GC and HPLC
- 1. GAS CHROMATOGRAPHY Dr. M. Sonia Angeline Assistant Professor Department of Life Sciences Kristu Jayanti College
- 2. INTRODUCTION Gas chromatography differs from other forms of chromatography in which the mobile phase is a gas and the components are separated as vapors. It is thus used to separate and detect small molecular weight compounds in the gas phase. The sample is either a gas or a liquid that is vaporized in the injection port. The mobile phase for gas chromatography is a carrier gas, typically helium because of its low molecular weight and being chemically inert. The pressure is applied and the mobile phase moves the analyte through the column. The separation is accomplished using a column coated with a stationary phase.
- 3. PRINCIPLE OF GC • The equilibrium for gas chromatography is partitioning, and the components of the sample will partition (i.e. distribute) between the two phases: the stationary phase and the mobile phase. • Compounds that have a greater affinity for the stationary phase spend more time in the column and thus elute later and have a longer retention time (Rt) than samples that have a higher affinity for the mobile phase. • Affinity for the stationary phase is driven mainly by intermolecular interactions and the polarity of the stationary phase can be chosen to maximize interactions and thus the separation.
- 4. GAS CHROMATOGRAPHY IS MAINLY COMPOSED OF THE FOLLOWING PARTS: 1. Carrier gas in a high-pressure cylinder with attendant pressure regulators and flow meters Helium, N2, H, Argon are used as carrier gases. Helium is preferred for thermal conductivity detectors because of its high thermal conductivity relative to that of most organic vapors. N2 is preferable when a large consumption of carrier gas is employed. Carrier gas from the tank passes through a toggle valve, a flow meter, (1-1000 ml/min), capillary restrictors, and a pressure gauge (1-4 atm). Flow rate is adjusted by means of a needle valve mounted on the base of the flow meter and controlled by capillary restrictors. The operating efficiency of the gas chromatograph is directly dependent on the maintenance of constant gas flow.
- 5. 2. Sample injection system Liquid samples are injected by a micro-syringe with a needle inserted through a self-scaling, silicon-rubber septum into a heated metal block by a resistance heater. Gaseous samples are injected by a gas-tight syringe or through a by-pass loop and valves. Typical sample volumes range from 0.1 to 0.2 ml. 3. The separation column The heart of the gas chromatography is the column which is made of metals bent in U shape or coiled into an open spiral or a flat pancake shape. Copper is useful up to 2500 Lock fittings make column insertion easy. Several sizes of columns are used depending upon the requirements. GAS CHROMATOGRAPHY IS MAINLY COMPOSED OF THE FOLLOWING PARTS:
- 6. 4. Liquid phases An infinite variety of liquid phases are available limited only by their volatility, thermal stability and ability to wet the support. No single phase will serve for all separation problems at all temperatures. • Non-Polar – Parafin, squalane, silicone greases, apiezon L, silicone gum rubber. These materials separate the components in order of their boiling points. • Intermediate Polarity – These materials contain a polar or polarizable group on a long non-polar skeleton which can dissolve both polar and non-polar solutes. For example. diethyl hexyl phthalate is used for the separation of high boiling alcohols. • Polar – Carbowaxes – Liquid phases with a large proportion of polar groups. Separation of polar and non-polar substances. • Hydrogen bonding – Polar liquid phases with high hydrogen bonding e.g. Glycol. • Specific purpose phases – Relying on a chemical reaction with solute to achieve separations. e.g AgNO3 in glycol separates unsaturated hydrocarbons.
- 7. 5. Supports The structure and surface characteristics of the support materials are important parameters, which determine the efficiency of the support and the degree of separation respectively. The support should be inert but capable of immobilizing a large volume of liquid phase as a thin film over its surface. The surface area should be large to ensure the rapid attainment of equilibrium between stationary and mobile phases. Support should be strong enough to resist breakdown in handling and be capable of packed into a uniform bed. Diatomaceous earth, kieselguhr treated with Na2CO3 for 9000 C causes the particle fusion into coarser aggregates. Glass beads with a low surface area and low porosity can be used to coat up to 3% stationary phases. Porous polymer beads differing in the degree of cross-linking of styrene with alkyl-vinyl benzene are also used which are stable up to 2500
- 8. GAS CHROMATOGRAPHY IS MAINLY COMPOSED OF THE FOLLOWING PARTS: 6. Detector Detectors sense the arrival of the separated components and provide a signal. These are either concentration-dependent or mass dependent. The detector should be close to the column exit and the correct temperature to prevent decomposition. 7. Recorder The recorder should be generally 10 mv (full scale) fitted with a fast response pen (1 sec or less). The recorder should be connected with a series of good quality resistances connected across the input to attenuate the large signals. An integrator may be a good addition.
- 9. PROCEDURE OF GC • Step 1: Sample Injection and Vaporization 1. A small amount of liquid sample to be analyzed is drawn up into a syringe. 2. The syringe needle is positioned in the hot injection port of the gas chromatograph and the sample is injected quickly. 3. The injection of the sample is considered to be a “point” in time, that is, it is assumed that the entire sample enters the gas chromatograph at the same time, so the sample must be injected quickly. 4. The temperature is set to be higher than the boiling points of the components of the mixture so that the components will vaporize. 5. The vaporized components then mix with the inert gas mobile phase to be carried to the gas chromatography column to be separated.
- 10. PROCEDURE OF GC • Step 2: Separation in the Column Components in the mixture are separated based on their abilities to adsorb on or bind to, the stationary phase. A component that adsorbs most strongly to the stationary phase will spend the most time in the column (will be retained in the column for the longest time) and will, therefore, have the longest retention time (Rt). It will emerge from the gas chromatograph last. A component that adsorbs the least strongly to the stationary phase will spend the least time in the column (will be retained in the column for the shortest time) and will, therefore, have the shortest retention time (Rt). It will emerge from the gas chromatograph first. If we consider a 2 component mixture in which component A is more polar than component B then: 1. component A will have a longer retention time in a polar column than component B 2. component A will have a shorter retention time in a non-polar column than component B
- 11. PROCEDURE OF GC • Step 3: Detecting and Recording Results 1. The components of the mixture reach the detector at different times due to differences in the time they are retained in the column. 2. The component that is retained the shortest time in the column is detected first. The component that is retained the longest time in the column is detected last. 3. The detector sends a signal to the chart recorder which results in a peak on the chart paper. The component that is detected first is recorded first. The component that is detected last is recorded last.
- 13. APPLICATIONS OF GC GC analysis is used to calculate the content of a chemical product, for example in assuring the quality of products in the chemical industry; or measuring toxic substances in soil, air or water. Gas chromatography is used in the analysis of: (a) air-borne pollutants (b) performance-enhancing drugs in athlete’s urine samples (c) oil spills (d) essential oils in perfume preparation https://www.youtube.com/watch?v=UycPljfrnWo
- 15. INTRODUCTION • High performance liquid chromatography (HPLC) has become a very versatile and powerful separation and analytical method over the years. • It is an advanced form of liquid chromatography (LC). • Instead of introducing the solvent into the column and allowing it to drip down under the influence of gravity, in HPLC the sample is forced through the column under high pressures of nearly 400 atm, resulting in faster and more efficient separation. • This technique is also called high pressure liquid chromatography. • HPLC makes it possible to perform structural, and functional analysis, and purification of many molecules within a short time. • This technique yields perfect results in the separation, and identification of amino acids, carbohydrates, lipids, nucleic acids, proteins, steroids, and other biologically active molecules.
- 16. PRINCIPLE OF HPLC • HPLC follows the same basic principle as chromatography. • Different components in the sample have varying affinities to the adsorbent material. • This causes a difference in the flow rate for each component which leads to their separation as they come out of the column. • The only difference is that the speed and sensitivity of HPLC is much higher than that of LC due to the application of a high pressure. • The magnitude of pressure applied depends on several factors such as the length and diameter of the column, flow rate, size of particles in the stationary phase, and mobile phase composition.
- 17. PRINCIPLE OF HPLC • The purification takes place in a separation column between a stationary and a mobile phase. • The stationary phase is a granular material with very small porous particles in a separation column. • The mobile phase, on the other hand, is a solvent or solvent mixture which is forced at high pressure through the separation column. • Via a valve with a connected sample loop, i.e. a small tube or a capillary made of stainless steel, the sample is injected into the mobile phase flow from the pump to the separation column using a syringe. • Subsequently, the individual components of the sample migrate through the column at different rates because they are retained to a varying degree by interactions with the stationary phase. • After leaving the column, the individual substances are detected by a suitable detector and passed on as a signal to the HPLC software on the computer. • At the end of this operation/run, a chromatogram in the HPLC software on the computer is obtained. • The chromatogram allows the identification and quantification of the different substances.
- 18. THE COMPONENTS OF HPLC • Columns: HPLC columns are normally made of stainless steel and are 50 - 300mm long with an internal diameter of 2 - 5mm. They are filled with the adsorbents (stationary phase) of particle size 3 – 10µm. • Sample Injector: The sample is injected into the column by an injector which is capable of handling sample volumes in the range of 0.1 - 100mL under high pressures of up to 4000psi. • Reservoir: The solvent or the mobile phase is placed in a glass reservoir. It is usually a blend of polar and non-polar liquids whose concentrations depend on the sample composition. • Pump: The solvent in the mobile phase is aspirated by a pump from the reservoir and forced through the HPLC column and then the detector. • Detector: The detector in a HPLC system is located at the end of the column and it detects the components of the sample that elute from the column. Different types of detectors such as fluorescence, mass-spectrometric, UV- spectroscopic, and electrochemical detectors are used.
- 19. INSTRUMENTATION
- 20. The Pump •The development of HPLC led to the development of the pump system. •The pump is positioned in the most upper stream of the liquid chromatography system and generates a flow of eluent from the solvent reservoir into the system. •High-pressure generation is a “standard” requirement of pumps besides which, it should also to be able to provide a consistent pressure at any condition and a controllable and reproducible flow rate. •Most pumps used in current LC systems generate the flow by back-and-forth motion of a motor-driven piston (reciprocating pumps). Because of this piston motion, it produces “pulses”. Injector •An injector is placed next to the pump. •The simplest method is to use a syringe, and the sample is introduced to the flow of eluent. •The most widely used injection method is based on sampling loops. •The use of the autosampler (auto-injector) system is also widely used that allows repeated injections in a set scheduled-timing. INSTRUMENTATION
- 21. INSTRUMENTATION • Column • The separation is performed inside the column. • The recent columns are often prepared in a stainless steel housing, instead of glass columns. • The packing material generally used is silica or polymer gels compared to calcium carbonate. The eluent used for LC varies from acidic to basic solvents. • Most column housing is made of stainless steel since stainless is tolerant towards a large variety of solvents. • Detector • Separation of analytes is performed inside the column, whereas a detector is used to observe the obtained separation. • The composition of the eluent is consistent when no analyte is present. While the presence of analyte changes the composition of the eluent. What detector does is to measure these differences. • This difference is monitored as a form of an electronic signal. There are different types of detectors available.
- 22. INSTRUMENTATION Recorder •The change in eluent detected by a detector is in the form of an electronic signal, and thus it is still not visible to our eyes. •In older days, the pen (paper)-chart recorder was popularly used. Nowadays, a computer-based data processor (integrator) is more common. •There are various types of data processors; from a simple system consisting of the in-built printer and word processor while those with software that are specifically designed for an LC system which not only data acquisition but features like peak- fitting, baseline correction, automatic concentration calculation, molecular weight determination, etc. Degasser The eluent used for LC analysis may contain gases such as oxygen that are non-visible to our eyes. •When gas is present in the eluent, this is detected as noise and causes an unstable baseline. •Degasser uses special polymer membrane tubing to remove gases. •The numerous very small pores on the surface of the polymer tube allow the air to go through while preventing any liquid to go through the pore. Column Heater The LC separation is often largely influenced by the column temperature. •In order to obtain repeatable results, it is important to keep consistent temperature conditions. •Also for some analysis, such as sugar and organic acid, better resolutions can be obtained at elevated temperatures (50 to 80°C). •Thus columns are generally kept inside the column oven (column heater).
- 23. COLUMN • Stainless steel tubing to withstand high pressure • Heavy-wall glass or PEEK tubing for low pressure (< 600 psi) • Analytical column: Straight column with length (5 ~ 25 cm) • Microcolumn: Length of 3 ~ 7.5 cm, high speed and minimum solvent consumption • Guard column: Remove particulate matter and contamination protect analytical column. Have similar packing as analytical column • Température control: < 150 °C± 0.1 °C
- 25. Detector type Measurement principle UV/Vis detector Absorbance PDA detector- Photodiode-Array Detection Absorbance Differential refractive index detector Refractive index Fluorescence detector Fluorescence Electrochemical detector Oxidation / reduction Electrical conductivity detector Conductivity Mass spectrometry detector Molecular size, mass Optical rotation detector Optical rotation Circular dichroism detector Circular dichroism Evaporative light scattering detector Light scattering • There is a variety of detectors that can be used depending on the target sample. • To detect only a few specific components, a highly sensitive fluorescence detector or a UV/Vis detector can be used. • To detect a wide range of components, then a PDA detector, an evaporative light-scattering detector, or a differential refractive-index detector is more appropriate. TYPES OF DETECTORS
- 26. TYPES OF HPLC • Normal Phase: Separation of polar analytes by partitioning onto a polar, bonded stationary phase. • Reversed Phase: Separation of non-polar analytes by partitioning onto a non-polar, bonded stationary phase. • Adsorption: In Between Normal and Reversed. Separation of moderately polar analytes using adsorption onto a pure stationary phase (e.g. alumina or silica) • Ion Chromatography: Separation of organic and inorganic ions by their partitioning onto ionic stationary phases bonded to a solid support. • Size Exclusion Chromatography: Separation of based in the paths they take through a “maze” of tunnels in the stationary phase.
- 27. TYPES OF HPLC 1.Normal phase: • Column packing is polar (e.g silica) and the mobile phase is non-polar. It is used for water-sensitive compounds, geometric isomers, cis-trans isomers, and chiral compounds. 2.Reverse phase: • The column packing is non-polar (e.g C18), the mobile phase is water+ miscible solvent (e.g methanol). It can be used for polar, non-polar, ionizable and ionic samples.
- 28. THE TECHNIQUE OF HPLC The key steps in the HPLC separation technique are as follows: Injection of the liquid sample into the column containing the stationary phase. There are two types of sample injection methods: manual injection in which a syringe is inserted into the injector and the sample is injected manually, and autosampling, whereby a large number of samples can be injected automatically. Individual sample components are forced down the tube by high pressure from the pump. Components are separated under the influence of various chemical/physical interactions with the particles in the stationary phase. The separated analytes are identified by the detector present at the end of the column. The detector measures the concentration of the components. Data from the detector is processed and a chromatogram is produced.
- 29. APPLICATIONS OF HPLC The HPLC has developed into a universally applicable method so that it finds its use in almost all areas of chemistry, biochemistry, and pharmacy. • Analysis of drugs • Analysis of synthetic polymers • Analysis of pollutants in environmental analytics • Determination of drugs in biological matrices • Isolation of valuable products • Product purity and quality control of industrial products and fine chemicals • Separation and purification of biopolymers such as enzymes or nucleic acids • Water purification • Pre-concentration of trace components • Ligand-exchange chromatography • Ion-exchange chromatography of proteins • High-pH anion-exchange chromatography of carbohydrates and oligosaccharides
- 30. LIMITATIONS 1. Cost: Despite its advantages, HPLC can be costly, requiring large quantities of expensive organics. 2. Complexity 3. HPLC does have low sensitivity for certain compounds, and some cannot be detected as they are irreversibly adsorbed. 4. Volatile substances are better separated by gas chromatography.
- 31. ADVANTAGES OF HPLC • Higher resolution and speed of analysis • HPLC columns can be reused without repacking or regeneration • Greater reproducibility due to close control of the parameters affecting the efficiency of separation • Easy automation of instrument operation and data analysis • Adaptability to large-scale, preparative procedures • Two major advances: • stationary supports with very small particle sizes and large surface areas • appliance of high pressure to solvent flow