Gas Analysis Flashcards
Electromagnetic radiation can be converted into other forms of energy:
electricity (gas discharge) heat (incandescence) and chemical (photoluminescence)
oxygen analysis
galvanic fuel cell.
how does the galvanic fuel cell work
the oxygen is reduced to hydroxide ions at the cathode. at the anode the hydroxide gives up electrons. an electron flow between the lead anode and the gold cathode is generated in a potassium hydroxide electrolyte solution, which is directly proportional to the partial pressure of oxygen
ie current flows in proportion to O2 concentration
how does the clark polargraphic oxygen electrode work?
the electrodes are immersed in an electrolyte cell. And O@ permeable membrane ( but not electrolyte) covers one surface of the cell. When a polarizing voltage is applied to the cathode, electrons combine with oxygen molecules and reduce them to hydroxide ions. The meter measures the current produced by the electrons consumed in the reaction at the cathode.
ie current flows in proportion to oxygen concentration
how does the pragmatic oxygen sensor work?
utilizes oxygen’s paramagnetic properties which causes it to locate itself within the strongest portion of a magnetic field. By passing a known concentration (or lack of) oxygen through one channel of a dual channel tubing connected by a transducer and a sample gas through the other a pressure difference can be measured.
ie the pressure difference is directly proportional to the concentration between the samples
how does the fluorescence quenching sensor work?
an electron of the fluorescent dye is excited to a higher energy level by an incident photon. The excited electron can return to a lower energy level either by emitting a photon (v2) or by interacting with an oxygen molecule and raising the latter to a higher vibrational energy level
ie oxygen has the ability to absorb energy from excited states in certain fluorescent dyes and prevents this energy from being emitted as light.
pH optode
utilizes the fluorescence quenching principles applied to hydrogen ions. pH changes the energy transfer
Severinghaus PCO2 electrode
consists of a pH sensitive glass electrode referenced to a silver-silver chloride electrode. The glass electrode is immersed in a solution with a CO2 permeable membrane covering n the surface. When CO2 diffuses into the cell, it reacts with water, producing carbonic acid, and the pH electrode detects the acidity change.
pH electrode measures the pH changes which is proportional to hydrogen ion concentration which is proportional to CO2. Can selectively measure the CO2 partial pressures in liquid or gas phase. Used in ABG analysis.
disadvantages to severinghaus
lag time 1-2 minutes
absorption measurements are based on
Beer-Lambert Law
gas liquid chromatography
“to write in color” Separates the mixture based on solubility of component parts. Polazrizing voltage applied, increase or decrease in voltage related to substance in concentration present. Must know what substances are being measured. Cannot give continuous measurements. Useful with measuring trace gases.
infrared absorption analysis
molecules may absorb infrared light if they are polyatomic and asymmetric. Infrared radiation is absorbed by molecules because the frequency of the radiation is the same as natural vibrational frequency of the molecules. Increases the amplitude of the naturally occurring vibrational frequency.
Advantage:
measures anesthetic gases, accurate, real times, portable
Disadvantage:
symmetric molecules such as O2, N2 and helium will not be detected through infrared absorption
mass spec
a gas ionized and passed through a curved tube in a magnetic field. The ionized gas molecules become deflected by the magnetic field based on their molecular weights.Several collectors are located along the field to collect samples of differing molecular weights. Measures all gases
