A Comparison of GC-Inlets for Simulated Distillation Analyses

Transcription

1 A Comparison of GC-Inlets for Simulated Distillation Analyses David Grudoski wemeasureit Albany,CA 1

2 A Comparison of GC-Inlets for Simulated Distillation Analyses Abstract: 2013 Gulf Coast Conference,Galveston Texas Presented by David Grudoski Simulated Distillation Methods allow for the use of either Programmable Temperature or Cool-On-Column inlets. The performance of each inlet type for ASTM D2887, D7500 and D7169 analyses is examined with a focus on the operational parameters required for quality analyses.

3 The Purpose of the GC Inlet in SimDis Analysis The function of the inlet is to allow the introduction of a liquid sample to the column of the gas chromatograph. Ideally the inlet provides a complete transfer of the injected sample to the column.

4 Principles to Keep in Mind Daltons Law of Partial Pressures Raoult s Law Bernoulli effect The Joule-Thomson Effect

5 Raoult s Law Raoult's law the partial pressure of a component in an ideal solution is equal to the vapor pressure of the pure component multiplied by its mole fraction The important consequence of Raoult's law is that the vapor above a boiling mixture is enriched in the lower boiling component.

6 Bernoulli Effect When the speed of horizontal flow through a fluid increases, the pressure decreases A common example used to explain the Bernoulli effect is the flow of fluid through a pipe. If the fluid is moving uniformly through the pipe, then the only forces acting on the fluid are its own weight and the pressure of the fluid itself. Now, if the pipe narrows, the fluid must speed up, because the same amount of fluid is traveling through a smaller space. However, if the fluid is moving uniformly, and the weight has not changed, then the only way in which the fluid will move faster is if the pressure behind the fluid is greater than the pressure in front. Thus, the pressure must decrease as the speed increases. *Info from

7 The Joule-Thomson Effect The Joule-Thomson (JT) effect is a thermodynamic process that occurs when a fluid expands from high pressure to low pressure at constant enthalpy. Such a process can be approximated in the real world by expanding a fluid from high pressure to low pressure across a valve. Under the right conditions, this can cause cooling of the fluid. At room temperature, all gases except hydrogen,helium and neon cool upon expansion by the Joule Thomson process.* *Info from Cryogenic Society of America

8 The Practical Consequences As the sample is ejected from the syringe needle into the inlet, the sample expands and cools due to the Bernouli effect and the Joule Thomson effect. With a straight thru liner; the sample components that boil below the temperature of the inlet would distribute in the vapor phase according to Raoults Law and pass onto the column. The liquid material remaining in the inlet would also vaporize over time also according to Raoults Law.

9 SimDis Methods: Requirements Hardware D2887 C3-C44 D7500 C7-C100 D7169 C1-C110 Inlet SSL,PTV,COC PTV,COC PTV,COC Cryo Optional Optional Required Column 10m,0.53 mm 3.0u 380 max Oven -20:350 40:350 10m,0.53 mm 5 m,0.53 mm 0.15u 400/435 max 0.53 mm 10m 0.15u 5 m 0.15u 400/435 max 40:400-20:425 Solvent Optional Optional Often required Optional Often required

10 SimDis Requirements Setup D2887 D7500 D % Sample Elution Complete Elution Complete Elution Not Required Blank Yes Yes Yes Calibration Yes Yes Yes Reference Optional Optional Required for % Recovery Calc Sample Yes Yes Yes

11 ASTM SimDis Requirements Column starting temperatures below ambient will be required if samples with IBPs of less than 93 C (200 F) are to be analyzed. The sample inlet system must be capable of operating continuously at a temperature equivalent to the maximum column temperature employed, or provide for on-column injection with some means of programming the entire column, including the point of sample introduction, up to the maximum temperature required. Connection of the column to the sample inlet system must be such that no temperature below the column temperature exists. Page 11

12 Challenges For High Temperature SimDis Neat injections are problematic. Increasing Boiling Point usually results in increasing viscosity of the sample and often requires dilution with a solvent. Sample boiling ranges can be narrow or very broad with tailing distributions Page 12

13 Challenges For High Temperature SimDis Cross contamination of samples and solvent can occur if the syringe is not completely washed of sample residue Any region of low or no flow in the inlet stream can deposit high boiling components which can subsequently elute either as peaks or bleed. Resulting in poor quality blanks and memory effects Page 13

14 Challenges For High Temperature SimDis Cold spots in the injection flow path can result in memory effects of the inlet where sample residuals from prior runs elute in later injections, especially for samples diluted in a solvent Back diffusion from the split vent line and or purge vent line can also appear in analyses, especially when operating at high oven and inlet temperatures Page 14

15 Inlets used for Simulated Distillation Split/Splitless (SSL) Cool-On-Column (COC) Programmed Temperature Vaporizing (PTV) Multi-Mode Inlet (MMI) Cold/Hot Split Cold/Hot Splitless Direct Injection (COC) Solvent Vent

16 COC Advantages/Challenges Advantages Minimal discrimination of light ends Challenges: Injection reproducability Retention Gap/Column Connection Union Bleed of High Boiling material from Retention Gap Page 16

17 COC Injection Port

18 COC Flow Diagram

19 COC Inlet Page 19

20 COC Inlet Page 20

21 COC Inlet (Neat Injection) Carbon # % Conc Difference Mean REL STDEV Run 1 Run 2 Run 3 Run 4 C % C % C % C % C % C % C % C % C % C % C % C % C % Page 21

22 PTV Advantages/Challenges Advantages Minimal discrimination of light ends Rapid Heating and Cooling of Inlet-Reduces Cycle Time Self Cleaning Inlet Challenges: Injection Volume limits Memory effects from vent/purge lines Page 22

23 PTV Inlet (circa 1990) Conventional vaporizing injectors are designed with high mass injector bodies and heating blocks to control temperature for large volume inserts. These inlets change temperature slowly, contributing to their temperature stability.

24 PTV Inlet (modern era) Modern vaporizing injectors are designed with low mass injector bodies which allow very rapid heating and cooling of the inlet and permit selective vaporization of the sample in the body of the inlet liner. This allows a pre-separation of the sample prior to introduction to the GC column which can result in a more efficient transfer of the sample to the GC column.

25 PTV Inlet Septum Carrier Gas Cooling Gas Heating Coil Septum Purge Seal Glass Wool / Packing Insert (vaporization Chamber) Cooling Gas Capillary Column Split Line Page 25

26 PTV Inlet Page 26

27 PTV Inlet Page 27

28 PTV Inlet Carbon # % Conc Difference Mean REL STDEV Run 1 Run 2 Run 3 Run 4 C % C % C % C % C % C % C % C % C % C % C % C % C % Page 28

29 MMI Advantages/Challenges Advantages Most versatile for injection and sample type Rapid Heating and Cooling of Inlet-Reduces Cycle Time Self Cleaning Inlet Challenges: Parameter setpoints can be complex to set Injection Volume limits Memory effects from vent/purge lines Page 29

30 Agilent Multi Mode Inlet Operational Modes: Cold/Hot Split Cold/Hot Splitless Direct Injection (COC) Solvent Vent

31 MMI Schematic

32 MMI Parameters Operational Mode: Split, Cold Splitless, Injection Volume Hot Splitless, Solvent Vent, Direct Septum Purge Purge Vent Time MMI Temperature Profile

33 MMI Inlet Liners Single Taper with Glass Wool Straight Through Narrow ID MMI Cool-on-Column Inlet Adapter Page 33

34 MMI Inlet (Split Mode 4.5% Solution) Carbon # % Conc Difference Mean REL STDEV Run 1 Run 2 Run 3 Run 4 C % C % C % C % C % C % C % C % C % C % C % C % C % MMI Split Mode 70:50:150:200:430 4:1 Split Page 34

35 MMI Inlet (Hot Splitless Mode) Carbon # % Conc Difference Mean %REL STDEV Run 1 Run 2 Run 3 Run 4 C % C % C % C % C % C % C % C % C % C % C % C % C % Hot Splitless Mode 150:0 min:720: ml purge flow 0.5 min 0.1ul Page 35

36 Inlets Compared (Peak Area %) Means Compared Carbon # PTV COC MMI Split MMI Hot Splitless C C C C C C C C C C C C C Page 36

37 Inlets Compared (Relative Standard Deviation) Relative Standard Deviation Carbon # PTV COC MMI Split MMI Hot Splitless C C C C C C C C C C C C C Page 37

38 Agilent SimDis Calculation Page 38

39 Agilent SimDis Calculation Page 39

40 Agilent SimDis Report Page 40

41 MMI Inlet SimDis Yield % Off Yield % Mean %RelSTDEV Run 1 Run 2 Run 3 Run 4 IBP: 0.5% % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % FBP: 99.5% % Page 41

42 SimDis Yield % Off Temp Compared (Mean Temp) Yield % PTV Mean COC Mean MMI Mean IBP: 0.5% % % % % % % % % % % % % % % % % % % % FBP: 99.5% Page 42

43 SimDis Yield % Off Temp Compared (% Rel Std Dev) Yield % PTV %Rel StDev COC %Rel StDev MMI %Rel StDev IBP: 0.5% 0.3% 0.3% 0.0% 5.00% 0.3% 0.0% 0.0% 10.00% 0.4% 0.2% 0.0% 15.00% 0.2% 0.2% 0.2% 20.00% 0.2% 6.2% 0.0% 25.00% 0.2% 0.1% 0.2% 30.00% 0.0% 0.1% 0.1% 35.00% 0.1% 0.1% 0.0% 40.00% 0.1% 3.7% 0.1% 45.00% 0.1% 0.1% 0.0% 50.00% 0.1% 0.1% 0.0% 55.00% 0.0% 0.1% 0.0% 60.00% 0.1% 0.1% 0.0% 65.00% 0.1% 2.2% 0.2% 70.00% 0.1% 0.1% 0.0% 75.00% 0.1% 0.0% 0.0% 80.00% 0.0% 0.1% 0.0% 85.00% 0.0% 0.1% 0.0% 90.00% 0.0% 0.1% 0.0% 95.00% 0.1% 0.1% 0.1% FBP: 99.5% 0.3% 0.1% 0.1% Page 43

44 Summary and Conclusion Each of the inlets discussed have advantages for specific sample types. All can reliably perform SimDis Analyses Page 44