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Cameron George Technical Support Engineer 26 April 2001 PowerPoint Presentation
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Cameron George Technical Support Engineer 26 April 2001

Cameron George Technical Support Engineer 26 April 2001

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Cameron George Technical Support Engineer 26 April 2001

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  1. Cameron GeorgeTechnical Support Engineer26 April 2001 An Optimized Dual Column System for the Analysis of Chlorinated Pesticides, Herbicides and PCBs by GC-ECD

  2. Cameron GeorgeApplications ChemistApril 26, 2001 An Optimized Dual Column System for the Analysis of Chlorinated Pesticides, Herbicides and PCBs by GC-ECD 11:00 a.m. ESTTelephone Number: 904-779-4715Chair Person: Lisa Lloyd

  3. Cameron GeorgeApplications ChemistApril 26, 2001 An Optimized Dual Column System for the Analysis of Chlorinated Pesticides, Herbicides and PCBs by GC-ECD 11:00 a.m. ESTTelephone Number: 904-779-4715Chair Person: Lisa Lloyd Starts in Five Minutes

  4. Cameron GeorgeApplications ChemistApril 26, 2001 An Optimized Dual Column System for the Analysis of Chlorinated Pesticides, Herbicides and PCBs by GC-ECD 11:00 a.m. ESTTelephone Number: 904-779-4715Chair Person: Lisa Lloyd Starts in One Minute

  5. AREAS OF FOCUS • Injector • Detector • Column (including guard column)

  6. TRACE ANALYSIS INJECTION TECHNIQUES5-2000 pg On-Column • Megabore direct • Splitless • PTV • On-Column (cold & hot) • Large volume

  7. SAMPLE INJECTIONGoals • Introduce sample into the column • Reproducible • No efficiency losses • Representative of sample

  8. INFLUENCE OF INJECTION EFFICIENCY Short Concentrated Solute Bands Long Diffuse Same column, same chromatographic conditions

  9. FIRST, SOME BASIC DEFINITIONS: Regarding Inlets • Backflash • Discrimination

  10. A FEW WORDS ABOUT BACKFLASH Definition: In a vaporization injection, a phenomenon wherein a portion of the sample expands beyond the boundary of the injection port liner towards the septum face and incoming gas line

  11. BACKFLASHEffects • Ghost peaks • Erratic quantitation • Poor accuracy

  12. BACKFLASHCauses • Highly volatile solvent • Excessive inlet temperature • Excessive injection volume • Small liner volume

  13. BACKFLASHPreventative Measures • Lower inlet temperature • Less volatile solvent • 1-2 µL injection volume • Chambered liner • Using pulsed split or pulsed splitless

  14. Yes NO!!! INJECTION PORT LINERSSplitless

  15. INLET DISCRIMINATION • Injected sample  Sample into the column • Due to compound volatility differences • Higher volatility = More into the column

  16. INLET DISCRIMINATIONIn Pesticide Analyses Generally inlet discrimination is not a concern for pesticide analyses when utilizing appropriate GC inlets such as Splitless, Pulsed Splitless and PTV

  17. OTHER INLET CONSIDERATIONS • Silylation • Using glass wool • Cleaning and reusing liners

  18. Semivolatile vs nonvolatile Worst offenders Sample prep A FEW WORDS ABOUT RESIDUES

  19. GUARD COLUMNSUse 0.53mm Or 0.32mm ID Deactivated Tubing • Fit all inlets • Enhanced deposition of residues • Easy to work with • Minimum 1 meter

  20. GUARD COLUMNTraps non-volatile sample residues Injector Detector DeactivatedFused SilicaTubing Column Union Usually 1-5 meters long and same diameter as the column

  21. COLUMN CONNECTORSThermal Mass, Inertness, Seal Integrity • Stainless steel • VU-Tight • Press-fits • Integral guard columns (Duraguard)

  22. Let’s Be Sensitive ANALYTE DETECTION

  23. SENSITIVITYAnalytical Definition The minimum amount of an analyte that can still be confidently identified as a peak (S/N > 4)

  24. SENSITIVITYAnalytical Definition • Detector Sensitivity: No sample influence (standard) • Method Sensitivity: Matrix influence (sample)

  25. RESPONSE TO A CONSTANT ANALYTE AMOUNT2 Cases S x S N N "Normal" response "Improved" response 1. High noise, detector, background2. Absorption, breakdown of analyte3. Sample prep losses 1. High quality circuit components and reagents2. Inertness3. Method optimization

  26. HP 6890 Series Micro-ECD Design

  27. Standard Micro-ECD < 0.040 < 0.008 MDL pg/sec lindane Dynamic range > 10^4 > 5 x 10^5 lindane Linear range lindane no spec. > 5 x 10^4 Linear Range, pg (ppb) CLP pesticides 5 - 80 1 - 500 Maximum data rate Hz 5 50 Comparison of HP 6890 ECDs

  28. Break Number 1 For Questions and Answers Press *1 on Your Phone to Ask a Question

  29. LETS GET TO THE CHROMATOGRAPHY

  30. WHAT EXACTLY ARE WE TRYING TO ACHIEVE • The best resolution possible • Minimize analysis time • Get MDLs as low as possible

  31. RESOLUTION VS SEPARATION • Separation: Time between the 2 peaks • Resolution: Describes how well 2 peaks are separated with regard to their widths

  32. WHICH PAIR OF SOLUTES HAVE BETTER SEPARATION? 11.24 12.72 (tm = 95.5) 10 11 12 13 14 15 11.14 11.61 (tm = 95.5) 10 11 12 13 14 15

  33. RESOLUTION VS SEPARATION Better Separation a= 1.17 Rs = 0.6 11.24 12.72 K = 6.07 K = 7.00 10 11 12 13 14 15 11.14 11.61 Better Resolution a= 1.05 Rs = 2.7 K = 6.00 K = 6.30 10 11 12 13 14 15

  34. RESOLUTION AND ANALYSIS TIME • Improving resolution often results in the opportunity to shorten analysis times • Many variables can affect resolution

  35. N = ¦ (L, rc) k = ¦(T, df, rc) a =¦(T, phase) RESOLUTION N k a - 1 æ ö æ ö R = ç ÷ ç ÷ s è ø è ø 4 k + 1 a

  36. IMPROVING RESOLUTION Retention The column must provide sufficient retention of the early eluting compounds without excessive retention of the late eluting compounds

  37. IMPROVING RESOLUTIONFilm Thickness Decreasing Film Thickness Results In: • Increased efficiency • Elution of analytes at lower temperatures • Decreased analysis time • Decreased bleed interference • Increased column activity • Decreased capacity

  38. IMPROVING RESOLUTIONEfficiency • High column efficiency is necessary to resolve large numbers of compounds • Improperly operated injectors and/or improperly optimized carrier gas can result in efficiency losses

  39. IMPROVING RESOLUTIONColumn Length Increasing Column Length Results In: • Increased efficiency • Increased analysis time • Increased bleed • Big increase in cost

  40. IMPROVING RESOLUTION Column Inner Diameter Decreasing Column Inner Diameter Results In: • Increased efficiency • Increased head pressure • Decreased capacity • Decreased carrier gas flow rates

  41. IMPROVING RESOLUTION Stationary Phase • Stationary phase selectivity has the largest impact on separation, thus resolution • Optimization of stationary phase selectivity should be approached cautiously

  42. For Years Environmental Laboratories Have Suffered With Pesticide Analyses Using Non-Optimal Stationary Phases

  43. TRADITIONAL STATIONARY PHASES • 5% Phenyl-methylpolysiloxane • 35-50% Phenyl-methylpolysiloxane • Trifluoropropyl-methylpolysiloxane • 14% Cyanopropylphenyl-methylpolysiloxane

  44. PROBLEMS WITH TRADITIONAL PHASES • Long analysis times (Over 30 minutes!) • High bleed resulting in decreased sensitivity • Poor resolution and confirmation capabilities • Poor inertness of some phases

  45. Coelution of peaks 10 & 11 608 Type Phase 1701 Type Phase Poor peak shape for Endrin aldehyde High Bleed at 280°C 40min 0 10 20 30 40 0 10 20 30 40 Time (min.) Time (min.) TRADITIONAL PESTICIDE COLUMNS

  46. EFFORTS TO IMPROVE PESTICIDE ANALYSES Application Specific Phases Stationary phases designed with a primary focus placed upon maximizing separation () for a specific group of target analytes

  47. CH H CF C 3 4 2 3 Si Si O O CH CH n 3 m 3 H CF C 4 2 3 Si Si O O CH n m 3 APPLICATION SPECIFIC PHASES Common CLP Pesticide Phases Phase 1 Trifluoropropyl-dimethylpolysiloxane Phase 2 Trifluoropropyl-diphenyl-dimethylpolysiloxane Dimethyl functionality of Phase 2 not shown

  48. EFFECT OF PHASE POLARITY Polarity Thermal Stability

  49. DRAWBACKS OF APPLICATION SPECIFIC PHASES • Limited thermal stability resulting in longer analysis times and hampered sensitivity • Excessive column conditioning times leading to increased column activity • Decreased column lifetimes

  50. PHASES DESIGNED WITH OPTIMUM PERFORMANCE IN MINDArylene Phase Technology