Instrumental Analysis Test 1 Review

Hehe (THE ONLY FLASHCARDS YOU COULD EVER NEED)

What is the order of electromagnetic spectrum from lower to higher energy?

Radio, Micro, Infrared, Visible, Ultraviolet, X-ray, Gamma Ray, Cosmic Rays

Radiation that interacts with molecular rotations

Microwaves

Radiation that interacts with the nuclear/electron spin

Radio Waves

Radiation that interacts with bond vibrations

Infrared waves

Radiation that interacts with inner core electrons/ionizes

X-rays

Radiation that interacts with valence electrons

UV and Visible light

Equation for absorption given extinction coefficient

A = ecl

Equation for % Transmittance

%T = P/Po

Equation for absorption given transmittance

A = -Log(%T)

Why is A more useful than %T

Absorbance allows for a linear form of data and has a direct relationship to the concentration of the substance measured.

What are some common UV-Vis materials?

Plastic (Polystyrene and PMMA) and Glass (Quartz and Borosilicate)

For Beer’s Law, what is the most common source of error?

Sample Prep

For Beer’s Law, what is the absorptivity coefficient dependent on?

Wavelength

For Beer’s Law, The range of the monochromatic light needs to be ___ than the absorption band

Shorter

For Beer’s Law, the wavelength of light should be selected at what value?

at the highest absorbance (lambda max)

What concentration should solutions be for UV-Vis?

equal or less to 0.01 M

UV-Vis can analyze which states of matter…?

Solids, Liquids and Gases

For UV-Vis, what are some reasons why wavelength should be selected at the maximum sample absorbance

1. To minimize error that can occur by choosing a reliable position. If the wavelength is off a little near the peak, there is little change in measured absorbance.

2. Can measure lower concentrations due to the light being most absorbed at the specific wavelength, and thus decreasing interference.

For UV-Vis measurements, what absorbance range is ideal precision?

0.3-2

For UV-Vis, why does the compartment need to be closed?

To prevent stray light

What types of energy in a Jablonski diagram are considered when a molecule absorbs a photon?

Rotational, Electronic and Vibrational

Fluorescence emission occurs at ___ wavelengths than the excitation wavelength?

longer wavelengths

How does Phosphorescence compare with Fluorescence in terms of energy?

Fluorescence emits a higher energy while Phosphorescence is a lower energy emission

The excited state of a molecule in which electron spins are parallel?

Triplet

Lowest energy state of a molecule?

Ground State

Emission from an excited T1 to ground S0 state?

Phosphorescence

Excited state of a molecule in which electron spins are opposite

Singlet

Emission from excited S1 to ground S0 state

Fluorescence

Radiation emitted from a heated object (incandescence)

Blackbody radiation

What are the lifetime ranges for Phosphorescence and Fluorescence?

P = 10^-4 to 10^2 s and F = 10^-8 to 10^-4 s

What is the typical light source for IR?

SiC Globar

What are some types of UV-Vis light sources?

Xenon Arc Lamp, Tungsten Halogen lamp, Deuterium Arc Lamp, Lasers, and LEDs

what do modern UV-Vis specs use for separating light?

grating monochromator

What do modern IR spec’s use for separating light

Michelson Inferometer

what are common sample cell materials for IR?

Diamond, NaCl, Germanium, KBr and ZnSe

How does Michelson Inferometer work?

Light source from SiC rod goes through slit to beam-splitter. Splits light 50/50 to both a movable and stationary mirror. Light reflects and recombines at the beam-splitter and hits sample and detector. Recombined bean is either out or in-phase and creates a interferogram.

Equation to find frequency given wavelength

c = λv

Equation to find energy given wavelength

E = hv —> E = hc/λ

What is up with absorbed vs appearing colors and stuff?

Color absorbed is complementary to the color that appears. This is because the eye perceives the remaining combination of non-absorbed light that is reflected.

What are the common UV-Vis detectors?

CCD(charge-coupled device), PDA(photodiode array) and PMT(photomultiplier tube)

What are the common IR detectors?

Ferroelectric(DTGS) and Pyroelectric(MCT)

What are the advantages of PDA compared to PMT?

1. Fast scanning

2. records entire spectrum at one time

3. more rugged due to no moving parts

4. Cheaper

What are the advantages of PMT compared to PDA?

1. Lower detection limit/Better resolution

2. Less stray light

Name of the cathodes in PMT

dynodes

how much can a PMT multiply electrons?

A MILLION!!!!

What is used in PDA to disperse light

Grating polychromator (because entire spectrum is emitted onto the array)

Why are CCD detectors becoming more popular in spectroscopy?

Combines the advantages of both PDA and PMT detectors in being fast and having low detection limits

What are the different ranges in light sources and give examples?

Line (Diode laser), Narrowband (LEDs), Broadband (Lamps and SiC globar)

How does a hollow cathode lamp work?

A cathode, made from the element whose emission line is being tested, is sent into the gas phase through the use of He or Ar cations to then emit an atomic emission through the collision of high energy electrons.

Symmetrical vibrations are better seen with which instrument?

Raman

Asymmetrical vibrations are better seen with which instrument?

IR

what is a risk involving the high power of a Raman laser?

The laser can decompose the sample if the power is too high.

Is fluorescence a problem for Raman Spectrums?

Yes, indeed.

What kind of samples can be used for Raman?

Solid and liquid samples

Can Raman instruments use glass cells?

Yes

What must be considered regarding concentration of sample when using Raman over IR?

Sample concentration must be higher for Raman than IR

What range of light sources does Raman usually use?

visible light

Is fluorescence a problem for IR Spectrums?

No!!!!!!!!!!!!!!!!!!!!!!!!!!

What needs to be taken into account regarding water samples for both IR and Raman?

IR will generally detect water and mask important functional groups within that region of the spectrum.

For XRF, which electrons are involved?

Inner shell electrons

Which frequencies of light are used in XRF?

X-Rays

What are two main sources of information that XRF and XRD provides?

1. crystal structure (XRD)

2. elemental composition (XRF)

What type of samples can XRF instruments use?

Solid and liquid Samples

What needs to be taken in consideration regarding XRF samples?

they must be homogeneous when determining concentration. (hetero not allowed)

What is the typical range in detection limit for XRF?

ppm to %

Can XRF measure all the elements at the same time, or one at a time?

All at the same time

are XRF and XRD destructive techniques?

NO!! They wouldn’t hurt a fly

What is XRF information in terms of qualitative or quantitative?

XRF is both qualitative (which elements are present) as well as quantitative (how much of each element)

What is the difference between Line spectra, Band spectra, and Continuum spectra in atomic spectroscopy

Line Spectrum: sharp, well-defined spectral lines caused by the excitation of individual atoms (emission and absorption spectrums)

Band spectrum: closely spaced lines that are difficult to separate and end up making “bands” of light. Caused by small molecules or radicals

Continuum spectrum: any radiation produced when solid is heated (blackbody radiation and continuous spectrum)

when a heat source heats up a cold gas, you get this spectrum

Absorption spectrum

when a gas is heated and allowed to cool, you get this spectrum

Emission spectrum

In Atomic spectroscopy, this broadening occurs due to the collisions of molecules deactivating the excited state

Collisional (pressure) broadening

In atomic spectroscopy, this occurs from the rapid motion of atoms as they emit or absorb radiation

Doppler broadening

In atomic spectroscopy, this occurs by the lifetime of excited states

Natural broadening

What are the benefits/properties of ICP?

1. Simultaneous multi-element analysis

2. Low detection limits

3. Wide sensitivity range

How is the sample heated in a Graphite Furnace AAS?

heated electrothermally in a graphite tube

Both FAAS and GAAS use this lamp (and you should too!)

hollow cathode lamp

GFAAS advantages over FAAS

1. detection limits in ppb

2. less sample required

Name at least 3 detectors used on UV-Vis instruments

1. Phototubes

2. Photomultiplier tubes

3. Silicon photodiodes (diode arrays)

4. photoconductive cells (CCDs)

Name at least 2 IR detectors (preferably the important ones cause Eklund wants it like that I guess idk guys this class is evil and I want my degree now)

1. Thermocouples

2. Pyroelectric devices

3. bolometers

4. pneumatic cells

What is the detector used in FAA/GFAA instruments?

PMTs

Describe how FTIR interferometer works by using a diagram

hehe, you got that my King/Queen/Monarch

Why would you be tempted to use Raman rather than FTIR?

1.If you need visible light source

2. can see those symmetric vibrations

3. can use glass cells in case you hate pellets

4. can use water samples

5. can use SERS attachment to enhance signal by a MILLION!!!

Why would you be tempted to not use Raman over FTIR?

1. If you have a low concentration of sample = Bad

2. Fluorescence (but you can use 1064 nm laser to minimize it)

3. Sample will probs decompose due to that high power laser

4. Not that groovy for asymmetric vibrations because Raman only wants the homo ones

What is Bathochromic shifts?

Shift to a longer wavelength in energy (red shift)

What is a Hypsochromic shift?

Shift to a shorter wavelength (blue shift)

If your UV-Vis instrument is a scanning type, what type of detector does it have?

Photomultiplier tube (PMT):

What is Electron Ionization? IS IT HARD OR SOFT?

hits sample with 70 ev, causing sample to break into fragments “fingerprint” of molecule. HARD method

What is chemical Ionization? IS IT HARD OR SOFT?

uses CH5 to collide with molecules to add that extra H and ionize the parent molecule. SOFT method

In mass spec, this is when you add up all the lowest isotopic masses

Monoisotopic Mass

In mass spec, this is when you add up the most abundant masses, and round to nearest integer (common method)

Nominal Mass

In mass spec, this is when you add all the average masses weighed for abundance

Average Mass

What is the most common use for a mass spectrometer?

To be a detector in chromatography, either gas or liquid, or to a lesser extent with an ICP

What is this Mass Spec?

Magnetic/electrostatic Sector

What is this Mass Spec

Quadrupole

What is this Mass Spec?

Ion-Trap

What is this Mass Spec?

MALDI-TOF

HELP!!!, tell me rn what Electronspray is and what it is used in mass spec or Lunch Money will get depressed

Electronspray is a method that produces charged droplets that de-solvate and are directed into a mass analyzer. Used to deliver samples from a LCC to a MS. (If you answered correctly, you saved Lunch Money from having to be medicated)

HEREY HEREY, WHAT DO BE FAAS, GFAAS AND ICP CALLED AND WHAT DO BE THEIR HEAT SOURCES???

1. FAAS (Flame Atomic Absorption Spectrometry) uses air/acetylene flame

2. GFAAS (Graphite Furnace Atomic Absorption Spectrometry) uses small graphite tube

3. ICP (Inductively Coupled Plasma) uses Argon plasma flame

HEREY HEREY, WHAT DO BE FAAS, ICP and GFAAS TECHNIQUES BE BASED ON (absorption or emission)?

ICP: emission

FAAS, GFAAS: absorption