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Tema 11
Fichas del conjunto (60)
- 1Classical methods (Wet chemistry methods)Are performed in liquid phase, and rely on matter-matter interactions, that is, chemical reactions of the analytes in solution
- 2Prior to a classical analysis, the analyte(s) can be separated from the matrix by:1- Precipitation: Addiction of a specific/ selective reagent; based on the different solubility between the compounds formed.
2- Distillation: Based on the different volatility (boiling point). Separation via selective boiling and condensation.
3- Extraction: Based on matter transfer: 2 inmiscible phases are brought into contact to transfer one or more components from one phase to other. - 32 types of analysis:Qualitative analysis and Quantitative analysis.
- 4Qualitative analysis:Detection and/or identification of the sample components based on their color, boiling or melting point...
- 52 types of Qualitative analysis: Qualitative inorganic analysisQualitative inorganic analysis:
- Analytical schemes: sequential orderly processes that use separation methods to divide species into groups where each analyte can be reliably identified.
- Direct identification: without separation. - 62 types of Qualitative analysis: Qualitative organic analysisIdentification of the elements and functional groups
- 7Quantitative analysisDetermination of the amount of an element or a compound in a sample. Generation of numeric information about the absolute amount (mass) or relative amount ([ ], %) of analyte in a sample.
Gravimetry --> Use analytical balance.
Volumetry --> Use the burette. - 8Examples of classical methods: Gravimetry.Measurement of the mass with an analytical balance of a compound that is directly related to the analyte.
- 9Examples of classical methods: Redox volumetry.Oxidation/Reduction of the analyte with a titrant agent and detection of the end point with a redox indicator.
- 10Examples of classical methods: Acid-base volumetry.Neutralization of the analyte with a tytrant agent and detection of end-point using an acid-base indicator.
- 11Examples of classical methods: Complexation volumetry.Formation of a chelating agent-analyte complex and use of a metallochromic indicator to detect the end point.
- 12Instrumental methodsBased on energy-matter interaction. A chemical reaction is not necessary.
The Analytical information is obtained via instruments different from the burette, balance and human senses.
Rely on the measurement of physical properties (absorption, emission of EMR)
Generally non-destructive.
Use of chromatographic or electrophoretic techniques to separate the components of the sample.
Qualitative, quantitative and structural analysis. - 13Analytical instrumentsDevices that transform the information related to the physical or chemical properties of the analyte into information that can be manipulated and interpreted by an analyst.
- 14Analytical instrumentsTo get the information about the analyte, a stimulus is required, usually in the form of energy. The interaction with the system under study causes a response that provides the analytical information.
- 15Analytical instrument:Provides analytical information related to the presence and/or concentration of the analyte(s) in the sample.
- 16ApparatusCarries out a specific function in the CMP, but does not provide analytical information.
- 17InstrumentIs a communication device between the system under study and the researcher.
- 18What does the instrument convert?Information contained in chemical and physical propierties of the analyte
IN
Information for human interpretation in terms of the property of interest. - 19Examples of instruments:Photometers, polarographs, fluorimeters, potentiometers...
- 20Examples of instruments:Photometers, polarographs, fluorimeters, potentiometers, chromatograph mass spectometers, X-ray spectrometers...
- 21ANALYTICAL INSTRUMENTS. 4 MAIN COMPONETS: SIGNAL GENERATOR.Provides a stimulus (light, heat) that interacts with the analyte and generates a signal directly related to the presence and/or concentration of the analyte.
- 22ANALYTICAL INSTRUMENTS. 4 MAIN COMPONETS: DETECTORConverts a property of the analyte (physical or chemical) into an electrical signal (transduction). e.g. When pH is measured, it is a glass electrode that transforms H+ activity into an electrical potential.
- 23ANALYTICAL INSTRUMENTS. 4 MAIN COMPONETS: SIGNAL PROCESSORElectronic device that modifies the detector signal adapting it to the readout device: Amplifier to increase intensity of the signal. Filter to reduce a background noise...
- 24ANALYTICAL INSTRUMENTS. 4 MAIN COMPONETS: READOUT DEVICEConverts the processed signal into a signal that can be read, registered or interpreted by the observer: needle movement on a scale, numerical value, graphic record on paper or on a monitor screen...
- 25Differences between intrumental and classical methods.Qualitative classical methods are calculable.
The measured property (P) is a direct function of the concentration C or mass, according to the relation P = K C.
One single measurement is enought to determine the concentration. - 26Classical methods are calculable:Yield a result from calculations based on laws that materialize in formulae involving constants and measurements made during the CMP such as titrant volume, precipitate weight.
- 27Absolute methods without analytical standards:Do not use analytical chemical standards (i.e. Gravimetry)
- 28Absolute methods with analytical standards:Use an analytical chemical standard without analyte. (use both instrumental (buret) and mehotdological calibration).
- 29Gravimetry and volumetry are stoichiometric methods:Rely on calculations based on the stoichiometric coefficients and the atomic weights of the chemical reaction on which the CMP relies.
- 30Instrumental methods are relativeComparison of the sample measurements with those provided by a set of analytical chemical standards containing the analyte.
- 31Interpolation/extrapolation methodsuse a methodological calibration to
establish a clear and direct correlation between the instrument signal and the
analyte concentration "calibration curve".
i.e. photometry, fluorimetry, atomic absorption spectrophotometry, polarography - 32Comparative methods:compare the sample signal with that produced by
standards (usually CRMs) of similar composition to that of the sample
Used when the instrument signal depends on the matrix sample matrix effect - 33ADVANTAGES OF INSTRUMENTAL METHOD VS CLASSICAL.1- More accurate, especially at low concentrations of analyte.
2- More sensitive. They have lower detection limits (trace analysis, environmental,
biological samples).
3- Greater selectivity, although varies from one technique to another. - 34ADVANTAGES OF INSTRUMENTAL METHOD VS CLASSICAL.Typically non-destructive methods.
Faster, especially for serial or routine analysis.
Possibility of automatization (less human
intervention)
Sophisticated and more expensive, albeit cost-effective for serial analysis
intervention, although more specialized)
and miniaturization: - 35Classification of instrumental techniques of analysis, Detection techniques- Optical: Based on the interaction of the EMR with matter.
- Electroanalytical: Based on the electrochemical properties of the species in solution.
- Other Techniques: magnetic, thermal, mass-to-charge ratio - 36Classification of instrumental techniques of analysis, Separation techniques- Chromatographic: According to the distribution between 2 phases (mobile and stationary), based on different
affinities of the components for the stationary
phase, when are transported by the mobile phase
- Electrophoretic: Based on the different speed of migration of
charged particles in a semi-conductive medium
under the influence of an electrical field - 37SIGNALCarries information about the analyte that is of interest to us.
- 38NOISEMade of extraneous information that is undisired since reduces the accuracy and precision of the analysis and affects the lower amount fo the analyte that can be detected.
- 39Why is used the Signal-to-noise ratio?To describe the quality of an analytical method.
- 40CHEMICAL NOISEArises from uncontrollable variables in the system such as:
Undetected variations in Tº or P that affect the chemical equilibrium.
Fluctuations in the relative humidity that change the humidity of the samples.
Vibrations that lead to an stratification of powdery solids.
Changes in the light intensity --> photosensitive materials.
Chemical fumes in the room that interact with the samples or reagents. - 41INSTRUMENTAL NOISEDue to the instrument itself. Can come from any of its components.
4 main types of instrument noise:
1- Thermal.
2- Shot.
3- Ficker.
4- Environmental. - 42Thermal noiseArises from thermal agitation of electrons or other charged carriers in resistors, capacitor, radiation detectors...
This agitation is random and periodically creates charge inhomogeneities that cause voltage fluctuations that appear as noise. - 43How can we reduce the Thermal noise?By Narrowing the bandwidth, lowering Tº, and decreasing the circuit electrical resistance.
- 44Shot noise:Random fluctuations of electrical current through a resistance
Encountered whenever e- and other charged particles cross a junction.
In electronic circuit, these junctions are found at pn interfaces. (semiconductores, diodos y transistores). - 45How can we reduce Shot noise?Only by reducing bandwidth.
Its magnitude is lower than that of thermal noise. - 46Flicker noiseIts origin is unknown: directly proportional to the nº of e- that reach a surface.
Its magnitude is inversely proportional to the frequency of the observed signal.
Its significant at frecuencies lower than 100Hz - 47How can we reduce Flicker noise?By using wire-wound/metallic film resistors.
- 48Environmental noiseMixture of noises from different sources in the environment surrounding the instrument.
Largely occurs because each conductor in an instrument is potentially an antenna capable of picking up EMR and converting it into an electrical signal. - 49How can we reduce the environmental noise?By working with a stabilized power supply.
- 50When do we use the signal-to-noise enhancement?When the analyte concentration is very low and it is neccesary accuracy in the analysis.
- 512 ways to approach the Signal-to-noise ratioHardware devices:
Noise is reduced by incorporating into the instrument components such as filters, shutters, choppers or modulators, attenuators, etc. - 52FiltersAre wavelength selectors, can be absorptive or interference.
- 53ChoppersAre rotatory disks used in double beam specttrophotometers that alternatively allow the radiation from the source to pass through the sample and the reference.
- 54ShuttersAre mechanical devices that block the passage of radiation emitted by a source. Are used to adjust the 0% transmittance.
- 55AttenuatorsDevices that decrease the beam power. Used in double beam-spectrophotometers.
The power of the reference beam is reduced to match that of the beam passing through the sample. - 56Software methodsBased on digital computer algorithms that permit extraction of signal from noisy environment.
. Digital filtering via Fourier Transformed (transform signals between the
time domain and the frequency domain). - 57Calibration in instrumental analysis INSTRUMENTAL CALIBRATION.Verification by using a standard that an instrument works perfectly.
Objective: adjust the answer of the instrument until the value that is considered as correct is reached.
The calibration is carried out using RM or CRM with well-known pysical/chemical properties. - 58RMMaterials with one or more properties that are sufficiently homogeneous and well-established to be used for the calibration of an instrument/apparatus, validation of a analytical method or for assigning values to materials.
Supplied by commercial houses with their characteristics on the label. - 59CRMCommercial or natural pure substances characterized by a metrologically valid procedure accompained by a certificate that provides the value of the specified property, its associated uncertainty, and a statement of metrological traceability.
- 60Methodological calibrationCompare the values of the measured magnitude with the values of known standards or reference materials.
Establishment of an unequivocal relationship between the instrumental signal and the analyte concentration that originates the signal. It's meaning is essentially quantitative.
The standards contain the analyte.
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- Descripción
- Tercero Técnicas analíticas Fichas sobre Tema 11, creado por canlin Jin el 01/03/2022.
- Creado por
- canlin Jin
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