Partitioning. Separation is based on the analyte s relative solubility between two liquid phases or a liquid and solid.

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1 Chromatography Various techniques for the separation of complex mixtures that rely on the differential affinities of substances for a gas or liquid mobile medium and for a stationary adsorbing medium through which they pass.

2 Partitioning Separation is based on the analyte s relative solubility between two liquid phases or a liquid and solid Mobile Phase Stationary Phase Solvent or gas Bonded Phase Solid or liquid

3 Separation The individual components are retained by the stationary phase differently. The components separate from each other since they are running at different speeds through the column with the eluent [gas or solvent(s)]. At the end of the column they elute one at a time depending on their retention governed by their polarity.

4 Separation Boiling point- lower bp compounds spend more time in gas phase. Temperature of column does not have to be above boiling pt. Solids have vapor pressure. High vapor pressure liquids used as solvents (water 25 mmhg whereas ether 520 mmhg/25c)

5 Separation Polarity like absorbs likes. Polar compounds have longer retention time on Polar columns. Non-polar compounds have longer retention on non-polar column. Two types of columns in GC3800, a silicone based column and a PEG column.

6 Separation Carrier gas flow- high flow rate decreases retention time. High gas flow may cause poor separation since components have little time to react with stationary phase. There is optimum gas flow for various columns. Too high a flow causes excessive back pressure.

7 Separation Column length- longer column usually improves resolution, but increases back pressure. Doubling length will not double resolution (resolution increases according to square root of length). Generally a 30 meter column gives best resolution, analysis time and head pressure

8 Separation An effective means to increase resolution is to decrease column ID. The efficiency of a capillary column increases (number of theoretical plates per meter) as the ID of column decrease. Makes sharper peaks,& decreases column bleed Decreasing ID decreases sample capacity. Ideal (most popular) ID is 0.25 mm.

9 Some Types of Chromatography Lid Paper chromatography (PC), Thin-layer chromatography (TLC), Paper Solvent front solvent Two experiments in MCAL demonstrate: Liquid chromatography (LC, including highperformance liquid chromatography, or HPLC), Gas chromatography (GC).

10 GC Experiment 1) To compare the separation of alcohols of increasing carbon number using a carbowax column and a FID detector in the Varian 3900 GC. 2) To compare separation of various compounds on a carbowax versus a silicone based column. 3) To measured sensitivity of instrument (LOD).

11 Gas Chromatography (a review) Chromatographic technique that can be used to separate volatile organic compounds. A gas chromatograph consists of a flowing mobile phase, an injection port, a separation column containing the stationary phase, detector and a controller (integrator) and data collection and storage. Organic compounds are separated due to differences in their partitioning behavior between the mobile gas phase and the stationary phase in the column.

12 Bruker Improving the Quality of our Beer New 456-GC Off-Flavor Beer Analyzers

13 Gas tanks He, N 2, H 2, Air Varian (Agilent) 3800 GC Detectors Autosampler Injectors Oven Computer control and data acquisition

14 Stationary Phases The most common stationary phases in gaschromatography columns are polysiloxanes, which contain various substituent groups to change the polarity of the phase. The nonpolar end of the spectrum is polydimethyl siloxane, which can be made more polar by increasing the percentage of phenyl groups on the polymer. Polyethylene glycol (carbowax) is commonly used as the stationary phase for more polar analytes.

15 Polysiloxanes

16 Polyethylene glycol

17 Low Bleed Phases (Arlenes)

18 Varian (Agilent) Factor Four Capillary GC Columns. Capillary columns are a thin fused-silica capillary. Typically m in length and 250 µm inner diameter. The stationary phase is coated on the inner surface.

19 Capillary Columns

20 FSOT Column

21 Capillary Columns Capillary columns provide much higher separation efficiency than packed columns but are more easily overloaded by too much sample. You need to dilute your sample to get good symmetrical (Gaussian) peaks Solvent peak dominates chromatogram due to normalization of peaks.

22 GC Column Oven

23 MCAL GC Columns GC two columns FID and ECD detector: 1) CP-sil 8 50 m, 0.2mm,.33um 5% phenyl 95% dimethyl polysiloxane 2) CP-sil 5CB 100% dimethyl polysiloxane 15 m 0.25mm 0.25um GC 3900 one column FID detector: 1) Supelco wax-10 15m x 0.32 mm, 0.5 u Polyetyylene glycol

24 Simple GC Gas control valve Sample injector port Computer FID, ECD, MS Detector Gas is He, N 2 or H 2 Separation Column Temperature controlled oven

25 Sequence of GC Injection 1. A small amount of liquid (microliters) is injected through a silicon rubber septum into the heated (>200 o C) GC injector that is lined with an inert glass tube. 2. The sample is immediately vaporized. 3. A pressurized, inert, carrier gas-which is continually flowing from a gas regulator through the injector and into the GC column-sweeps the gaseous sample, solvent, and analyte, onto the column. 4. Septum purge: a small ancillary flow of carrier gas bathes the underside of the injector's septum so that hot vaporized sample gases can't interact and possibly stick to the septum. This improves peak shape and reproducibility.

26 Split / Splitless Injector Helium

27 Split / Splitless Injector

28 ECD detector FID Detector Injectors

29 FID Detector Organic compounds burning in a hydrogenoxygen flame produce ions and electrons. These charged particles created in the combustion process create a current between the detector's electrodes. One electrode is the metallic jet itself, the other is above the jet. The detector housing is heated so that gases produced by the combustion (mainly water) do not condense in the detector before leaving the detector chimney.

30 Insulator FID Detector Cathode Anode Air Hydrogen Sample plus Helium from Column

31 FID Detector

32 The ECD or Electron Capture Detector The ECD or electron capture detector measures electron capturing compounds (usually halogenated) by creating an electrical field in which molecules exiting a GC column can be detected by the drop in current in the field

33 ECD Detector

34 ECD Detector Electrode insulator waste + electrode Radioactive Beta emitter (electrons) - electrode GC column Electron cloud insulator

35 Separation of Alcohols C1 to C8 on carbowax column

36 GC Exp: ECD Detector Dichlorobenzene Hexane Solvent??

37 GC Exp: Fid Detector Solvent and contamination dichlorobenzene

38 GC Exp: FID Detector Expanded dichlorobenzene

39 HPLC in MCAL Solvents rescence ctor Autosampler Manual injector V Vis iode array etector Pumps

40 HPLC Image System control- Data storage HPLC column (packing) Injector Autosampler Sample Solvent(s) Pump(s) Detector(s) (Diode Array & Fluorescence) Waste

41 Separation in HPLC Seperation depends on : Polarity of molecule RP verses NP, Hilic, Hydrophilic-Interaction Chrpmatography Hic, Hydrophobic-interaction Chromatography Electrical charge (ion exchange). Anion exchanger attracts charged analyte Cation exchanger attracts + charged analyte Molecular size Size exclusion gel permeation or size exclusion

42 Columns - Heart of System Solid Support (column packing) - Backbone for bonded phases. Usually 10µ, 5µ, 3µ, 2.5µ siloxane or polymeric particles. Porous or solid core Packing has different degrees of polarity depending on functional groups attached Bonded Phases - Functional groups chemically bound to the solid support.

43 HPLC - Modes Normal Phase - Polar stationary phase and nonpolar solvent. Reverse Phase (used for caffeine and quinine separation) - Non-polar stationary phase and a polar solvent.

44 Normal Phase versus Reverse Phase HPLC Packing Polar packing Non-polar packing C4 C8 C18

45 HPLC Solid Support C18RP Si O CH 3 Si CH 2 CH 2 CH 2 CH 2 (CH 2 ) 14 O O CH 3 Si OH O O Si O CH 3 Si (CH 2 ) 18 Gel Surface CH 3 Bonded phase

46 HPLC Solid Support C18RP End Capping Si O CH 3 Si CH 2 CH 2 CH 2 CH 2 (CH 2 ) 14 O O CH 3 Si OH + Si (CH 2 ) 2 O O Si O CH 3 Si (CH 2 ) 18 Gel Surface CH 3 Bonded phase

47 HPLC Solid Support C18RP Polymeric Si O CH 3 Si CH 2 CH 2 CH 2 CH 2 (CH 2 ) 14 O O CH 3 Si O Si (CH 2 ) 18 O O Si O CH 3 Si (CH 2 ) 18 Gel Surface CH 3 Bonded phase

48 HPLC Solid Support C18RP Polymeric Si O OH Si CH 2 CH 2 CH 2 CH 2 (CH 2 ) 14 O O O Si O Si (CH 2 ) 18 O O Si O CH 3 Si (CH 2 ) 18 Gel Surface CH 3 Bonded phase

49 Solid Core Particle Solid Core Porous Outer Layer

50 Core-Shell Particle

51 Core-Shell Particle

52 HPLC Columns (MCAL) C18 Microsorb (Varian)5 u 100 A 250 x 4.5 mm C18 Polar Synergi (Phenomenex) 4 u 80 A 250 x 4.5 mm C18 RP Particil column (Varian) 3 u 300 A 100 x 2.0 mm C18 Hilic column (Phenomenex) 5 u 200 A 150 x 4.6 mm XB-C18 RP Kinetex (Phenomenex) 2.6 u 100 A 100 x 4.6 mm C18 Microsorb (Varian) 5 u 100 A 250 x 4.5 C8 Polaris (Varian) 3 u A 50 x 20 mm

53 nual ctor HPLC columns

54 Solvents for RP H 2 O most polar with decreasing polarity as solvent B added to mix. Solvent B usually MeOH, acetonitrile, iso-propanol Can be isocratic mixture - 1 or 2 pump system or Gradient need at least two pumps and mixing apparatus. Caffeine-quinine exp. uses buffer-acetonitrile or buffer- methanol gradient mixing.

55 The Theoretical Plate Model of Chromatography The plate model supposes that the chromatographic column is contains a large number of separate layers, called theoretical plates (N). Separate equilibrations of the sample between the stationary and mobile phase occur in these "plates". The analyte moves down the column by transfer of equilibrated mobile phase from one plate to the next.

56 Chromatographic Resolution Depends On: 1.Column efficiency (N) peak width Particle diameter Flow rate Sol. Viscosity Temp. Col. Length Col. diameter 2. Solvent efficiency (α) retention time Stationary phase Mobile phase Solvent composition Temperature

57 Column Efficiency -Theoretical plate numbers (N) Theoretical plate numbers are indirect measure of peak width for a peak at a specific retention time. Columns with high plate numbers are considered to be more efficient, that is, have higher column efficiency, than columns with a lower plate count. A column with a high number of theoretical plates will have a narrower peak at a given retention time than a column with a lower N number. N=5.545(t r /w h ) 2

58 Column Efficiency -Height equivalent to theoretical plates Measure of the resolving power of the column HETP = L/N L = Length of column N = Theoretical plates At each theoretical plate one equilibrium distribution of solute between mobile phase and stationary phase occurs.

59 Peak Seperation (α) On stationary phases where the alphas (α) are small, more efficient columns (higher N) are beneficial. Column efficiency is a function of: a) the column dimensions (diameter, length and film thickness), b) the type of carrier solvent and its flow rate or average linear velocity, and c) the compound and its retention.

60 Band broadening theory (Van Deemter equation) column band broadening originates from three main sources: multiple path of an analyte through the column packing; molecular diffusion; effect of mass transfer between phases.

61 Multiple path The velocity of mobile phase in the column may vary significantly across the column diameter, depending on the particle shape, porosity, and the whole bed structure.

62 Measure of the Resolving Power of the Column HETP = A + B / u + C u A = eddy diffusion take different paths (different lengths). B = longitudinal diffusion analyte diffuses from centre to outer edge. C = resistance to mass transfer: analyte strong affinity for stationary and veloscity of mobile phase is high. U = avg veloscity of mobile phase

63 Resolving Power α N

64 Column efficiency is reported as plates per meter (N/Meter). Smaller average packing particle size = Larger N Broader particle size distribution = Smaller N Better packing procedures = Larger N

65 Polarity - Elotropic Series Water is at the polar end of mobile-phasesolvent scale, Hexane, an aliphatic hydrocarbon, is at the non-polar end. In between, single solvents, as well as miscible-solvent mixtures

66 Stationary Phase Polarity Spectrum Silica has an active, hydrophilic [waterloving] surface containing acidic silanol [silicon-containing analog of alcohol] The polarity of the silica surface may be modified selectively by chemically bonding to it less polar functional group like n-octylsilyl- [C8], and n-octadecylsilyl- [C18, ODS] moieties. The latter is a hydrophobic [water-hating], very non-polar packing.

67 HPLC Experiment Seperation and identification of caffeine, quinine and added theophylline (internal standard) in commercial drinks Comparison of different quantitation methods (external standard, internal standard) Uv verses fluorescent detection Diode array detection

68 HPLC Experiment The separation is done on a C18 RP column. The solvent is a 20% methanol in water (low ph with TEA added) increased to 30% methanol. The caffeine comes off column before the quinine.

69 HPLC Exp: Caffeine and Quinine Quinine Rt = 11.6 min Caffeine wavelength 206 Rt = 9.2 min Caffeine wavelength 273 Rt = 9.2 min

70 Diode Array Detector Caffeine

71 Detection with HPLC Ultraviolet light source (deuterium lamp 190 to 950nm) Visible light source (quartz iodide 350 nm and beyond) Flurescent light (Xenon lamp) Excitation and emmission wavelength selection

72 Concentration Of Analytes Concentration is determined by measuring the area of known concentrations of caffeine and quinine, and making a standard curve. Concentration of caffeine is also determined by adding an internal standard (IS) and calculating caffeine based on the response factor of the IS.

Chromatography. Gas Chromatography

Chromatography. Gas Chromatography Chromatography Chromatography is essentially the separation of a mixture into its component parts for qualitative and quantitative analysis. The basis of separation is the partitioning of the analyte mixture