Mini GC Experiment Procedures

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Questions and Answers

In the context of the experiment, what is the purpose of injecting 0.2 μL of the unknown mixture?

  • To test the sensitivity of the Mini GC's detector to various compounds.
  • To vaporize the unknown mixture and separate its components based on their volatility. (correct)
  • To maximize the concentration of the unknown mixture for accurate integration of peaks.
  • To ensure that the Mini GC is properly calibrated and ready for analysis.

What is the significance of integrating the peaks from left to right in the chromatogram of the unknown mixture?

  • It facilitates the comparison of peak areas to those obtained from known substances.
  • It helps to calibrate the Mini GC by creating a standard peak area for reference.
  • It ensures that the area of each peak is accurately calculated for quantitative analysis.
  • It allows for easier identification of the individual components based on their retention times. (correct)

Which of the following steps is NOT included in the procedure for testing a known substance with the Mini GC?

  • Saving the data file for later analysis.
  • Integrating the peaks of the chromatogram to analyze the components.
  • Injecting 0.2 μL of the substance into the Mini GC. (correct)
  • Adjusting the Temperature-Pressure profile of the Mini GC.

When testing the unknown mixture, why is it essential to save the data file?

<p>To compare the unknown mixture's data to the known substances' data for identification. (C)</p> Signup and view all the answers

Which of the following is the MAIN purpose of the Mini GC in this experiment?

<p>To identify the individual components of a mixture based on their volatility. (D)</p> Signup and view all the answers

What is the specific volume of propyl acetate to be drawn up for injection?

<p>0.10 μL (D)</p> Signup and view all the answers

What should be done if the syringe needle sticks while being inserted into the injection port?

<p>Rotate it slightly while inserting. (A)</p> Signup and view all the answers

How many flushes might be needed to clean the syringe and needle adequately?

<p>More than three flushes (D)</p> Signup and view all the answers

What indicates that the syringe and needle are suitably clean?

<p>The syringe plunger moves smoothly. (C)</p> Signup and view all the answers

What action should be taken immediately after starting data collection?

<p>Depress the syringe plunger. (C)</p> Signup and view all the answers

What is the recommended procedure after collecting a sample with the syringe?

<p>Wipe the needle and prepare for injection. (A)</p> Signup and view all the answers

What should be done with the name of the compound after selecting and integrating the peak?

<p>Replace it with the compound's name. (A)</p> Signup and view all the answers

What should be selected to initiate data collection for a new sample?

<p>New Experiment (C)</p> Signup and view all the answers

What is the purpose of cleaning the syringe with methanol during the procedure?

<p>To prevent contamination of the known substances (D)</p> Signup and view all the answers

What is the final temperature set in the Mini GC procedure?

<p>65°C (D)</p> Signup and view all the answers

What is the recommended action if the syringe plunger is pulled back too far?

<p>It could damage the syringe and affect measurements (A)</p> Signup and view all the answers

What is the primary purpose of gas chromatography in this lab experiment?

<p>To identify substances in a mixture based on retention times (D)</p> Signup and view all the answers

What is the pressure setting for the Mini GC?

<p>4.0 kPa (B)</p> Signup and view all the answers

In gas chromatography, what role does the stationary phase play?

<p>It interacts with the compounds to separate them (D)</p> Signup and view all the answers

Why is it important to wait for the Mini GC to indicate it is ready before injecting the sample?

<p>To ensure accurate data collection (B)</p> Signup and view all the answers

Which of the following is essential when disposing of chemicals after the experiment?

<p>Dispose in the Non-halogenated Organic Waste Container (A)</p> Signup and view all the answers

What property of a compound allows it to pass more quickly through the gas chromatography column?

<p>Fewer intermolecular interactions with the stationary phase (D)</p> Signup and view all the answers

What is the total length of the gas chromatography run?

<p>10.0 min (D)</p> Signup and view all the answers

Which component serves as the mobile phase in the gas chromatography setup detailed in the experiment?

<p>Atmospheric air (C)</p> Signup and view all the answers

How does the retention time of a compound in gas chromatography generally relate to its intermolecular interactions with the stationary phase?

<p>Stronger intermolecular interactions result in longer retention times (C)</p> Signup and view all the answers

What is the initial temperature setting for the gas chromatography process?

<p>35°C (B)</p> Signup and view all the answers

Which of the following is an application of gas chromatography?

<p>Performing drug tests and toxin screens (C)</p> Signup and view all the answers

What characteristic of the Vernier Mini GC's column affects the retention time of the compounds?

<p>The nonpolar coating of the stationary phase (B)</p> Signup and view all the answers

Which type of chromatography is primarily used by chemists for identifying organic compounds?

<p>Gas chromatography (C)</p> Signup and view all the answers

What does the retention time in gas chromatography indicate?

<p>The specific time a compound takes to exit the column after injection (C)</p> Signup and view all the answers

Which factor does NOT significantly affect a compound's retention time in gas chromatography?

<p>Molecular shape of the compound (C)</p> Signup and view all the answers

How do more volatile compounds behave in gas chromatography?

<p>They move through the column more rapidly (B)</p> Signup and view all the answers

What is the role of the chemical sensor in gas chromatography?

<p>To produce electrical responses proportional to the concentration of the compounds (B)</p> Signup and view all the answers

Which of the following compounds would most likely interact strongly with a polar stationary phase?

<p>Ethanol (D)</p> Signup and view all the answers

What safety precautions should be taken when using methanol and other volatile substances?

<p>Avoid flames and do not inhale or swallow any chemicals (C)</p> Signup and view all the answers

What is the primary purpose of identifying unknown compounds in gas chromatography?

<p>To identify the specific substances present in a mixture (D)</p> Signup and view all the answers

Which compound is least likely to be highly retained in a nonpolar stationary phase?

<p>Ethanol (A)</p> Signup and view all the answers

Flashcards

Retention Time

The unique time for a compound to exit the chromatography column.

Gas Chromatography

A technique for identifying compounds in a mixture based on their retention times.

Stationary Phase

The nonpolar coating that retains solutes of similar polarity in chromatography.

Mobile Phase

The phase that carries compounds through the chromatography column.

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Volatile Compounds

Compounds with lower boiling points that move quickly through the column.

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Hydrogen Bonds

Interactions that can affect retention time, especially in polar compounds.

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Molecular Weight

A factor that may slightly influence the retention time in chromatography.

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Chromatogram

A visual output showing the presence of compounds by peaks.

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Handwashing Protocol

Wash hands with soap and water before lab exit.

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Non-halogenated Waste Disposal

Use Non-halogenated Organic Waste Container for chemical disposal.

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Gas Chromatography Setup

Prepare Vernier Mini GC for data collection: temperature and time settings.

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Initial Temperature Setting

Set the initial temperature to 35°C for gas chromatography.

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Final Temperature in GC

Final temperature for the GC process is set to 65°C.

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GC Pressure Setting

Set pressure to 4.0 kPa for the GC operation.

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Syringe Cleaning Procedure

Clean glass syringe with methanol; fill, expel, and repeat.

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Syringe Handling Care

Handle the glass syringe gently to avoid damage.

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Gas Chromatography (GC)

A technique used to separate and analyze compounds in gaseous mixtures.

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Intermolecular Interactions

Forces that determine how compounds adhere to the stationary phase.

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Vernier Mini GC

An apparatus used in the lab for gas chromatography experiments.

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Affinity

The tendency of a substance to interact with the stationary phase.

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Mini GC profile

The temperature-pressure setting specific for the Mini Gas Chromatograph during analysis.

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Unknown mixture

A sample with uncharacterized components to be identified using chromatography.

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Integration of peaks

The process of calculating the area under peaks on a chromatogram to quantify components.

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Data file saving

The action of storing test results in the Vernier Instrumental Analysis program for later use.

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Propyl Acetate

A solvent used in gas chromatography for sample injection.

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Syringe Cleaning

The process of flushing the syringe to remove previous samples before use.

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Injection Port

The entry point on the Mini GC where the sample is injected.

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Data Collection Start

The moment data analysis begins after injecting the sample.

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Peak Integration

Selecting and quantifying a peak on the chromatogram for analysis.

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Retention Time Measurement

The time a compound takes to pass through the detector in chromatography.

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Temperature-Pressure Profile

Settings for the Mini GC that must be replicated for each run.

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Kimwipe® Usage

A special wipe used to clean the syringe needle carefully.

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Study Notes

Gas Chromatography

  • Gas chromatography (GC) is a technique for separating complex mixtures of volatile substances
  • It separates compounds based on their interactions with a stationary phase and a mobile phase
  • Substances with stronger interactions with the stationary phase will take longer to elute
  • The unique time a compound takes to exit the column is called retention time
  • Retention time is used to identify components in a mixture
  • Retention time depends on volatility (lower boiling point = faster elution) and the forces between the stationary and mobile phases
  • A gas chromatograph (GC) has a nonpolar stationary phase (coated column) that carries the sample through the column
  • The mobile phase is atmospheric air

Experimental Objectives

  • Measure and analyze the retention time of six substances using a Vernier Mini GC
  • Measure and analyze the retention time of an unknown mixture
  • Identify the substances in the unknown mixture based on retention times

Safety Note

  • Methanol, ethanol, propyl acetate, butyl acetate, 2-butanone, and 4-methyl-2-pentanone are flammable. Avoid open flames.
  • Handle chemicals carefully. Avoid inhaling vapors. Wear appropriate PPE
  • 4-methyl-2-pentanone is hazardous to skin, eyes, ingestion and inhalation
  • Do not inhale or swallow any chemicals
  • Wear appropriate safety equipment
  • Wash hands with soap and water before leaving the lab

Waste Disposal

  • Dispose of chemicals in the "Non-halogenated Organic Waste Container"

Procedure Part 1: Testing Known Compounds

  • Obtain vials of six known substances and an unknown mixture
  • Prepare the Vernier Mini GC for data collection
  • Set Temperature and Pressure values for the Mini GC
  • Clean the syringe with methanol, then propyl acetate
  • Inject 0.1µL of each known compound into the column
  • Collect and record data for each compound, noting retention times and peak areas.
  • Repeat steps 3-5 for the unknown mixture, using 0.2µL

Procedure Part 2: Testing Unknown Mixture

  • Repeat steps 4-10 from part 1 for each unknown compound

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