Quantitative Analysis Cheat Sheet free essay sample

Analytical chemistry: science of chemical measurement. Its object is the generation, treatment and evaluation of signals from which information is obtained on the composition and structure of matter Measurement: process of obtaining the magnitude of a quantity Example: The amount of saturated fat in the sample is 3 g/serving. Quantity: attribute of a phenomenon that may be distinguished qualitatively and determined quantitatively Value: magnitude of a particular quantity expressed as a unit of measured * a number Unit: particular quantity defined and adopted by convention for comparison of magni ? Globalization requires comparability of measurements Metric system: Meter Convention led to the signing of the Meter (1875) establishing the Bureau International des Poids et Measures In 1960, the 11th General Conference on Weights and Measures adopted the name Systeme International d’Unites (ISU) for recommended practical system of units of measurement Fundamental SI units: length (m), mass (kg), time, electric current (a), temp, luminous intensity – candela (cd), amount of substance (mol), plane angle (radian), solid angle (steradian) Meter: from 1/110^7 distance from equator to north pole ? distance travelled by light in a vacuum in 1/299, 792, 458 second Kg: only remaining unit whose definition is based on an international prototype ? Prototype 52 (Germany) 18 (UK) 20 (US) International proto (Sevres, France) 90% Pt, 10% Ir alloy SI derived: frequency(1/s), force, pressure (pascal), work, power (watt), charge (coulomb), electric potential (volt), elec resistance (ohm) 24-(-24) yotta, zetta, exa, peta, tera, giga, kilo, hector, deka, deci, centi, milli, micro, nano, pico, femto, atto, zepto, yocto amount of substance: number of some specified elementary entity: mole (quantity: amount) unit: mole One serving of milk contains 195 mg PHOSPHORUS (matrix ? value ? unit ? specie/analyte) Matrix: where the specie is being determined Concentration: how much solute is contained in a given mass or volume Molarity: mol/L * Molality: mol/kg*weight percent: mass of substance per mass solution (g/g % or wt%) *volume percent: Vol % * mole fraction: amount of substance in the total amount of solution (unitless) Normality: number of equivalence per liter solution Parts per million (ppm) is expressed in units mg/kg or  µg/mL Parts per billion (ppb) is expressed in  µg/kg or ng/g. aqeous:  µg/L or ng/mL Volumtetric flask: used to prepare solutions of exact concentration (contains a specified volume) Chapter 2: Tools of the trade laboratory notebook (objectives: state what was done, observed, be easily understandable) analytical balance (principle of operation – sample on balance pushes pan down with a force (m x g), balance pan with equal and opposing mass(mechanical: standard mass, electronic: opposing electromagnetic force, tare – mass of empty vessel) double-pan balance: balance beam suspended on a sharp knife edge, standard weights are added, weight of sample is equal to total weight of standards electronic balance: uses electromagnetic force to return the pan to original position (electric current required to generate force is proportional to sample mass) 2. Methods of weighting: basic operational rules: don’t place chemicals directly on weighing pan, balance in an arrested position (decrease sensitivity if not followed), weight by difference (useful when hygroscopic: readily absorb water from air), taring 3. Errors in weighing: sources (any factor that could affect mass – dirty or moist sample container, not at room temp, adsorption of water, vibration of wind currents, non-level balance) buoyance errors: failure to correct for weight difference due to displacement of air by sample correction: m = (m’(1-(da/dw))/(1-(da/d) m- true mass, m’ – mass read from balance, d – density of sample, da – density of air (0. 0012 g/ml at 1 atm at 25 C), dw – density of calibration weights (8 g/ml) density of air changes with temp and pressure (da under non standard conditions: =0. 46468(B-0. 3783 V/T) B= barometer pressure (torr), V= vapour pressure of water in the air (torr), T= temperature (K) Volume measurements: 1. Burets (used to deliver multiple aliquots of a liquid in known vols – tolerance: ? the smallest graduation) Correct use of buret: read buret at bottom of concave meniscus, read at eye level (avoids parallax errors, from above: smaller), estimate buret reading nearest 0. 1 division, expel all air bubbles, rinse buret 2-3x with solution, near end of titration, volume of 1 drop or less 2. Volumetric flask:correct use: add reagent of solution to flask and dissolve in volume of solvent less than total capacity of flask, slowly add more solvent until mark, mix solution by inversion (40 or more times), glass adsorbs trace amount of chemicals ? clean using acid wash (adhere to surface) 3. Pipets and Syringes (deliver a given volume of liquid) Types of pipets: transfer pipet (transfers a single volume, fill to calibration mark, last drop does not drain out of pipet (do not blow out), more accurate than measuring pipet(similar to vol flask) measuring pipet: calibrated similar to buret, use to deliver a variable volume micropipette: deliver volumes of 1 to 1000  µL(fixed and variable), uses disposable polypropylene tip, stable in most aqueous and organic solvents (not chloroform), need periodic calibration syringes: deliver volumes of 1 to 500  µL (accuraprec: 0. 5-1%, steel needle permits piercing stopper to transfer liquid under controlled atmosphere (attacked by strong acid and contaminate solution with iron) correct use: use a bulb for drawing solutions, rinse pipets and syringes before using, remove bubbles Filtration: mechanical separation of a liquid from the undissolved particles floating in it Purpose: used in gravimetric analysis for analysis of a substance by mass of a precipitate it produced (solid collected in paper or fritted-glass filters) Drying: remove moisture from reagents, convert sample to more readily analysable form Oven drying: common for sample prep, 110 C for water removal, use loose covers to prevent contamination from dust Dessicator: cool and store reagent or sample over long periods of time (contains drying agent to absorb water from atmosphere, airtight seal) Primary standard: may be used to prepare standard solution used as reference for knowing amount of subtstance or calibrate an analytical measurement (KHP f or determining NaOH) 99. 9% pure or better, not decompose under ordinary storage, stable when dried by heat or vacuum (should not be a hydrate), of high molecular weight Chapter 3: Propagation of Error significant figures: minimum number of digits needed to write a given value (in sci not) without loss of accuracy zeros are simple place holders and are counted significant only if, in between, to the right of the decimal point the last significant figure in any number is the first digit with any uncertainty (minimum uncertainty is +/- 1 unit in the last significant figure) addition/subtraction (least amount of decimal points), multiplication/division: least sig figs logs and antilogs ? a = 10^b or log(a)=b ? log(339)=2. 530 (2, character) and (. 530, mantissa) log – resulting mantissa should be same as total number of sig figs in original number (a) antilog: number of sig figs in the result should be same as total number of sig figs in the mantissa of original logarithm â€Å"b† graph: spread coordinates over as much of the graph as possible systematic or determinate error: error caused consistently in all results due to inappropriate methods or experimental techniques, results in a definite difference from true value, can be discovered/corrected random or indeterminate error: caused by random variations, results in scatter of results centered on true value(error type A), stdev accuracy: close to true value(systematic error), precision: close to each other(precision)(error type B, bias) absolute and relative uncertainty: both measures of the precision associated with a given measurement absolute uncertainty: margin of uncertainty associated with a measurement (like from the device) relative uncertainty: compare s size of the absolute uncertainty with the size of its associated measurement (absolute uncertainty/measured value) if percentage: multiply by 100 measurement of uncertainty: parameter that characterizes the dispersion of the quantity values that are being attributed to a measurand based on the information used we need it: demonstrates metrological quality, documents in transparent way the measurement procedure, gives confidence to the results and allows comparison, demonstrates compliance with limits and establishment of acceptance criteria estimation: specify the measurand (equation, scope of measurement and bias), identify the uncertainty sources (create cause and effect diagram), quantify the uncertainty components, convert the standard uncertainties, calculate the combined standard uncertainty, multiply obtained standard uncertainty by a coverage factor 2(95% confidence level) statistical distributions: 1) normal distribution: use to estimate uncertainty due to random errors ( repeatability precision) u(x)=s 2) triangular: estimate uncertainty when maximum range (+/- a) is given u(x)=a/v6 Rectangular distribution: estimate uncertainty when specification gives limit (+/-a) without specifying the level of confidence (e. g. limits in the specifications of concentration of standards, instrument error) u(x)=a/v3 Selectivity (specificity) – being able to distinguish your analyte from other species in the matrix Sensitivyt – being able to respond reliably and measurably to changes in analyte concentration (slope of calibration curve) Standardization of NaOH solution (C of NaOH = MKHP*P KHP *1000/(M KHP * V NaOh)) propagation of uncertainty: absolute or relative uncertainty of a calculated result can be estimated usig the absolute or relative uncertainties of the values Addition or subtraction: absolute uncertainty obtained using absolute uncertainties used in the calculations (v(abs uncertainty )^2+(abs uncertainty 2)^2†¦ check formula 2. 1 relative uncertainty: still divide the absolute uncertainty by the measurement Chapter 4: Statistics all measurements contain random error (always have uncertainty), uncertainty are used to determine if two or more experimental results are equivalent or different (statistics is used to accomplish this task) Gaussian Curve – distribution of results of large number of experiments done under identical conditions (for a series of experimental results with only random error) Plotted number of occurences (y) vs value (x) and then high population about correct value at peak goes from  µ to 1sigma sa right and -1sigma sa left 2. Any set of data (and corresponding Gaussian curve) can be characterized by two parameters: mean or average value (sum of all values/total number of values taken) standard deviation (take the square root of the sum of the (value taken – mean)/(number of values taken – 1)(better when smaller) variance: related to standard deviation (how wide or precise a distribution of results is) = s^2 (s= stdev) Range: difference in highest and lowest values in a set of data (H-L) Median: value in a set of data which has an equal number of data values above and below it (get the middle, if odd siya, get the two sa middle then divide by 2) Formula for a gaussian curve: check image ( µ= mean, sigma = stdev, e =e) 1. 1 By knowing stdev and mean of a set, the probability of the next result falling in any given range can be calculated by: z = (x-mean)/s (probability of a result falling in the portion in GC is equa to the normalized area of the curve in that portion (+/1s = 86. 3%, 2 95. 5 %, 3-99. 7%, 4-99. 9%) Check formula sheet 1. 2 Get the z, check the area of it, total ? area is 0. 5, remaining area is 0. 5-area Knowing the stdev of a data set indicates the precision of a measurement, precision of many analytical measurements is expressed as: mean+/- 2s (there is only 5% chance that any given measurement on the sample will be outside this range) The precision of a mean result is expressed using a confidence interval (relationship between the true mean value ( µ) and the measured mean is ( µ=mean +/- ((ts/vn) ? confidence interval) s=stdev, n= num of measurements, t= student’s t value degrees of freedom = (n-1) (as n increases, confidence interval becomes smaller and  µ becomes more precisely known) Student’s t: statistical tool frequently used to express confidence intervals (a probability distribution that addresses the problem of estimating a mean of normally distributed population when the sample size is small) check 1. 3 – table Confidence interval: the probability that the range of numbers contains the â€Å"true† mean (50% confidence – range of numbers contains true mean 50% of the time, 90% 90% of time – mas malaki range of values ng 90%) Comparison of data against a set of values get tcalculated – (x-mean/s)(vn)* get tcritical using table (DOFreedom: n-1)95% CL If tcalculated tcritical – data is same as the set of data being compared; if not then different Comparison of Two Data Sets: determine if two results obtained by the same method are statistically the same Tcalculated: (mean result of sample 1 – mean of sample two/stdevn pooled)(v(number of measurements of 1*num of measurements of 2)/(num of measurements of 1 + num of measurements of 2)) CHECK 1. 4 FORMULA SHEET Compare calculated to to value on student’s t probability table (DOF: (n1 + n2 – 2) If calculated t is greater than, then the two are different (easier to achieve for lower % confidence level) Comparison of two methods: check 1. 5 formula sheet Bad data: Q test: used to decide whether or not to reject a â€Å"bad† data point (arrange data increasing order, get range) Q = gap/range (gap = the value minus the value nearest it) Grubbs test: accept or not an outlier = Gcalculated= lOutlier-meanl/s (less than or equal to, retain) 1. 6 Chapter 5: Chemical Bonding and Interactions It’s all about stability: noble gases are intert, it comes from their electronic structure Isolectronic: same electron configuration Ionic bonding: due to electrostatic attraction arising from an exchange of electrons Covalent bonding: chemical bond in which two or more electrons are shared by two atoms Polar covalent or polar bond: covalent bond with greater electron density around one of two atoms (electronnegativy) VSEPR: linear, bent, trigonal planar (bent if AX2E), tetrahedral(trigonal pyramidal, 1 lone; bent 2 lone), (seesaw, t-shaped, linear), octahedral (square pyramidal, square planar) Chapter 6: Intermolecular forces of attraction intermolecular forces: attractive forces between molecules; intramolecular forces: hold atoms together in a molecule (stronger) â€Å"measure of intermolecular force: boiling, melting, heat of vaporization, fusion, sublimation intra: ionic, covalent, metallic inter: ion-dipole (ion charge – dipole charge, ion-polar) ? H bonding (F,O,N-H) ? dipole-dipole (dipole charges or two polar) ? Ion-induced dipole (ion and nonpolar, ion charge-polarizable e- cloud) ? Diple-induced dipole (polar and non polar) ? Dispersion (london)(polarizable e- clouds the more polar, the stronger the interaction, higher dipole moment, higher boiling point hydrogen bonds are responsible for: ice floating, ice is ordere with an open structure to optimize H-bonding, therefore ice is less dense than water thus creates insulating layer on water hydrogen bonding responsible for protein structure: protein folding and DNA transport Polarizability: ease with which the electron distribution in the atom or molecule can be distorted (increases with greater number of electrons and more diffuse electron cloud) Instantaneous dipole: in that instant a dipole is formed, increase with molar mass, increase with length of molecule (not compact) Surface tension: amount of energy required to stretch or increase the surface of a liquid by a unit area Strong intermolecular forces = high surface tension Cohesion: intermolecular attraction between like molecules (pataas meniscus); adhesion – attraction between unlike molecul es (concave meniscus) Viscosity: measure of a fluid’s resistance to flow (strong intermolecular forces = high viscosity) Ultrahydrophobic surfaces Chapter 7: Kinetics reaction rate: changes in the concentrations of reactants or products per unit of time collision theory: atoms, ions, and molecules react to form products when they collide with one another, provided that the colliding particles have enough kinetic energy activation energy minimum energy that colliding particles must have in order to react requirements: must have proper orientation; must have enough kinetic energy to reach activation energy factors that influence reaction rate: concentration (molecules must collide), physical state (must mix), temperature (must collide with enough energy), catalyst reactant concentrations decrease while product concentrations increase (A ? B) rate of reaction= -(change in concentration of A/change in time)= -(conc A2-conA1)/t2-t1 aA + bB ? cC + dD Rate = -(1/a)(? [A]/? t)= -1/b([B]/? t numerical value of the rate depends upon the substance that serves as the reference. The changes in concentration of other reaction components are relative to their co efficients in the balanced chemical equation reaction orders: see formula sheet Integrated Rate Laws: rate = -? [A]/? t = k[A] First order rate equation see formula sheet K[A]^2 second-order rate equation ? [A]/? t = k[A]^0 zero order rate equation = -kt Units of the rate constant k for several reaction orders see formula sheet Arrhenius equation: effect of temperature on reaction rate see formula sheet Frequency factor: importance of molecular orientation to an effective collision Reaction mechanisms: see formula sheet table (example: elementary step A? product, molecularity: unimolecular: rate law: k[A] Rate-determining step: overall rate of a reaction is the slowest step Correlating the mechanism with the Rate law: Elementary steps must add up to the overall balanced equation Elementary steps must be physically reasonable Mechanism must correlate with the rate law Chapter 8: Acid-base titrations Bronsted-Lowry definition of Acids and bases (acids-proton donors; bases-proton acceptors) Acid-base neutralization reaction results into the formation of the conjugate acid and base of the reaction base and acid respectively (stronger acid, weaker the conjugate base) Water undergoes autoprotolysis. This is the disassociation of water into H3O+ and OH- Kw=[H3O+][OH-]ph = -log[H+] pOH = -log[OH-] ph+ pOH =14 pH: measure of the degree of acidity of solutions. The lower the pH, the more acidic the solution battery acid (0), lemon juice(2. 2), vinegar (2. 7), apples (3), tomato juice (4. 3), rain (5. 6), milk (6. 8), human urine and blood (7. 5), seawater (8. 1), milk of magnesia (10. 5), ammonia (12), lye (13) alkaline strengths of acids and bases depend on the extent of reaction/dissociation to produce H+ and OH- respectively strong: complete dissociation, forward reaction *weak: incomplete, equilibrium strong acids: HCl, HBr, HI, H2SO4, HNO3, HClO4 bases: Li, Na, K, Rb, Cs, R4 + OH weak acid and bases do not completely dissociate in water. The degree of dissociation is described by the acid or base dissociation constants Acid dissociation constant (Ka) ? HA + H2O H3O+ + A-Ka = [H3O+][A-]/[HA] Base dissociation constant (Kb) A- + H2OOH- + HAKb = [OH]][HA]/[A-] Conjugate pairs Kw = KaKb A buffer is a solution that can resist the change in pH when small amounts of acids and bases are added when diluted (a lot of reactions are dependent on pH, buffers are important in the control of ph) Henderson-Hasselbalch equation: pH = pKa + log ([A-]/[HA] Stong base vs strong acid ? equivalence point: steepest point Acid-base indicator changes color as it is protonated or deprotonated, different indicators change color at different pH because they have different dissociation constants Weak acid Vs Strong base: graph has two pa-curve, one for when pH = pKa then one for equivalence Kjeldahl titration: total nitrogen and total protein Microtitration Chapter 9: Gravimetric and Combustion Analysis in gravimetric analysis, the mass of the product is used to estimate the amount of the original analyte, one of the earlierst analytical chemistry techniques analytical balance and desiccator are two most important equipment in gravimetry constant weighing: series of drying, cooling, and weighing until constant weight is reached commonly used desiccants in order of decreasing efficiency: magnesium perchlorate, barium oxide, alumina, phosphorus pentoxide, calcium chloride, drierite (calcium sulfate), silica gel indicator: copper sulfate (blue ? pink) Representative gravimetric techniques: % Moisture, Total Fat, Homogenous precipitation, Ignition, Combustion analysis see formula sheet Precipitation gravimetry: properties of precipitates: Readily filtered and washed free of contamints, sufficiently low solubility so that no significant loss of the analyte occurs during filtration and washing, unreactive with constituents of the atmosphere, not hygroscopic, of known composition after drying or ignition Techniques that promote particle growth: raising temperature to increase solubility and decrease supersaturation, adding precipitant slowly with vigorous mixing to avoid local supersaturation, keep volume of solution large and concentrations of analyte low Formation of crystals occur in two phases: nucleation, particle growth (bigger crystals: particle growth) Types of precipitates: colloidal (NiS), curdy (AgCl), fine crystalline (BaSO4), coarse crystalline (PbCl2), gelatinous (Fe(OH)3). Coprecipitations and other challenges of gravimetry Adsorption vs absorption and inclusion (ordered inside molecule) vs occlusion (kalat sa molecule, possibly containing solvent) Digestion, reprecipitation Aging (Ostwald ripening) and pe ptization Ignition and Thermogravimetric analysis Combustion and elemental analyses Chapter 9: Properties of Solutions â€Å"like dissolves like† two substances with similar intermolecular forces are likely to be soluble in each other ionic compounds are more soluble in polar solvents remember: physical state of solvent determines the physical state of the solution solubility increases as the shape/length of molecule increases Gas solutions: all gases are infinitely soluble in one another Gas-solid solutions: when gas dissolves in a solid, it occupies the spaces between closely packed particles Solid-solid solutions: example, brass Why substances dissolve? ? three types of interactions in the solution process: solvent-solvent interaction, solute-solute interaction, solvent-solute interaction (? Hsoln = ? Hsolvent + ? Hsolute + ? Hmix) Solution process: exothermic vs endothermic (exothermic, final amount of energy is less than initial) Heats of hydration: ? Hsoln = ? lattice + ? hydr (? hydr is the combination of enthalphy changes for separating solvent and mixing the solute) Change in entropy: solution usually has higher entropy than the pure solute and pure solvent Systems tend toward a state of lower enthalpy and higher entropy Solubility as an equilibrium proce ss A saturated solution contains the maximum amount of solute that will dissolve in a given solvent at a specific temperature An unsaturated solution contains less solute than the solvent has the capacity to dissolve at a specific temperature A supersaturated solution contains more solute than is present in a saturated solution at a specific temperature Effect of temperature on solubility: most solids are more soluble at higher temperatures; gas solubility in water decreases with rising temperature Effect of pressure on solubility: Sgas = Kh x Pgas (Kh is Henry’s law constant; specific for given gas-solvent at a given temperature) ? inversely proportional formula sheet Colligative properties – properties that depend only on the number of solute particles and not on the nature of the solute particles Electrolyte: dissociates into ions in aqeous solutions and nonelectrolyte: does not Vapour-pressure lowering – vapor pressure of the solution is lower than the vapor pre ssure of the pure solvent see formula sheet (called Raoult’s law) Boiling-Point elevation: solution boils at higher temperature than the pure solvent (formula) Freezing-point depression: solutions freeze at lower temperature than pure solvent? Osmotic Pressure (? ) – pressure required to stop osmosis Osmosis – selective passage of solvent molecules through a porous membrane from a dilute solution to a more concentrated one Semipermeable membrane allows the passage of solvent molecules but blocks the passage of solute molecules Proportional to (n solute/Vsolution ) or to Molarity May be computed through ? = MRT (molarity)(gas constant)(temperature) Colligative properties of strong electrolyte solutiosn Van’t hoff factor, i, tells us what the effect number of ions are in the solution Measured value for electrolyte solution/(expected value for nonelectrolyte solution) Actual number of particles in solution after dissociation/(number of formula units initially dissolved in solution) Chapter 10: analytical Separations sample purity: many chemical analysis are not specific for a compound, often necessary to purify compound of interest techniques: extraction, distillation, precipitation, chromatography, centrifugation, filtration Extractions: transfer a compound from one chemical phase to another (two phases used can be liquid-liquid, liquid-solid, etc)Sphase ? k? Sphase 2 k= partition coefficient Extraction efficiency – fraction of moles of S remaining in phase 1 after one extraction can be determined if the value of k and the voumes of phases 1 and 2 are known When n approaches infinity, eventually the amount of S remaining in phase 1 becomes 0 (responsible for water memory, (homoepathic med water memory activity of drug even; detects antibody after 110^120 dilution, placebo effect) pH affects extractions ? for weaks acid and bases, protonated and non-protonated forms usually have different partition coefficients (k) charged form (A- or BH+) will not be extracted, neutral form (HA or B) will be extracted Partitioning is described in terms of the total amount of a substance Individual concentrations of both B and BH+ or HA and A- are more difficult to determine Partitioning is regardless of form in both phases (described by the distribution coefficient (D) Distribution of a weak base or weak acid is pH dependent Ability to change distribution ratio of weak acid/base useful in selecting conditions for extraction some but not all Use low ph to extract HA but not BH+ and high pH to extract B but not A- Extraction with a metal chelator Metal ions may be separated from one another by using various organic complexing agents (soluble in organic solvent) Common complexing agents: cupferron, 8-hyroxyquionaline, dithizone, crown ethers Many of the complexing agents bind to a varity of metals (diff erent strengths and equilibrium constants) A metal ion extraction may be mode selective for a particular metal by choosing a complexing agent at high affinity to the metal and by adjusting the pH of extraction Chromatography: separation technique based on the different rates of travel of solutes through a system composed of two phases Stationary phase: chemical phase which remains in the column (chromatographic system) and mobile phase: chemical phase which travels through column (eluent in ? column ? eluate out) Support: solid onto which the stationary phase is chemically attached or coated Chromatography detects compounds emerging in column by changes in absorbance, voltage, current, etc Solutes are separated in chromatography by the different interactions with the stationary phase and mobile phase (solutes that interact more with the stationary phase take longer to pass) Retention time: time it takes a compound to pass through a column Retention volume: volume of mobile phase needed to push a solute through the column Fundamental measures of solute retention: Adjusted retention time: (tr’) additional time required for a solute to travel through a vacuum beyond the time required for non-retained solute (tr’ = tr-tm) Relative retention: ratio of adjusted retention between two solutes (higher relative ret, higher separation, higher capacity factor) Capacity factor (k’): longer the component is retained by the column, greater this is (may be used to monitor performance of a column if you will use a standard)(directly proportional to partition coefficient, k) Efficiency of separation: the width of a solute peak is important in determining how well one solute is separated from another (one measure of this is the width of the peak at half-height (w1/2) The separation of two solutes in chromatography depends both on the width of the peaks and their degrees of retention Resolution, you want this /=1. 5 (tr2-tr1/((wb2+wb1)/2) Measure of column efficiency: number of theoretical plates (N), similar to number of extractions, as N increases, greater the separation between the two compounds Height equivalents of a theoretical plate (H or HETP): distance along the column that corresponds to â€Å"one† theoretical separation plate As H decreases, more steps per column are possible (results in narrower peaks and better separation between two neighboring solutes) H is affected by flow of rate of mobile phase, size of support (directly proportional), diffusion of solute (inversely prop), strength of retention Improve resolution by increasing column length Why bands spread? Efficiency is dependent on peak width through the column C (described as standard dev) Factors: sample injection, longitudal diffusion, finite equilibriation between phases, multiple flow paths Sample injection: sample is injected on the column with a finite width which contributes to the overall broadening (similar broadening may occur in detector) Longitudinal diffusion: bands slowly broaden as molecules difuse more from high contentration in band to regions of lower concentrations Finite equilibriation time between phases: finite time is required to equilibriate between stationary and mobile phase at each plate (same solute is stuck in stationary phase as remainder moves forward in mobile phase) Multiple flow paths – some arrive sooner than others because of different paths travelled and distances description of band spread: plate height is proportional to band width (smaller plate height, narrow the band) ? Von Deemter equation Types of Liquid Chromatography Adsorption chromatography: solutes are separated based on their abilities to adsorb the support’s surfaces (uses an underivatized solid support, stationary phase = solid support)(oldest) Partition chrom – solutes are separated based on their ability to partition between stationary and mobile phase (uses solid support coated or chemically derivatized w/a a polar or nonpolar layer)(most common)(good for organic compounds) reversed phase: stationary is nonpolar Ion-exchange chromatography: separate ions based on their abilities to interact with fixed exchange sites (uses solid support containing fixed charges (exchange sites) on surface (cation exchange: support neg groups; anion-exchange: supports positive groups) Size exclusion chrom: separates large and small solutes based on their different abilities to enter the pores (uses porous support that does not absorb solutes)(used to separate biological molecules/polymers which differ in size/MW) Affinity chromatography: base d on ability to bind to the affinity liquid (support that contains an immobilized biological molecule (affinity ligand)(purify bio molecules) and most selective) Packed and open-tubular columns (higher resolution, increased sensitivity but small capacity - no bond spreading from multiple paths; higher flow rates, longer columns – more theoretical plates and resolution) Chapter 11: Spectrophotometry colorimetry: analytical technique in which the concentration of an analyte is measured by its ability to produce or change the color of a solution changes the solution’s ability to absorb light; comes in two kinds: instrumental, non-instrumental spectrophotometry: any technique that uses light to measure chemical concentrations a colorimetric method where an instrument is used to determine the amount of an analyte in a sample by the sample’s ability or inability to absorb light at a certain wavelength example: measurement of ozone above south pole Properties of Light Particles