Anachem 2 LECT Reviewer PDF

Preview

Summary

Warning: TT: undefined function: 32 Warning: TT: undefined function: 32CO 1Diagnostic testMEAT 6.CEREAL 5.DAIRY 6.MOHR METALS ARE FOLLOWING 1:1 RATIO TRASNFORM TO WHAT IS ASKEDEDTA IS ALSO1:1 WITH METALSJONES NAGIGING 6 FEH IS RELATED TO NORMALITYGREATER MR MEANS NAHCO AND NACOLOWER MEAN NAOH AND NA...

Description

ANACHEM REVIEWER CO 1

Method Diagnostic test

MEAT 6.25 CEREAL 5.7

A means for analyzing a sample for a specific analyte in a specific matrix. Procedure

DAIRY 6.38

Written directions outlining how to analyze a sample.

MOHR METALS ARE FOLLOWING 1:1 RATIO TRASNFORM TO WHAT IS ASKED

Protocol

EDTA IS ALSO1:1 WITH METALS

A set of written guidelines for analyzing a sample specified by an agency.

JONES NAGIGING 6 FE

Analytical Techniques

# H IS RELATED TO NORMALITY

LOWER MEAN NAOH AND NACO

Total analysis techniques - a technique in which the signal is proportional to the absolute amount of analyte; also called “classical” techniques (gravimetry and titrimetry)

CO 2

S=kn

Introduction to instrumental analysis

Concentration techniques - a technique in which the signal is proportional to the analyte’s concentration; also called “instrumental” techniques. (spectroscopy and electrochemistry)

GREATER MR MEANS NAHCO AND NACO

General Analytical Strategy 1. Obtain Sample The sample must be representative of the bulk system; 2. Prepare the sample A portion of the sample is prepared for the analysis by weighing it (or measuring its volume) and carrying out certain physical and/or chemical processes 3. Carry out the analysis Method Obtain weight or volume data on the prepared sample Prepare reference standards of the analyte or substances with which the analyte will react. 4. Work the data This requires calculations and/or the plotting of a calibration curve from which the desired results can be derived 5. Calculate and report the results A final calculation may be necessary to obtain the desired results.

S=kC Accuracy A measure of the agreement between an experimental result and its expected value.

Precision An indication of the reproducibility of a measurement or result. Sensitivity

Terms Analysis A process that provides chemical or physical information about the constituents in the sample or the sample itself. Analytes

A measure of a method’s ability to distinguish between two samples; reported as the change in signal per unit change in the amount of analyte (k).

The constituents of interest in a sample. Matrix All other constituents in a sample except for the analytes. Determination An analysis of a sample to find the identity, concentration, or properties of the analyte.

Selectivity A measure of a method’s freedom from interferences as defined by the method’s selectivity coefficient.

Measurement An experimental determination of an analyte’s chemical or physical properties.

Selectivity coefficient

Technique A chemical or physical principle that can be used to analyze a sample.

A measure of a method’s sensitivity for an interferent relative to that for the analyte (KA,I) .

ANACHEM REVIEWER A selectivity coefficient greater than +1 or less than –1 indicates that the method is more selective for the interferent than for the analyte.

Robustness and Ruggedness Robust - a method that can be applied to analytes in a wide variety of matrices is considered robust. Rugged - a method that is insensitive to changes in experimental conditions is considered rugged. Quantitative Instrumental analysis involves sophisticated electronic instrumentation that generates electrical signals that are related to some property of the analyte Instrumental analysis Categories Spectroscopic Methods involve the use of light and measure the amount of either light absorbed (absorbance) or light emitted by solutions of the analyte under certain conditions. Chromatographic Methods involve more complex samples in which the analyte is separated from interfering substances using specific instrument components and electronically detected, with the electrical signal generated by any one of a number of detection devices. Electroanalytical Methods involve the measurement of a voltage or current resulting from electrodes immersed into the solution. Instrumental Measurement Four components of instrument Sensor (converts a property of the solution into a weak electrical signal) Signal processor (amplifies or scales the signal and converts it to a useable form; involves mathematical treatment) Readout device (displays the signal for the analyst to see) Power supply (converts the alternating current (ac) line power (or battery power) to voltage levels needed to operate the other functional elements of the instrument) Preparation of Standards Methods Dilution of a stock standard solution Prepared by diluting various volumes of a stock or standard solution prepared or purchased Serial dilution In this procedure, the second solution is prepared by diluting the first, the third by diluting the second, the

Account for interference by other species in the sample and for traces of analyte found in reagents a solution that contains all the substances present in the standards, and the unknown if possible, except for the analyte. The readout for such a solution should be zero or adjusted to read zero useful as a sort of pre-calibration step for the instrument. Reagent blank – is similar to a method blank but it has not been subjected to all sample preparation procedures. Field blank – is similar to a method blank, but it has been exposed to the site of sampling Controls a standard solution of the analyte prepared independently, often by other laboratory personnel, for the purpose of cross-checking the analyst’s work. Standardization Determines the relationship between the analytical response and the analyte concentration . Accomplished against a standard, adjusting Smeas until it agrees with the standard’s known signal. Could obtain the method's sensitivity constant, k Single point Standardization Any standardization using a single standard containing a known amount of analyte. The simplest way to determine the value of k. The least desirable way to standardize a method due to experimental error. Could obtain the method's sensitivity constant, k From S=kC it becomes k= Sstd/C Multiple Standardization Any standardization using two or more standards containing known amounts of analyte. A calibration curve is prepared by plotting S std vs CS Calibration plots Shows the response of an analytical method to known quantities of analyte The response must be corrected by subtracting the response of the blank. Maybe: External standard, Standard addition, Internal standard External standard A standard solution containing a known amount of analyte, prepared separately from samples containing the analyte. The calibration curve produce is known as the normal calibration curve. The slope of the line gives the value of k Standard addition method A standardization in which aliquots of a standard solution are added to the sample. Especially appropriate when the sample composition is unknown or complex and affects the analytical signal . Signal is directly proportional to the analyte concentration

fourth by diluting the third, etc. Blanks

Approach A: Analyte without and with standard are analyze separately. Equation:

ANACHEM REVIEWER Cell Representation: reference electrode|salt bridge|analyte solution|indicator electrode Ecell= Eind- Eref+ Ej Electrode Approach B: Directly adding standard to the sample after measuring the sample signal. Equation:

a conductor at the surface of which electron transfer to or from the surrounding solution takes place. Maybe:

Reference

Indicator

Reference Electrode

Calibration Plot Prepared by plotting Sspike versus an appropriate measure of the amount of added standard.

is a half cell having a known electrode potential that remains constant at constant temperature and is independent of the composition of the analyte solution always treated as the left-hand electrode (anode) Common reference electrodes: Hydrogen electrode (SHE) The ultimate reference electrode. Difficult to work with. Eo= 0.000000V Calomel Electrode (SCE)

Internal standard addition method A known amount of compound, different from analyte, added to the unknown. Signal from analyte is compared with signal from the internal standard to find out how much analyte is present. A known mixture of standard and analyte are prepared to measure the relative response of the detector to the two species

More commonly used electrode Hg/Hg2Cl2(sat), KCl// Chloride is used to maintain constant ionic strength. The electrode maybe separate or built into the sensing electrode (combination electrode). Use different concentrations of KCl 0.1M & 1.0 – least temperature sensitive. Saturated (4.6M) – E0=0.2444V at 250C . most widely used due to the ease of preparation. Temperature dependent . Advantageous because of the [Cl-] does not change if some liquid evaporates. Silver/Silver chloride electrode also a common reference electrode . easier to produce a combination electrode. Employs a silver electrode immerse in a solution saturated with both KCl and AgCl. (Ag/AgCl(sat’d), KCl(sat’d)//). Potential is 0.199 V at 250C Salt bridge Used to minimize the liquid junction potential The salt bridge is effective if it can make the mobilities of the ions equal at the junction and their concentrations large

CO 3

Indicator (sensing) electrodes

Potentiometry

Has a potential that varies in a known way with variations in the concentration of an analyte

Electroanalytical Techniques Potentiometry branch of electrochemistry concerned with the relationship between the potential of an electrochemical cell and the concentration of the contents of the cell. Basis of the methods:

It should response rapidly and reproducibly to changes in the concentration of an analyte Types: Metallic (simple metal) A bare metal in contact with a solution of its cation: Mn+ + neM(s) (indicator electrode)

difference between the E values of two halves of a cell giving rise to Ecell if one half reaction is known and held constant, the concentration of species on the other side can be measure Voltammetry

Classes: Electrodes of the first kind

Coulometry Potentiometric method

Pure metal electrode that is in direct equilibrium with its cation in the solution A single reaction is involved: Xn+(aq) + ne- ⇌ X(s) Not widely used for potentiometric determinations not

ANACHEM REVIEWER very selective and respond not only to their own cations but also to other more easily reduced cations

It is the indicator potential Three components: Boundary potential Potential of the internal Ag/AgCl reference electrode Small asymmetry potential Alkaline error False response when the electrode responds not only to H3O+ but also to alkali metals (Na+, K+) Acid error Values registered by the glass electrode tend to be somewhat high when pH < 0.5 Liquid Membrane Electrode

Electrodes of the second kind Metals not only served as indicator electrodes for their own cations but also respond to the activities of anions that form sparingly soluble precipitates or stable complexes with such cations Electrode reaction: AgCl(s) + e- ⇌ Ag(s)+ Cl-(aq)

Similar to a pH electrode except the membrane is an organic polymer saturated with a liquid ion exchanger Interaction with target ions results in a potential across the membrane that can be measured Ca2+ electrode is one of the best example Solid state Electrode Solid membranes that are selective towards anions A very popular type of ion specific electrode As easy to maintain as a pH electrode F- electrode Enzyme Electrode

Electrodes of the third kind A metal electrode can be made to respond to a different cation Example: mercury electrode has been used for the determination of the pCa of calcium-containing solutions Metallic redox Electrodes fashioned from platinum, gold, palladium, or other inert metals often serve as indicator electrodes for redox systems The inert electrode acts as a source for electrons transferred from redox system in the solution Membrane (Glass membrane, Liquid membrane, Solid State, Enzyme, Gas sensing) Commonly known as ion-selective electrodes because of the high selectivity of most of these devices Also referred as pIon electrodes because their output is usually recorded as a p-function, such as pH, pCa or pNO3 Properties: Minimal solubility, Electrical conductivity, Selective reactivity with the analyte, Ionsensitive field effect transistors (ISFET) Typical electrode system for measuring pH: (a) A glass electrode (indicator) and SCE (reference) immersed in a solution of unknown pH (b) Combination probe consisting of an indicator glass electrode and a Silver/silver chloride referencecc Glass Membrane electrode A potential difference is created across a membrane that can be measured There is no change in the solution of actual contact Example: pH electro de Boundary Potential Difference in potential between the two boundaries Asymmetry Potential

Arises when the boundary

A normal pH electrode is coated with a urease impregnated gel Urea will permeate the gel where the enzyme will attack resulting in the formation of ammonium The resulting change in pH can be measured Gas-sensing Probes Gas-sensing probe is a galvanic cell whose potential is related to the concentration of a gas in a solution Analytical techniques Direct Potentiometry Simply calculate concentration based on E cell Electrode Calibration Method Null Point Potentiometry Standard Curve Method CO 4 UV-Vis & Introduction to Spectrochemical Method The science that deals with light and its absorption and emission by solutions and other material substances The sample solution absorbs electromagnetic radiation from an appropriate source, and the amount absorbed is related to the concentration of the analyte in the solution Most widely used tools for the elucidation of molecular structure as well as the quantitative and qualitative determination of both inorganic and organic compounds A form of radiant energy that is propagated as a transverse wave. Vibrates perpendicular to the direction of propagation, and this imparts a wave motion to the

potential is not zero Glass Electrode Potential

radiation Amplitude, A provides a measure of the electric or magnetic field strength at a maximum point in the wave.

ANACHEM REVIEWER Period, P time in seconds that it takes for successive maxima or minima to pass a point in space Frequency, 1 second.

The number of oscillations that occur in

Wave velocity, v The speed of the wave which is dependent on both the medium and the frequency In vacuum: c=2.99792 x 108m/s Wavelength, The linear distance between any two successive maxima or minima Common units: μm (10-6), nm (10-9), Å (10-10) Wave number

The reciprocal of wavelength

The emission of photons is measured after absorption Maybe: fluorescence or phosphorescence Fluorescence The initial absorbance of a photon followed by the emission of a second photon Takes place rapidly and complete in about 105s (or less) from the time of excitation Phosphorescence Similar to fluorescence except there is a delay before emission. The delay can be just a few seconds or can take hours. Line spectra Involves atomic species lines but still complex

Has relative narrow

Band spectra Involves molecular species Continuous spectra Produced by many solids that are heated until they glow Light is emitted over a wide energy range Sample is stimulated by applying energy in the form of heat, electrical energy, light, particles or chemical reaction Stimulation causes some of the analyte species to undergo transition from the ground state to the excited state

Transmittance is a measure of the light that passes through the solution (transmitted) The fraction of the original light that passes through the sample

The amount of electromagnetic radiation absorbed or emitted gives information about the analyte. Absorption Light is absorbed by an atom, ion or molecule, taking it to a higher energy state Absorption Process Light is absorbed by a substance only when the energy corresponds to some energy need or transition of a substance

Absorbance Governed by Beer-Lambert’s Law that states that the amount of light absorbed by a solution is an exponential function of concentration and path length of the solution

Modes: Rotational Occurs in the far-IR and microwave region . Changes in the energy of a molecule as it rotates about a center of gravity – IR Vibrational changes in the average separation of nuclei (bond length) – IR Occurs in the mid- and far IR regions Electronic Emission The release of a photon by an atom, ion or molecule, taking it to a lower energy state Methods in which the stimulus is usually heat or electrical energy Chemiluminescence Excitation of the analyte by a chemical reaction

Absorbance has a direct relationship with concentration Transmittance is the one directly measured Some instruments gave both absorbance and transmittance information but transmittance is the preferred parameter As the absorbance of the solution increases, the transmittance decreases Measuring Absorbance Must be done at the wavelength of maximum absorbance ( λmax) Errors is also possible during measurement of...