Instrumental E1

---- is the atom, ion, or molecule of interest that is being identified or quantified

Analyte

-- analysis: odor, color, boiling or melting points, etc.

Qualitative

Classical Methods:

1. Separation

2. Qualitative Analysis

3. Quantification

Instrumental methods:

1. Directly measuring analyte physical properties

Molecular properties include the — properties, —

properties, and —- properties of molecules.

physical, chemical, and structural

A —- property is any property that is measurable, whose

value describes a state of a —- system

physical

A —- property is any of a material's properties that

becomes evident during, or after, a —- reaction

chemical

A chemical structure determination includes

a chemist's specifying the —- and, when feasible

and necessary, the —- structure of the target molecule.

molecular geometry, electronic

—-: Records a change in a variable in the environment. Part of an instrument (most general).

Detector

—-: Converts between the non-electrical domain

and the electrical domain (both ways).

Transducer

—-: Monitors chemical species continuously and

reversibly. Has chemical-specific component and a

transducer.

Sensor

Ohm’s Law

V = IR V = voltage (volts), I = current (amperes), R = resistance (ohms)

—- Law: The sum of currents around any point in a circuit is 0

Current

—- Law: Algebraic sum of voltages around a closed electrical loop is 0

Voltage

—- = Resistance to change in current of an AC current

Inductor

—- = Resistance to change in voltage of an AC voltage

Capacitor

—-: Two metal plates are separated by a dielectric (insulator). Charge up the two plates at a specific voltage. Store the charge. Later, release the stored charge with a

switch

Capacitors

— EMR: Same direction as incident EMR

Transmitted

—- EMR: In all directions

Emitted and Scattered

—- EMR: Opposite direction of incident EMR.

Reflected

—- transmits through the sample and is detected .The source wavelength can identify the sample. The amount of —- transmitted provides the quantity.

EMR

In Atomic Absorption Spectroscopy, a —- will serve as the sample holder,

containing —- atomized sample

flame, gaseous

—- is based on light absorption and (via electronic transitions, all in the UV-VIS domain) of atoms in the gas phase

Atomic absorption spectroscopy (AAS)

The electrons involved in AAS are the ground-state and excited-state —- in gaseous atoms

valence electrons

What is the goal of AAS?

The goal is elemental analysis to identify and determine the concentration of a specific element in the sample

Why can’t you see chemical and structural information when using AAS?

Chemical and structural information are lost because the sample is destroyed when getting atoms in the gas phase (atomization)

In AAS, light is absorbed by a ground state atom/electron at a

very specific wavelength, resulting in —-

line spectra

The —- of the atom, consists of a small, dense nucleus surrounded by orbiting electrons in defined energy levels

Bohr model

The main components in AAS include what?

atomization, a hollow cathode lamp, a monochromator, a detector, and a recorder

Atomic absorption methods are highly specific because the atomic absorption lines are very —— and the electronic transition energies are —- for each element.

narrow (0.002 – 0.005 nm), unique

In AAS, we use a radiation source that emits the —- line

spectra of the element that we are trying to detect

same (aka: Want to look for copper? Then use a copper lamp)

With atomic absorption, a —- is

required to reduce interferences from other

elements and background

line source

A hollow-cathode lamp consists of a —- anode and a —- cathode sealed in a glass tube filled with —- at a pressure of 1-5 torr

tungsten, cylindrical, neon or argon

In a hollow-cathode lamp, the —- is constructed of

the metal whose spectrum is desired or serves to support a layer of that metal.

cathode

In a hollow-cathode lamp, ionization of the inert gas occurs when a potential difference on the order of —- V is applied across the electrodes

300

If the voltage in a hollow-cathode lamp is sufficiently large, the gaseous cations acquire enough kinetic energy to disloadge some of the —- from the —- surface and produce an atomic cloud in a process called sputtering

metal atoms, cathode

A portion of the sputtered metal atoms are in excited states

and thus emit their —- as they return to

the ground state

characteristic radiation

—- is constructed from a sealed quartz tube containing a few torr of an inert gas such as argon and a small quantity of the metal (or its salt) whose spectrum is of interest

Electrodeless discharge lamps (EDLs)

Electrodeless discharge lamp is energized by an intense field of ——- radiation

radio-frequency or microwave

Electrodeless discharge lamps (EDLs) provide radiant intensities usually one to two orders of magnitude greater than —-

hollow-cathode lamps

EDL’s performance is not as reliable as hollow-cathode lamp,

but for elements such as —-, EDLs exhibit

better detection limits than do hollow-cathode lamps

Se, As, Cd, and Sb

EDLs are —- cost and difficult to operate in comparison to

hollow cathode lamps.

higher

AAS requires the conversion of the sample to gaseous atoms, which absorb —-

radiation

For AAS, the solution is drawn in through a small tube and taken to the —- where the solution is broken up into a fine mist (this is similar to an aerosol can).

nebulizer

in AAS, when the mist reaches the flame, the intense heat breaks up the sample into its individual atoms. This final process is called —-

atomization

—- is the process that converts the constituents of a sample to gaseous atoms or ions, which can then be determined by absorption, emission or mass spectral measurements

Atomization

The —- atomizer, such as flame and plasma, introduces the

samples in a steady manner

continuous

The discrete atomizer introduces samples in a discontinuous manner

with a device such as a syringe or an autosampler. The most

common discrete atomizer is the —- atomizer.

electrothermal

—- is a device that introduces a

liquid sample into the AAS

Nebulizer

A —— nebulizer converts a sample

solution into an aerosol of tiny droplets

using a jet of compressed gas. The flow

of inert gas carries the droplets to an

atomizer

pneumatic

An —- nebulizer creates an

aerosol of tiny droplets by pumping a

sample solution onto the surface of a

piezoelectric crystal that vibrates at a

frequency of 20 kHz to several MHz.

ultrasonic

In a flame, what is the primary combustion zone?

initial decomposition, molecular fragments, cool

In a flame, what is the Interzonal region

hottest, most

atomic fragments, used for

emission or fluorescence

In a flame, what is the Secondary combustion zone

cooler, conversion of atoms to

stable molecules, oxides.

—- is the most reproducible of all liquid-sample-

introduction methods that have been developed for AAS

Flame atomization

What are the setbacks of Flame atomization?

A large portion of the sample flows down the drain.

The residence time of individual atoms in the optical path in

the flame is brief (~10-4 s).

The major difference in the instrumentation arrangement

between AAS and AES lies in the —- and the

—- technique

light source, measurement

In —-, the light source is a hollow cathode lamp that emits light at a specific wavelength, and the measurement is based on the absorption of light by atoms in the ground state

AAS

In —-, the light source is an electric discharge or a flame that excites the atoms in the sample, causing them to emit light at characteristic wavelengths. The measurement is based on the emission of light by atoms in excited states

AES

—-: The high temperatures used to excite the atoms cause them to move at ——. This creates a —- effect, where light emitted by atoms moving toward the detector is shifted to a shorter wavelength (blue-shifted), and light from atoms moving away is shifted to a longer wavelength (red-shifted). The overall result is a broadened emission peak

Doppler broadening, high velocities

—-: In the high-temperature, high-density environment of an AES source, collisions between —- and other particles are frequent. These collisions perturb the excited state of the atoms, leading to a smearing of the emitted energy and a broadening of the spectral line

Pressure (collisional) broadening, analyte atoms

—-: In the AES plasma or flame, —- atoms at the cooler edges of the source can absorb the radiation emitted by excited atoms in the hotter core. This causes the signal at the center of the peak to be diminished, further broadening the peak

Self-absorption (or opacity broadening), unexcited (ground-state)

—-: Excites bonding valence molecular electrons. Requires vacuum instrumentation below 200 nm because O2 and N2 in air absorb high-energy UV light. Focuses primarily on conjugated organic molecules. Commonly bundled with visible range systems

UV spectroscopy

For —-: You want a continuum source whose power does not change significantly over a wide range of wavelengths

UV-VIS

—- Lamps

350 nm to 2500 nm (Visible and Near IR)

Limited by glass housing

2870 K Blackbody radiation

Tungsten Filament

—- Diodes

pn junctions that emit light when forward-biased

GaAlAs, GaAsP, GaP, GaN, InGaN

Anywhere from 375 to 1000 nm

Light Emitting

—- Lamps

Pass current through Xenon

200 nm to 1000 nm

Xenon Arc

For Sample Holders, they must be:

• Must be —- to the wavelengths of interest

• Must be placed in the instrument the —- every time.

• You can use the same cuvette for the solvent only and solvent plus

analyte

• Or you can use matched cuvettes

• A double-beam instrument requires matched cuvettes

transparent, same way

For —- sample holders: glass and some plastic cuvettes

Visible Range

For —- sample holders: quartz cuvettes

UV Range

Use a —- array to detect all wavelengths simultaneously.

photodiode array or CCD

Limitations of Beer’s law: —-, apparent chemical deviation, instrument deviations, mismatched cells

high concentration (>0.01 M)

—- is the wavelength where the

absorbance is the maximum

λmax

UV spectroscopy is mainly used to —- electrons,

specifically those featuring conjugated double bonds and aromatic rings

detect molecules with 𝜋

for UV spectroscopy, molecules with —- bonds require too much energy to shift electrons, absorbing outside the standard UV range

only single sigma

—- have UV absorbance because light waves give their

electrons enough energy to jump between different energy levels

Transition metals

When a transition metal binds to other atoms or molecules (called ligands), it forms a compound. This action triggers (——) —the movement of electrons from a lower-energy slot to a higher-energy slot—by absorbing light

electronic transitions

Transition metals use two main types of electron jumps to absorb UV light:

1. —-

2. ——

1. Charge-Transfer Transitions (The Main UV Absorber)

2. High-Energy d-to-d Transitions

—- have broad UV absorption bands from non-bonding electrons.

Inorganic anions

—- and complexes absorb visible light upon excitation between filled and unfilled d-orbitals. Dependent upon oxidation state and coordination environment.

Transition metal ions

UV-VIS: The molecules can be measured by absorbance directly as long as they absorb in the UV-vis range. Non-absorbing molecules can be reacted or tagged with a —- for analysis.

strongly absorbing chromophore,

—-: Cannot be used alone to give molecular identity. It can give an idea of functional groups. NMR, IR, Mass Spectrometry, and melting point information must also be used to identify the molecule.

UV-VIS

In —-, Solvents eliminate fine structure. Must use the same solvent for identification purposes. Different solvents can also absorb, making them only useful over a certain range of wavelengths.

UV-VIS

In UV-VIS, —- should be used for identification purposes to avoid distortion and broadening of bands

Minimum slit width

In UV-VIS, —- or polarity effects can help identify some functional groups. The UV-vis spectrum of benzene is sensitive to ring substitution.

Aromatics, carbonyls, and pH

Some Issues to Consider in Quantitative Analysis is that you need to measure at the wavelength of —- and If you can’t reproduce the —- condition, use the standard addition method

maximum absorbance, analyte solution

Too high flow rate will cause the flame to —— the burner.

Too low flow rate will cause the flame to —— back into the burner, giving a flashback

blow off, propagate

—- is the most reproducible of all liquid-sample- introduction methods that have been developed for AAS

Flame atomization

Why does flame atomization has low sampling efficiency?

o A large portion of the sample flows down the drain.

o The residence time of individual atoms in the optical path in

the flame is brief (~10-4 s)

Electrothermal atomization generally provides —- for small volumes because the entire sample is atomized in a short period, and the average residence time of the atoms in the optical path is a second or more

enhanced

sensitivity

—- atomization is relatively slow typically requiring several minutes per element because of the heating-cooling cycles

Electrothermal

The analytical range of —— atomization is relatively narrow, usually less than two orders of magnitude.

electrothermal

In Wavelength Selectors, the goal is to select only —- to use for the analysis from a source that has many wavelengths. The better you can do this, the more sensitive the measurement will be and the better selection you will get for a specific analyte

1 wavelength

The true output of a wavelength selector is a

small, continuous group of wavelengths.

This is referred to as a —-.

band

—- has a variable thickness wedge that is the dielectric material. This allows selection of the wavelength over a range. Usually visible range (400-700 nm), near IR (1000-2000 nm), and IR (2.5 to 14.5 um

Interference Wedges

—-: Light is filtered by passing through colored glass or dyes in gelatin.

Certain wavelengths are then absorbed, allowing others to pass through. Inferior to Interference Filters but adequate in some applications.

The bandwidth is larger, and if you reduce the bandwidth, then the transmittance is low.

Absorption Filters

Atomic absorption should follow Beer’s law with absorbance being directly proportional to concentration.

However, calibration curves are often —-

nonlinear

The —- method is also widely used in AAS to partially or completely compensate for the chemical and spectral interference introduced by the sample matrix.

standard-addition

The single-beam system sends all light directly through the flame to the detector, requiring —- calibration. In contrast, a double-beam system splits the light into a sample path and a reference path to correct for —- automatically.

manual blank, lamp drift