1,4-Diphenyltriphenylene grafted polysiloxane as a stationary phase for gas chromatography

Article abstract of DOI:10.1039/c9nj04918e

In this work, 1,4-diphenyltriphenylene-grafted (14.2%) polysiloxane (DPTP) was successfully synthesized and statically coated on capillary columns as a stationary phase for gas chromatography. The DPTP columns exhibited excellent efficiencies of 3646 plates m^-1 for a 30 m column and 3125 plates m^-1 for a 10 m column, as evidenced by naphthalene measurements at 120 °C, which demonstrated the good film-forming ability of DPTP. Thermogravimetric analysis showed that the weight of DPTP is reduced by 2% at 380 °C. Separation of the polyethylene pyrolysis product indicated that the maximum allowable operating temperature of the DPTP column is 360 °C. The moderate polarity of the DPTP column was investigated in terms of McReynolds constants. The DPTP column was utilized to separate analytes, including aromatic isomers, fatty acid esters, ethers, polycyclic aromatic hydrocarbons and their derivatives, and nitrogenous heterocyclic compounds, on the basis of the column's strong π-π stacking, dipole-induced dipole, and dispersion interactions with solutes. In general, the DPTP column offers great potential as a novel stationary phase for separating various analytes due to its special structure and remarkable separation performance.

Full text of DOI:10.1039/c9nj04918e

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1,4-Diphenyltriphenylene grafted polysiloxane as
a stationary phase for gas chromatography
Cite this:DOI: 10.1039/c9nj04918e
Li Xu, Jianchun Bai, Aiqin Du, Zaixiao Yang and Bo Wu
*
In this work, 1,4-diphenyltriphenylene-grafted (14.2%) polysiloxane (DPTP) was successfully synthesized
and statically coated on capillary columns as a stationary phase for gas chromatography. The DPTP
ꢀ1
ꢀ1
columns exhibited excellent efficiencies of 3646 plates m for a 30 m column and 3125 plates m for
a 10 m column, as evidenced by naphthalene measurements at 120 1C, which demonstrated the good
film-forming ability of DPTP. Thermogravimetric analysis showed that the weight of DPTP is reduced by
2% at 380 1C. Separation of the polyethylene pyrolysis product indicated that the maximum allowable
operating temperature of the DPTP column is 360 1C. The moderate polarity of the DPTP column was
investigated in terms of McReynolds constants. The DPTP column was utilized to separate analytes,
including aromatic isomers, fatty acid esters, ethers, polycyclic aromatic hydrocarbons and their
derivatives, and nitrogenous heterocyclic compounds, on the basis of the column’s strong p–p stacking,
dipole-induced dipole, and dispersion interactions with solutes. In general, the DPTP column offers
great potential as a novel stationary phase for separating various analytes due to its special structure and
remarkable separation performance.
Received 28th September 2019,
Accepted 5th December 2019
DOI: 10.1039/c9nj04918e
rsc.li/njc
1
2–15
According to some reports,
aromatic ring-grafted polysiloxane toward polar substances,
Gas chromatography has been widely applied in analysis, especially especially aromatic compounds, largely depends on the polar-
the separation selectivity of
1
. Introduction
1
2
3
4
in food, drug, environment, and petrochemical industries,
izability of aromatic rings. Increasing the polarizability of
because of its excellent characteristics, which include a wide range aromatic rings plays an extremely important role in improving
of applications, rapid analysis, small sample size, and high sensi- the separation selectivity of the stationary phase. For example,
tivity. Gas chromatographic stationary phases have been intensively Martin synthesized a single phenyl-substituted methylphenyl-
developed over the last few decades, and new stationary phases have polysiloxane stationary phase and demonstrated that the intro-
been gradually replacing traditional materials. For instance, carbon duction of phenyl groups improves the stability and separation
5
,6
7,8
9,10
16
nanotubes,
graphene,
and metal–organic frameworks
selectivity of the material. A number of gas chromatographic
have emerged as novel gas chromatographic stationary phases stationary phases with different polarities and properties have
exhibiting special retention behaviors due to their unique been subsequently obtained by introducing different numbers
structures and properties.
of aromatic rings into the polysiloxane backbone or side chains.
Previous studies have been carried out on polysiloxane Lee et al. synthesized polysiloxane stationary phases containing
stationary phases, which have good film-forming ability, low biphenyl or naphthyl groups, and these phases showed excellent
vapor pressure, small viscosity coefficients, and high thermal separation performance for aminophenanthrene isomers by promot-
1
1
stability. Continuous developments in gas chromatography ing enhanced dipole-induced dipole interactions. However, because
have been focused on the separation of complex compounds these stationary phases could only be used below 280 1C, their
17
possessing similar structures and polarities, and high boiling applications were severely limited. Based on the work by Lee et al.,
points and molecular weights, thereby increasing the perfor- Naikwadi synthesized a side-chain liquid crystalline polysiloxane, the
mance requirements of gas chromatographic stationary phases. structure of which includes four phenyl rings; this stationary phase
Therefore, the development of stationary phases with good separa- exhibited high thermal stability and selectivity for separating iso-
tion efficiency, high temperature resistance, and excellent selectivity meric compounds, including polychlorinated dibenzo-p-dioxins and
is an urgent problem that should be addressed by researchers to polycyclic aromatic hydrocarbons (PAHs), due to the presence of
18
meet increasing demands for separation and analysis.
a fused-ring aromatic system on the side-chains. In general,
replacing a single phenyl group with concentrated multiple aro-
matic rings improves the polarizability of the stationary phase,
resulting in remarkable chromatographic separation performance.
College of Chemistry and Chemical Engineering, Shandong University,
2
7 Shanda South Road, 250100, China. E-mail: wubo@sdu.edu.cn
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Corporation, Kyoto, Japan) and MS50 mass spectrometer (British
Karasto Company, London, UK) were employed to characterize
the intermediates and ultimate products. Chromatographic
evaluations were performed on a Shimadzu GC-2014 gas chromato-
graph (Shimadzu Corporation, Kyoto, Japan) with a split/splitless
injection system and a flame ionization detector. Nitrogen (N
9.999% purity) served as the carrier gas. All chromatographic
evaluations were accomplished under the same split ratio (30 : 1).
2
,
9
2
.2 Synthesis of the DPTP polymer
.2.1. Synthesis of 1,3-di(phenyl)cyclopenta[l]phenanthren-
-one (chemical formula: C H O). Phenanthrenequinone
2
2
2
9
18
(
10.5 g, 0.0504 mol) and dibenzyl ketone (10.8 g, 0.0514 mol)
were dissolved in 100.0 mL of absolute ethanol under heating
and continuous stirring in a N atmosphere. When the mixture
2
ꢀ
1
began to boil, 3.00 mL of 3.60 mol L KOH in ethanol solution
was added dropwise to it. The color of the mixture changed
from orange to dark green, and the reaction was continued for
another 30 min, during which large quantities of solids were
Fig. 1 Reaction scheme for the preparation of DPTP.
In this work, 1,4-diphenyltriphenylene grafted polysiloxane precipitated from the solution. The mixture was cooled in an
DPTP) was synthesized (Fig. 1) according to ref. 19 and utilized ice bath, and the solids were filtered. The crude product was
(
as a gas chromatographic stationary phase to systematically recrystallized from ethanol/toluene (V : V = 3 : 2) to produce 15.3 g
ꢀ1
evaluate its chromatographic performance. The proposed DPTP of black crystals with a yield of 79.3%. FTIR (KBr, n/cm ): 3055.95
1
stationary phase was expected to show good separation for [n(Ar–H)]; 1692.11 [n(CQO)]; 1591.59, 1483.95 [n(CQC)]. H NMR
aromatic isomers, PAHs and their derivatives, and heterocyclic (CDCl , 300 MHz, ppm): 6.93–7.80 (m, Ar–H, 18H). ESI-MS m/z for
3
+
compounds on account of p–p stacking and dipole-induced (C H O + H) , calcd: 383.1431; found: 383.1437.
2
9 18
dipole interactions originating from the rigid coplanar structure
of the 1,4-diphenyltriphenylene group.
2.2.2 Synthesis of the DPTP stationary phase. According to
ref. 22, polymethylvinylsiloxane containing 19.0% vinyl groups
The composition and structure of the stationary phase were were synthesized through ring-opening polymerization of octa-
1
1
characterized by H nuclear magnetic resonance ( H NMR) methylcyclotetrasiloxane and tetramethyltetravinylcyclotetra-
spectroscopy and Fourier transform infrared (FTIR) spectroscopy. siloxane. The DPTP polymer was obtained by the Diels–Alder
McReynolds constants and Abraham solvation parameters were used reaction of 1,3-di(phenyl)cyclopenta[l]phenanthren-2-one and
to evaluate the polarity of DPTP and interaction between DPTP and polymethylvinylsiloxane. The synthetic process was as follows.
analytes. Finally, the application of DPTP in the analysis of aromatic Polymethylvinylsiloxane (5.00 g, including 0.0124 mol vinyl)
isomers, fatty acid esters, ethers, PAHs and their derivatives, and with 50.0 mL of diphenyl ether as a solvent was added to a four-
nitrogenous heterocyclic compounds was investigated.
necked flask under a N atmosphere. The polymethylvinylsilox-
2
ane was completely dissolved in diphenyl ether under heating
conditions, after which a slight excess of 1,3-di(phenyl)cyclopenta[l]-
phenanthren-2-one (5.40 g, 0.0141 mol) was added to it. The mixture
was continuously reacted at 220 1C for 48 h. A large number of
bubbles were produced, and the color of the mixture gradually
2
. Experimental
2.1 Reagents and equipment
Phenanthrenequinone was purchased from Zhengzhou Alpha turned from brown to yellow during the reaction. The reaction
Chemical Co. Ltd (Zhengzhou, China). All reagents used were of was considered complete when bubble formation was no longer
analytical grade. A polyethylene pyrolysis product and a Grob observed. The solvent was removed under vacuum distillation, and
test mixture were prepared on the basis of ref. 20 and 21, the residue was dissolved in 10.0 mL of toluene and precipitated
respectively. Fused-silica capillaries (10 and 30 m, i.d. 0.25 mm) with 30.0 mL of methanol. This step was repeated four times. The
2
were produced from the fiber level (SiO ; 99.999% purity) with a solvent was evaporated, and DPTP (6.50 g, 78.5%) was obtained as
ꢀ
1
drawing machine in our laboratory. A commercial DB-17 column a transparent yellow viscous liquid. FTIR (KBr, n/cm ): 3058.29
was purchased from Agilent Technologies for comparison. [n(Ar–H)]; 2962.32, 1603.81, 800.80 [n(C–H)]; 1408.77, 1594.26
1
Chromatographic analyses of all analytes, except that of the [n(Si–CQC)]; 1093.73, 1019.22 [n(Si–O–Si)]. H NMR (CDCl
3
,
polyethylene pyrolysis product, were performed on a 30 m 300 MHz, ppm): 7.02–8.42 (m, Ar–H, 19H). The peaks at 5.97 and
column; analysis of the pyrolysis product was conducted on a 0.03 ppm corresponded to vinyl and C–H on Si atoms, respectively.
1
0 m column.
2.3 Preparation of capillary columns
A DPX-300 NMR spectrometer (Bruker, Bremen, Germany),
LCT-2 TGA analysis instrument (Beijing Optical Instrument Prior to static coating, 5.0 mL of dichloromethane was flushed
Factory, Beijing, China), FTIR-8400S spectrometer (Shimadzu into 10 and 30 m fused-silica capillaries. The columns were
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2
then maintained at 260 1C for 1 h with continuous N . Subse-
quently, 0.8% (W/V) DPTP, including dicumyl peroxide (4% of
the weight of DPTP) in dichloromethane, was statically coated
on the capillary columns. Dicumyl peroxide served as a free
2
3
radical initiator to accelerate cross-linking. The columns were
ꢀ1
conditioned from 40 1C to 160 1C at a rate of 1 1C min ; this
condition was maintained for 2 h. Then, the temperature was
ꢀ1
increased to 360 1C at a rate of 2 1C min and held for 10 h
to remove low-molecular weight polymers. All operations of
programing temperature were conducted under N flow. The
2
columns were coated with films with a thickness of 0.5 mm,
which was calculated on the basis of ref. 24.
Fig. 3 Chromatogram of the polyethylene pyrolysis product on the DPTP
column (10 m ꢁ 0.25 mm). Conditions: the temperature was increased
from 100 1C (maintained for 2 min) to 360 1C (maintained for 4 min) at
3
. Results and discussion
3.1 Polymer characterization by NMR spectroscopy
ꢀ1
ꢀ1
1
4 1C min . Carrier gas velocity: 14 cm s . The injection and detector
1
H NMR results revealed that 14.2% 1,4-diphenyltriphenylene
was grafted to the polysiloxane side-chains. The grafting rate
was obtained by calculating the ratio of the integral at 7.027–
temperatures were both 400 1C.
The polyethylene pyrolysis product was separated on the
8.421 ppm (corresponding to Ar–H of the 1,4-diphenyltriphenylene
10 m DPTP column to further characterize the thermal stability
group) to the integral at 0.098 ppm (corresponding to Si–CH ). The
3
of DPTP, and the related chromatogram is displayed in Fig. 3.
Baseline separation was achieved with sufficiently sharp symmetrical
peaks. The DPTP column retained noteworthy column efficiency
and separation performance until 360 1C. The thermogravimetric
analysis and polyethylene pyrolysis product separation results thus
confirm that the high-temperature resistance of DPTP enables the
separation of high-boiling point substances.
calculated ratio of the integral at 5.983 ppm (corresponding to
Si–CHQCH ) to the integral at 0.098 ppm showed that DPTP
2
contains 4.8% vinyl groups. Groups with large steric hindrance
restrict the reaction from being completed, leading to a small
amount of vinyl available for cross-linking.
3.2 Thermal stability of the DPTP stationary phase
Thermogravimetric analysis was carried out to assess the thermal
stability of the DPTP stationary phase. DPTP was conditioned
3
.3 Column efficiency of DPTP
ꢀ
1
ꢀ
1
Column efficiencies of 3646 and 3125 plates m were observed
by determining naphthalene at 120 1C with the 30 and 10 m
columns, respectively. The coating efficiencies of DPTP in the
from 50 1C to 700 1C at 10 1C min under helium. Fig. 2 shows a
weight loss of 2% in DPTP at 380 1C. The presence of 1,4-
diphenyltriphenylene, which presents large steric hindrance,
effectively prevents DPTP from undergoing cyclization and rear-
30 and 10 m columns were calculated in accordance with ref. 23
25
to be 78.3% and 75.4%, respectively. Moreover, the crosslinking
degrees of DPTP, which were obtained by calculating the ratio
of the capacity factors before and after the DPTP columns were
rangement degradation at high temperatures. Therefore, the
thermal stability of DPTP was significantly improved compared
with that of polydimethylsiloxane.
2
6
rinsed with 5 mL dichloromethane, were 81.2% (30 m) and
9.6% (10 m). These findings show that DPTP has good film-
7
forming and cross-linking abilities. Golay curves were created
by evaluating naphthalene at different linear velocities to describe
the relationship between the height equivalent of a theoretical plate
and linear velocity. Fig. 4 reveals that the optimal linear velocities of
ꢀ
1
ꢀ1
the 30 and 10 m columns range from 8 cm s to 15 cm s
.
3.4 McReynolds and Abraham system constants of the DPTP
columns
2
7
McReynolds constants were quantitatively measured to inves-
tigate the polarity of DPTP. Five probe compounds were eluted
0
on the prepared DPTP column in the following sequence: Y
0
0
0
(
n-butanol) - X (benzene) - Z (2-pentanone) - U (1-nitro-
propane) - S (pyridine). As demonstrated in Table 1, the DPTP
0
column has moderate polarity with a CP index of 17.3. The
13
27
McReynolds constants of DPFP and OV-11, the side-chain groups
of which are 7,10-diphenylfluoranthene and benzene, respectively,
Fig. 2 TGA analysis of the DPTP polymer.
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Table 2 Abraham system constants of DPTP and DPFP
Interaction parameter
Stationary Temperature
2
phase
(1C)
c
e
s
a
b l
n
R
DPTP
80
ꢀ2.376 0.021 0.743 0.612 0 0.669 32 0.99
ꢀ2.425 0.050 0.670 0.533 0 0.643 31 0.99
ꢀ2.501 0.093 0.564 0.383 0 0.587 31 0.99
ꢀ2.927 0.013 0.733 0.603 0 0.663 39 0.99
ꢀ3.001 0.020 0.666 0.492 0 0.658 39 0.99
ꢀ2.996 0.091 0.559 0.379 0 0.608 39 0.99
1
00
20
80
00
20
1
1
3
DPFP
1
1
and dipole-induced dipole interactions, between DPTP and the
analytes. Furthermore, DPTP has considerable potential for
separating polarizable compounds, such as aromatic compounds,
via dipole-induced dipole and dispersion interactions, which is in
accordance with the McReynolds constants obtained.
Fig. 4 Golay curves of the DPTP capillary columns.
The computed McReynolds and Abraham system constants
confirm that the introduction of 1,4-diphenyltriphenylene groups,
which is characterized by a rigid coplanar structure containing
polyphenyl and a large p-conjugated group, could enhance the p–p
CP index stacking, dipole-induced dipole, and dispersion interactions
Table 1 McReynolds constants of DPTP, DPFP and OV-11
0
0
0
0
0
S
Column
DPTP1
X
Y
Z
U
Sum
between DPTP and various analytes.
121
118
102
139
136
142
153
142
145
182
178
219
138
135
178
733
704
786
17.3
16.7
18.6
3
DPFP
27
3.5 Selectivity, repeatability and reproducibility of the DPTP
OV-11
column
As shown in Fig. 5, the Grob mixture was analyzed to evaluate
are presented in Table 1 to analyze the factors affecting the polarity.
As computed in accordance with ref. 28, the average molecular
polarizability values of benzene, 7,10-diphenylfluoranthene, and 1,4-
the comprehensive performance of the chromatographic columns,
including their column efficiency, adsorption activity, and acid–
base properties. All substances expressed baseline separation with
sharp symmetrical peaks, except for peak S. The leading peak
3
diphenyltriphenylene are 10.40, 44.79, and 48.26 Å , respectively.
Table 1 shows that the values of the five characteristic constants
of DPTP (containing 14.2% 1,4-diphenyltriphenylene) are slightly
larger than those of 7,10-diphenylfluoranthene-grafted (15.9%)
polysiloxane (DPFP), although the grafting amount of the former
is slightly smaller than that of the latter. These results reveal that
different structures of the grafting groups significantly influence
the interaction between the stationary phase and the analyte. 1,4-
Diphenyltriphenylene, which is a rigid coplanar group, promotes
p–p stacking, dipole-induced dipole, and dispersion interactions
to a certain extent with increasing average molecular polarizability.
The polarity of DPTP is smaller than that of OV-11 (35% phenyl-
methyl polysiloxane), although the average molecular polarizability
31
of 2-ethylhexanoic acid (peak S) resulted from overloading.
2,6-Dimethylaniline (peak A) revealed a longer retention time
3
of benzene is only 10.40 Å . Therefore, the polarizability of the
grafting group and the grafting amount jointly affect the polarity of
the stationary phases.
2
9,30
Abraham system constants
were applied to determine
individual intermolecular interactions between DPTP and the
analytes. The results are shown in Table 2; here, c represents
the phase ratio of a given column, e represents n–p/p–p inter-
actions, s represents dipole interactions, a represents hydrogen-
bond basicity, b represents hydrogen-bond acidity, and l represents
dispersion interactions. The results revealed that dipole-induced Fig. 5 Chromatogram of the Grob test mixture on the DPTP column.
Conditions: the column temperature was increased from 40 1C to 170 1C
dipole interactions (s) are the main interactions occurring between
ꢀ1
ꢀ1
at 4 1C min . Carrier gas velocity (N ): 10 cm s . The injection and detector
2
DPTP and the analytes, followed by dispersion interactions (l).
Nearly all interaction parameters of DPTP were larger than those of
DPFP. Thus, large rigid coplanar groups containing delocalized
temperatures were both 220 1C. Peaks: (D) 2,3-butanediol; (C10) decane;
11) undecane; (ol) n-octanol; (al) nonanal; (S) 2-ethylhexanoic acid; (P) 2,6-
dimethylphenol; (A) 2,6-dimethylaniline; (E10) methyl decanoate; (E11) methyl
(C
electrons significantly improve the interactions, especially n–p/p–p undecanoate; (am) dicyclohexylamine; (E12) methyl dodecanoate.
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Table 3 Repeatability and reproducibility of the DPTP column
Month-to-month (n = 6) Column-to-column (n = 3)
Analytes
Mean (min) RSD (%) Mean (min)
RSD (%)
Heptane
5.532
6.087
6.943
7.963
9.836
11.114
12.038
0.15
0.43
0.22
0.10
0.38
0.51
0.13
5.545
6.099
6.951
7.972
9.833
11.128
12.047
2.63
3.82
2.83
2.57
4.32
3.30
2.37
Butyl acetate
Chlorobenzene
Bromobenzene
Octanol
p-Cresol
Acetophenone
than 2,6-dimethylphenol (peak P), thus indicating that the DPTP
column retains alkaline analytes more strongly than acidic
analytes. Undecane and n-octanol have similar boiling points
(195.6 1C and 194.0–195.0 1C, respectively). However, the retention
time of n-octanol was noticeably longer than that of undecane.
Thus, DPTP has stronger retention capacity for alcohols than
alkanes with identical boiling points.
Column repeatability and reproducibility after a long-term
use were obtained by separating several analytes of different
classes at 120 1C. As shown in Table 3, the relative standard
deviations (RSD%) of the retention time were below 0.51% for
month-to-month and 4.32% for column-to-column, demonstrating
good repeatability and reproducibility of the DPTP column.
3.6 Application of the DPTP column
The DPTP stationary phase could interact with analytes through
p–p stacking, dipole-induced dipole, and dispersion interactions
because of its special structure. Therefore, multiple analytes,
including substituted benzene and a series of isomers, FAEs, ethers,
PAHs, nitrogenous heterocyclic compounds and diesel, were used to
evaluate the chromatographic performance of the DPTP stationary
phase. The corresponding chromatograms are shown in Fig. 6–12.
3.6.1. Separation performance of DPTP for substituted
benzene and a series of isomers. As seen from the results
of the McReynolds and Abraham system constants of DPTP,
1,4-diphenyltriphenylene could improve the stationary phase’s
dipole-induced dipole interactions with polar substances and Fig. 6 Chromatograms of substituted benzene on the DPTP (A) and
DB-17 (B) columns. Conditions: the temperature was increased from
p–p stacking effects with aromatic substances. Fig. 6 and 7
ꢀ1
ꢀ1
6
0 1C to 140 1C at 4 1C min . Carrier gas velocity: 10 cm s . The
show the chromatograms of substituted benzene and a series of
isomers. A comparison of the separation effects of the DPTP
and DB-17 columns on substituted benzene is illustrated in
Fig. 6. Baseline separation was observed for all substances on
the DPTP column, particularly p-xylene (peak 4, b.p. 137.0–
injection and detector temperatures were both 220 1C. Peaks: (1) benzene;
(
2) toluene; (3) ethylbenzene; (4) p-xylene; (5) m-xylene; (6) o-xylene;
7) tert-butylbenzene; and (8) n-butylbenzene.
(
138.0 1C), m-xylene (peak 5, b.p. 139.3 1C), and o-xylene (peak 6, formate (peak 6, b.p. 107.0 1C)/ethyl acrylate (peak 7, b.p.
b.p. 144.4 1C), which were co-eluted on the DB-17 column. As 99.4 1C), ethyl butyrate (peak 9, b.p. 120.0–121.0 1C)/ethyl
seen in Fig. 7, a series of isomers, including butanol, pinene, methacrylate (peak 11, b.p. 119.0 1C), and methyl laurate (peak 27,
nitroaniline, and cyanobenzaldehyde, were effectively separated b.p. 262.0 1C)/ethyl 10-undecenoate (peak 28, b.p. 259.0 1C).
via enhanced sensitive dipole-induced dipole and p–p interactions. Propyl propionate (peak 10, b.p. 122.0 1C–124.0 1C) and ethyl
Based on these tests and the analytical results, the DPTP stationary methacrylate (peak 11, b.p. 119.0 1C) achieved baseline separation
phase may be an ideal candidate for separating a variety of isomers. on the DPTP column but were co-eluted on the DPFP column
3.6.2. Separation performance of DPTP for FAEs. As shown (Fig. 8 in ref. 13). These findings may be due to the improved
in Fig. 8, the FAEs composed of polar and nonpolar compounds dipole-induced dipole interactions between the CQC double bond
were directly separated on the DPTP column with good selectivity. of the unsaturated FAEs and the DPTP stationary phase, which
The figure also shows that the retention time of unsaturated strengthens the retention behavior of the latter for unsaturated
FAEs was longer than that of saturated FAEs, such as butyl FAEs. The elution time of benzyl acetate (peak 25, b.p. 213.0 1C)
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Fig. 7 Chromatograms for separation of (A) butanol isomers, (B) pinene isomers, (C) nitroaniline isomers (D) cyanobenzaldehyde isomers at 80 1C,
ꢀ1
1
80 1C, 300 1C and 240 1C, respectively. The solvents for them were ether and their N
2
linear velocity was 13 cm s . The injection and detector
temperatures were 220 1C for A and B, 340 1C for C and 300 1C for D.
was later than that of 2-(2-ethoxyethoxy)ethyl acetate (peak 23, possibly because 1,4-diphenyltriphenylene serves as a functional
b.p. 219.0 1C). This result could be due to the p–p stacking group that enhances dipole-induced dipole interactions with ethy-
interactions between benzene moieties in benzyl acetate and lene glycol diethyl ether. As seen from these findings, the DPTP
concentrated aromatic rings in the DPTP stationary phase. In stationary phase differs from the traditional stationary phase by
addition, ethyl cyanoacetate (peak 24, b.p. 206.0 1C) was eluted virtue of the former’s p–p stacking and dipole-induced dipole
after 2-(2-ethoxyethoxy)ethyl acetate (peak 23, b.p. 219.0 1C). interactions with analytes. Thus, DPTP is suitable for separating
The sensitive dipole-induced dipole interaction between –CRN weak polar substances.
and the DTPP stationary phase may be a reasonable explanation
for this finding.
3.6.4. Separation performance of DPTP for PHAs. High-
boiling-point PAHs are widely found in food and environmental
3
2,33
3.6.3. Separation performance of DPTP for ethers. Ethers contaminants.
The proposed DPTP was used to separate
were separated on the DPTP column to evaluate the separation PAHs. As observed in Fig. 10, 22 components were separated
ability of DPTP for resolving weak polar substances. As can be with well-shaped peaks within 42 min on the DPTP column. In
seen in Fig. 9, all compounds demonstrated effective separation particular, 2-methylnaphthalene (peak 4, b.p. 241.0–242.0 1C)
with sharp chromatographic peaks. The analytes (except for some and 1-methylnaphthalene (peak 5, b.p. 240.0–243.0 1C) were
specific compounds) were eluted in the order of an increasing successfully separated on the DPTP column, thereby indicating
boiling point. The retention time of anisole (peak 15, b.p. the material’s advantageous separation capability for certain iso-
155.5 1C) was longer than that of bis(2-methoxyethyl)ether mers of PAHs. Moreover, 4-nitrobiphenyl (peak 14, b.p. 340.0 1C),
(peak 14, b.p. 162.0 1C), likely due to the presence of p–p stacking anthracene (peak 16, b.p. 342 1C), and phenanthrene (peak 17, b.p.
interactions between the DPTP stationary phase and anisole. More- 340.0 1C), which have similar boiling points, revealed baseline
over, the elution sequences of dibutyl ether (peak 11, b.p. 142.0 1C– separation. The elution sequence of benzil (peak 15, b.p. 346.0–
143.0 1C) and ethylene glycol diethyl ether (peak 13, b.p. 121.4 1C) 348.0 1C) and phenanthrene (peak 17, b.p. 340.0 1C) was against
were reversed on the DPTP and DPFP columns (Fig. 9 in ref. 13), their boiling points. A possible reason for this finding is that the
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Fig. 8 Chromatograms of the separation of FAEs on the DPTP column.
Conditions: the temperature was increased from 45 1C (maintained for 8 min)
Fig. 10 Chromatogram of polycyclic aromatic hydrocarbons on the DPTP
column. Conditions: the column temperature was increased from 80 1C to
290 1C at 5 1C min . Carrier gas velocity: 10 cm s . The injection and detector
temperatures were both 340 1C. Peaks: (1) decahydronaphthalene; (2) tetralin;
ꢀ1
ꢀ1
to 90 1C at 4 1C min , and then to 250 1C at 12 1C min . Carrier gas velocity:
ꢀ1
ꢀ1
ꢀ1
1
2 cm s . The injection and detector temperatures were both 320 1C. Peaks:
1) ethyl acetate; (2) vinyl acetate; (3) ethyl propionate; (4) propyl acetate;
5) ethyl propionate; (6) butyl formate; (7) ethyl acrylate; (8) isobutyl acetate;
9) ethyl butyrate; (10) propyl propionate; (11) ethyl methacrylate; (12) butyl acetate;
13) amyl acetate; (14) methyl crotonate; (15) butyl propionate; (16) isoamyl
acetate; (17) n-propyl methacrylate; (18) allyl methacrylate; (19) butyl acrylate;
20) ethyl caproate; (21) propyl hexanoate; (22) 2-hydroxyethyl methacrylate;
23) 2-(2-ethoxyethoxy)ethyl acetate; (24) ethyl cyanoacetate; (25) benzyl acetate;
26) methyl decanoate; (27) methyl laurate; and (28) ethyl 10-undecenoate.
(
(3) naphthalene; (4) 2-methylnaphthalene; (5) 1-methylnaphthalene; (6) biphenyl;
(
(
(7) di-benzyl ether; (8) 8-hydroxyquinoline; (9) acenaphthylene; (10) dihydroa-
cenaphthylene; (11) naphthyl-ethyl ether; (12) fluorenone; (13) a-nitro-
naphthalene; (14) 4-nitrobiphenyl; (15) benzil; (16) anthracene; (17) phenan-
threne; (18) phenanthrenequinone; (19) 1,8-dihydroxyanthracene-9,10-dione;
(
(
(20) pyrene; (21) 1,2-benzanthracene; and (22) chrysene.
(
(
Fig. 9 Chromatograms of the separation of ethers on the DPTP column.
Conditions: the temperature was increased from 50 1C (maintained for 5 min)
ꢀ
1
ꢀ1
to 240 1C at 6 1C min . Carrier gas velocity: 10 cm s . The injection and
detector temperatures were both 320 1C. Peaks: (1) diethyl ether; (2) ethyl vinyl
ether; (3) tetrahydrofuran; (4) isopropyl ether; (5) 2,3-dihydrofuran; (6) 2-methyl-
tetrahydrofuran; (7) ethyl propenyl ether; (8) 1,2-dimethoxyethane; (9) allyl ether;
Fig. 11 Chromatograms of the separation of nitrogenous heterocyclic com-
pounds on the DPTP column. Conditions: the temperature was increased from
ꢀ1
50 1C (maintained for 8 min) to 320 1C at 6 1C min . Carrier gas velocity:
ꢀ1
8 cm s . The injection and detector temperatures were both 380 1C. Peak:
(1) piperidine; (2) pyridine; (3) morpholine; (4) a-picoline; (5) b-picoline;
(6) 2,6-lutidine; (7) 2-ethylpyridine; (8) 3,5-lutidine; (9) 2,4,6-trimethylpyridine;
(10) a-aminopyridine; (11) 1-methyl-2-pyrrolidone; (12) a-amino-3-methylpyri-
dine; (13) benzothiazole; (14) quinoline; (15) isoquinoline; (16) 1-methyl-2-(3-
(
10) 1,4-dioxane; (11) dibutyl ether; (12) ethylene glycol monomethylether;
13) ethylene glycol diethyl ether; (14) bis(2-methoxyethyl)ether; (15) anisole;
16) ethylene glycol monobutyl ether; (17) isopentyl ether; (18) dibutylsulfide;
(
(
0
(
19) dichloroisopropyl ether; (20) 2,2 -oxybis-ethanomonoethylether; (21) 2-
ethoxyethyl ether; (22) 2-(2-ethoxyethoxy)ethyl acetate; (23) diethylene glycol
monobenzyl ether; (24) 4-methoxyphenol; (25) diphenyl ether; (26) 2-nitro-
anisole; (27) ethyl naphthylether; and (28) benzyl ether.
0
pyridyl) pyrrolidine; (17) imidazole; (18) 8-hydroxyquinoline; (19) 2,2 -bipyridyl;
0
0
(20) 4,4 -dimethyl-2,2 -dipyridyl; (21) carbazole; (22) b-naphthoquinoline;
(23) benzimidazole.
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polyphenyl group, and its performance as a novel gas chromato-
graphic stationary phase. The analysis results demonstrated
that DPTP exhibits good film-forming ability, high column
efficiency, high thermal stability, and moderate polarity. In
addition, the DPTP column revealed a unique retention behavior
and remarkable separation performance for multiple isomers, FAEs,
ethers, PAHs, heterocyclic aromatic hydrocarbons and diesel due to
its enhanced p–p stacking, dipole-induced dipole, and dispersion
interactions derived from the 1,4-diphenyltriphenylene group of the
polysiloxane side-chain. In conclusion, DPTP deserves further study
as a high-selectivity and temperature-resistant stationary phase
that may address increasing demands for accurate separation in
many fields.
Conflicts of interest
There are no conflicts to declare.
Fig. 12 Chromatogram of the separation of a kind of diesel on the DPTP
column. Conditions: the temperature was increased from 80 1C to 320 1C
at 6 1C min . Carrier gas velocity: 15 cm s . The injection and detector
temperatures were both 380 1C.
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3.6.6 Separation performance of DPTP for the real sample.
2
The n-alkanes in diesel have important influence on its combustion
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