989
Anal. Chem. 1984, 56,989-991
Determination of Alkylphenols by Gas Chromatography, Elution Liquid Chromatography, and Gel Permeation Chromatography Susan Wittmann,* ZoltPn Ddcsy, Susan Regensperger, and Elisabeth Pudmer Hungarian Oil a n d Gas Research Institute, H-8200 VeszprQm, J6zsef A. u. 34, Hungary
The separatlon and determlnatlon of groups of alkylphenols wlth C,5-Cs lsoalkane chalns by gas chromatography, elution llquld chromatography, and gel permeatlon chromatography are descrlbed. Parafflnlc hydrocarbons, monoalkylphenols, dialkylphenols, and bls( hydroxypheny1)alkanes were ldentlfled In lndustrlal alkylphenols by mass spectrometry. Elution llquld chromatography was carrled out on a 25 cm by 1 cm 1.d. column packed wlth 80-120 pm silica gel. Paraffinic hydrocarbons were eluted by n-hexane, dlalkylphenol by 95:5 n -hexane:chloroform, monoalkylphenols by chloroform, and bls( hydroxypheny1)alkanes by ethanol, respectively. The Separation procedure takes about 3 h, and the reproduclblllty Is f 8 re1 %. A gas chromatograph wlth a flame lonlratlon detector, a glass column (0.5 m X 1.8 mm 1.d.) packed wlth a 3 wt % OV-1 on Gas Chrom Q 120-150 pm, an argon carrier gas flow rate of 20 cm3/min, an Injector temperature of 250 O C , a detector temperature of 300 OC, and a column temperature programmed from 150 to 330 OC at 8 OC/mln was used. The procedure takes 40 mln and reproduciblllty of the method Is f5 re1 %. The gel permeation chromatography was carrled out by uslng 20 cm by 14 mm 1.d. column packed wlth 25-100 pm Sephadex LH-20. The moblle phase was dlchloromethane contalnlng 10% (v/v) methanol at a flow rate of 1.0 cma/mln and a temperature of 25.0 f 0.2 O C . The eluted sample was detected spectrophotometrlcalty. The separatlon procedure takes 15 mln and reproduclblllty of the method Is f l O re1 %.
Complicated mixtures of isomers and homologues of alkylphenols are obtained by the alkylation of phenol with c15-c33 isoalkane chains. Different studies can be found in the literature about the separation of alkylphenols. These works reported the identification, determination, and behavior of alkylphenols with short or relatively short hydrocarbon chains. Mass spectrometric analysis of isomers and homologues of alkylphenols with C5-Cll a-olefins have been studied by Brodskii and co-workers (1). ZakUpra (2) separated alkylphenols with C12-C19alkenes on silica gel with n-hexane and dichloromethane by elution liquid chromatography. Monoalkylphenols with C8-Clo n-alkenes have been analyzed by gas chromatography and by other analytical techniques by Raverdino and Sasetti (3). Nichikova and co-workers (4) separated monoalkylphenols from dialkylphenols and isomeric monoalkylphenols from each other (alkylphenols with C8-Clo alkenes) by gas chromatography using a flame ionization detector. The retention behavior of several alkylphenols with short hydrocarbon chains has been studied in an HPLC system by Schabron, Hurtubise, and Silver (5). The latest HPLC method for determination of alkylphenols with short alkane chains is described by Ogan and Katz (6) and Hurtubise, Hussain, and Silver (7).
The three separation procedures of gas chromatography, elution liquid chromatography on silica gel, and HPLC seemed applicable for the analyses of alkylphenols with short or relatively short hydrocarbon chains. This paper describes methods for separation and determination of groups of compounds in alkylphenols with 15 to 33 carbon atoms in the alkyl chains.
EXPERIMENTAL SECTION Elution Liquid Chromatography. This procedure was used to separate diluent oil and groups of compounds in alkylphenols with C15-C33isoalkane chains on the basis of their polarity. A 25 cm by 1cm i.d. column was packed with 80-120 Fm silica gel (heated at 160 "C for about 5 h). A 0.5-g sample was dissolved in n-hexane and added to the top of the column. The column was washed with about 50 cm3of n-hexane to elute the paraffinic hydrocarbons. A second fraction was eluted with about 30 cm3 of 955 n-hexane:chloroform, and subsequent fractions were eluted with 30 cm3of chloroform and 50 cm3of ethanol. Cut points were established gravimetrically. The separation procedure takes about 3 h. Gas Chromatography. Gas chromatography was also used to separate and determine the quantity of the groups of compound types the samples. A gas chromatograph with a flame ionization detector was used. A glass column (0.5 m x 1.8 mm i.d.) was packed with 3 wt % OV-1 on Gaschrom Q 120-150 pm. The argon carrier gas flow rate was 20 cm3/min. The injector and detector temperatures were 250 "C and 300 "C, respectively, and the column temperature was programmed from 150 to 330 "C at 8 "C/min. The gas chromatography of the alkylphenols takes 40 min. Gel Permeation Chromatography. The separation and quantitation of the various groups of C16-C33substituted alkylphenol compounds by molecular size were carried out by using gel permeation chromatography. Separation was carried out on a 20 cm by 14 mm i.d. column packed with 25-100 pm Sephadex LH-20. Dichloromethane containing 10% (v/v) methanol was used as the mobile phase at a flow rate of 1.0 cm3/min and a temperature of 25.0 f 0.2 "C. The absorbance of the eluted sample at 278 nm was determined spectrophotometrically., The gel permeation chromatography of the alkylphenol takes 15 min. Mass Spectral Analysis of Alkylphenols. A type of highresolution double-focusing mass spectrometer with HerzogMattauch geometry and equipped with direct probe type sample inlet system was used at an ionization potential of 15 eV. The sample tube was heated from ambient to 400 "C, source temperature was 310 "C, scan rate was 8.4 s/decade, and instrument resolution was 2000 (10% valley). The groups of compound types separated from the industrial alkylphenol samples were characterized by mass spectrometry on the basis of their molecular ions.
RESULTS AND DISCUSSION On the basis of the mass spectra of industrial alkylphenols, the main groups of compounds were identified as paraffinic hydrocarbons (CnH2n+2), monoalkylphenols (CnH2n+lCSH40H), dialkylphenols (C,N2,+1)2CsH30H, and bis(hydroxypheny1)alkanes C,H2,(C6H40H),. The fractions obtained by elution liquid chromatography were also identified by means of their mass spectra. The polarity of the eluents characterized by
0003-2700/84/0356-0989$01.50/0 0 1984 American Chemical Society
990
ANALYTICAL CHEMISTRY, VOL. 56, NO. 6, MAY 1984 %
loo(,
3,50
*t z c
z
0,oo
0 .../-
Munoalkylphenol
0,OL 650
7
do
720
800
850
M/E
Flgure 2. Gas chromatogram of an alkylphenol sample with an average 24 hydrocarbon chaln: (1) paraffinic hydrocarbon, (2) monoalkylphenol, (3) bls(hydroxyphenyl)alkane, (4) dialkylphenol.
Dlel!+phenol
, ,
350
600
650
M,E
700
Figure 1. Mass spectra of components of alkylphenol obtained by elution liquid chromatography.
Table I. Names of Eluents and Eluted Alkylphenols for Elution Liquid Chromatography dielectric constants eluefits (at 20 "C) eluted components n-hexane 1.89 paraffinic hydrocarbon n-hexane:chloroform, 2.06 dialkylphenol 95:5 (v:v)
chloroform ethyl alcohol
5.10 26.93
monoalkylphenol his( hydroxypheny1)alkane
their dielectric constants and the identification of the eluted alkylphenols are shown in Table I. The mass spectra of the
three groups of compounds are represented in Figure 1. Figure 2 shows the gas chromatogram of an industrial alkylphenol. The peaks of the gas chromatogram were identified by standard additions, using the fractions obtained by liquidphase chromatography and identified by mass spectral analysis. The peaks in order of elution were paraffinic hydrocarbon, monoalkylphenol, bis(hydroxyphenyl)alkane, and dialkylphenol. Figure 3 shows the gel permeation chromatogram of an industrial alkylphenol. The peaks of the gel permeation chromatogram were again identified by standard additions using the fractions obtained by elution liquid chromatography and identified by mass spectral analysis. The peaks in order of decreasing molecular size were dialkylphenol, bis(hydroxyphenyl)alkane,monoalkylphenol,and paraffinic hydrocarbon. The data from several analyzed industrial alkylphenols obtained by gas chromatography, elution liquid chromatography and gel permeation chromatography are compared in Table 11. The results of the three methods show good agreement. The reproducibility of the gas chromatography for alkylphenols is *5 re1 %, that of the elution liquid chromatography is f8 re1 %, and that of the gel permeation chromatography is rtl0 re1 %.
Table 11. Components of Industrial Alkylphenols are Determined by Gas Chromatographj,, Elution Liquid Chromatography, and Gel Permeation Chromatography wt % bis(hydroxyparaffinic pheny1)alkane dialkylphenol hydrocarbon monoalkylphenol sample method 15.0 25.5 12.1 41.4 GC 25.3 16.1 10.1 48.5 LC 28.4 14.3 11.0 46.3 GP C 27.1 21.8 16.0 35.1 2 GC 29.1 20.3 15.3 34.7 LC 26.8 22.3 14.4 GPC 36.5 26.7 19.4 16.2 3 37.7 GC 29.5 17.7 17.6 LC 35.2 29.3 17.2 18.7 GPC 34.8 29.0 22.6 1e.o 30.4 4 GC 27.2 24.8 16.3 31.7 LC 29.7 20.3 19.1 30.9 GPC 32.5 17.0 22.1 28.4 GC 5 30.1 21.5 21.3 27.1 LC 30.3 17.2 23.9 28.6 GPC 36.9 20.4 17.0 25.7 GC 6 34.1 18.6 23.5 23.8 LC 35.5 21.9 24.4 18.2 GPC 33.2 24.4 18.3 24.1 7 GC 31.7 22.8 19.5 26.0 LC 31.3 24.5 18.7 25.5 G1'C
991
Anal. Chem. 1984, 56, 991-995
.
?
gel permeation chromatography. The main groups of components separated by the three methods are paraffinic hydrocarbon, monoalkylphenols, dialkylphenols, and bis(hydroxypheny1)alkanes. Accuracies of the three methods are almost equivalent. Gel permeation chromatography gives results quicker than gas chromatography and elution liquid chromatography, but the gas chromatography method is slightly more precise.
3
ACKNOWLEDGMENT The authors with to express their gratitude to K. B6ldi and E. Ker6nyi for their attention to detail in performing the laboratory analysis. LITERATURE CITED
0
1
I
5
10
(1) Brodskii, E. S.; Lukashenko, J. M.; Lebedevskaya, V. G.; Polyakova, A. A. Khim. Tekhnol. Topl. Masel 1973, 16, 54-58. (2) Zakapra, V. A.; Chernetskaya, T. J. Khlm. Tekhnol. Top/. Masel 1973; 16, 51-55. (3) Raverdino, Vittorio; Sassetti, Plerguido J. Chromafogr. 1978, 753,
I
ELUTION V O L U M E , c m
__
181-188. -
3
Flgure 3. Elution curve of an alkylphenol with an average 24 hydrocarbon chain on Sephadex LH-20: (1) dialkylphenol, (2) bis(hydroxyphenyl)alkane,(3) monoalkylphenol, ( 4 ) paraffinic hydrocarbon.
CONCLUSIONS The concentration of the compound type in industrial grade alkylphenols with CI5-C3 isoalkane chains can be determined by gas chromatograhy, elution liquid chromatography, and
(4) Nichikova, P. R.; Rud, A. N.; Tember, G. A.; Getmenskaya, Z. J.; Ivanov, U. N.; Zerzeva, I . M.; Martynushkina, A. V. Neftepererab. Neftekhim. (Moscow) 1979, 3 , 46-48. (5) Schabron, J. F.; Hurtubise, R. J.; Silver, H. F. Anal. Chem. 1978, 50, 1911-1917. (6) Ogan, Kenneth: Katz, Eiena Anal. Chem. 1981, 5 3 , 160-163. (7) Hurtubise, R. J.; Hussain, A.; Silver, H. F. Anal. Chem.1981, 5 3 , 1993- 1997.
RECEIVED for reiew September 23, 1983.
Accepted January
10, 1984.
Multivariate Curve Resolution in Liquid Chromatography David W. Osten and Bruce R. Kowalski*
Laboratory for Chemornetrics, Department of Chemistry BG-10, University of Washington, Seattle, Washington 98195
Self-modeling curve resolution has been shown to allow resolution of two coeiuting chromatographic peaks without requiring any assumption of an underlying peak shape. The subsequent problem of quantitation of these coeiuting peaks Is limited both by the Chromatographic resolution (separation in time antl difference in elution profile) and by the degree of spectral uniqueness. An experimental system of two watersoluble vitamins has been used to examine the effects of varying chromatographic resolution on the quantitative accuracy of the curve resolution method.
The importance of high-performance liquid chromatography in the analysis of complex chemical mixtures has been recognized for some time. The chromatographer is often faced with the problem of unresolved or only partially resolved chromatographic peaks eluting from the analytical column. The accepted response to inadequate resolution has generally been increased attempts with complex and expensive gradient elution methods to improve the chromatographic conditions; however, this will not always provide a solution to the general chromatographic problem of coeluting peaks. Davis and Giddings (I) have shown that the likelihood of overlapping chromatographic components is much higher than previously
realized. The availability of multiwavelength absorbance data from the new generation linear diode array UV/visible liquid chromatography detectors presents a challenge to analytical chemists to develop methods for analyzing the large volume of data generated. This additional information can be used to determine the number of components in a single chromatographic peak and to accomplish both qualitative and quantitative resolution of the underlying components. Single wavelength absorbance detectors provide a record of the total amount of material eluting from the chromatographic column as a function of time. Unfortunately, these detectors force the chromatographer to rely on peak shape criteria to determine if the eluting peak is a single component or a mixture. Poor peak shape or the presence of a valley point can suggest the presence of at least two components, but with only the absorbance a t a single wavelength, no resolution of the mixture is possible. Dual wavelength detectors provide an additional means of detecting the presence of a mixture eluting from the chromatographic column. The ratio of the absorbance a t two different wavelengths can be used to both evaluate peak purity and confirm peak identity (2). A multiwavelength absorbance detector, such as the linear diode array detectors now available from several manufacturers, does provide the chromatographer with the raw data necessary to determine the number and identity of the eluting chroma-
0003-2700/84/0356-0991$01.50/00 1984 American Chemical Society
