week 3
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Questions and Answers

What is the main principle behind chromatography?

  • Different components move at different speeds through a stationary phase. (correct)
  • Components are identified based on their color.
  • Chromatography separates components based solely on their mass.
  • All components of a mixture are dissolved in a single solvent.

Which statement about Thin Layer Chromatography (TLC) is accurate?

  • TLC involves a thin absorbent layer for separation. (correct)
  • The TLC technique is suitable for identifying components by their electrical charge.
  • The stationary phase in TLC is always a gas.
  • TLC uses a liquid mobile phase only.

How can spectroscopy and spectrometry be utilized in forensic science?

  • To determine the concentration of gases in the air.
  • To identify molecules based on their color spectrum.
  • To analyze the interaction between light and matter to identify substances. (correct)
  • To analyze the weight of solid compounds.

What is typically investigated when analyzing fibres in forensic examinations?

<p>The specific dyes present if the fibre is colored. (A)</p> Signup and view all the answers

What role does the mobile phase play in chromatography?

<p>It carries the different components through the stationary phase. (D)</p> Signup and view all the answers

What does the area under each peak in HPLC represent?

<p>The amount of that compound present (D)</p> Signup and view all the answers

Which of the following is NOT an advantage of HPLC compared to GC?

<p>Rapid analysis time (C)</p> Signup and view all the answers

Which statement about HPLC and GC is true?

<p>Both methods can distinguish structurally similar compounds. (B)</p> Signup and view all the answers

What is a primary advantage of using Gas Chromatography (GC)?

<p>It offers simple and inexpensive equipment (C)</p> Signup and view all the answers

Which of the following is an application of HPLC?

<p>Determining the presence of illegal drugs (C)</p> Signup and view all the answers

What is the basis of infra-red spectroscopy?

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

What factors affect the stretching frequency in molecular vibrations?

<p>Masses involved and stiffness of the bond (C)</p> Signup and view all the answers

Why is chromatographic comparison not always definitive as evidence?

<p>It leaves room for reasonable doubt (C)</p> Signup and view all the answers

Which of the following is NOT a component measured by infra-red spectroscopy?

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

What type of molecular features does infra-red spectroscopy detect?

<p>Different modes of vibrations (A)</p> Signup and view all the answers

In terms of retentivity, what is a necessary comparison in chromatographic evidence?

<p>Against standard samples (C)</p> Signup and view all the answers

What property differentiates IR absorptions among various molecules?

<p>The specific frequencies absorbed due to their structures (B)</p> Signup and view all the answers

What does HPLC stand for in the context of evidence collection?

<p>High Pressure Liquid Chromatography (C)</p> Signup and view all the answers

What is the range for the fingerprint region in infrared spectroscopy?

<p>1500 - 1700 cm-1 (B)</p> Signup and view all the answers

In mass spectrometry, which factor primarily affects the deflection of ions in a magnetic field?

<p>The mass of the ion (A)</p> Signup and view all the answers

What process is described when a sample is vaporized and bombarded by electrons in mass spectrometry?

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

Which bond type is associated with the highest energy and thus found at the highest frequency in infrared spectroscopy?

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

What is the significance of the mass of the molecular ion (M+) in a mass spectrometry analysis?

<p>It represents the molecular weight of the compound. (D)</p> Signup and view all the answers

What component is known as the active ingredient in heroin according to infrared spectroscopy?

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

In infrared spectroscopy, what does a match in the fingerprint region indicate about an unknown compound?

<p>It is the same as the standard compound. (B)</p> Signup and view all the answers

How does the voltage applied during ionization in mass spectrometry typically range?

<p>100 - 10,000 V (C)</p> Signup and view all the answers

Which type of bond is associated with lower energy absorption in infrared spectroscopy?

<p>Single bonds (C)</p> Signup and view all the answers

What is the outcome if an unknown compound's infrared spectrum matches that of a known standard?

<p>The unknown compound is identified definitively. (A)</p> Signup and view all the answers

What is the primary purpose of using a thin layer chromatography (TLC) plate?

<p>To analyze the mixture of compounds by their distance traveled (C)</p> Signup and view all the answers

In thin layer chromatography, how can invisible compounds be made visible?

<p>Through chemical staining or UV light (A)</p> Signup and view all the answers

What indicates that an unknown sample in TLC possibly contains standard compounds?

<p>Match of distance traveled with standard compounds (B)</p> Signup and view all the answers

Which of the following accurately describes gas chromatography (GC)?

<p>It operates by controlling temperature in an oven (D)</p> Signup and view all the answers

What does the area under the peak in gas chromatography represent?

<p>The amount of that compound present (C)</p> Signup and view all the answers

How does high performance liquid chromatography (HPLC) differ from gas chromatography (GC)?

<p>HPLC uses a liquid mobile phase (C)</p> Signup and view all the answers

What prevents all components from showing distinct spots on a TLC plate?

<p>Having too many compounds in the mixture (B)</p> Signup and view all the answers

What is a common characteristic of compounds in gas chromatography?

<p>They move through the column at different speeds (B)</p> Signup and view all the answers

Which of the following is NOT a feature of gas chromatography?

<p>Operates solely at room temperature (A)</p> Signup and view all the answers

What role does pressure play in high performance liquid chromatography?

<p>It helps move the liquid sample through the packed stationary phase (A)</p> Signup and view all the answers

Why might an unknown sample in TLC not show a corresponding standard spot?

<p>The sample contains different components than standards (C)</p> Signup and view all the answers

Which method is considered primarily qualitative in nature, indicating the presence of compounds but not their quantities?

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

What is a determining factor for the separation of compounds in gas chromatography?

<p>Volatility and interaction with the stationary phase (A)</p> Signup and view all the answers

What happens when an unknown sample passes through a gas chromatography column?

<p>Components separate based on their retention time (C)</p> Signup and view all the answers

What is the molecular weight of cocaine (C17H21NO4)?

<p>303 (B)</p> Signup and view all the answers

What does the fragmentation pattern in mass spectrometry act like?

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

Which process combines separation and identification in a single instrument?

<p>GC-MS (C)</p> Signup and view all the answers

What are isomers?

<p>Different molecules with the same atoms arranged differently (A)</p> Signup and view all the answers

In mass spectrometry, the degree of deflection of ions depends on what ratio?

<p>Mass-to-charge ratio (C)</p> Signup and view all the answers

What technique is typically used to separate mixtures before mass spectrometry?

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

Which statement about mass spectrometry is true?

<p>It identifies substances by ionization and fragmentation (C)</p> Signup and view all the answers

How is identification achieved in Infrared spectroscopy?

<p>By observing molecular stretching and bending (A)</p> Signup and view all the answers

What is the role of an auto-sampler in GC-MS?

<p>To automate the injection of samples (C)</p> Signup and view all the answers

Which component of cocaine does not prove its identity?

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

What happens to most molecules in a mass spectrometer during the process?

<p>They break into fragments (D)</p> Signup and view all the answers

Why might two molecules with the same molecular weight differ in mass spectrometry?

<p>They have different arrangements of atoms (C)</p> Signup and view all the answers

What is a key function of Gas Chromatography in GC-MS?

<p>To isolate compounds for analysis (B)</p> Signup and view all the answers

Flashcards

Chromatography

A technique to separate components of a mixture based on their different movement speeds through a stationary phase.

Thin Layer Chromatography (TLC)

A type of chromatography using a thin layer of absorbent material (stationary phase) on a flat surface (plate).

Stationary Phase

The absorbent material in chromatography, that the components of the mixture move over.

Mobile Phase

The liquid or gas that carries the components of the mixture through the stationary phase.

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Mixture Separation

Chromatography separates different components based on their varying movement through a stationary phase.

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HPLC

High Performance Liquid Chromatography is a technique used to separate components of a mixture. It uses a liquid mobile phase and a packed stationary phase.

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HPLC Peak Area

In HPLC, the area under each peak is proportional to the amount of the corresponding compound in the mixture.

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Why use HPLC?

HPLC is efficient, selective, and widely applicable for separating and identifying compounds. It requires small samples and can be used for quantitative analysis (measuring amounts) of components.

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HPLC vs. GC

HPLC is suitable for non-volatile and thermally unstable samples, while GC is better for volatile and thermally stable samples.

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Benefits of GC

Gas Chromatography (GC) is a simpler, faster, and less expensive technique. It's commonly used to analyze volatile and thermally stable substances such as illegal drugs.

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TLC Standard

Known compounds used in TLC to compare with unknown substances.

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Presumptive Test

A test revealing a possible substance, not a definitive confirmation.

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Gas Chromatography (GC)

Technique separating mixtures by boiling point and interactions with stationary material in a column.

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Mobile Phase (GC)

The gas that carries the sample through the column in GC.

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Stationary Phase (GC)

Absorbent material inside the column in GC, influencing component behavior.

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Retention Time (GC)

Time taken for a component to move through the GC column.

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Quantitative Analysis (GC)

Estimating substance amounts using peak areas under GC curves.

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High Performance Liquid Chromatography (HPLC)

Similar to GC, but uses liquid mobile phase for separating components in a mixture.

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Mobile Phase (HPLC)

The liquid that carries the sample through the HPLC column.

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Stationary Phase (HPLC)

Absorbent material in a packed column in HPLC, influencing component behavior.

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Sample Preparation

Process of preparing substances for analysis in analytical methods.

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Infra-red Spectroscopy

A technique that uses infrared radiation to identify and analyze molecules based on their unique vibrational patterns.

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Molecular Vibrations

The movement of atoms within a molecule, such as stretching or bending of bonds.

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Stretching Frequency

The rate at which a bond in a molecule vibrates, determined by the masses of the atoms involved and the stiffness of the bond.

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Bending Modes

Different ways a molecule can bend, causing variations in the infrared absorption pattern.

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Infrared Spectrum

The unique pattern of infrared absorption by a molecule, reflecting its specific molecular vibrations.

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How does IR spectroscopy help identify substances?

By analyzing the absorption pattern of infrared radiation, different molecules can be identified based on their unique vibrational frequencies.

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What are the limitations of IR spectroscopy?

While useful for identifying substances, IR spectroscopy alone is not definitive proof in forensic analysis. Other techniques are needed to confirm findings.

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Fingerprint region

The area in an IR spectrum between 1500 cm-1 and 3000 cm-1, showing complex patterns of absorption caused by various bond vibrations and distortions.

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Diagnostic region

In IR spectroscopy, this region, usually above 3000 cm-1, shows characteristic peaks for specific functional groups like C-H, O-H, or N-H bonds.

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Mass spectrometry (MS)

A technique that identifies and quantifies components of a sample based on their mass-to-charge ratio. Ions are created, accelerated, and sorted by magnetic field, allowing for identification of molecules and fragments.

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Molecular ion (M+)

The ion that represents the complete, unfragmented molecule in mass spectrometry, giving information about the molecule's overall mass.

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Electron bombardment

The process in mass spectrometry where a high-energy electron beam is applied to the sample, causing the molecules to lose electrons and become positively charged ions.

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Deflection in magnetic field

Ions produced in mass spectrometry are separated based on their mass-to-charge ratio. Lighter ions are deflected more strongly in a magnetic field than heavier ions.

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Spectroscopy

A technique that studies the interaction of electromagnetic radiation with matter. Molecular vibration and bond stretching are analyzed to identify molecules and their structures.

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IR spectrum

The graphical representation of the absorption of infrared radiation by a compound, showcasing characteristic peaks that relate to different bonds and functional groups.

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Functional group

A specific group of atoms within a molecule that are responsible for its characteristic chemical properties and reactivity.

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Vibrational modes

The different ways in which molecules can vibrate and stretch their bonds, each producing a unique absorption in the IR spectrum.

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Molecular Weight

The sum of the atomic weights of all atoms in a molecule.

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Isomers

Molecules with the same chemical formula but different structural arrangements of atoms.

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Why does molecular weight not guarantee identity?

Isomers have the same molecular weight but different structures, making it impossible to identify a molecule based on weight alone.

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Mass Spectrometry

A technique that measures the mass-to-charge ratio of ions, allowing for molecular identification.

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Fragmentation in Mass Spectrometry

The process of breaking down molecules into smaller fragments, which provides a characteristic pattern unique to each molecule.

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Mass Spectrum

A graph that shows the abundance of each fragment ion based on its mass-to-charge ratio.

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Mass Spectrum as a Fingerprint

The unique fragmentation pattern of a molecule in a mass spectrum acts as a fingerprint for its identification.

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GC-MS

A hyphenated technique that combines gas chromatography (GC) with mass spectrometry (MS) for separation and identification of components in a mixture.

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MS in GC-MS

Mass spectrometry is used as a detector in GC-MS, identifying each separated component by its fragmentation pattern.

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Auto-sampler

A robot that automatically introduces samples into a GC-MS system for analysis.

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Combining Techniques for Analysis

Techniques like GC, MS, and IR spectroscopy can be combined to provide comprehensive information about a substance's composition and structure.

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Study Notes

Forensic Science - Analysis of Mixtures and Compounds

  • Chromatography is used to separate mixtures. Common types include TLC, GC, and HPLC.

  • Thin Layer Chromatography (TLC) uses a thin absorbent layer (usually silica or alumina) as the stationary phase. A sample is applied, and a solvent moves it up the plate. Colored compounds are visible to the eye; others need chemical staining or UV light. Standards are used for comparison. Presumptive tests can be done, but not definitive.

  • Gas Chromatography (GC) separates components based on their boiling points. A sample is vaporized and carried by a carrier gas through a column. Different components travel at different speeds. The detector measures this and gives a chromatogram. This helps identify the components in the mixture.

  • High Performance Liquid Chromatography (HPLC) uses a liquid mobile phase instead of gas; suitable for non-volatile compounds. Separates by how different components interact with the stationary phase. The detector measures and provides a graph for identification and quantity, similar to GC.

  • Infrared Spectroscopy (IR) identifies compounds based on their molecular vibrations (stretching and bending of chemical bonds). Characteristic absorption bands (peaks) in the IR spectrum act as a fingerprint, identifying a compound.

  • Mass Spectrometry (MS) identifies compounds by their mass-to-charge ratio, which is measured as ions are deflected in a magnetic field by their mass. Fragmentation patterns are unique to different compounds, enabling identification.

  • GC-MS combines gas chromatography and mass spectrometry. GC separates components, and MS identifies each separated component. This is an effective hyphenated technique.

Additional Notes

  • Identifying compounds and the substances present in mixtures are part of forensic science in situations like drug analysis, identifying unknown dyes in fibers and blood or other biological samples from crime scenes.
  • The quantity of certain components can be measured in mixtures.
  • Various techniques are used in forensics to analyze complex mixtures and identify the exact composition.

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Week 3 - Analysis of Mixtures and Compounds PDF

Description

This quiz focuses on various chromatographic techniques used in forensic science to analyze mixtures and compounds. Learn about Thin Layer Chromatography, Gas Chromatography, and High Performance Liquid Chromatography, their principles, and applications in identifying substances. Test your knowledge on key concepts and techniques in forensic analysis.

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