UV-VIS Spectroscopy Flashcards

This is a set of flashcards for reviewing the fundamentals of UV-VIS Spectroscopy.

What is the composition and nature of electromagnetic waves?

Electromagnetic waves consist of perpendicular electric and magnetic waves traveling through space at the speed of light; they exhibit both wave-like and particle-like properties.

How do different regions of the electromagnetic spectrum interact with matter?

Different regions of the electromagnetic spectrum can induce various energy transitions in matter, such as changes in nuclear energy levels (gamma rays), inner electron levels (X-rays), valence electron levels (UV-Vis), molecular vibrations (IR and Raman), rotational levels (microwave), and nuclear spin levels (radio waves).

What is the basic principle of spectroscopy?

Spectroscopy involves measuring the interaction between radiation and matter.

What is frequency in the context of electromagnetic waves?

Frequency is the number of oscillations of a field per unit time, determined solely by the radiation source and independent of the medium.

What is wavelength?

Wavelength is the distance between two consecutive maxima or minima of a wave.

What is a wave number?

Wave number is the number of waves per centimeter.

What is the refractive index?

The refractive index measures how much a medium interacts with radiation.

What does frequency depend on?

Frequency depends only on the source of radiation.

What are chromophores?

Chromophores are groups of atoms within a molecule that cause electronic transitions.

What are auxochromes?

Auxochromes increase absorption (absorptivity) and shift absorption to longer wavelengths; examples include hydroxyl, alkoxy, halogen, and amine groups.

What is hyperchromicity?

Hyperchromicity increases absorption intensity

What is hypochromicity?

Hypochromicity decreases absorption intensity.

What is thermal noise?

Thermal noise (white noise or Johnson noise) is caused by thermal agitation of electrons in a conductor and is directly proportional to the square root of the frequency.

What is shot noise?

Shot noise arises from discontinuities in current flow across a semiconductor junction and is directly proportional to the square root of the frequency.

What is flicker noise?

Flicker noise (pink noise) decreases with increasing frequency and is most significant at frequencies less than 100 Hz.

What is environmental noise?

Environmental noise is due to external factors and is reduced by proper shielding and grounding.

How can the signal-to-noise ratio be improved?

Signal-to-noise ratio can be improved by signal averaging.

Why is flicker noise important in IR spectroscopy?

Frequency is lower in IR spectroscopy.

What is the effect of auxochromes on aromatic rings?

Auxochromes cause a shift towards longer wavelengths.

Why don't alkanes show UV-Vis absorption?

Alkanes do not show absorption in UV-Vis because sigma to sigma star transitions require high energy.

A = εbc What is the Beer-Lambert Law?

Beer-Lambert Law

What does molecular absorptivity depend on?

Molecular absorptivity depends on the molecule and wavelength.

What are the limitations of Beer-Lambert Law?

System deviates from Beer-Lambert Law when complex formation occurs, fluorescence or phosphorescence happens, photochemical reactions take place, or thermal equilibrium is not maintained.

What contributes to the noise in spectrophotometer?

Noise contributes significantly to spectrophotometer measurements.

Why does butane not show UV absorption around 180-380 nm?

Butane shows no UV absorption because it only has sigma bonds, and the energy in the UV region is not sufficient for sigma* transitions.

How can quantitative analysis be done in UV-Vis spectroscopy?

Add an increasing standard to the sample to UV-Vis spectroscopy.

What is equal to one in sample calculations?

Pathlength: b = 1 cm

How does stray light affect Beer’s Law?

Stray light causes the Beer-Lambert Law to not hold, and causes a constant error.

How can error from stray light be corrected?

Can be corrected by formula

A solution of quinine with a concentration of 4,10 ppm has absorbance of .832 in 2cm cell (pathlenght). If 25 mL of this solution is mixed with 10 mL of solution with 23.4 ppm concentration then diluted to 50 mL, what percent of the light is transferred?

Transmittance: 8.15%

A solution of quinine with a concentration of 4,10 ppm has absorbance of .832 in 2cm cell (pathlenght). If 25 mL of this solution is mixed with 10 mL of solution with 23.4 ppm concentration then diluted to 50 mL, what is the ppm?

20.1 ppm

Complex DA has absorptivity value .375 per nm. If a solution of this concentration with b=1 has an absorbace of .575, what is the molar of DA?

2.9 * 10^(-4)

What happens to transmittence when there is a double source?

There is no transmittence with a doubled source

What kind of deviation occurs in beer-lambert law that is caused by high concentrations?

There's a negative deviation in high concentrations because it increases the refractive index and decrease molar absorptivity.

What is the rule for applying the Beer-Lambert law?

The Beer-Lambert Law applies for absorbances less than one.

What is in the event that you want to improve spectral resolution in quantitative analysis?

To have quantitative analysis of UV-Vis spectroscopy.

Does reduced average noise or high average noise improve spectral resolution of lower limit of detection?

Increased Noise reduces the lower limit of detection.

What measurement affects percent transference as a way to improve spectral resolution.

0.115 mL of standard solution used

What are the sources of derivation in beer-lambert UV/VIS

Chemical deviations

Example deviation with Benzal Alchol, what deviation is this?

Polymerixiation

What derivations depend upon solvent differences?

Red and Blue

What crystal shows different refractive index with different views and position in UV/Vis?

Toromalin

What qualities of refractive index are desired?

Use a higher refractive index, also must adhere to a dispersion law.

What is the equation to prevent refractive index deviation?

(n'+n)/2

Why is it important to select a refractive index that causes minimum error?

Because the law applies only to monochromatic light

Is a glass prism the only way to measure in Vis-UV?

It must be transparent and has the possibility to change strength

What section should measure high energy?

Region where absorption is present. (abnormal)

For the most accuracy, which region should a measurement take place within?

The absorption should take place close to the abnormal line

When polarity in an auxochrome increases, auxocrhome what color shifts?

The red

Will an aromatic electron transfer during acidic environment in triethylamine?

Aromatic electrons will undergo transfer

How is the UV/Vis detector setup?

With sample, then detector, then amplifier

Why does the UV Vis need setting up in this format?

To provide a steady light source and prevent decomp and fluoresence

Why is it bad to do one beam? One at a time?

Due to source output and sensitivity of detector

What is equal to lambda?

The grating angle

What are other names for UV Vis parts?

Photo cell

What radiation is used to generate UV in a lamp?

It will generate UV radiation

How accurate does the mono light meter have to be?

More than 1,000th more accurate than normal

How often does mono chromic use berz?

More

Interference filters consist of a dialectic layer such as?

CaF, MgF

What condition must occur for constructive interactions to occur?

There must be constructive and destructive interactions

Is theta proportional to radiant light?

Important - Theta increases, that's why light increases

Is glass high reflective or low?

Higher

If the thickness of one diameter is 300 what is nm ?

455555 nm.

How do frequency and rate change in a new state when lambda is transferred from vacuum?

Decrease and constant.

How would you describe what happens in spectrometer when opening slot size for grating?

Increase, and decrease signal strength.

List some general facts about the UV/VIS apparatus.

Made of 10-100 cells of glass ,plastic, or quarts, measures UV and VIS.

Describe sodium cell.

Creates a photovoltaic cell.

What occurs during photodetection?

Very low heat and electrical resistance

What are results of phototeum effect?

Made of UV or light energy, 10x intensity of photovoltaic effect

What effect does varying voltage do in photo tube?

Not much

What forms photo resistance?

PBT and CDS

Pros and cons of photo multiplier?

High end and used for little light. However also easy to damage from high light!

What is the equation to describe the total output electrons in a light cell?

The total electron that come out: D equals =EN

How to increase sample ppm?

102x dilution. That is about it.

Whats some properties of the dispersal rate of a spectrometer?

In some areas it will produce high power in others it is nothing. In a normal dispersion rate

How to show absorbency is measured at equilibrium (in the most simple manner.)?

A=Av

How to shift the absorption wavelength?

Decrease the energy of the excited state. Thus transferring it lower in spectrum

What will the UV light do in the presence of triethalomin with water and acid state.

The absorption will go blue