Gc-AAS (Gas chromatography - Atomic Absorption Spectroscopy).pptx

GC - AAS for Master of Pharmacy Students from Chemistry background having spectral analysis subject.

1. HYGIA INSTITUTE OF PHARMACEUTICAL EDUCATION AND RESEARCH Ghaila Road, Gazipur Balram Rd, near IIM Road, Prabandh Nagar, Lucknow , Uttar Pradesh 226020 A presentation on GC - AAS (Advanced Spectral Analysis) Presented to Mrs. Samiksha Srivastava Department of Pharmaceutical Chemstry Presented by Kartik Tiwari M.Pharm 1 st Year

2. Contents Introduction of Gc-AAS Instumentation of Gc-AAS 1) Flow Regulator 2) Injection Devices 3) Column 4) Light Source 5) Atomizer 6) Monochromator 7) Detector Application of Gc-AAS

3. GC – AAS (Gas Chromatography And Atomic Absorption Spectroscopy) Gas Chromatography (GC) - is technique which is used to the analysis of small, relatively volatile molecules. It can be used both to identify and quantify substances. In general, for measurements a sample or solution of the pure material and these are often obtained from specialist suppliers. AAS quantitatively measures the concentrations of elements present in a liquid sample. It utilizes the principle that elements in the gas phase absorb light at very specific wavelengths which gives the technique excellent specificity and detection limits. The sample may be an aqueous or organic solution; indeed, it may even be solid provided it can be dissolved successfully. The liquid is drawn into a flame where it is ionised in the gas phase. Light of a specific wavelength appropriate to the element being analysed is shone through the flame, the absorption is proportional to the concentration of the element. Quantification is achieved by preparing standards of the element.

4. INSTRUMENTATION The instrument used in GC - AAS are : GC unit Light source Atomizer Monochromators Detector Amplifier Read out device

5. Diagram - GC unit Diagram - Atomic Absorption Spectroscopy Gas Chromatography + Atomic Absorption Spectroscopy = GC-AAS

6. Diagram – GC - AAS

7. GC unit GAS CHROMATOGRAPHY Inert carrier gas Flow regulators & Flow Meters Injection devices Columns Detectors CARRIER GAS Inertness Suitable for the detector High purity Easily available Cheap Should not cause the risk of fire Should give best column performance It should be Hydrogen, Helium and Nitrogen are inert gas taken in GC because it has high thermal conductivity, inexpensive and inflammable Diagram - GC unit

8. Flow regulators & Flow meters Deliver the gas with uniform pressure/flow rate - Rota meter & Soap bubble flow meter Rota meter - Placed before column inlet it has a glass tube with a float held on to a spring. the level of the float is determined by the flow rate of carrier gas Soap Bubble Meter - Similar to Rota meter & instead of a float, soap bubble formed indicates the flow rate.

9. Injection Devices The injection port consists of a septum through which a syringe needle is inserted to inject the sample. The sample is injected into a stream of inert gas usually at an elevated temperature by a micro syringe. The vaporized sample is carried into a column packed with the stationary phase. To ensure rapid & complete solute volatilization temp of injector → 30-50 degree Celsius >column temp The injection port Is a hollow, heated, glass-lined cylinder. The injector is heated so that all components in the sample will be vaporized. If the temperature is too low, separation is poor and broad spectral peaks should result or no peak develops at all. If the injection temperature is too high, the specimen may decompose or change its structure. The temperature of the sample port is usually about 50°C higher than the boiling point of the least volatile component of the sample.

10. Injector Types Split/ Split less Injector On-Column Injector High Oven Temperature On-Column Injector Large Volume On-Column Injector Packed Column Injector Purged Packed Injector Programmable Temperature Vaporizing Injector 1. Split mode The split vent is open, part of the sample goes into the column. When analyzing high concentration or neat samples. Yields the sharpest peaks if the split gas is properly mixed. Standard for capillary columns. Split-less mode The split vent is closed, most of the sample go into the column. When analyzing low concentration or diluted samples. Splitless times of ~ 1 minute are typical. Standard for capillary columns.

11. Columns Column is one of the important parts of GC which decides the separation efficiency. Columns are made up of glass and stainless steel. Is where the chromatographic separation of the sample occurs. Several types of columns are available for different chromatographic applications. The heart of the system. It is coated with a stationary phase which greatly influences the separation of the compounds.

12. Light Source Hollow Cathode Lamps HCL is the most common radiation source in AAS. It contains a tungsten anode and a hollow cylindrical cathode made of the element to be determined. These are sealed in a glass tube filled with an inert gas (neon, argon). Each element has its own unique lamp which must be used for that analysis. Electrode less Discharge Lamp A small amount of the metal or salt of the element for which the source is to be used is sealed inside a quartz bulb. This bulb is placed inside a small, self-contained RF generator or “driver”. When power is applied to the driver, an RF field is created. The coupled energy will vaporize and excite the atom inside the bulb causing them to emit their characteristic spectrum. They are typically much more intense and, in some cases, more sensitive than comparable HCL. Hence better precision and lower detection limits where an analysis is intensity limited. EDL are available for a wide variety of elements, including Sb , As, Bi, Cd , Cs, Ge , Pb , Hg, P, K, Rb , Se, Te, Th , Sn and Zn.

13. Atomizer Atomization is separation of particles into individual molecules and breaking molecules into atoms. This is done by exposing the analyte to high temperatures in a flame or graphite furnace Atomizer converts the liquid into small droplets which are easily vaporized. Types of Atomizers Flame atomizer a.) Total consumption burner Total consumption burner. In this whole sample is atomized into the flame, hence named as total consumption burner. In this burner, the sample solution, the fuel, and oxidizing gases are passed through separate passages to meet at the opening of the base of flame. Then the flame breaks the sample in liquid form into the droplets which are evaporated and burns. Leaving the residue which is reduced to atoms. Fuel used – H 2 / acetylene b.) Premixed burner It is most widely used because of uniformity in flame intensity. In this the sample solution, fuel and oxidant are mixed before they reach the tip. The fine droplets get carried out along with the fuel gas at outlet, the large drops of sample get collected in chamber and are drained out.

14. Advantages Non-turbulent Noiseless Stable Disadvantages Only 5% sample reaches to the flame Rest 95% is wasted. II. Non-flame atomizer (Electro thermal atomizer) Nebulization - Conversion of the liquid sample to a fine spray Desolvation - Solid atoms are mixed with the gaseous fuel. Volatilization - Solid atoms are converted to a vapor in the flame. There are three types of particles that exist in the flame: Atoms Ions Molecules

15. Nebulization : - Before the liquid sample enters the burner, it is converted into droplets this method a formation of small droplets its called nebulization. Common method of nebulization is by use of gas moving at high velocity, called pneumatic nebulization. Monochromators Important part in an AA spectrophotometer. It is used to separate out all of the thousands of lines. Without a good monochromator, detection limits are severely compromised. A monochromator is used to select the specific wavelength of light which is absorbed by the sample, and to exclude other wavelengths. The selection of the specific light allows the determination of the selected element in the presence of others. They are of two types: Prism monochromator : - Quartz material is used for making prism, as quartz is transparent over entire region. Grating Monochromator : - It consists of a series of parallel straight lines cut into a plane surface.

16. Detector The light selected by the monochromator is directed onto a detector that is typically a photomultiplier tube, whose function is to convert the light signal into an electrical signal proportional to the light intensity. The processing of electrical signal is fulfilled by a signal amplifier. The signal could be displayed for readout, or further fed into a data station for printout by the requested format. Photomultiplier Tubes Components Made of a glass vacuum tube Photocathode Several dynodes One anode

17. APPLICATIONS Quantitative metal concentrations in solution Analysis of lead in paint Monitoring of trace metals in industrial effluent streams Trace elements in product/raw materials along with ICP-MS Analysis of additives and purity in steels and other metal alloys Analysis of low-level contaminants