Gas Chromatography and HPLC Flashcards
GC is simalar to HPLC except for (3)
- mobile phase _____
_ p______ instead of solvent pump
- _____ samples
Mobile phase is gas
- analytes don’t interact with mobile phase
pressurized has instead of solvent pumps
works with volatile samples
Sample Injection:
Samples are typically injected using a ____ μL _____.
Goes through a _____ ____ .
Use a syringe. Air Solvent Air Sample Air
Air _____ sample and solvent from ____ or ____ too quickly.
10, syringes
rubber septum
prevents mixing, evaporating
Carrier gas
_____ is the most common and compatible with most detectors.
Others used include ____ and _____.
Nitrogen gives best ______ ______ and but helium gives better ______.
Hydrogen is probably the ____, but explosive, so there’s that.
Helium
nitrogen, hydrogen
detection limits, resolution
best
A small column that goes right before the analytical column.
Accumulates _____ substances that would _____ the main column.
Can be ____ periodically.
About _____ meters in length.
Gaurd column
nonvolatile, contaminate
trimmed
3-10
GC columns are either ____ or ____ tubular.
Open tubular offer:
_____ resolution
_____ analysis time
____ sensitivity
Packed columns provide:
_____ sample capacity but _____ peaks
____ retention times
____ resolution
packed, open
higher resolution
shorter
greater
greater, broaden
longer
less
GC columns have different types of open tubular capillary column:
- A thin film of liquid
- A thick layer of a porous solid SP
- A thin film of liquid coated solid packing material
- Wall coated open tubular (WCOT)
- Porous layer open tubular (PLOT)
- Support coated open tubular (SCOT)
GC: Temperature Programming
The temperature of the column is raised throughout the_______
Increase analyte ____ pressure
_____ retention times of late-eluting components.
Usually a ____ or ____ change.
Typically end with a _____ temperature for a few minutes to burn everything off.
“_____”
Have to wait for it to _____ back down before the ____ injection.
separation
vapor
decrease
stepwive, linear
high
baking
cool, next
Qualitative: Typically have one or two peaks you’re comparing to a library of spectra.
Quantitative: Measures peak areas and all dimensions. Hint: thermal \_\_\_\_\_ flame \_\_\_\_ electron \_\_\_\_\_
Mass spec
thermal conductivity
flame ionization
electron capture
Detectors:
Simple and universal, responds to all analytes.
Useful for packed columns.
Better detection than thermal conductivity.
Sensitive to halogens, conjugated carbonyls, nitriles, nitro compounds, and organometallic compounds.
Insensitive to hydrocarbons, alcohols, and ketones.
thermal conductivty
flame ionization
electron capture
Uses high pressure to force solvent through closed columns contain fine particles that give high-resolution separations.
non volatile analytes
HPLC
Injection:
Pumps produce a ____ flow through the system.
Can have four ______ solvents set up to a _____ and you choose which one(s) you want.
Injection valves have _____ sample loops.
Hold a fixed volume (2-1000 uL).
steady
different, pump
interchangleable
Solvents:
Solvent molecules will compete with solute molecules for sites on the SP.
Elution occurs when solvent ____ solute form the SP.
Two Types of Method
displaces
isocratic and gradient
Single solvent or constant solvent mixture.
Increasing amounts of one solvent over time (B). Reducing the amount of the first solvent (A).
Typical solvent used:
A:
B:
isocratic
Gradient
A: methonal
B: acetonitrle
what type of solvent to use
pure solvents
What type of columns to used?
Packed columns only
The efficiency of a packed column _____ as the size of the stationary phase particles _______.
\_\_\_\_\_\_ particles are best. van Deemter proves this. They provide more universal flow through the column. Reduces diffusion and multipath. Allow higher pressure. Lower detection limit. Higher plate number.
increases, decreases
smaller
Columns:
Normal
Reverse
Polar SP
Nonpolar MP
Nonpolar SP
polar MB
Normal Phase:
use ____ analysts
the SP is ____ polar than the MP
- _____ occurs based on polarity
SP is typically packed with ____ or a ___-___ support with amino, diol, or cyano functional groups bonded.
polar
more
- paritioning
silica, silica-based
Normal phase
MP may be a gradient that starts _____ and becomes more _____ over time.
____ polar components in your sample will ______ first.
nonpolar, polar
least, elute
Reverse Phase:
use for _____ analytes
The MP is ____ polar than the SP.
The ____ polar analytes will elute ___.
SP is typically packed with ___ or octadecyl (___)_____ chain bonded to silica beads.
non polar
more
least, last
octane, C18
Reverse phase:
MP can start _____ and _____ in polarity over time.
Many times, it’s _______ water.
Go from methanol or acetonitrile to an _____ of a organic solvent.
polar, decrease
decreasing
increase
