quantitative pharmaceutical analysis

titrant

reagent with a known concentration

equivalence point

volume theoretically necessary for complete reaction with titrant

final point

actual volume of titrant necessary to complete reaction

titration error equation

vol eq. point - vol final point

molarity

number of moles per liter of solution

molecular weight

sun of atomic weights of all atoms (independent of reaction)

equivalent weight

quantity of mass capable by dissociation of 1mol of H+ or OH- ions (acid/base), supplying / consuming 1mol of e- (redox), or reacting with 1mol of a monovalent carbon (ppt/complex)

equation for equivalent weight

PE = PM / alpha

alpha

number of protons, electrons, or species based on the reaction

primary standard

solid substance that can be used for solutions of precisely known concentrations

qualifications to be a primary standard (5)

high purity

stable during weighing operations

must react with well defined stoich

molecular weight high enough to reduce error

easily available / inexpensive

ways to identify a titration endpoint (2)

chemically (indicators) and instrumentally (spectrophotometric)

direct titration

addition of a titrant to a solution until endpoint is reached

indirect titration

reaction of analyte with a reagent to obtain a titrant

reverse titration

reaction of analyte with a known titrant B in excess, then the excess is determined with titrant C

when is a reverse titration used?

when no suitable indicator

blank proof

titration without analyte to determine potential error

acidimetry

base content of a sample determined by titration with a known acid

alkalimetry

acid content of a sample determined by

precipitometry

reaction technique for precipitation of an analyte with the addition of a suitable precipitant

precipitometry end point indicators (3)

K2CrO4, ferric ammonium sulfate, and fluorescein

what type of titration is argentometry

precipitation

argentometry

titration exploiting the insolubility of silver salts

Mohr method (pptometry)

NaCl + AgNO3

K2CrO4 indicator (yellow → red)

must buffer with sod. bicarb. to be weakly basic (7-8)

non-selective method

Fajans method (pptometry)

for chlorides, bromides, and iodides

fluorescein indicator (yellow green → pink red)

uses chromatic variation on surface for endpoint

Liebig method (pptometry)

CYANIDES ONLY

indicator = clear → white cloudy

pptometry + complexometry together (rxn = complex, endpoint = ppt)

Volhard method (pptometry)

for chlorides, bromides, iodides, + thiocyanides

indicator = ferric alum (clear → red)

reverse titration

must have no cations or ox agents present (consume SCN-)

redox reaction

titration that involves the exchange of e- and changes in oxidation state

e- donor

reducing agent

e- acceptor

oxidizing agent

what does it mean to have a higher E⁰ value?

greater oxidizing strength / ease of being reduced

Nernst Equation

to calculate reduction potential when not in standard state

E⁰ conditions to proceed spontaneously?

oxidant must have much higher volt than reducing agent

types of indicators (redox)

auto (dont need one)

ox-red (independent from rxn, dependent on variation in system potential)

specific (reacts w/ participant and makes different complexes)

oxidimetry

reducing substance titrated with an oxidizing agent of known titre

reducimetry

oxidizing substance titrated with reducing agent of known titre (usually very impractical, oxidized w/ exposure to O₂ )

permanganometry (redox)

oxidimetric determination of reducing substances using KMnO4 as a titrating reagent

indicator = none (indicates itself)

primary standard(s) = oxalic acid dihydrate + sodium oxalate, electrolytic iron, and arsenious anhydride + sulfuric acid

cerimetry (redox)

oxidimetric determination of reducing substances using cerium

indicator = ferroin

primary standard(s) = no common ones (very expensive)

iodimetry (redox)

oxidimetric determination of reducing substances using iodine

indicator = starch solution

primary standard(s) =

much more selective than others (can only use strong reducing agents)

iodometry (redox)

(indirect) reducimetric determination of oxidizing substances using iodine

indicator = starch solution OR chloroform + CCl4

primary standard(s) = potassium iodate, potassium dichromate, and potassium bromate

titrations are ALWAYS indirect

bromometry (redox)

oxidimetric determination of reducing substances using bromine

indicator = starch solution

indirect reverse titration (X reacts with excess Br and then concluded with iodometry)

bromatometry (redox)

oxidimetric determination of reducing substances using bromate

indicator = p-ethoxychrysoidin, methyl red/orange, or none

primary standard(s) = KBrO3 or As2O3

dichromatometry (redox)

oxidimetric determination of reducing substances using dichromate

indicator = ferroin or methylene blue

primary standard(s) = K2Cr2O7 or As2O3

nirosometry (redox)

oxidimetric determination of reducing substances using nitrite

indicator = starch-iodine paper or conductometric methods

primary standard(s) = Na2C2O4 or standard KMnO4 solution

can be used to determine primary amines at 0C

complexometry

volumetric branch of titrations that uses rapid, right-shifted complexation reactions in a 1:1 ratio

direct determination

complexometry for alkali, alkaline earth, and transition anions

indirect determination

complexometry for some other anions

complex

molecule/ion which a metal atom is bonded to a given number of molecules/negative ions by covalent bonds

coordination number

number of bonds a metal can form with a ligand

types of complexes formed (3)

monodentate, polydentate, and chelate

chelate

when a complex has more than one doublet to share AND creates a cyclic compound

chelation effect

increase in basic sites = fewer molecules involved = less freedom = entropy more favorable

complexometry and pH

you must have a constant that accounts for a working pH

masking agent

complexing agent that forms a complex with a high stability (Kf) with an interfering metal

ex: F^- is a good masker of Al³⁺, Fe³⁺, etc

Ca²⁺ + Al³⁺ + 6F^- <→ [AlF₆]^3- + [Ca²⁺ EDTA]

the F masks the Al so that the Ca can complex with EDTA

ways to determine endpoint (complex)

instrumental → UV-Vis

chromic metal indicators → eriochrome black t, calcon, etc

direct titration (complex)

add mettalochromic indicator to analyte and mix with EDTA until color changes

most useful because its the fastest

back titration (complex)

known excess of EDTA added and back titrated with a solution of ZnCl2/ZnSO4 of known concentration until the color changes

useful when the reaction has slow kinetics or pH leads to OH ppt

indirect titration (complex)

unknown excess of EDTA complex with a metal less stable than the analyte are displaced from the complex, then titrated with EDTA

useful when theres no indicator for direct titration

temporary water hardness

when the salts are in the form of bicarbonates → when boiled, the hardness disappears

permanent water hardness

when calcium and magnesium remain after boiling due to ionization of chlorides/nitrates/sulfates

total water hardness

total content of calcium, magnesium, etc; determined before being subjected to heat

water hardness equation

temporary = total - permanent

emission method (UV-Vis)

measure the radiation emitted when the analyte is exposed to thermal/electrical energy

absorption method (UV-Vis)

measure the attenuation of the radiation beam as a result of the interaction with the analyte

wave-particle duality

the idea that radiation can be described as both a wave and a particle

wave theory

the idea that radiation is represented as a sinusoidal wave formed by electric and magnetic vectors, perpendicular and in the direction of propagation

corpuscular theory

the idea that radiation consists of discrete particles called quanta / photons

forms of internal energy in an isolated molecule (5)

translational, rotational, vibrational, electronics, and nuclear

difference in energy with different types of energy states

rotational << vibrational << electronic

which energy transition does IR measure?

vibrational

which energy transition does UV-Vis measure?

electronic (valence e-)

which energy transition does X-rays measure?

electronic (internal e-)

emission

radiation emitted when analyte returns to ground state after being excited

absorption

radiation absorbed after passing through sample (ground → excited)

fluorescence

radiation emitted followed by excitation, characterized by if wavelength is >/= to the absorbed one

spectrum

graphic representation of degree of absorption/emission as a function of frequency, wavelength, or range of frequency used

spectroscopy

study of interaction between electronic radiation and matter (describes the physical principles underlying analysis)

spectrometry

refers to the instruments or techniques used to obtain data

spectrophotometry

a specific technique that measures absorption or transmission of light by a substance as a function of wavelength (typically about UV-Vis)

molecular orbital theory

interaction between atomic orbitals leads to formation of filled and empty molecular orbitals

sigma bonds

e- density concentration along the nuclear axis, absorb <180 nm

pi bonds

e- density concentration above / below axis (double / triple bonds), absorb >180 nm

UV-Vis orbital transition

from highest occupied molecular orbital to lowest unoccupied molecular orbital (HOMO → LUMO)

chromophore

unsaturated functional group that absorbs UV-Vis

dependents of lambda max location and intensity (5)

type of chromophore

functional groups linked

solvent

pH

steric effects

auxochrome

group that doesn’t exhibit significant absorption, but when near a chromophore it determines the bathochromic and hyperchromic effects

equation for number of independent vibrations possible

3N-6

what type of molecules are NOT active in IR?

homonuclear diatoms (N2, O2, etc)

why does an IR spec have more peaks?

all functional groups absorb in IR, in UV-Vis only chromophores do

transmittance

the ratio between outgoing radiation and fraction-transmitted

Lambert-Beer’s Law

the relationship between attenuation of radiation and the concentration of the analyte (absorbance = molar absorptivity x optical path x molar concentration)

is UV-Vis better for qualitative or quantitative data?

quantitative - other molecules can have the same absorptions, but has a great sensitivity for quantitative data

is IR better for qualitative or quantitative data?

qualitative - each spec is unique for each species, so it is one of the most important qualitative tools ever

parts of a spectroscopy instrument (5)

lamp for continuous radiation

wavelength selector (filter or prism/grating)

sample container

detector

recorder

standard method used for spectroscopy

external (interpolation) - series of standards → calibration curve → unknown determined from calibration curve

matrix effect

signal variation caused by everything except the analyte

causes of the matrix effect (4)

complexation

masking compounds

change in activity

pH alteration

solid-liquid extraction

isolation of solid mix of compounds in an appropriate solvent

liquid-liquid extraction

separation implemented by a distribution of components of a mixture between 2 immiscible liquid phases