the truth about sample prep
TRANSCRIPT
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XThe
TRUTHabout sample prep_
Jvercammwww.is-x.be
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Sample prep plays a vital role in virtually every
analytical procedure_
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Efficiency & of a measurement method are
quality primarily determined by sample
preparation_
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Sampling_ 6%
Analysis_ 6%
Data analysis_ 27%
Sample prep_ 61%
Duration sample prep is often tedious and
time-consuming_
61%
6%
6%
27%
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Error sources sample prep is prime contributor_
Contamination_ 4%
Integration_ 6%
Injection_ 6%
Chromatography_7%
Instrument_ 8%
Calibration_ 8%
Columns_ 11%
Operator_ 19%
Sample prep_ 30%
30%
8%
8%
6%
7%
6%
4%11%
19%
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What can we
do about it…?
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Adagium the best prep is no prep_
What you want is what you get_
(Unfortunately)
• Dilute-and-shoot_
• Generic methods_
• Less selective methods_
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New hardware to address this issue_
Powerful 'black box mass spectrometers_
• Single quad and ion trap_
• Triple quad_
• Q/TOF, orbitrap_
• TOF/TOF
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Reality check sample prep remains mandatory
Selective detection does not tackle injection issues_
• GC/MS and inlet contamination_
• LC/MS and ion suppression_
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Nobody likes sample prep…
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Solutions are ubiquitous_
Scientific literature, discussion forums and application
notes from manufacturers.
Can you still find your way in this maze…?
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Recycling is commonplace in analytical
chemistry publications_
Unique and original publications are hard to find in the
vast and continuously growing amount of data.
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SPE SPME SDME SBSE
Num
ber
of
pu
blic
ati
on
s
0.0
100,000.0
200,000.0
Example ScienceDirect @ Jan 2011_
x 10
180.000
80.000
12.000 10.000
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Be vigilant…
vig·i·lant ”vij-uh-luh nt”
1. keenly watchful to detect danger; wary 2. ever awake and alert; sleeplessly watchful
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Classify on,
• Compound volatility_
• Polarity & reactivity_
• Intended concentration level_
1Know your target compounds_
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Compound volatility,
• Permanent gases_
• Volatile compounds_
• Semi-volatile compounds_
• Non-volatile compounds_
Know your target compounds_
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Polarity & reactivity,
• Apolar
• Semi-polar
• Polar acidic
• Polar basic
Know your target compounds_
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Classify on concentration level,
• percentage level_
• parts-per-million level_
• parts-per-billion level_
• parts-per-trillion level, 1 s in 32.000 year_
Know your target compounds_
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2Know your matrix_
Classify on,
• Similarity to targets_
• Overall complexity_
• MW distribution_
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Know your matrix_
Unsimilarity is the basis of clean-up,
• Exploit orthogonality_
• Use normal phase_
• Ionisable at different pH_
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Know your matrix_
Combined complexity & similarity,
• Good chromatography_
• Heart-cut GC_
• Backflush_
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Know your matrix_
High molecular weight interferences,
• Matrix solid phase dispersion_
• Backflush_
• Gel permeation_
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3Know your techniques_
Combine information,
• Direct injection_
• Preconcentration_
• Extraction_
• Derivatisation_
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Know your techniques_
Permanent gases with GC,
• High levels, direct injection_
• Trace levels, air server_
• Complex matrix, chromatography_
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Know your techniques_
Volatile components with GC,
• High levels, static headspace_
• Trace levels, thermal desorption_
ITEX_
• Complex matrix, multiple headspace_
thermal extraction_
pyrolysis_
• Polar compounds, derivatisation_
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Know your techniques_
Semi-volatile components with GC,
• High levels, LLE, SPE
• Trace levels, evaporate solvent_
MEPS_
• Complex matrix, clean-up_
• Polar compounds, derivatisation_
• High boilers, on-column injection_
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Know your techniques_
Non-volatile components with LC,
• GC is possible, derivatisation_
• High levels direct injection_
• Trace levels, SPE_
• Complex matrix, clean-up_
• Polarity, LC mode_
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4Use smart calibration solutions_
Exploit the power of MS,
• Isotope dilution analysis_
• Internal standards prior to prep_
• Surrogates prior to injection_
• Standard addition for complex matrices_
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5Take your time & evaluate_
Developing a sample prep method is often challenging
and quite frustrating. Immediate success is highly
uncertain, even for experienced users..
Take your time and carefully assess all possibilities.
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But what about sorption…?
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Definition of sorptive extraction
Family of miniature extraction techniques that use
polydimethyl siloxane or polyacrylate as enrichment
phase_
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Applications of sorptive extraction
Sorptive extractions are particularly popular in scientific
literature. Applications include,
• Headspace extraction_
• Direct extraction_
• In-situ derivatisation_
• Passive sampling_
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Typical configurations
Several techiques have been introduced,
• solid phase microextraction_
• stir bar sorptive extraction_
• solid phase dynamic extraction_
• single drop microextraction_
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Advantages of sorptive extraction
Applied configurations are simple to use and eliminate
extraction solvents. After sampling, trapped components
are released by heat, without partial losses (sensitivity)_
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Some remarks to take into account
Sorptive extraction uses equilibrium extraction,
• Takes some time to complete
• Non-exhaustive extraction
• Equilibrium depends on matrix
Preserve for clean matrices !
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Comparison fiber versus stir bar
Use a mixed mode SPME fiber to attain sensitivities
superior to SBSE,
• Fully automated_
• In a fraction of time_
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Concluding remarks
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Don’t forget these things…
• Nobody likes sample prep_
• Neglecting sample prep is riskful_
• Be vigilante_
• Know your business_
• Take your time_
Good luck !