Instrumentation Flashcards
spectrophotometry
Spectrophotometry is a method to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through sample solution.
atomic absorption
used to measure concentration by detecting absorption of electromagnetic radiation by atoms rather than by molecules; used to measure heavy metals
chemiluminescence
the emission of light during a chemical reaction which does not produce significant quantities of heat.
electrophoresis
migration of charged solutes or particles in an electrical field. Iontophoresis is migration of small molecules; zone electrophoresis is migration of charged macromolecules in a porous support
fluorometry
excitation (absorption of energy by a molecule) followed by emission (fluorescence) as energy.
ion-selective electrodes
potentiometric method of analysis for direct measurement of electrical potential due to activity of free ions. designed to be sensitive to individual ions.
isoelectric focusing
modification of electrophoresis where charged proteins migrate through a support medium the has a continuous pH gradient. individual proteins migrate in the electric field until they reach a pH equal to their isoelectric point, at which point they have no charge.
capillary electrophoresis
separation is performed in a narrow bore fused silica capillary tube (ID = 25-75 micrometer)
2D electrophoresis
a form of gel electrophoresis commonly used to analyze proteins. Mixtures of proteins are separated by two properties in two dimensions on 2D gels.
Electroendosmosis
the movement of liquid in a porous material due to an applied electric field
Beer law
the concentration of a substance is directly proportional to the amount of light absorbed or inversely proportional to the logarithm of the transmitted light. A=abc; A=2-log%T; Cu=Au/As x Cs (where u = unknown and c = standard)
Spectrophotometer components
light source (tungsten, deuterium, mercury); monochromator (isolation of individual wavelengths of light); sample cell (cuvette; quartz for UV); photodetector (conversion of transmitted radiant energy into an equivalent amount of electrical energy; photocell, phototube; photomultiplier)
Flame photometry
flame emission photometer, which measures light emitted by excited atoms. have been replaced by ion-selective electrodes.
turbidity
the amount of light blocked by a suspension of particles depends on concentration and size of particles; sample handling critical due to tendency of particles to aggregate and settle.
nephelometry
light is scattered by small particles and is measured as an angle to the beam incident on the cuvette
laser applications
based on the interaction of radiant energy with suitably excited atoms or molecules. Leads to stimulated emission of radiation; 3-6 times more sensitive that conventional spectrophotometers
galvanic cells
also known as voltaic cells, are electrochemical cells in which spontaneous oxidation-reduction reactions produce electrical energy.
electrolytic cells
are composed of two half-cells–one is a reduction half-cell, the other is an oxidation half-cell. The direction of electron flow in electrolytic cells, however, may be reversed from the direction of spontaneous electron flow in galvanic cells, but the definition of both cathode and anode remain the same, where reduction takes place at the cathode and oxidation occurs at the anode. Because the directions of both half-reactions have been reversed, the sign, but not the magnitude, of the cell potential has been reversed.
half-cells
A half-cell is half of an electrolytic or voltaic cell, where either oxidation or reduction occurs.
pH electrodes
The most widely used ion-selective electrode is the glass pH electrode, which utilizes a thin glass membrane that is responsive to changes in H+ activity.
Gas-sensing electrodes
A sensor composed of an indicator and a reference electrode in contact with a thin film of solution which is separated from the bulk of the sample solution by a gas-permeable membrane or an air gap. Designed to detect specific gas species (i.e. CO2 and NH3); used in clinical labs to for measuring serum electrolytes and blood gases.
Enzyme electrodes
ion selective electrode covered by immobilized enzymes that can catalyze a specific chemical reaction. (i.e. urease to detect urea; glucose oxidase to detect glucose)
Coulometric chloridometers
historically used to detect chloride
anodic stripping coltammetry
historically used to detect lead
osmometry
used to measure the concentration of solute particles in solution.
surface plasmon resonance (SPR)
he resonant oscillation of conduction electrons at the interface between negative and positive permittivity material stimulated by incident light. Used to study the binding of ligands to surface receptors (i.e. membrane proteins) in real time.
Osmolality
osmotic coefficient x number of dissociable particles (ions) x concentration in mol/kg of solvent (mOsmol/kg of H2O); 1.86 [Na+] + GLU/18 +BUN/2.8
Osmolar Gap
difference between the calculated and measured osmolality of a solution (measured - calculated)
Osmolar Gap
difference between the calculated and measured osmolality of a solution (measured - calculated)
Rate of mobility of a molecule (u)
net charge (Q)/constant (K) ionic radius (r) viscosity (n); thus rate of migration is directly proportional to the net charge and inversely proportion to its size and the viscosity of the buffer
electro osmotic flow (EOF)
bulk flow of the liquid toward the cathode upon application of an electric field and it is superimposed on electrophoretic migration. Controls amount of time solutes remain in the capillary; cations migrate the fastest
