Instrumental Analysis: UV-Visible Spectroscopy
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Questions and Answers

What is the primary purpose of fluorescence spectroscopy in the context of chemical analysis?

  • To analyze the thermal properties of solutions
  • To determine the molecular weight of a substance
  • To estimate the concentration of fluorescent chemicals (correct)
  • To measure the total absorbance of a solution

In the calibration curve provided, what is the value of R², indicating the strength of the correlation between glucose concentration and absorbance?

  • 0.9
  • 0.5
  • 0.75
  • 0.975 (correct)

Calculate the glucose concentration when the absorbance is 0.9 using the provided equation.

  • 8.25 mg/L
  • 7.66 mg/L (correct)
  • 9.10 mg/L
  • 6.50 mg/L

Which of the following is NOT a technique mentioned for elemental analysis?

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

What key difference is highlighted between fluorescence and phosphorescence?

<p>Fluorescence occurs during a brief excited state, whereas phosphorescence lasts longer (C)</p> Signup and view all the answers

What is the primary role of an indicator in chemical analysis?

<p>To change color under specific conditions (C)</p> Signup and view all the answers

How does UV spectroscopy determine the concentration of a colored chemical?

<p>By measuring the absorbance value which is proportional to concentration (D)</p> Signup and view all the answers

In a typical calibration curve, what is plotted on the x-axis?

<p>Concentration of chemicals (C)</p> Signup and view all the answers

What does the term 'monochromator' refer to in UV spectroscopy?

<p>A device that separates wavelengths of light (B)</p> Signup and view all the answers

How is an unknown concentration of a chemical estimated in a solution?

<p>Using the calibration curve prepared from known concentrations (D)</p> Signup and view all the answers

What property of light is mainly measured in UV spectroscopy?

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

When using a calibration curve, how do you calculate concentration from absorbance?

<p>By solving the equation $y = mx + b$ for concentration (C)</p> Signup and view all the answers

What is the purpose of preparing samples with known concentrations before testing unknown samples?

<p>To create a calibration curve for accurate concentration estimation (A)</p> Signup and view all the answers

Flashcards

Calibration Curve

A graph that shows the relationship between the absorbance of a solution and the concentration of the analyte. It is used to determine the concentration of an unknown sample by measuring its absorbance and finding the corresponding concentration on the curve.

Fluorescence Spectroscopy

A technique that measures the fluorescence (emission) of a solution when it is excited at a specific wavelength. The intensity of the fluorescence is dependent on the concentration of the fluorescent chemical.

Emission Wavelength

The wavelength at which the maximum fluorescence emission is observed for a fluorescent compound. It is unique to each fluorescent molecule.

Excitation Wavelength

The wavelength at which a fluorescent compound absorbs the maximum amount of light to become excited. It is unique for each fluorescent molecule.

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Fluorescence

The ability of a substance to absorb light and emit light at a longer wavelength. It is used to measure the antioxidant capacity of substances and can be measured by using a fluorescence spectrometer.

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Indicators

Chemicals that change color under specific conditions, often used to indicate pH levels or the presence of a specific chemical.

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UV (Ultraviolet) Spectroscopy

A technique that measures the amount of light absorbed by a solution at specific wavelengths, often linked to the concentration of a colored substance.

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Monochromator

A component of a UV-Vis spectrometer responsible for separating and focusing specific wavelengths of light onto the sample.

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UV-Vis Spectrophotometry

The process of using a calibration curve to determine the concentration of an unknown sample based on its measured absorbance.

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Absorbance (A)

The amount of light absorbed by a sample, directly related to the concentration of the substance absorbing the light.

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Unknown Sample

A solution of unknown concentration whose concentration needs to be determined using UV-Vis spectrophotometry.

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Blood Test for Glucose

The procedure involving measuring known glucose solution absorbance to create a calibration curve, allowing for the determination of unknown blood glucose concentrations.

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Study Notes

Instrumental Analysis

  • Techniques for measuring chemical composition and properties
  • Indicators are chemicals that change colors under specific conditions
  • pH-dependent indicators change color based on H+ concentration
  • Some indicators react with specific chemicals altering their color

UV (Ultraviolet) Spectroscopy

  • Measures absorbance (A) of solutions
  • Absorbance is directly proportional to concentration of colored chemicals
  • Intensity of colors depends on the concentration of colored chemicals

Monochromator

  • Separates wavelengths, directing the desired wavelength to the target
  • Uses a prism or diffraction grating

UV-Visible Spectrometer and Working Principle

  • Includes a light source, wavelength selector, monochromator, sample, detector, and signal processing unit
  • Measures absorbance proportional to concentration of the chemical

Methodology (UV-Vis)

  • Prepare solutions with known concentrations of a chemical
  • Generate a calibration curve
  • Measure absorbance of an unknown solution
  • Use the calibration curve to determine the unknown concentration

Example

  • Calibration curve showing absorbance values for various known chemical concentrations
  • Shows a linear relationship between chemical concentration and absorbance
  • Provides an example of calculating the concentration of an unknown sample (0.36 mM)

Blood Test Question

  • Indicator for measuring glucose concentration in blood
  • Measure absorbances of samples with known glucose concentrations at 500 nm
  • Data used for creating calibration curves

Blood Glucose Concentration

  • Demonstrates relationship between glucose concentration (mg/L) and absorbance
  • Calibration curve shows linear relationship between concentration and absorbance (f(x)= ... formula included)
  • Uses the calibration curve or formula to determine unknown concentrations (example of calculation)

Fluorescence Spectroscopy

  • Measures fluorescence (emission) of samples after excitation at a specific wavelength
  • Emission depends on excitation wavelength and concentration
  • Estimates concentration of fluorescent chemicals
  • Antioxidant capacity measurements

Fluorescence Spectrometer and Working Principle

  • Light source, excitation monochromator, sample holder, emission monochromator, detector, readout device
  • Directs and detects emitted light for analysis

Calibration Curve for Fluorescence Spectrometer

  • Prepare samples with known concentrations
  • Measurements taken at specific excitation and emission wavelengths

Elemental Analysis

  • Techniques used for analyzing chemical composition of elements
  • Includes flame photometer, atomic absorption, and ICP methods

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Related Documents

Week 10 UV and Fluorescence Analysis PDF

Description

Explore the techniques and principles of UV-Visible spectroscopy in this quiz. You'll learn about the measurement of absorbance, the role of monochromators, and how concentration affects color intensity in solutions. Test your knowledge on the methodologies used in instrumental analysis.

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