Analytical Chemistry Flashcards
Titration
alkalinity and acidity Acid + Base = Salt + Water
gravimetric analysis
pre-weight filters with specific pore size (5 m)
Electrochemistry
- Potentiometry– measures the potential developed between 2 electrodes (nernst equation), pH & Ion specific tests
- Anodic Stripping Voltammetry – lead, cadmium, copper at ppb levels
- Gold film Hg sensors – change in resistance as Hg dissolves Au
Chromatography
Good for mixtures/separation techniques. Stationary phase absorbs analytes and causes separation.
Gas Chromatography (GC)
Analyze must have high vapor pressure, Stable at High Temperatures. Carrier gas usually Nitrogen, Hydrogen, and Helium. Good for Organics and Ogano-metals. 50% of NIOSH techniques specify this device.
High Pressure Liquid Chromatography
Uses pressure instead of heat. Extremely quick. Good for Drugs and Vitamin detection.
Flame Ionization Detector (FID)
A stainless steel burner in which hydrogen is mixed with the sample stream; combustion air feeds in and diffuses around the jet (burner) where ignition occurs. The current carried across the gap of a platinum loop collector electrode is proportional to the number of ions generated by burning the sample.
Large linear range. Response uniform to from compound to compound. Not as sensitive as other detectors (DL - 0.01 ppm).
Compounds detected: Organics, best with hydrocarbons, response decreases with substitutions in the chain.
Photo ionization Detector (PID)
A sealed UV light source emits photons with an energy level high enough to ionize compounds in the sample. In a chamber exposed to the light source containing a pair of electrodes, ions formed by absorption of photons are driven to the collector electrode where a current is produced that is proportional to the concentration.
Large linear range; high sensitivity; selectivity can be introduced by different lamps. Response varies from compound to compound. (DL - 1-100 ppb).
CIH Study Guide 19 of 92
19 of 92
Compounds detected: Organics some inorganics, responses lower to low-molecular-weight hydrocarbons. Can detect aliphatic, aromatic, halogenated hydrocarbons. Sensitive to water. Esp. good for aromatics.
Electron Capture Detector (ECD)
Utilizes radioactive sources such as 63Ni to supply energy to the detector in the form of radiation. Intensity of the electron beam arriving at a collection electrode is monitored. When an electron capturing species passes through the cell the intensity of the electron beam decreases, sending out an electronic signal.
Responses vary widely from compound to compound. Highly sensitive and selective. Potential problems include excessive heat, which could vaporize some of the source; ―aging‖ of the coated foil, which must be replaced; gradual loss of the source‘s activity. (DL - 0.1-100 ppb).
Compounds Detected: compounds containing halogens, cyano or nitro groups; ECD has a minimal response to hydrocarbons, alcohols, and keytones.
Spectroscopy
Absorption/emission in a gaseous state. Ions in a high-energy state reverting back to a lower state emit a photon. This photon is what is being detected.
AA Spectrometry
(Flame AA, Graphite Furnace AA) - metals in a solution.
Flame AA - Fast. Must set for each element.
Graphite Furnace AA - Higher temperatures. Detects more than one element at a time. Extremely
sensitive.
Cold Vapor AA - Elemental Hg
Inductively Coupled Plasma Emission Spectroscopy (ICP):
Higher temperature plasma is used to raise atoms to higher energy level, quickly replacing AA because simultaneous, multi-element capacity, Plasma is an ionized gas, which enables extreme excitation of all atoms. 20-40 elements simultaneously. Low detection limits. High temperatures. Detects in about 30 sec.
Infrared Spectroscopy (IR) –
Relies on the adsorption of IR radiation by molecular bonds. Has to be a solvent in a solution. More qualitative than quantitative
Mass Spectroscopy (MassSpec) -
Sample ionized by electron impact and measurement of action of ions in a magnetic field. Ions accelerated by a high voltage. Best when used as a detector on GC because it shatters the molecules.
X-Ray Diffraction -
when an x-ray beam impinges upon crystalline samples a characteristic spectrum is formed. This is used to identify the material being analyzed. (uses Bragg‘s Law n = 2d Sin )
