Visible Light Spectrum and Spectrophotometry

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Questions and Answers

How does atomic absorption spectrophotometry (AAS) determine the concentration of a sample?

By calculating the reflectance of the sample

By measuring the emitted light after atomization

By detecting the amount of UV light transmitted

By measuring the light absorbed by an atom (correct)

What is a primary clinical application of flame emission spectrophotometry (FES)?

Determining molecular weight of proteins

Measuring electrolytes like Na and K (correct)

Analyzing trace metals in tissues

Detecting impurities in colorless solutions

What light source is used in atomic absorption spectrophotometry?

Xenon flash lamp

Incandescent bulb

Hollow-cathode lamp (correct)

Laser diode

Which of the following best describes the Beer-Lambert law?

Absorbance is directly proportional to both concentration and path length Signup and view all the answers

What principle does infrared spectrophotometry primarily measure?

The vibrational spectrum of molecules Signup and view all the answers

In flame emission spectrophotometry (FES), how is concentration determined?

By measuring the emitted light from excited atoms Signup and view all the answers

Which technique is generally considered obsolete due to the development of ion selective electrodes (ISE)?

Flame emission spectrophotometry Signup and view all the answers

Which type of spectrophotometer is primarily used for measuring colorless solutions?

UV light spectrophotometer Signup and view all the answers

What is the wavelength range of visible light?

350-700 nm Signup and view all the answers

Which type of cuvette is most suitable for a UV light spectrophotometer?

Quartz cuvettes Signup and view all the answers

What is the purpose of the photomultiplier tube (PMT) in a spectrophotometer?

To convert light into electrical energy Signup and view all the answers

Which spectrophotometer type uses one beam of light and measures only one sample at a time?

Single beam spectrophotometer Signup and view all the answers

How does a double beam spectrophotometer improve accuracy?

It uses two beams to eliminate light fluctuations. Signup and view all the answers

What does the readout system in a spectrophotometer provide?

Display of the output from the photodetector Signup and view all the answers

Which color corresponds to the wavelength range of 651-700 nm?

Orange Signup and view all the answers

What does lambda max (λmax) signify in spectrophotometry?

The wavelength of maximum absorbance of a substance Signup and view all the answers

What is the principle behind photoelectric colorimetry?

It uses a filter to isolate a specific wavelength of light for analysis. Signup and view all the answers

How is the concentration of an unknown solution in a photoelectric colorimetry setup calculated?

By taking the ratio of absorbance of the unknown to the concentration of the standard. Signup and view all the answers

Which of the following solutions can a spectrophotometer analyze that a photoelectric colorimeter cannot?

Both colored and non-colored solutions. Signup and view all the answers

What does the Beer-Lambert Law relate to in spectrophotometry?

The relationship between absorbance and concentration. Signup and view all the answers

What type of light sources can spectrophotometry utilize that photoelectric colorimetry cannot?

Both UV and infrared light. Signup and view all the answers

In spectrophotometry, what is the role of the monochromator?

To disperse white light into a spectrum of colors. Signup and view all the answers

What is the primary difference between a spectrometer and a colorimeter?

Colorimeters use filters, while spectrometers use monochromators. Signup and view all the answers

What aspect of a solution is measured by a spectrophotometer to determine concentration?

Light transmittance. Signup and view all the answers

Study Notes

Band of Visible Light

Visible light ranges from 350 to 700 nm.
Color spectrum includes:
- Violet (350-430 nm)
- Blue (431-475 nm)
- Green (506-555 nm)
- Yellow (576-600 nm)
- Orange (601-650 nm)
- Red (651-700 nm)
Specific color wavelengths:
- Green-blue (476-495 nm)
- Blue-green (496-505 nm)
- Yellow-green (556-575 nm)

Spectrophotometer Components

Sample Cells (Cuvettes):
- Made of glass or quartz, hold colored solutions.
- Must be scratch-free for accurate light passage.
- Glass cuvettes are used for visible light; quartz for UV light.
Light/Photo Detector:
- Converts transmitted light energy into electrical energy.
- Common types: photocell, phototubes, photomultiplier tubes (PMT).
- PMT is preferred for its sensitivity and rapid response.
Readout System:
- Displays output from the photodetector.
- Formats include meters, galvanometers, LED displays.

Types of Spectrophotometers

Single Beam Spectrophotometer:
- Uses one light beam; measures at wavelengths from 325 nm to 1000 nm.
- Reads test samples and blanks sequentially.
Double Beam Spectrophotometer:
- Operates from 185 nm to 1000 nm; splits light into two beams.
- One beam for reference and the other for sample, minimizing error.

Applications of Spectrophotometers

Analyzes solution concentration qualitatively and quantitatively.
Requires unknown concentration to fall within the standard curve range.

Standard Curve

Example table shows concentration (mg/dl) vs. absorbance:
- Concentrations of 60, 70, 80, 90, 100, 110 correlating with specific absorbance values.

Finding Unknown Concentration

Formula: Concentration of unknown = (Au/As) x Concentration of standard
- Au: absorbance of unknown
- As: absorbance of standard

Photoelectric Colorimetry

Principle:
- White light through a filter only allows specific wavelengths.
- Colored solution absorbs some light; transmitted light strikes a photoelectric cell which converts it to electrical energy.
- Outputs percent transmittance or absorbance.

Spectrophotometer Overview

Combination of spectrometer and photometer; measures light absorption to determine concentration.
Can analyze colored and non-colored solutions using visible, UV, and infrared light.

Spectrophotometer Measurement Principle

Light passes through a monochromator, creating a spectrum.
Sample absorbs light; remaining light strikes a detector to quantify absorbance or transmittance.

Additional Spectrophotometric Applications

Analyzes reaction rates (e.g., enzyme analysis).
Determines molecular weights of substances.
Detects impurities in solutions.

Atomic Absorption Spectrophotometry (AAS)

Measures concentration based on light absorption by atoms, not molecules.
Uses hollow-cathode lamp; atomizes samples via flame.
Sensitive technique, ideal for trace metals (e.g., magnesium, copper, lead, calcium).

Flame Emission Spectrophotometry (FES)

Measures emitted light from excited atoms post-atomization by flame.
Emission color correlates to specific metal ions (e.g., red for lithium, yellow for sodium).
Primarily measures electrolytes (Na, K, Li).

Infrared Spectrophotometry

Measures vibrational spectra of samples using infrared radiation.
Records absorbed frequencies and their extent.

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Description

Explore the band of visible light from 350 to 700 nm with this quiz. Test your knowledge on the colors associated with specific wavelengths and the basic components of a spectrophotometer. Enhance your understanding of light absorbance in various substances.