week 3

Podcast

Play an AI-generated podcast conversation about this lesson

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?

The specific dyes present if the fibre is colored. Signup and view all the answers

What role does the mobile phase play in chromatography?

It carries the different components through the stationary phase. Signup and view all the answers

What does the area under each peak in HPLC represent?

The amount of that compound present Signup and view all the answers

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

Rapid analysis time Signup and view all the answers

Which statement about HPLC and GC is true?

Both methods can distinguish structurally similar compounds. Signup and view all the answers

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

It offers simple and inexpensive equipment Signup and view all the answers

Which of the following is an application of HPLC?

Determining the presence of illegal drugs Signup and view all the answers

What is the basis of infra-red spectroscopy?

Molecular vibrations Signup and view all the answers

What factors affect the stretching frequency in molecular vibrations?

Masses involved and stiffness of the bond Signup and view all the answers

Why is chromatographic comparison not always definitive as evidence?

It leaves room for reasonable doubt Signup and view all the answers

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

Ionization energy Signup and view all the answers

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

Different modes of vibrations Signup and view all the answers

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

Against standard samples Signup and view all the answers

What property differentiates IR absorptions among various molecules?

The specific frequencies absorbed due to their structures Signup and view all the answers

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

High Pressure Liquid Chromatography Signup and view all the answers

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

1500 - 1700 cm-1 Signup and view all the answers

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

The mass of the ion Signup and view all the answers

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

Ionization 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?

Triple bonds Signup and view all the answers

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

It represents the molecular weight of the compound. Signup and view all the answers

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

Diamorphine Signup and view all the answers

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

It is the same as the standard compound. Signup and view all the answers

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

100 - 10,000 V Signup and view all the answers

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

Single bonds Signup and view all the answers

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

The unknown compound is identified definitively. Signup and view all the answers

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

To analyze the mixture of compounds by their distance traveled Signup and view all the answers

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

Through chemical staining or UV light Signup and view all the answers

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

Match of distance traveled with standard compounds Signup and view all the answers

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

It operates by controlling temperature in an oven Signup and view all the answers

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

The amount of that compound present Signup and view all the answers

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

HPLC uses a liquid mobile phase Signup and view all the answers

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

Having too many compounds in the mixture Signup and view all the answers

What is a common characteristic of compounds in gas chromatography?

They move through the column at different speeds Signup and view all the answers

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

Operates solely at room temperature Signup and view all the answers

What role does pressure play in high performance liquid chromatography?

It helps move the liquid sample through the packed stationary phase Signup and view all the answers

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

The sample contains different components than standards Signup and view all the answers

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

Thin layer chromatography Signup and view all the answers

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

Volatility and interaction with the stationary phase Signup and view all the answers

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

Components separate based on their retention time Signup and view all the answers

What is the molecular weight of cocaine (C17H21NO4)?

303 Signup and view all the answers

What does the fragmentation pattern in mass spectrometry act like?

A molecular fingerprint Signup and view all the answers

Which process combines separation and identification in a single instrument?

GC-MS Signup and view all the answers

What are isomers?

Different molecules with the same atoms arranged differently Signup and view all the answers

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

Mass-to-charge ratio Signup and view all the answers

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

GC Signup and view all the answers

Which statement about mass spectrometry is true?

It identifies substances by ionization and fragmentation Signup and view all the answers

How is identification achieved in Infrared spectroscopy?

By observing molecular stretching and bending Signup and view all the answers

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

To automate the injection of samples Signup and view all the answers

Which component of cocaine does not prove its identity?

Fragmentation pattern Signup and view all the answers

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

They break into fragments Signup and view all the answers

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

They have different arrangements of atoms Signup and view all the answers

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

To isolate compounds for analysis Signup and view all the answers

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.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

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.