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Method Optimization Series: Purge Parameters Selection Amy Nutter August, 2018
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Method Optimization Series: Purge Parameters Selection Amy Nutter - - PowerPoint PPT Presentation
Method Optimization Series: Purge Parameters Selection Amy Nutter - - PowerPoint PPT Presentation
Method Optimization Series: Purge Parameters Selection Amy Nutter August, 2018 1 Overview The fundamentals of purge parameters Purge gas Purge volume Purge flow rate and time In-vial vs. traditional Purge and trap 101: What
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Purge and trap 101: What is purge and Trap? ■ Purge and Trap is a technique used to improve the sensitivity of volatile samples beyond the capabilities
- f static headspace.
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Purge and trap 101: How does purge and Trap work? ■ Purge Equilibrium Theory
■ Compounds migrate out of a concentrated solution and into a dilute solution to reach equilibrium.
■ Purge and Trap
■ The headspace above the sample is constantly replaced with fresh gas, preventing equilibrium from being reached.
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Static Headspace VS Purge and Trap
Static Headspace Purge and Trap
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Basic Purge and Trap Set Up – Purge
Trap Gas Chromatograph Heated Transfer Line 6-port valve To Vent Carrier/Desorb Gas Purge Gas
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Method Parameters Of Purge and Trap ■ Trap selection ■ Sample volume ■ Purge Method (in-vial vs traditional) ■ Purge gas type and volume (time and flow rate) ■ Dry Purge (time and flow rate) ■ Desorb (time and GC flow rate)
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Method Parameters Of Purge and Trap ■ Trap selection ■ Sample volume ■ Purge Method (in-vial vs traditional) ■ Purge gas type and volume (time and flow rate) ■ Dry Purge (time and flow rate) ■ Desorb (time and GC flow rate)
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What is the Purge of Purge and Trap? ■ Process through which the VOCs are stripped out of the sample for analysis ■ Purging allows us to collect only the volatile portion
- f the sample, solid, liquid portions are retained in the
glassware and not transferred to GC inlet ■ Facilitates sample concentration without the use of expensive and/or toxic solvents
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Fundamentals of Purge Gas
■ Must be inert
■ Cannot react with VOCs or any other component of the sample, known or unknown
■ Cannot be combustible and/or unstable
■ H2 or O2
■ Must be free of VOCs
■ Cannot contribute to the total VOC sample collected, creating false positives and/or “dirty” blanks
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Purge Gas Selection
■ Helium
■ Traditional choice for superior inertness, stability and compatibility with carrier gas for GCMS ■ Is somewhat expensive and occasionally difficult to source
■ Nitrogen
■ Good alternative to Helium thanks to similar inertness and low cost/ability to use generators ■ Is a larger molecule which can have minor affect on purge efficiency and MS vacuum during desorb
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He to N2 Purge Gas Comparison – EPA 524.3/4 ■ P&T parameters
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Helium/Nitrogen
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He to N2 Purge Gas Comparison – EPA 524.3/4 ■ GC Parameters
■ 524.3
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He to N2 Purge Gas Comparison – EPA 524.3/4 ■ GC Parameters
■ 524.4
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Results - Gases
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Results - Midrange
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524.4 524.3
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Results – Late Eluters
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Purge Gas Conclusions ■ Method requirements were easily met with both purge gases ■ Excellent sensitivity was seen across all ranges of the chromatogram ■ This is due to sensitivity of modern MSDs as well as the use of Helium as the carrier gas
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Considerations of Purge Volume
■ Flow rate
■ Faster flow means more purge gas in the same length of time ■ Flow too aggressively, can cause pressure issues and/or push compounds too deeply into sorbent bed
■ Purge time
■ Longer times mean more purge gas ■ Purge too long, waste of purge gas and/or push compounds too deeply into sorbent bed
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Considerations of Purge Volume
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Purge Volume Comparison – EPA 524 – Parameters
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Purge Volume Comparison – EPA 524 – Data
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Purge Volume Comparison – EPA 524 – Data
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Purge Volume Comparison – EPA 524 – Data
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Purge Volume Comparison – EPA 524 – Data
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Purge Volume Comparison – EPA 524 – Data
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Purge Volume Comparison – EPA 524 – Data
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Purge Volume Comparison – EPA 524 – Conclusions
■ Purge time can be greatly reduced, resulting in more samples processed during a time period ■ Gases can be affected at higher purge flow rates ■ Heavier compounds can decrease with the shorter purge times ■ Staying within recommended 524.2 parameters – data should look great
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In-Vial vs. Traditional Purge – 8260 – Parameters
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In-Vial vs. Traditional Purge – 8260 – Parameters
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In-Vial vs. Traditional Purge – 8260 – Data
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In-Vial vs. Traditional Purge – 8260 – Data
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In-Vial vs. Traditional Purge – 8260 – Data
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In-Vial vs. Traditional Purge – 8260 – Data
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In-Vial vs. Traditional Purge – 8260 – Data
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In-Vial vs. Traditional Purge – 8260 – Data
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In Vial vs. Traditional Purge – 8260 – Conclusions
■ Method requirements were easily met with both In- Vial and Traditional purge ■ MDLs for In-Vial purge were slightly higher ■ Increased % Accuracy/Recovery for Traditional purge
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Thank You!
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Amy Nutter Amy.Nutter@Teledyne.com
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