Additive – acids, bases and other chemicals added to the co-solvent portion of the mobile phase to improve the chromatography
Back pressure – pressure after the column at the back pressure regulator, it is also the pressure set by the user to control system pressure
Back pressure regulator (BPR) – instrument module used in SFC to control the back pressure on the system at a user determined set point
Chiral – a compound is considered chiral if it has one or more chiral centers resulting in optical isomers or enantiomers that are “mirror images” of each other
Chiral center – typically a carbon (C) atom within a molecule that has four different bonded functional groups
Chiral columns – specific column chemistries required to separate optical isomers (chiral compounds)
Chromophore – molecular group which absorbs light at a particular frequency
Collection timing delay – the time between when the peak exits the detector and reaches the collection selector valve or solenoid
Column oven – oven used in SFC systems for temperature control and column selection
Column volume – volume inside the column “cylinder” based on length and ID minus the approximate volume of the stationary phase
Conditioning solvent – solvent used with the splitter to enhance signal in the MS detector (QDa)
Co-solvent – in SFC, the organic portion of the mobile phase (solvent B)
Critical point – the specific temperature and pressure point for a fluid above which it exists as a supercritical fluid
Density – mass per volume (grams per liter)
Detector channels – single channels that can be monitored independently and in parallel for detection or collection
Diastereomers – compounds that differ in the optical orientation of two chiral centers
Diffusion coefficient – the rate at which a diffusing substance is transported between opposing systems when there is a concentration difference between them
Diffusivity – in chromatography, the ability of a substance to diffuse into and out of the stationary phase particles of the column based on the diffusion coefficient
Dwell volume – the volume from the point of the gradient mixing to the head of the column in a chromatographic system
Efficiency – chromatographic efficiency is measured by the number of theoretical plates or plate height, a low plate height indicates high efficiency and results when a peak has good retention and narrow width
Enantiomers – compounds that differ in the optical orientation of a single chiral center
Extra-column volume – volume of the system between the injector and the detector without the column; impacts peak quality
Extraction – to separate or obtain a product (extract) from a mixture (or matrix) by force
Focused gradient – shallow gradients generated to optimize the separation of a target compound based on the elution percentage from a scouting gradient
Fraction analysis – qualitative and/or quantitative analysis of the collected fractions
Front pressure – pressure before the column in SFC (system pressure)
Gradient methods – chromatography method in which the mobile phase composition changes over the course of a defined period of time
Gradient slope – the rate of change in organic solvent composition per column volume during a gradient
Hydrophilic – miscible with or soluble in water, polar
Hydrophobic – is not miscible with or soluble in water, non-polar
Inlet pressure – pressure of the CO2 before it enters the pump
Isocratic methods – chromatography methods in which the mobile phase composition remains constant over the course of the separation
Joule-Thomson cooling – the cooling of a real gas or liquid when it expands through a valve or opening
Loading – the amount of sample injected onto the chromatographic system
Loading capacity – the amount (mass) of compound that can be loaded based on the dimensions of the column
Lypophilic – lipid soluble, typically used to indicate low polarity
Make-up solvent – solvent used to aid in collection in SFC systems after the CO2 has evaporated
Mass spec detection (MS) – a detection technique that separates compounds based on mass
Mass-flow control – CO2 pumps that control flow based on mass of CO2 (g/min)
Matrix – the substance containing the target compound or isolate
Matrix effects – detection and chromatographic interferences caused by components in the matrix
Mixed-stream injection – injections are performed into the pre-mixed mobile phase
Mobile-phase – the solvent or solvents used to elute compounds from the stationary phase (column)
Modifier – in SFC this is synonymous with co-solvent or the organic portion of the mobile phase
Modifier-stream injection – injections are performed into the co-solvent (modifier) stream before mixing with CO2
Multi-step purification – when purification is accomplished using multiple methods with differing selectivity, whether using two techniques like LC with SFC, or different columns achiral with chiral
Non-polar – describes compounds or solvents that have low polarity, or are hydrophobic and have high LogP values
Normal-phase liquid chromatography (NPLC) – a separation technique in which the mobile phase is typically non-polar and the separation occurs on a stationary phase that is polar
Open-bed collection – collection systems that deposit fractions into tubes or bottles placed in racks in a bed open to the atmosphere
Orthogonal – describes mutually independent or well separated capabilities that span the entire capability range
Phase separation – when a single substance or composition of substances separate into two or more distinct phases
Photodiode array detection (PDA) – a two dimensional UV detection technique where one axis shows time and the other shows UV spectral scans
Polar – describes compounds or solvents that have high polarity, or are hydrophilic and have low LogP values
Pressure drop – the drop in pressure across the column measured by the difference between the front pressure and the back pressure
Productivity – the rate at which the final product can be generated or purified
Purity – a measure of how pure a fraction is based on analytical analysis
Recovery – a measure of the amount of product collected compared to the amount injected or the amount of starting material
Resolution – a measure of the width of two peaks relative to the distance between those peaks
Reversed-phase chromatography (RPLC) – a widely used separation technique in which the mobile phase is polar and the separation occurs on a stationary phase that is non-polar
Scale-up – transferring an analytical scale method to a preparative scale method
Shallow gradient – chromatography method in which the rate of change of organic solvent per column volume is low
Solvating capacity – the amount of compound that can be dissolved per volume of solvent
Split ratio – the ratio of the total preparative flow that is directed to the detectors by the splitter
Splitter – device used send a small ratio of the preparative flow stream to the detectors, accompanied by make-up or conditioning solvent to enhance signal
Stationary phase – the active particles in the column where chromatographic separation occurs
Supercritical fluid – the result when a fluid is above its critical pressure and critical temperature and there is no longer an interface between liquid and gas phases.
System pressure – typically stated as the pump pressure in liquid chromatography, same as front pressure in SFC
Throughput – amount of sample processed and collected per unit time
Van Deemter curves - A plot of plate height vs. average linear velocity of the mobile phase
Viscosity – The degree to which a fluid resists flow under an applied force
Volume-flow control – CO2 pumps that control flow based on volume of CO2 (mL/min)
