790 likes | 1.04k Views
Cameron George Technical Support Engineer 26 April 2001. An Optimized Dual Column System for the Analysis of Chlorinated Pesticides, Herbicides and PCBs by GC-ECD. Cameron George Applications Chemist April 26, 2001.
E N D
Cameron GeorgeTechnical Support Engineer26 April 2001 An Optimized Dual Column System for the Analysis of Chlorinated Pesticides, Herbicides and PCBs by GC-ECD
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
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
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
AREAS OF FOCUS • Injector • Detector • Column (including guard column)
TRACE ANALYSIS INJECTION TECHNIQUES5-2000 pg On-Column • Megabore direct • Splitless • PTV • On-Column (cold & hot) • Large volume
SAMPLE INJECTIONGoals • Introduce sample into the column • Reproducible • No efficiency losses • Representative of sample
INFLUENCE OF INJECTION EFFICIENCY Short Concentrated Solute Bands Long Diffuse Same column, same chromatographic conditions
FIRST, SOME BASIC DEFINITIONS: Regarding Inlets • Backflash • Discrimination
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
BACKFLASHEffects • Ghost peaks • Erratic quantitation • Poor accuracy
BACKFLASHCauses • Highly volatile solvent • Excessive inlet temperature • Excessive injection volume • Small liner volume
BACKFLASHPreventative Measures • Lower inlet temperature • Less volatile solvent • 1-2 µL injection volume • Chambered liner • Using pulsed split or pulsed splitless
Yes NO!!! INJECTION PORT LINERSSplitless
INLET DISCRIMINATION • Injected sample Sample into the column • Due to compound volatility differences • Higher volatility = More into the column
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
OTHER INLET CONSIDERATIONS • Silylation • Using glass wool • Cleaning and reusing liners
Semivolatile vs nonvolatile Worst offenders Sample prep A FEW WORDS ABOUT RESIDUES
GUARD COLUMNSUse 0.53mm Or 0.32mm ID Deactivated Tubing • Fit all inlets • Enhanced deposition of residues • Easy to work with • Minimum 1 meter
GUARD COLUMNTraps non-volatile sample residues Injector Detector DeactivatedFused SilicaTubing Column Union Usually 1-5 meters long and same diameter as the column
COLUMN CONNECTORSThermal Mass, Inertness, Seal Integrity • Stainless steel • VU-Tight • Press-fits • Integral guard columns (Duraguard)
Let’s Be Sensitive ANALYTE DETECTION
SENSITIVITYAnalytical Definition The minimum amount of an analyte that can still be confidently identified as a peak (S/N > 4)
SENSITIVITYAnalytical Definition • Detector Sensitivity: No sample influence (standard) • Method Sensitivity: Matrix influence (sample)
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
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
Break Number 1 For Questions and Answers Press *1 on Your Phone to Ask a Question
WHAT EXACTLY ARE WE TRYING TO ACHIEVE • The best resolution possible • Minimize analysis time • Get MDLs as low as possible
RESOLUTION VS SEPARATION • Separation: Time between the 2 peaks • Resolution: Describes how well 2 peaks are separated with regard to their widths
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
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
RESOLUTION AND ANALYSIS TIME • Improving resolution often results in the opportunity to shorten analysis times • Many variables can affect resolution
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
IMPROVING RESOLUTION Retention The column must provide sufficient retention of the early eluting compounds without excessive retention of the late eluting compounds
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
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
IMPROVING RESOLUTIONColumn Length Increasing Column Length Results In: • Increased efficiency • Increased analysis time • Increased bleed • Big increase in cost
IMPROVING RESOLUTION Column Inner Diameter Decreasing Column Inner Diameter Results In: • Increased efficiency • Increased head pressure • Decreased capacity • Decreased carrier gas flow rates
IMPROVING RESOLUTION Stationary Phase • Stationary phase selectivity has the largest impact on separation, thus resolution • Optimization of stationary phase selectivity should be approached cautiously
For Years Environmental Laboratories Have Suffered With Pesticide Analyses Using Non-Optimal Stationary Phases
TRADITIONAL STATIONARY PHASES • 5% Phenyl-methylpolysiloxane • 35-50% Phenyl-methylpolysiloxane • Trifluoropropyl-methylpolysiloxane • 14% Cyanopropylphenyl-methylpolysiloxane
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
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
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
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
EFFECT OF PHASE POLARITY Polarity Thermal Stability
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
PHASES DESIGNED WITH OPTIMUM PERFORMANCE IN MINDArylene Phase Technology