instruments, Houston, Texas, USA) equipped with two 200 μL loops was
employed for hyphenation of HT-HPLC and HT-SEC. The 8-port valve was
switched every 2 min in order to inject 200 μL of effluent from the HPLC into the
SEC column from the moment of injection in the HPLC column (50 μL injection
loop). The 2D-LC system was handled with software provided by Polymer Char
(Valencia, Spain). The data acquisition and evaluation was performed by
WinGPC-Software v. 7.0 (Polymer Standards Service, Mainz, Germany).
• Columns. Chromatograph 1: Hypercarb column (Thermo Scientific, Dreieich,
Germany) packed with porous graphite particles with the following parameters:
column size 250 mm  4.6 mm i.d., average particle size 5 μm, surface area
120 m
2 /g, average pore size 250 A ˚ . Chromatograph 2: PL Rapide H,
150 mm  7.5 mm (Polymer Laboratories, Church Stretton, England).
• Mobile phase. Chromatograph 1: linear gradient 1-decanol to TCB starting with
100 % of 1-decanol for 40 min, the volume fraction of TCB was linearly
increased to 100 % within 80 min and then held constant for 80 min. The flow
rate was 0.1 mL/min. Chromatograph 2: TCB with a flow rate of 2.5 mL/min.
• Detectors. ELSD PL-ELS 1000 (Polymer Laboratories, Church Stretton,
England). The following parameters were set on the ELSD: air flow rate 1.5 L/
min, nebulizer temperature 160
C, evaporator temperature 260
C.
• Column temperature. 160
C.
• Sample concentration. 2–3 mg/mL. All samples were dissolved in 1-decanol.
• Injection volume. 50 μL (first dimension).
3.4.1.4 Preparatory Investigations
The separation in the first dimension was conducted according to the method that
was published by Macko and Pasch [85] using Hypercarb as the stationary phase
and a solvent gradient of 1-decanol-TCB. The separation is according to tacticity of
PP and chemical composition, separating PP and PE. In preliminary investigations,
it has been found that iPP elutes in two peaks. The first peak elutes in decanol before
the start of the gradient while the second peak elutes with the solvent gradient. To
investigate this phenomenon in more detail, iPP samples with different molar
masses were analysed by HT-2D-LC; see Fig. 3.40.
The contour plots prove that in all cases the portion of iPP, which elutes in the
gradient, has a larger molar mass than the fraction that elutes in 1-decanol.
Moreover, the higher the molar mass of the injected iPP standard, the larger is the
fraction that elutes in the gradient. The standard with M w 350 kg/mol is almost
completely retained and elutes mostly with the gradient. At present it is not quite
clear what the reason for the elution behaviour is. This should be considered in
future investigations.
3.4.1.5 Measurement and Evaluation
The separation of a blend of iPP, sPP, aPP and PE is presented in Fig. 3.41. As
expected, all components are fully separated from each other. Their molar masses
are different, as is proven by the different elution volumes in the second dimension.
3.4 Two-Dimensional Liquid Chromatography
123
employed for hyphenation of HT-HPLC and HT-SEC. The 8-port valve was
switched every 2 min in order to inject 200 μL of effluent from the HPLC into the
SEC column from the moment of injection in the HPLC column (50 μL injection
loop). The 2D-LC system was handled with software provided by Polymer Char
(Valencia, Spain). The data acquisition and evaluation was performed by
WinGPC-Software v. 7.0 (Polymer Standards Service, Mainz, Germany).
• Columns. Chromatograph 1: Hypercarb column (Thermo Scientific, Dreieich,
Germany) packed with porous graphite particles with the following parameters:
column size 250 mm  4.6 mm i.d., average particle size 5 μm, surface area
120 m
2 /g, average pore size 250 A ˚ . Chromatograph 2: PL Rapide H,
150 mm  7.5 mm (Polymer Laboratories, Church Stretton, England).
• Mobile phase. Chromatograph 1: linear gradient 1-decanol to TCB starting with
100 % of 1-decanol for 40 min, the volume fraction of TCB was linearly
increased to 100 % within 80 min and then held constant for 80 min. The flow
rate was 0.1 mL/min. Chromatograph 2: TCB with a flow rate of 2.5 mL/min.
• Detectors. ELSD PL-ELS 1000 (Polymer Laboratories, Church Stretton,
England). The following parameters were set on the ELSD: air flow rate 1.5 L/
min, nebulizer temperature 160
C, evaporator temperature 260
C.
• Column temperature. 160
C.
• Sample concentration. 2–3 mg/mL. All samples were dissolved in 1-decanol.
• Injection volume. 50 μL (first dimension).
3.4.1.4 Preparatory Investigations
The separation in the first dimension was conducted according to the method that
was published by Macko and Pasch [85] using Hypercarb as the stationary phase
and a solvent gradient of 1-decanol-TCB. The separation is according to tacticity of
PP and chemical composition, separating PP and PE. In preliminary investigations,
it has been found that iPP elutes in two peaks. The first peak elutes in decanol before
the start of the gradient while the second peak elutes with the solvent gradient. To
investigate this phenomenon in more detail, iPP samples with different molar
masses were analysed by HT-2D-LC; see Fig. 3.40.
The contour plots prove that in all cases the portion of iPP, which elutes in the
gradient, has a larger molar mass than the fraction that elutes in 1-decanol.
Moreover, the higher the molar mass of the injected iPP standard, the larger is the
fraction that elutes in the gradient. The standard with M w 350 kg/mol is almost
completely retained and elutes mostly with the gradient. At present it is not quite
clear what the reason for the elution behaviour is. This should be considered in
future investigations.
3.4.1.5 Measurement and Evaluation
The separation of a blend of iPP, sPP, aPP and PE is presented in Fig. 3.41. As
expected, all components are fully separated from each other. Their molar masses
are different, as is proven by the different elution volumes in the second dimension.
3.4 Two-Dimensional Liquid Chromatography
123