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Gas Chromatography Testing

Gas Chromatography (GC) incl. TCD &FID

Gas Chromatography
Volatile Organic Compound Image

What is GC?

The gas chromatography (GC) analytical testing method is used to separate and analyze components of a complex mixture based on their differences in physical and chemical properties. GC is typically used for various applications such as analyzing the composition of gases, separating complex mixtures, determining purity of compounds, identifying unknown substances, and more. For example, it can be used to separate compounds in a gas-liquid and allow volatile substances in the gas phase to be analyzed. In gas chromatography, a sample’s components are dissolved in a solvent and vaporized. By distributing the sample between two phases – a stationary phase and a mobile phase – the analytes are separated. Thus, GC allows us to detect small molecules in a big structure, so we often use this method to test fatty samples, which typically contain small components.

How Gas Chromatography Works:

  1. Sample Injection: A small amount of the analyte (often a dissolved sample) is injected into the gas chromatograph.
  2. Column: The sample is then passed through a long, narrow column usually internally coated with a stationary phase (a solid or a liquid). The column is typically housed in an oven to maintain a constant temperature. This process separates the various compounds within the sample.
  3. Carrier Gas: An inert gas such as hydrogen is used as the carrier gas in what is called the “mobile phase” as the gas helps move the sample through the column.
  4. Separation: As the sample travels through the column, it interacts with the “stationary phase.” Different components in the sample interact differently with the stationary phase based on their molecular weight, boiling point, polarity, and other properties. This interaction causes the components to separate.
  5. Detection: Different compounds within the sample are then separated by interacting in the stationary phase and eluting at different times. As the separated components exit the column, they are detected by a detector. The time taken for a component to travel through the column (retention time) is characteristic of that component and is used for identification. Common detectors include flame ionization detectors (FID), thermal conductivity detectors (TCD), electron capture detectors (ECD), and mass spectrometers (MS).
  6. Output: The output of the detector is a chromatogram, which is a graph that shows the intensity of the detected components as a function of time. The area under the peaks in the chromatogram is proportional to the amount of each component in the sample, allowing for quantitative analysis.

When Is GC Commonly Used?

Gas chromatography (GC) is commonly used across various scientific and industrial fields due to its versatility and ability to separate and analyze a wide range of compounds. Any samples containing large amounts of organic volatiles can easily be analyzed using GC. Some common applications of gas chromatography that we test for at NJ Labs include:

  1. Pharmaceutical drug analysis to assess product quality and purity
  2. Cosmetics product analysis
  3. Compound identification & purity analysis in chemical research and quality control
  4. Volatile Organic Compounds (VOC) analysis related to the environment
  5. Food and Beverage flavor and aroma analysis and food safety testing

Gas chromatography (GC) is also a versatile analytical technique because it can be used to analyze a wide range of compounds, including gases, liquids, and solids. Here are some examples of compounds from that can be analyzed using gas chromatography:

  • Volatile organic compounds (VOCs) like benzene, toluene, and xylene
  • Hydrocarbons (e.g., methane, ethylene, propane)
  • Alcohols (e.g., ethanol, methanol)
  • Esters (e.g., ethyl acetate, methyl benzoate)
  • Aromatic compounds (e.g., phenol, aniline)
  • Organic acids (e.g., acetic acid, citric acid)
  • Polymers (e.g., polyethylene, polypropylene)
  • Fats and oils (e.g., triglycerides)
  • Pharmaceuticals (e.g., aspirin, ibuprofen)

Gas chromatography is a valuable tool used across a wide range of industries and applications due to its high sensitivity, accuracy, and the ability to provide valuable insights into the composition and characteristics of various compounds in different states of matter.


 

Residual Solvent Analysis by Headspace Gas Chromatography (HSGC)

Residual solvents in pharmaceutical products are organic volatile compounds that are used or created when drug substances, excipients, or additives are manufactured, prepared, or packaged and stored. Residual solvents are often crucial in the synthesis of drug substances because they are necessary to ameliorate the quality of drug substances or excipients. However, because they have no therapeutic value, if residual solvents are not completely removed by practical manufacturing methodologies, they must be evaluated and justified. Pharmaceutical products should contain low levels of residual solvents as determined by safety data. However, residual solvents may be harmful to human health and to the environment if their presence exceeds tolerance limits as determined by safety data. As a result, residual solvents testing has become an important quality control player in pharmaceuticals.

What is Headspace Analysis?

In recent years, testing for residual solvents has grown as the demand by the FDA for such testing has increased. New Jersey Laboratories owns the latest technology in this space, called Headspace GC (HSGC). HSGC is ideal because of its ability to quantify individual solvents. The term “headspace” refers to that portion of the sample container above the sample material where gas or vapor accumulates. Headspace analysis focuses upon analyzing this gas or vapor phase, which typically contains volatile organic compounds (VOCs), residual solvents or other substances that can be released from the sample into the headspace. The headspace technique also allows for the analysis of volatile compounds present in the sample without necessarily introducing the entire sample into the instrument. This is particularly useful for samples that are sensitive to temperature changes or where direct introduction of the sample may alter its composition or characteristics. Some examples of volatile compounds that fit this description include the following:

  1. Volatile Organic Compounds (VOCs):Many organic compounds, including hydrocarbons, alcohols, ketones, and ethers, can be sensitive to temperature changes. Direct exposure to high temperatures can lead to thermal degradation or altered composition.
  2. Fragrance Compounds:Fragrance compounds used in perfumes, air fresheners, and other consumer products can be sensitive to temperature changes and may undergo changes in composition or odor profile when exposed to heat.
  3. Flavor Compounds:Volatile flavor compounds found in food and beverages, such as esters, aldehydes, and terpenes, can be sensitive to temperature. Temperature changes can alter the sensory characteristics and taste perception.
  4. Essential Oils:Essential oils obtained from plants contain a variety of volatile compounds that contribute to their aroma and therapeutic properties. These compounds can be sensitive to temperature, which may affect the oil’s composition and fragrance.
  5. Pharmaceuticals:Volatile compounds in pharmaceutical products, especially those used in inhalation therapies or as volatile drug formulations, may be sensitive to temperature changes that could alter their stability, potency, or delivery characteristics.
  6. Polymer Residuals:Volatile compounds that may remain as residuals in polymer products can be sensitive to temperature changes, potentially leading to off-gassing or altered product properties.

Headspace analysis allows for the controlled extraction and analysis of these volatile compounds without exposing them to the direct analytical system, mitigating potential alterations in composition or characteristics that might occur with direct sample introduction. Although most laboratories do basic testing on residual solvents, New Jersey Laboratories also performs more difficult tests on solvents such as poloxamers which are excipients that can also aid in drug delivery. We are highly proficient in residual solvent analysis by headspace gas chromatography and can walk you through every step.

Methods NJ Labs Performs for Residual Solvents

We perform the following methods for residual solvents:

USP
Chapter
Test
<228>Ethylene Oxide and Dioxane
<467>Organic Volatile Impurities
<469>Ethylene Glycol, Diethylene Glycol and Triethylene Glycol in Ethoxylated Substances

The International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals (ICH) categorizes residual solvents into three classes based on toxicity and potential risks to human health. These classifications have been widely adopted by regulatory agencies and pharmacopeias throughout the world including the United States Pharmacopeia (USP). Class 1 solvents are known to carcinogenic or highly toxic and are to be avoided. Class 2 solvents have low toxic potential but may cause adverse effects if they exceed the acceptable daily intake (ADI) and the maximum daily dose of the pharmaceutical product. Finally, Class 3 solvents have low toxic potential and are generally regarded as safe for pharmaceutical use at low levels. Implementing methods such as USP <467> (above) requires specialized equipment with careful selection of operating parameters. Our scientists have extensive experience in meeting your gas chromatography and residual solvent testing requirements.

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