Use the Browser FIND function (NOT the Search function) to locate a term or scan the alphabetical listing below. If the term is missing, submit the form below to request it to be added to the CH 315 glossary:
(required)
Please also use this form to report broken or incorrect links.
Name (*optional):
E-mail (*optional):
*Optional but recommended so that I can notify you when the term has been added to the glossary.
Absorbance, A, is the negative log10 of transmittance; A = - log T. This variable is the dependent variable in Beer's law.
Absorptivity, a, is the proportionality constant that appears in Beer's law. A = a * b * C, where A = absorbance, which is unitless, b = cell thickness in distance units and C = concentration. Units on absorptivity are distance-1 concentration-1.
Absorption in spectroscopy is the process of transferring energy from electromagnetic radiation to atoms, ions or molecules in a sample. This process leaves the absorbing species in an excited state. The type of excited state motion depends on the energy of the photon absorbed. Only photons having an energy that match the energy difference between two energy levels in the absorbing species will be absorbed. A graph of transmittance, T, % T, absorbance, A, or absorptivity, a, plotted on the y-axis vs energy, frequency, wavelength or wave numbers on the x-axis is called an absorption spectrum. See also wavelength, emission (opposite of absorption).
An acid or a conjugate acid is any chemical species that is capable of losing a H+ ion in solution. The product of an acid losing a H+ is its conjugate base. The product of a base gaining a H+ (and only one H+) is its conjugate acid.
In chromatography, the adjusted retention time of a component, tr', is the time from when an unretained peak elutes to when the component to elutes. Times are measure to the peak elution in each case. The adjusted retention time is the average time that the component spends in the stationary phase. See also retention time and mobile phase retention time.
In chromatography, the adjusted retention volume of a component, Vr', is the volume from when an unretained peak elutes to when the component to elutes. Volumes are measure to the peak elution in each case. The adjusted retention volume is the extra volume of mobile phase that is required to elute a component that is retained. See also retention volume and mobile phase retention volume.
An aliquot is a part or portion of a solution.
The word amount is a term used to express the quantity of a substance in units of moles or any of its scaled units such as mmol or µmol.
An amphiprotic species is any chemical species that behaves as a base in one reaction and an acid in another. All partly ionized polyprotic acids are amphiprotic. The completely protonated form is only an acid and the completely deprotonated from is only a base.
The analyte is the substance for which one analyzes.
An anion is a negatively charged ion.
An anion exchange resin is an ion exchange resin that can exchange with anions. Anion exchange resins usually have either a secondary amine, -NH(R)2+Cl-, or a tertiary amine, -CH2N(CH3)3+Cl-, functional group attached to a polymer backbone. The anion, Cl- in this case, on the resin can exist in equilibrium with other anions in solution. See also cation exchange resin.
Anionic surfactant: see surfactant
The anode is the electrode where oxidation occurs. For a galvanic cell, the negative electrode is the anode, but for an electrolytic cell, the positive electrode is the anode.
A base or a conjugate base is the product chemical species when an acid loses a hydrogen ion, H+. A base always has one fewer hydrogens in the chemical formula and one unit lower charge.
Beer's law describes the dependence of intensity of light (electromagnetic radiation) transmitted through a sample on 1) sample thickness and 2) concentration. A = a * b * C, where A = absorbance, which is unitless, b = cell thickness in distance units and C = concentration in any valid concentration units.
A blank is a solution prepared exactly like your samples and standards except that the concentration of analyte is zero.
A buffer is a solution containing a mixture of a conjugate acid-base pair of reactants as solutes. For example a solution that contains both acetic acid and its conjugate base, acetate ion. It is given that name because a buffer resists a change in pH on adding either strong acid or strong base.
The capacity factor or capacity ratio in chromatography is the adjusted retention time expressed as a multiple of the retention time for an unretained peak.
Capillary Electrophoresis (CE) or Capillary Zone Electrophoresis (CZE) is a method of separation in which charged species migrate by a combination of electrophoresis and electroosmosis and neutral species in solution migrate by electroosmosis only.
The cathode is the electrode where reduction occurs. For a galvanic cell, the positive electrode is the anode, but for an electrolytic cell, the negative electrode is the anode.
A cation is a positively charged ion.
A cation exchange resin is an ion exchange resin that can exchange cations adsorbed on its surface with cations in solution. Certain glasses particularly designed for use in pH electrodes serve as very good ion exchangers specifically for H+. A glass ion exchanger works because of hydrated silica bonds, -SiO-H+, bonds that are exposed to solutions at the surface. The -SiO-H+ functions as a weak acid forming -SiO- at the glass surface and H+ in solution. Other ion exchange resins usually have either a -COO-H+ or a -SO3-H+ functional groups attached to a polymer backbone. These other ion exchange resins can exchange with ions other than H+. See also anion exchange resin.
Cationic surfactant: see surfactant
The character in a logarithm is the number before the decimal which is related to the power of 10 multiplier of the antilogarithm of the number. The character does not affect the number of significant figures of the antilogarithm. See also mantissa.
Chromatography is method of separation that requires the distribution of a component between two physical phases.
A confidence interval is a range of values having a state probability of included the expected value with no random error. For example a 95 % confidence interval has a 95 % change of including the result with no random error. A confidence interval about an observed value is the observed value ± the confidence limit.
A confidence limit is a value that when both subtracted from and added to an observed value gives a confidence interval. A confidence limit is calculated multiplying the Student's t value times the standard error in the observed value.
A conjugate acid - base pair is a pair (two) chemical species, one of which is an acid and the other of which is a base. The conjugate pair differs only in one H+ in the chemical formula; the acid has one more H in its chemical formula and algebraically one greater charge than the base.
An electrolytic cell is a cell that behaves as a battery which is being recharged. Electrons are forced by an external power supply to flow from the positive electrode to the negative electrode, which is opposite to the direction they would flow spontaneously. The chemical reactions at the two electrodes occur in the reverse direction from which they would occur spontaneously. The negative electrode is the cathode and the positive electrode the anode in an electrolytic cell.
Deprotonated is a term used in acid/base chemistry which means H+ removed; protonated means H+ attached. The deprotonated form of an acid is a base.
Deviation is a term used to describe the "incorrectness" of data. It is often used interchangeably with error. Both error and deviation are often preceded by an adjective to describe alternative ways of expressing error or deviation mathematically. For example: 1) absolute deviation, 2) relative deviation, 3) percent deviation, 4) standard deviation.
Electroosmosis is the flow of ionic solutions under the influence of an electric field.
Electrophoresis is the migration of ions in a viscous medium under the influence of an electric field.
Eluate is a term used in chromatography that means the same thing as the mobile phase. However, it specifically refers to the mobile phase at the outlet of the column. As each component elutes, the eluate will have component dissolved in the eluent. See also eluent.
Eluent is a term used in chromatography that means the same thing as the mobile phase. However, it specifically refers to the mobile phase at the inlet of the column. See also eluate.
To elute literally means "to wash". In chromatography to elute means to wash a component through a column.
In spectroscopy, emission refers to the process of an excited state atom, ion or molecule losing its excitation energy by emitting a photon. The wavelength of radiation emitted is determined by the energy difference between the initial and final energy states of the emitting species. A plot of intensity (or a signal proportional to intensity) vs wavelength, frequency, wavenumbers or energy is called a emission spectrum. Luminescence is a synonym for emission spectroscopy in the visible region. See also absorption (opposite of emission), luminescence and wavelength.
The equivalence point in a titration the point where one has a stoichiometric mixture of analyte and titrant. The equivalence point volume is the volume of titrant necessary to react with all of the analyte if the reaction were to form 100 % product.
The end point is the point in a titration where one stops the titration. The endpoint volume is often he volume of titrant required to cause some color change in an indicator. Ideally the color change occurs at the equivalence point.
Error is a term used to describe the "incorrectness" of data. It is an observe value minus the expected value and is often used interchangeably with the term deviation. There are two types of error: 1) random error and 2) systematic error. Both error and deviation are often preceded by an adjective to describe alternative ways of expressing error or deviation mathematically. For example: 1) absolute error, 2) relative error, 3) percent error, 4) standard deviation, 5) standard error.
A flash back is an explosion that can occur in a premix burner. When the burning velocity of the combustion mixture exceeds the flow velocity of the combustion gasses, the flame front can burn back into the premix chamber where the gasses explode.
A galvanic cell, which is a cell that behaves as a battery. Electrons flow from the negative to the positive electrode, which results from spontaneous chemical reactions at the two electrodes. The negative electrode is the anode and the positive electrode is the cathode.
The height equivalent to a theoretical plate (HETP or hetp) is a term in chromatography used to describe the column efficiency. It is defined to be the column length, L, divided by the number of theoretical plates, N.
A heterogeneous reaction is a chemical reaction that occurs between two physical phases; i.e. between a solid and a liquid, a solid and a gas, a gas and a liquid or between immiscible liquids.
Ion exchange reactions are heterogeneous reactions between ions in solution and ions adsorbed on an ion exchange resin.
An ion exchange resin is a solid which has a high concentration of ionic sites at its surface. These ions at the surface can exist in equilibrium with ions dissolved in solution. There are two types of ion exchange resins: 1) a cation exchange resin and 2) an anion exchange resin.
Ionic strength, µ, is a measure of the total ion concentration in solution. If ci = ion molarity and zi = ion charge, then:
An isosbestic point is a point (i.e. a wavelength) where the molar absorptivity is the same for both a reactant and a product in a chemical reaction, when the reactant and product have overlapping absorption spectra. At the isosbestic point, the absorbance is proportional to make-up concentration (i.e. the sum of the molar concentration of each). A = a * b (CR + CP)
A LIF detector is a laser induced fluorescence detector. This detector is one that is suitable to capillary electrophoresis.
Luminescence in spectroscopy refers to the emission of electromagnetic radiation after an atom, ion or molecule becomes elevated to an excited electronic state. In the visible range, there are several types of luminescence which differ mostly in terms of how an electron becomes elevated to an excited state. These types are: thermoluminescence (such as flame emission) - heat energy; chemiluminescence - chemical energy; fluorescence and phosphorescence (absorption of UV radiation); scintillation - high energy charged particles; and electroluminescence - electrical energy such as from a light emitting diode.
The mantissa in a logarithm is the number after the decimal point. For example log 1234 = 3.0912152. The value 0.0912152 is the mantissa. In expressing a logarithm to the correct number of significant figures, retain as many digits in the mantissa as those in the argument of the logarithm. In this example, 3.0912. In expressing the correct number of significant digits in an antilogarithm, retain as many significant figures as digits in the mantissa. The antilog of 1.2345 = 17.159317, which should be rounded to 17.16 since there are four digits in the mantissa. See also character.
A micelle in an aqueous phase is a aggregate of surfactant molecules that have their hydrophobic end pointed away from an aqueous phase toward the center of the micelle and their hydrophylic end pointing towards the aqueous phase on the surface of the micelle.
Micellar Electrokinetic Chromatography (MEC or MEKC) is a variation on capillary electrophoresis based on the distribution of neutral components between the supporting electrolyte and the micelle.
A micro analysis is an analysis of a small sample, which may have a high concentration; "small" is a relative term, but for estimation say less than a mg or μL of sample.
In chromatography, mobile phase retention time, tm, is the time for an unretained component to elute. This time represents the minimum time a component remains on the column, which is the time all components spend in the mobile phase. See also retention time and adjusted retention time.
In chromatography, the mobile phase is the fluid phase that flows through a column. It may be gas, liquid or super critical fluid.
Mobile phase volume see void volume.
Molar absorptivity is the absorptivity expressed in units of cm-1M-1. These units are equivalent to cm2/mmol. Molar absorptivity is often give the symbol, e, instead of a, the symbol for any other units on absorptivity.
Monochromatic light is literally light having one color. More generally it means light having one wavelength. However, it is not possible to isolate light of only one wavelength. The best one can do is isolate a narrow range of wavelengths. A working definition of monochromatic follows: A monochromatic light source is one which emits light over less than 0.1 the range of wavelengths absorbed by a sample. Thus, if a sample absorbs over a 10 nm range, a source that emits over a 1 nm range is monochromatic. However, if the sample absorbs over only a 0.001 nm range, a source that emits of a 1 nm range is non monochromatic. Thus a source that emits over a 1 nm range may be monochromatic is one situation, but non monochromatic in another.
Non-ionic surfactant: see surfactant
Non monochromatic light is light which is emitted over a broad wavelength range. In the context of this course, broad is a relative term. Broad means a wide wavelength range compared to the range of wavelengths absorbed. It is easier to quantitate what is meant by monochromatic; non monochromatic means not monochromatic.
Normal phase liquid chromatography is liquid chromatography in which the stationary phase is polar and the mobile phase is non polar. See also reverse phase liquid chromatography.
An oxidation reaction is one in which there is a gain in charge; that is a gain in charge in an algebraic sense which results from a loss of one or more electrons. For example: 1) -2 to -1, 2) -1 to 0, 3) 0 to 1 or 4) 1 to 2 are all examples of a charge gain or an increase in the charge. A reduction reaction is the opposite of an oxidation.
A physical phase is a state of matter which includes solids (s), liquids (l), gasses (g) and supercritical fluids (scf).
A physical phase boundary is a boundary between two non identical phases like a solid-liquid or a liquid-liquid interface. If the liquids are immiscible in a liquid-liquid phase boundary, the phases will separate into two layers. However, if the liquids are miscible, a boundary between two solutions having different concentrations qualifies as a phase boundary.
The number of theoretical plates, N, in chromatography is a figure of merit describing the number plates in a fractional distillation column that would cause the same peak width for a component that moves through a chromatographic column. The defining relationship is N = (tr/σ)2, where tr is the peak retention time measured from injection and σ is the standard deviation of the Gaussian peak that elutes from a column. Two alternate working relationships are mathematical identities for a peak that is perfectly Gaussian: 1) N = 16 * ( tr / w)2, where w = base width of the triangle drawn tangent to the sides of the Gaussian peak, and 2)N = [2 (2 ln 2)1/2]2 * ( tr / w1/2)2 = 5.55 * ( tr / w1/2)2, where w1/2 = full width of the Gaussian peak and 1/2 the peak height.
A primary standard solution is a standard solution which is prepared by weighing a very pure (>99.9% purity) compound containing the analyte and dissolving it in a solution whose dilution volume is accurately known. If the compound from which the standard is prepared happens to be a liquid, its volume might be accurately measured rather than its weight.
Protonated is a term used in acid/base chemistry which means H+ attached; deprotonated means H+ removed. The protonated form of a base is an acid.
A random error is an error that averages to zero if a measurement is repeated an infinite number of times. See also systematic error.
A redox couple is a pair of chemical species related to one another by a reversible oxidation-reduction reaction. In principle, the product of an oxidation can be reduced by reversing the reaction and the product of a reduction can be oxidized by reversing the reaction. In oxidation-reduction chemistry, the species referred to as a redox couple are related to one another as the species referred to as a conjugate acid-base pair are related in acid-base chemistry.
Redox reagents are chemical species that can be either oxidized or reduced. In principle, the product of an oxidation can be reduced by reversing the reaction and the product of a reduction can be oxidized by reversing the reaction. The oxidized form and the reduced form of a chemical species are referred to as a redox couple.
A reduction reaction is one in which there is a reduction in charge; that is a decrease in charge which results from a gain of one or more electrons. The charge loss is an decrease in the algebraic sense. For example: 1) +2 to +1, 2) +1 to 0, 3) 0 to -1 or 4) -1 to -2 are all examples of a decrease in charge. An oxidation is the opposite of a reduction.
In chromatography, retention time for a component, tr, is the time from injection to the when then component elutes. Times are measured to peak elution. See also adjusted retention time and mobile phase retention time.
In chromatography, retention volume for a component, Vr, is the volume from injection to the peak volume of mobile phase when then component elutes. Vr = F tr, where tr = retention time and F = volume flow rate. See also adjusted retention volume and mobile phase retention volume.
Reverse phase liquid chromatography is liquid chromatography in which the stationary phase is non polar and the mobile phase polar. See also normal phase liquid chromatography. Components often elute in reverse order from normal phase liquid chromatography.
A secondary standard solution is a standard solution which is prepared with only its approximate analyte concentration known. However, the concentration of the secondary standard is determined by an analytical procedure which is referenced to a primary standard.
Writing a number to the correct number of significant figures or significant digits is a convention which allows the reader to infer the uncertainty of the value from the number of digits written. All digits that are certain plus one which is estimated are considered significant.
A standard deviation is a measure of random error in experimental data. It is calculated by taking the square root of the sum of squares of error divided by the number of independent estimates of error. The exact equation depends on how errors are calculated. Two of the frequently used standard deviations in the physical sciences are given by equations 4 and 10 on the linked equation sheet. Equation 4 is the standard deviation for repeated measurements and equation 10 is the standard deviation for measurements that fall on a straight line.
A standard error is a measure of random error in values calculated from data that have random error. In the physical sciences one of the most frequently used standard errors is the standard error in the mean which is given by equation 6 on the linked equation sheet. The standard error in the mean is the standard deviation in the repeated measurements divided by the square root of the number of measurements averaged. On this equation sheet, odd equations 11-31 describe a number of algebraic operations. The next even equation, equations 12-32, give the standard error that results from these algebraic operations. Standard errors are the result of propagating errors in values calculated from data for which one has a measured standard deviations.
A standard solution is one with the following properties: 1) its concentration is accurately known and 2) it is stable under ordinary conditions. There are two types of standard solutions: 1) primary and 2) secondary.
The Student's t value is the error expressed as a multiple of the standard error determined from a finite number of measurements. This constant can be looked up in a Student's t Table or calculated from the TINV function in Excel.
A surfactant is a molecule that has a hydrophobic end and a hydrophylic end. The hydrophobic end is usually a long chain hydrocarbon functional group, R, is a long linear chain like C16H33 or C18H37 and the hydrophylic end is usually one three functional groups: 1) it may be positively charged as in a trimethyl quaternary ammonium salt RN(CH3)3+, it may be negatively charged as in a salt of a fatty acid, RCOO-, or it may be neutral, but polar, as in a high molecular weight alcohol, ROH. If the hydrophylic end is positively charge, the surfactant is called a cationic surfactant; if negatively charged - an anionic surfactant and if neutral - a non-ionic surfactant.
A systematic error is an error which does not average to zero. See also random error.
The tare of container is its initial weight. The tare is often set to zero on an analytical balance.
A trace analysis is an analysis of a sample that has a low concentration, but one may have a large quantity of sample; "low" is a relative term, but for estimation say less than 1 mg analyte/mL or 10 mM.
Transmittance, T, is the fraction of light (electromagnetic radiation in general) transmitted through a sample. If P = transmitted intensity and P0 = incident intensity, then T = P/P0. Transmittance is used to define absorbance in Beer's law, the quantitative law relating intensity of light to concentration.
Uncertainty is a term used to describe one of several ways of estimating error in a measured or calculated value. The two most popular ways are 1) standard deviation and 2) confidence interval.
Void volume, V0, or mobile phase volume, Vm, is the volume of mobile phase in a chromatographic column. This volume is the volume to elute an unretained peak. It is the smallest volume into which any component can be eluted.
Wavelength in spectroscopy is the distance between corresponding points on an oscillating electromagnetic wave. Wavelength (λ), energy (E), frequency (ν) and wave number () are all related to one another by the following relationships: E = h ν, where E = energy / photon, h = Planck's constant = 6.626 x 10-34 J s / photon and n is the frequency in Hz (sec-1). The relationship between wavelength and frequency is: l * ν = c; c = velocity of light = 3.00 x 108 m/s, where wavelength is measure in distance units like m, cm, µm, nm, etc. Energy is proportional to frequency and wavenumbers, but inversely proportional to wavelength. As energy of a photon increases, frequency and wavenumbers increase, but wavelengths become shorter.
Wave number in spectroscopy is 1/wavelength. It has units of cm-1. Wavenumbers are directly proportional to frequency and to energy.
Common Symbols and Abbreviations in Chromatography, Electrochemistry, Spectroscopy and Statistics.
In Chromatography:
H - HETP
HETP - height equivalent to a theoretical plate
HPLC - high performance liquid chromatography
k' - capacity factor or capacity ratio
N - number of theoretical plates
tm - retention time for the mobile phase or retention time for the void volume
tr - retention time
tr' - adjusted retention time
V0 - retention volume for the mobile phase
Vm - retention volume for the mobile phase
Vr - retention volume
α- relative retention ratio