IH Analytical Methods / Equipment

Question 1

How does atomic emission spectroscopy work?

Answer 1

1) Energy is emitted onto electrons
2) Electrons go from a lower energy state to a higher energy state
3) Atom absorbs the difference in energy
4) Energy is emitted via wavelength of light
5) The wavelength of light emitted by different atoms (electrical signal) is unique to each element – and this is how spectrometers can identify different elements.

Question 2

Atomic absorption is good at at analyzing…

Answer 2

Metals

Question 3

What is XRF

Answer 3

An X-ray fluorescence (XRF) spectrometer is an x-ray instrument used for routine, relatively non-destructive chemical analyses of rocks, minerals, sediments and fluids.

A combination of atomic emission and atomic absorption

Question 4

What is atomic absorption spectroscopy?

Answer 4

1) Energy is emitted onto electrons
2) Electrons go from a lower energy state to a higher energy state
3) Atom absorbs the difference in energy
4) The wavelength of light absorbed by different atoms is unique to each element

Question 5

What is a fluorescence detector?

Answer 5

Measures emission of light by fluorescing elements. Light source raises energy of electrons that decay emitting light at longer wavelengths.

Question 6

What is mass spectometry?

Answer 6

A technique for separating substances based on the mass of the molecule. Molecules are given an electrical charge and are accelerated into an electromagnetic field. Molecules are selected based on the mass/charge (M/z) ratio.

Helpful in identifying unknowns.

Question 7

How does UV absorbance work

Answer 7

Measures the amount of UV light absorbed by a sample. The amount of light absorbed is proportional to concentration of absorbing material.

Question 8

Accuracy

Answer 8

The percent difference between the measured and true values, thus highly accurate results have a low numerical accuracy

A = (Cm - Ct)[100]/Ct
Where:
A = accuracy (%)
Cm = measured concentration
Ct = true concentration

Question 9

AIHA Laboratory accreditation is good for how many years?

Answer 9

2 years

Question 10

Spectrophotometers use the following…

Answer 10

Spectrophotometry is a group of analytical techniques which utilize electromagnetic radiation to conduct qualitative or quantitative analysis based on the measurement of the reflection or transmission properties of a material as a function of wavelength. Spectrophotometry uses spectrophotometers that can measure the intensity of a light beam at different wavelengths

UV light
Infrared light
Visible light
x-ray
Ultraviolet
Microwave

Question 11

What is gas chromatography?

Answer 11

A technique used to separate chemical substances. Chemicals move through the column at varying rates. A gas is used as the carrier medium. Used frequently for hydrocarbons.

Used for volatile compounds because they easily evaporate at room temperature.

Question 12

HPLC

Answer 12

High performance liquid chromatography

Question 13

What is HPLC?

Answer 13

Similar to gas chromatography except that the carrier medium is a liquid. Contaminant must be soluble in mobile phase.

Question 14

What is ion chromatography?

Answer 14

A form of liquid chromatography that uses ion-exchange resins to separate atomic or molecular ions based on their interaction with the resin.

Question 15

What is ion chromatography used for?

Answer 15

Anionic and cationic species, ions of alkali and alkaline earth metals, inorganic compounds, and aldehydes

Question 16

The major law of chemistry upon which visible and ultraviolet spectrophotometry is based is?

Answer 16

Spectrophotometry is based upon Beer’s Law which states: Absorbance at a particular wavelength is equal to the chemicals molar absorptive constant times the path length of the cell times the concentration of the chemical.

Question 17

What are two major disadvantages of ion chromatography?

Answer 17

• Inability to analyze non-ionic species
• Interference with ions of a similar selectivity/exchange coefficient

Question 18

What is a main characteristic of ion chromatography?

Answer 18

• It provides analysis of several ionic species from a single sample

Question 19

Which materials cannot be used as a prism in an infrared spectrophotometer?

Answer 19

• Sodium chloride
• Potassium bromide
• Cesium iodide

Question 20

Filter sample submitted for light microscopy or TEM analysis must be lightly loaded and on what type of filter paper?

Answer 20

Cellulose ester

Question 21

When a welding fume sample is analyzed and a metal scan is requested, an analytical technique is used to quantitate multiple metals simultaneously. This analytical technique is is called:

Answer 21

ICP or inductively coupled plasma discharge has made multiple simultaneous metal analyses possible.

Question 22

What diameter can be determined directly from the cumulative distribution plot of cascade impactor data?

Answer 22

Cascade impactors distribute particles to the various stages based on their aerodynamic diameter, and the stages are weighed to determine the mass of particles collected in each size range. The cumulative distribution plot of cascade impactor data will thus yield the mass median aerodynamic diameter at the 50% point of the distribution.

Question 23

What law does UV absorbance follow?

Answer 23

Beer-lambert law

Question 24

What law does fluorescence detector use?

Answer 24

Beer-lambert law

Question 25

How many elements can you analyze per analysis with atomic absorption spectroscopy?

Answer 25

5-6

Question 26

How do PIDs work?

Answer 26

• Can detect hydrocarbons
• Uses a UV light with a particular eV energy
• The UV light will shoot photons and ionize particles
• Ionized particles produce an electric current and create a signal output for the PID detector

Think of a PID as a very powerful UV lamp. When the energy from that lamp comes into contact with a gas molecule, it temporarily splits (ionizes) the gas molecule into pieces (ions). These ions migrate to positive (+ve), and negative (–ve) ions migrate to a detector which measures the current the ions generate, amplify and massage the current and produce a ppm or a ppb reading.

Question 27

What is eV and where is it used?

Answer 27

eV = electron volt and it’s used for PIDs

An eV is a unit of measurement contained in a photon generated by a UV lamp. Example: a 10.6 eV lamp will generate photons with an energy of 10.6 eV

Question 28

What are PID advantages?

Answer 28

• Immediate qualitative results
• Quantitative results for individual known contaminants
• Can analyze a wide range of chemicals
• Unaffected by atmospheric conditions

Question 29

What is a flame ionization detector (FID)?

Answer 29

Uses a hydrogen flame, mixed with oxygen and a carrier gas to ionize compounds instead of using a UV light (PIDs)

FIDs are essentially carbon counters: positively charged carbon atoms are collected on a negatively charged electrode. Current is proportional to the number of ions formed and the concentration

Question 30

Compare / contrast PID to FID

Answer 30

• hydrogen / oxygen / carrier gas ionizes instead of a UV light
• FIDs more difficult to operate than PIDs
• FIDs respond to more chemicals than PIDs and are linear over a greater range

Question 31

What is the most common adsorbent? (aka solid sorbent)

Answer 31

Activated charcoal

Question 32

What is activated charcoal made out of?

Answer 32

Coconut shell or petroleum. Activated charcoal has a high surface area to weight ratio.

Major advantage: okay with up to 90% humidity

Question 33

What is activated charcoal desorbed with?

Answer 33

CS2

Question 34

Is silica gel hydrophilic or hydrophobic?

Answer 34

Hydrophilic - loves and binds to H2O

Question 35

How much breakthrough is allowed in solid sorbent active sampling?

Answer 35

10%

Question 36

What can cause solid sorbent breakthrough?

Answer 36

• High humidity
• Concentration too high
• Migration of chemicals
• High temperature
• Channeling
• High flow rates