This document discusses using convergence chromatography (UPC2) coupled with UV and MS detection for analyzing liquid crystal materials. UPC2 provides advantages over traditional HPLC and GC methods due to its ability to separate compounds that may not be stable at high temperatures or volatile. Examples are given of using UPC2-UV for impurity profiling and compositional analysis of liquid crystal intermediates. The document also explores interfacing UPC2 with MS detection for increased selectivity and specificity in analyzing these materials. In summary, UPC2 coupled with various detection methods is presented as an effective technique for characterizing compounds used in liquid crystal displays.

1. ©2014 Waters Corporation 1
Hyphenating Convergence Chromatography
with UV and MS Detection for Compositional,
Impurity and Degradation Analysis of High
Performance Electronic Materials
Jane Cooper
Tue 20th May, 2014
[Click Here] - Link to Poster

2. ©2014 Waters Corporation 2
Introduction
 Background information about Liquid Crystals
 Current Analytical Methods
 Convergence Chromatography (UPC2)
 Examples:
o Impurity and degradation analysis
o Compositional analysis
 Interfacing UPC2 with MS detection

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Background - Liquid Crystals
 Properties:
o Some properties of liquids:
• Flow, pour like liquids and take the shape of containers
o Some optical properties of solids:
• Birefringence
• Optical activity
o React predictably to an electric current, enabling the control of
light passage
 Liquid crystal intermediates:
o Building block compounds used to prepare liquid crystals
• Used in mixtures (10 to 20 singles used in a typical mixture)

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Background - Liquid Crystals
A twisted nematic cell
In the “off” state, in the absence of an electric field, the assembly is transparent to light.
In the “on” state, an applied field destroys the twist of the nematic, rendering the assembly opaque.
Credit: Encyclopedia Britannica. Inc.

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Background - Liquid Crystals
 Uses:
o Electronic displays:
• Watches, calculators, notebooks, mobile phones, projectors,
desktops monitors / TVs, viewfinders on cameras /
camcorders…..

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Current Analytical Methods
 Existing methods used to characterize liquid crystal intermediate
compounds:
• Differential Scanning Calorimetry
• Fourier Transform Infrared
• Raman Spectroscopy
• Ultraviolet Absorption Spectrophotometry
• Optical Microscopy
– For the impurity profiling and compositional analysis typically a
chromatographic technique would be used:
• HPLC with UV detection
• HPLC with MS detection
• GC with MS detection

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Current Analytical Methods
– These techniques have some limitations:
• The compounds might not be thermally stable and / or volatile
• Limited sample availability
• The sample solubility might be incompatible with the solvent
required for the technique
• Therefore requiring additional sample preparation stages
• Long analysis times with insufficient selectivity and sensitivity

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Convergence Chromatography (UPC2)
 Convergence Chromatography (CC)
is a normal phase separation
technique
– Uses carbon dioxide as the primary
mobile phase
– Choice of adding an co-solvent such
as methanol or acetonitrile
 The Waters UltraPerformance
Convergence Chromatography
(UPC2) builds upon the potential of
CC while using proven and robust
Waters UPLC technology.
[Click Here] for detailed product Info

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Convergence Chromatography (UPC2)
 Many liquid crystal intermediate compounds:
– Are not very stable at high temperatures
– Have low volatility
– Have similar UV spectra
 Therefore, utilizing the separation powers of UPC2 with CO2 as
the mobile phase is an ideal alternative to both HPLC and GC
analysis

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UPC2 Examples
 Impurity Profiling Analysis
– Impurities can be present due to many factors, including
contamination, as by-products, or as degradation products
– Purity is critical to ensure the optimum quality, performance
and lifetime of the electronic display device
 Compositional Analysis
– Composition is critical to ensure physical properties and
characteristic of the liquid crystal.
o Even just small changes can have pronounced effects

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Liquid Crystal Intermediate Compounds
4-(Octyloxy)benzoic acid
4-Butoxybenzoic acid
4-Cyanobenzoic acid
4,4′-Azoxyanisole-d14
(internal standard)
4-Butylbenzoic acid
4-Octylbenzoic acid

12. ©2014 Waters Corporation 12
Methods
UPC2 conditions
CCM back pressure: 2000 psi
Sample temp.: 20 oC
Column temp.: 50 oC
Injection volume: 1 µL
Column: ACQUITY UPC2 CSH Fluoro-phenyl, 3.0 mm
x 100 mm, 1.7 µm
Mobile phase A: CO2
Mobile phase B: Methanol (2% Formic Acid +
15 mM ammonium acetate)
PDA conditions
UV system: ACQUITY UPC2 PDA Detector
Range : 210 to 450 nm
Resolution: 1.2 nm
Sampling rate: 20 pts/sec
Filter time constant: Slow (0.2 sec)

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Liquid Crystal Intermediate Compounds
Chemical Substance
CAS
Number
Retention
time
(minutes)
UV optimum
absorbance
(nm)
4,4′-Azoxyanisole-d14 39750-11-3 0.69 346
4-Butylbenzoic acid 20651-71-2 1.39 235
4-Octylbenzoic acid 3575-31-3 1.62 235
4-Cyanobenzoic acid 3575-31-3 1.75 252
4-Butoxybenzoic acid 1498-96-0 1.90 252
4-(Octyloxy)benzoic acid 2493-84-7 2.09 235

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Calibration Curve

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UV Chromatograms and UV Spectra

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252 nm
235 nm
346 nm
4-Cyanobenzoic acid
(0.001 mg/mL)
4-Butylbenzoic acid
(1 mg/mL)
4,4′-Azoxyanisole-d14
(internal standard)
4-(Octyloxy)
benzoic acid
(0.001 mg/mL)
4-Butoxybenzoic acid
(0.001 mg/mL)
Impurity Profiling

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Liquid Crystal Intermediate Compounds
Merck E7 (liquid crystal intermediate compounds)
4-cyano-4'-n-pentyl-biphenyl 4-cyano-4'-n-heptyl-biphenyl
C18H19N C20H23N
4-cyano-4'-n-oxyoctyl-biphenyl 4-cyano-4''-n-pentyl-p-terphenyl
C21H25NO C24H23N

18. ©2014 Waters Corporation 18
Methods
UPC2 conditions
CCM back pressure: 1800 psi
Sample temp.: 20 oC
Column temp.: 60 oC
Injection volume: 1 µL
Column: ACQUITY UPC2 BEH 2-EP, 3.0 mm
x 100 mm, 1.7 µm
Mobile phase A: CO2
Mobile phase B: Acetonitrile
PDA conditions
UV system: ACQUITY UPC2 PDA Detector
Range : 190 to 450 nm
Resolution: 1.2 nm
Sampling rate: 20 pts/sec
Filter time constant: Slow (0.2 sec)

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Liquid Crystal Intermediate Compounds
Chemical Substance
CAS
Number
Retention time
(minutes)
UV optimum
absorbance (nm)
4-cyano-4'-n-puntyl-biphenyl 5CB 40817-08-1 0.889 269
4-cyano-4'-n-heptyl-biphenyl 7CB 41122-71-8 1.012 269
4-cyano-4'-n-oxyoctyl-biphenyl 8OCB 52364-73-5 1.469 287
4-cyano-4''-n-pentyl-p-terphenyl 5CT 54211-46-0 1.742 292

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Calibration Curve

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UV Chromatograms and UV Spectra
4-cyano-4'-n-heptyl-
biphenyl
4-cyano-4'-n-oxyoctyl-
biphenyl
4-cyano-4'-n-puntyl-
biphenyl
4-cyano-4''-n-pentyl-p-
terphenyl

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Compositional Analysis
blank
Correct ratio
Incorrect ratio
51%
25% 16%
8%
40%
25% 23% 12%
Chemical Substance
Correct ratio Incorrect ratio
Prepared
%
Calculated
%
Prepared
%
Calculated
%
4-cyano-4'-n-puntyl-biphenyl 5CB 51.0 51.3 40.0 40.4
4-cyano-4'-n-heptyl-biphenyl 7CB 25.0 24.9 25.0 24.9
4-cyano-4'-n-oxyoctyl-biphenyl 8OCB 16.0 15.9 23.0 22.7
4-cyano-4''-n-pentyl-p-terphenyl 5CT 8.0 8.0 12.0 12.1

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Compositional Analysis
Correct ratioIncorrect ratio

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Interfacing UPC2 with MS detection
MS splitter
From the Column
manager or PDA
From the
makeup pump
To the
convergence
Manager
To the MS
Waters ACQUITY UPC2 configured with PDA and MS detection (here illustrated with an SQD),
including MS splitter and a makeup pump

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Interfacing UPC2 with MS detection
 Electrospray Ionization (ESI)
– An electrically charged field is used to generate charged droplets,
then analyte ions are formed by evaporation prior to MS analysis
– The addition of a protonation source such as formic acid to the
makeup solvent can be used to enhance ionization and increase
sensitivity
 Atmospheric Pressure Photo Ionization (APPI)
– Ultraviolet light produced from a krypton lamp ionizes gas phase
analytes and dopants leading to gas-phase reactions
– Therefore, the addition of a dopant such as toluene to the makeup
solvent can enable and enhance ionization
 Atmospheric Pressure Chemical Ionization (APCI)
– The solvent present, from both the co-solvent and the makeup
solvents, acts as chemical ionization reagent gas in order to ionize
the sample

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Interfacing UPC2 with MS detection
MS conditions
Mass Spectrometer Xevo TQD
Ionization mode APCI APPI ESI
Corona 3.0 µA N/A N/A
Capillary N/A N/A 5.00 kV
APCI probe temp. 300 o
C 300 o
C N/A
Source temp. 150 o
C
Repeller N/A 0.50 kV N/A
Desolvation gas 800 o
C 600 o
C 600 o
C
Cone gas 0 L/hr
Acquisition Multiple Reaction Monitoring (MRM)
MS splitter conditions
Makeup pump Waters 515
Solvent Methanol Methanol + 10% toluene Methanol + 1% formic acid
Flow 0.4 mL/min

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Interfacing UPC2 with MS detection
 Tuning:
– 2 ppm standards in methanol
– The compounds were tuned in APCI
– MRM, transitions, cone and collision energy values optimized using Xevo TQD fluidics
only:
Compound CAS Mol formula
Molecular
weight
APCI
(+/-)
Cone
Voltage (V)
MRM
Transition
(m/z)
Collision
energy
4-(Octyloxy)benzoic acid 2493-84-7 C15H22O3 250.33 + 40
251.2 > 121.0* 20
251.2 > 139.0 20
4,4′-Azoxyanisole-d14 39750-11-3 C14H13DN2O3 272.36 + 30
273.2 > 114.1* 25
273.2 > 142.1 20
4-Butoxybenzoic acid 1498-96-0 C11H14O3 194.23 + 30
195.0 > 95.0* 20
195.0 > 121.0 20
4-Butylbenzoic acid 20651-71-2 C11H14O2 178.23 + 30
179.1 > 123.0 10
179.1 > 161.0* 15
4-Cyanobenzoic acid 619-65-8 C8H5NO2 147.13 - 25 146 > 102.0* 15
4-Octylbenzoic acid 3575-31-3 C15H22O2 234.33 + 35
235.0 > 123.0* 15
235.0 > 217.0 20
*refers to the quantification transition

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Interfacing UPC2 with MS detection
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4-Octylbenzoic acid
4-(Octyloxy)benzoic acid
4-Butoxybenzoic acid
4-Butylbenzoic acid
4-Cyanobenzoic acid
4,4′-Azoxyanisole-d14

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Conclusion
 Separation by UPC2 is an ideal alternative to both HPLC
and GC analysis
 UPC2 with PDA detection offers a cost effective and
efficient impurity profiling and compositional analysis
 UPC2 with MS detection:
– greater selectivity and specificity
– orthogonal technique
 Many business and analytical benefits, when compared
HPLC for the analysis of liquid crystal intermediate
compounds

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 [Click Here] – Link to document

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