T E S
Figure 2. Separation of synthetic mixtures for determination of nylon 6,66 Conditions described in apparatus section. Sensitivity full scale 8 mV. Sample, 10 pl. Derivatives 1. Glutaric acid Me ester 2. Adipic acid Me ester 3. y-Amino-n-butyric acid Me ester-TFA 4. &Amino-n-caproicacid Me ester-TFA
50150
50150 50150 50150
50150 a
b 0
51.2/48.8 51.3148.7 48.9151.1 49,5150.5 51.0/49.0
Mean of five measurements. Five measurement values were 15.0, 15.0, 15.1, 15.1, and 15.2. Sum corrected to 100%.
5. Hexamethylenediamlne-TFA 6. Octamethylenediamine-TFA ANALYTICAL CHEMISTRY, VOL. 42, NO. 1, JANUARY 1970
139
was needed. Separation of each component was complete (Table I). Some pairs of derivatives, heptamethylenediamine cs. A-amino-rz-lauric acid, P-alanine us. adipic acid, and yamino-n-butyric acid C J . suberic acid, were close to one another. Careful adjustment of initial column temperature and temperature program rate effected best resolution of these same pairs of derivatives. The calibration curves for determination of nylon 6,66 were constructed in the usual manner with octamethylenediamine (C& glutaric acid (C5),and y-amino-n-butyric acid (C,) as the internal standards. The slopes of the curves were 12.8 for the e-aminocaproic acid and 8.48 for the hexamethylenediamine, and yield milligrams of the amino acid and the diamine per unit area ratio. The internal standards for other copolyamides could be selected from Table I. The gas chromatograms for the determination of nylon 6,66 are shown in Figure 2. The glutaric, adipic, y-amino-n-butyric, and e-amino-n-caproic acids, and hexamethylene- and octamethylenediamines were weighed (6 to 10 mg), esterified, and dried; 0.7 nil of the trifluoroacetyl anhydride and 0.5 ml of the mcthylene chloride were added and gas-chromatographed.
The data presented in Table I1 indicate that the method has a n average relative error of about +2%. Gas chromatography of the reaction mixtures proved the trifluoroacetylation of diamines to be quantitative. Application of the homologs to the internal standards reduced the error caused by esterification and acetylation to a minimum. The complete acid hydrolysis of nylon 6 was accomplished in 2 hours, nylon 66 in 4 hours, and nylon 11 and nylon 12 in 8 hours. Twice the time of hydrolysis was satisfactory. The degree of acid hydrolysis of the polyamides was examined by gas and thin-layer chromatography (TLC). For TLC, glass plates were coated with silica gel G. The plates were developed with 1-butanol-25 ammonia-watcr (70 : 25 : 5). Staining was effected with ninhydrin. ACKNOWLEDGMENT
The authors are indebted to the Toyo Rayon Co., Ltd., for supplying polyamide samples and to K. Kobayashi for her technical assistance. RECEIVED for
review August 28, 1969. Accepted October 21,
1969.
I AIDS FOR ANALYTICAL CHEMISTS Graph for Attaining Maximum Separation in Unidimensional Multiple Chromatography Gilbert Goldstein Dicision of Laboratories, Beth Israel Medical Center, 10 Nathan D. Perlnzun Place, New York, N . Y. 10003
INTHE TECHNIQUE of unidimensional multiple chromatography (UMC), employed with paper and thin layers, an alternating sequence of development and drying takes place repeatedly with the same solvent in the same direction. This method was devised to gain the advantages of a greater effective distance of travel of the solvent front while retaining a shorter length for the support medium itself. The theory of U M C has been documented in a series of publications (1-8). The treatment by Thoma (5, 6) is especially exhaustive. R values are reproducible only under rigidly uniform conditions. They depend upon layer activity and thickness, chamber saturation, development distance, distance of starting point from solvent surface, quantity of test substance applied and solvent in which it is applied, as well as other factors (9). (1) A. Jeanes, C. S. Wise, and R. J. Dimler, ANAL.CHEM., 23, 415 (1951). (2) . , H. C. Chakrabortty and D. P. Burma, Anal. Clzim. Acta, 15, 451 (1956). (3) H. P. Lenk, Z . Anal. C/iem., 184, 107 (1961). (4) N. Zollner and G. Wolfram, Klin. Wochendzr.,40,1098 (1962). ( 5 ) J. A. Thoma, ANAL.CHEM., 35,214 (1963). (6) J. A. Thoma, J . Cliromatog., 12, 441 (1963). ( 7 ) H. Halpaap, C/iem.-6ig.-Tec/z., 35, 488 (1963). (8) R. Riidiger and H. Rfidiger, J . C/ii.ornaiog., 17, 186 (1965).
(9) G. Pataki, “Techniques of Thin-Layer Chromatography in Amino Acid and peptide Chemistry (Revised Edition),” Alln Arbor Science Publishers, Inc., Ann Arbor, Mich., 1968, PP 40-6. 140
Nevertheless, the theoretical and the observed values generally agree well enough to permit use of the theory in determining approximate behavior ( I , 2). A fundamental equation of UMC, due to Jeanes et al. ( I ) is nRf= 1 - (1 - R,)n, where nRf is the relative distance travelled by a substance after n solvent passes. As it increases, the distance separating two substances with differing R, values increases to a maximum and then decreases ( I , 3-5, 7, 8). Also due to Jeanes et al. ( 1 ) is an equation which may be written N =
log ( a b ) log (1 - b/1 - a )
where N is the number of passes producing maximum separation, and a and b represent the Rfvalues. We may express Equation 1 in exponential form, and set it equal to y , giving y = a (1
- a)N = b (1 - b)”
(2)
Only those N values that are positive and integral, and those a (or b) values that lie between 0 and f l are physically meaningful in the context of UMC. If, subject to these restrictions, we now plot y cs. a for various values of N , those regions where > > we Obtain a series of Curves as in Figure 1. (For higher N values, the ordinate can be constructed on an expanded scale).
ANALYTICAL CHEMISTRY, VOL. 42, NO. 1, J A N U A R Y 1970
+
‘3
