How does gas chromatography work? All you need to know

Overview

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• Source: Microbioz India


• Date: 18 Oct,2023

Compounds that can be vaporized without decomposing can be separated from one another and examined using the analytical technique known as gas chromatography (GC). Particularly useful in the pharmaceutical business, forensics, environmental analysis, and chemistry.

Here is a description of the operation of gas chromatography:

Sample Injection:

The procedure starts with the injection of a tiny quantity of the sample into the GC apparatus. Either manually or via an autosampler, this can be done.

Vaporization:

The sample is vaporized in the injector port if it is not already gaseous. In most cases, this entails heating the sample to turn it into a gas.

Carrier Gas:

A carrier gas is used to transport the vaporized sample through the GC column. This gas is commonly an inert gas, such as helium, nitrogen, or hydrogen. The application and the substances being studied determine the best carrier gas to use.

GC Column:

The column is the brain of the GC system. This is a lengthy, narrow tube that is coated with or filled with a stationary phase. The stationary phase can interact with the sample chemicals in a variety of ways, depending on whether it is polar or nonpolar.

Schematic diagram of gas chromatography operation

Separation:

The various chemicals in the sample interact with the stationary phase to variable degrees as the carrier gas forces the vaporized sample through the column. Stronger interactions cause compounds to move through the column more slowly than weaker interactions for them to move through the column more quickly.

Detector:

A detector at the bottom of the column gauges the concentration of the compounds as they emerge. Mass spectrometers (MS), thermal conductivity detectors (TCD), and flame ionization detectors (FID) are examples of common detectors.

Data analysis:

As substances elute from the column, a signal is produced by the detector. The compounds in the sample are identified and quantified using the retention time (the amount of time it takes for a chemical to exit the column) and the peak area in the detector signal.

Chromatogram:

A chromatogram, which is a graph of detector response (y-axis) vs time (x-axis), represents the data gathered from the detector. A distinct compound is represented by each peak in the chromatogram.

Identification:

Retention durations and mass spectra of sample peaks (if using a mass spectrometer) are often compared to established standards or a database of chemicals in order to identify a compound.

Troubleshooting Gas Chromatography: Tips and Techniques

A potent analytical method for isolating and measuring the chemicals in a mixture is gas chromatography (GC). But like any analytical technique, it occasionally runs into problems that need to be fixed. Here are some strategies and advice for resolving typical issues with gas chromatography:

Bad peak form:

1. A polluted column is the most frequent reason for an unsatisfactory peak shape. Try conditioning the column for many hours at a high temperature (about 10–20 °C above the maximum working temperature).
2. Broad peaks may result from oversampling the column, which overloads it. The sample size should be decreased or diluted.
3. Make sure your sample is sufficiently dissolved in the solvent by checking its solubility. Alternately, change the injection volume or use a suitable solvent.

Standard Noise:

1. Leaks: Inspect the system for leaks, paying special attention to the septum, connections, and column. Tighten connections and swap out any damaged parts.
2. A contaminated detector can be present. According to the manufacturer’s recommendations, clean or replace the detector’s components.
3. Check the purity of the carrier gases to make sure they’re very pure. The gas’s impurities may cause noise.

Decreased Sensitivity

1. A dirty injector or detector should be cleaned in accordance with the manufacturer’s instructions.
2. Column Deterioration: Over time, columns deteriorate. If the column is outdated or damaged, replace it.
3. Flow Rate: Verify that the flow rate is in accordance with the parameters of the procedure. Sensitivity problems can result from deviations.

Shifts in Retention Time:

1. Make sure the temperature in the column oven isn’t fluctuating. Retention times can alter even with little variations.
2. Retention times might also be impacted by incorrect flow rates. calibrate and keep the flow control system up to date.

Phantom Peaks

1. Column Bleed: Stationary phase bleed may result in ghost peaks. If one is available, use a low-bleed column.
2. Ghost peaks may be the result of sample impurities, or contaminants. Make sure to prepare your samples properly and use high-purity solvents.

Peaks that are in front or behind:

1. Peaks that are tailing may indicate an excessively high injector temperature. Reduce the pressure or split-inject.
2. Saturation of the detector may occur if peaks are in front. Or, divide the injection and use a smaller sample concentration.

No Peaks or Resolution Loss

1. Installation of the Column: Ensure that the column is correctly installed, with appropriate connections and carrier gas flow.
2. Details of the method: Verify that the method’s settings for temperature, flow rate, and other variables are appropriate for the analytes and sample type.

Breakage of a column

Handle carefully: The columns are flimsy. Refrain from overtightening connections, extreme temperature changes, and bodily harm.

Carrier Gas Flow Loss

Check Gas Supply: Verify that there are no obstacles in the gas lines and that your gas cylinders or sources are not empty.

Pressure Issues

1. Column Backpressure: A blocked column or restrictor may be indicated by a high backpressure. Examine and clean these parts.
2. Gas Leaks: Gas leaks may be the cause of pressure drops. Verify the system for leaks and seal them.

Since it is so adaptable, gas chromatography can be used for a variety of purposes, such as environmental analysis, food testing, drug testing, and other things. It is a useful method in analytical chemistry since it allows for the exact separation and quantification of molecules within a mixture.