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The ITD is a variation of a quadrupole mass spectrometer, and is designed to function specifically as a GC detector. Due to the design variances of the ITD compared to a true quadrupole mass spectrometer, the ITD mass spectrum of an organic compound may not be identical but should be very similar to its classical electron impact EI mass spectrum, such as those found in the National Bureau of Standards library of mass spectra.
The ITD spectrum of the unknown will be compared to the EI spectra of several different classes of compounds. Thus, the characteristic features of a MS spectrum for a given class may be recognized, and the chemical structure determined.
Introduction Gas chromatography is a physical method of separation in which the components to be separated are distributed between two phases, one being a stationary bed of large surface area, and the other a gas that percolates through the stationary bed.
When the stationary phase is a solid, the separation process is more precisely called gas solid chromatography. This technique is generally used to separate gases in a gaseous solution. The more common technique which will be used in this experiment is gas liquid chromatography GLC in which the stationary phase is a porous solid covered with an absorbing liquid.
GLC is used to separate a wide variety of organic compounds. The basic requirements for GLC are that the sample be volatile and that it not decompose in the vaporization process.
Since the vaporization occurs in an inert atmosphere, decomposition of the sample is generally not a problem. The stationary phase is coated in a thin layer on solid particles solid support of large surface area and then packed uniformly into a column.
A constant flow of the carrier gas passes through the column and transports solute molecules in the gas phase. The column is wound to fit inside an oven for precise temperature control.
A sample of the analyte is introduced by syringe injection into the heated injector tube, where it is vaporized and mixed with carrier gas. As the sample vapor is carried through the column by the carrier gas, the analyte partitions between the gas and liquid phases according to the analyte components' solubility in the liquid at the column operating temperature.
This equilibrium partitioning continues as the sample is moved through the column by the carrier gas. The rate at which the sample travels through the column is determined by the sample solubility in the stationary phase, the carrier gas flow rate, and the temperature. Each component travels at a characteristic rate, and if the column has sufficient length and resolving power, the sample will be completely separated by the time it reaches the detector.
The detector located at the column exit is the ITD mass spectrometer. It records the total number of ions entering the mass analyzer from the column.
The chromatogram produced is called the total ion chromatogram. Each point in the chromatogram is a mass spectrum.
Each component is identified by comparing its "retention time", the length of time that it remains in the column, to that of a standard.
The retention time of a vapor depends on the column temperature limits and ramp rate, the column length, type of stationary phase, and carrier gas velocity.
If these variables are kept constant, the retention time of a component may be tentatively identified by comparison to the retention time of a known standard run under identical operating conditions.
If the response of the detector is linear, the area under a peak accurately represents the quantity of the component present. If it is not, calibration for detector response to the types of components expected to be in the analyte yields a set of response factors which convert the reported area percentages to quantitative weight percentages.
For a given gas chromatography column, the van Deemter theory is useful for determining the flow rate, which gives optimum efficiency at a given column temperature for a particular compound. HETP is the "height equivalent to a theoretical plate," and results from the treatment of gas chromatographic separations in terms of repeated equilibrations between a moving and a stationary phase.
HETP for a particular gas flow rate is calculated from the total number of theoretical plates N and column length Li. The first term in the van Deemter equation accounts for eddy diffusion, the second term accounts for molecular diffusion, and the third term accounts for non equilibrium effects due to flow of the mobile phase.
For a particular column at constant temperature, the optimum carrier gas flow rate is that for which the HETP is a minimum. If the sample contains materials with a wide range of boiling points, separation of all components isothermally is not practical.
When the column is operated at low temperatures, the more volatile components will be distributed between the gas and liquid phases and will pass rapidly through the column, giving sharp, well-resolved peaks. The high-boiling components, however, will remain dissolved in the stationary phase and will be eluted very slowly, if at all.
Since the vapor pressure of the latter solutes is low, partitioning will occur over broad bands of stationary phase, resulting in broad, poorly resolved peaks.Thermo Fisher Scientific is dedicated to improving the human condition through systems, consumables, and services for researchers.
In this lab, we will examine the phosphoric acid catalyzed dehydration of 2-methylcyclohexanol. Gas chromatography will be used to monitor the outcome of the reaction. From the chromatogram, we will calculate the retention times of the product(s) as well as the relative ratio of product(s).
Nov 18, · chromatography, the mobile phase is a gas that carries the analytes through the column and is therefore referred to as the carrier gas. The stationary phase for this experiment is a silicon phase. Chromperfect chromatography software and chromatography data systems for gas and liquid chromatographs HPLC and GC analysis.
In gas chromatography, the moving phase ("mobile phase") is a carrier gas, usually an inert gas such as helium or an unreactive gas such as nitrogen. The stationary phase is a microscopic layer of liquid or polymer on an inert solid support, inside a piece of glass or metal tubing called a column (a homage to the fractionating column used in /5(13).
Experiment 8: Gas Chromatography (GC) In this experiment, mixtures of volatile organic compounds will be separated and temperature in your lab notebook. The carrier gas flow rate is adjustable for both columns and, You will write formal report for this laboratory.