Se ha denunciado esta presentación.
Se está descargando tu SlideShare. ×

RAMYA SAVITHRI K SELECTION OF AN ANALYTICAL METHOD.pptx

Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Anuncio
Cargando en…3
×

Eche un vistazo a continuación

1 de 16 Anuncio

Más Contenido Relacionado

Similares a RAMYA SAVITHRI K SELECTION OF AN ANALYTICAL METHOD.pptx (20)

Más reciente (20)

Anuncio

RAMYA SAVITHRI K SELECTION OF AN ANALYTICAL METHOD.pptx

  1. 1. JSS MAHAVIDYAPEETHA JSS SCIENCE AND TECHNOLOGY UNIVERSITY SELECTING AN ANALYTICAL METHOD Presented by : RAMYA SAVITHRI K UP222505 Department of Chemistry
  2. 2. Introduction Accuracy Precision Sensitivity Selectivity Robustness Ruggedness Scale of operation Equipment, time and cost Making the final choice References
  3. 3. Analytical chemistry is a branch of chemistry which deals with the study of the seperation, identification, qualitative and quantitative determination of the compositions of different substances. An analytical method is the application of a technique to a specific analyte in a specific matrix. The best method is chosen based on the requirements of the analysis. Some of the criterias which are considered for selecting the method are, 1. Accuracy 2. Precision 3. Sensitivity 4. Selectivity 5. Robustness 6. Ruggedness 7. Scale of operation 8. Equipment,Time and cost
  4. 4. 1. ACCURACY • Accuracy is how closely the result of an experiment agrees with the “true” or “expected” value. • It is defined as ‘A measure of agreement between the experimental value and theoretical value’ • Errors are of two types, a. Absolute error [ Ea] Ea=Xi-Xt b. Relative error [Er] Er= Xi-Xt x 100 Xt If the relative error is within 1%, the value is said to be highly accurate. If the relative error is between 1-5%, the value is moderately accurate. If the relative errror is more than 5%, the value is considered to be of low accuracy.
  5. 5. 2. PRECISION • When a sample is analysed several times, the individual results are rarely the same. Instead the results are randomly scattered • It is defined as ‘A measure of the variabilities of results obtained in different trials of the same experiment.’ • The closer the agreement between the individual analysis, the more precise the results. • Precision doesn’t imply accuracy. In determining the concentration of K+ in serum, The results in (a) are more precise than those in (b), but (b) may have more accurate values.
  6. 6. 3. SENSITIVITY • Sensitivity is the ability of a method to demonstrate that two samples have different amount of analyte. • It is defined as ‘The change in signal per unit change in the amount of analyte’. • It is equivalent to the proportionality k If nA is the number of moles of analyte, SA is the signal obtained by analyte, and CA is the concentration of analyte, k is given by 𝐒𝐀 𝐧𝐀 = k or SA = knA , In total analysis method. 𝐒𝐀 𝐂𝐀 = k or SA =kCA , In concentration method. • The method with greatest k value [Sensitivity] is best able to discriminate among smaller amounts of analyte.
  7. 7. 4. SELECTIVITY • An analytical method is selective, if its signal is a function of only the amount of analyte present in the sample. • It is defined as ‘The measure of methods of freedom from interferences’ • The signal of sample, containing interferent is given by, SSample = SA+ SI where, SA & SI are signals of analyte and interferent respectively or SSample = kAnA+ kInI (In total analysis method) SSample = kACA+ kICI (In concentration method) where,kA & kI are sensitivities of analyte and interferent respectively. nA & nI are no: of moles and CA & CI are concentrations of analyte and interferent respectively.
  8. 8. • The selectivity of a method is given by selectivity coefficient KA,I, KA,I = 𝐤𝐈 𝐤𝐀 where kI and kA are sensitivities of interferent and analyte respectively. • The selectivity coefficient greater than +1 or lesser than -1 indicates that the method is more selective for the interferent than for the analyte. or kI =KA,I*kA Substituting this equation in the above equations, SSample = kA (nA+ KA,I*nI) (In total analysis method) ............(1) SSample = kA (CA+ KA,I*CI) (In concentration method) ............(2) • For a method to be selective, KA,I*nI should be smaller than nA in (1) and KA,I*CI should be smaller than CA in (2).
  9. 9. 5. ROBUSTNESS • For a method to be useful it must provide reliable results. Unfortunately, methods are subject to a variety of chemical & physical interferences that contribute uncertainity to the analysis. • When a method is relatively free from chemical interferences it can be applied to the determination of analytes in a wide variety of sample matrices. Such methods are considered robust. 6. RUGGEDNESS • Random variations in experimental conditions also introduce uncertainity. • If a method’s sensitivity is highly dependent on experimental conditions such as temperature, acidity or relaxation time, then slight changes in those conditions may lead to significantly different results. • A rugged method is relatively insensitive to changes in experimental conditions
  10. 10. 7. SCALE OF OPERATION • Another way of narrowing the choice of methods is to consider the scale on which the analysis must be conducted. • Three limitations of particular importance are i. The amount of sample available for the analysis. ii. The concentration of analyte in the sample. iii. The absolute amount of analyte needed to obtain a measurable signal. The first and second limitations define the scale of operation. The last limitation positions a method within the scale of operation.
  11. 11. 8. EQUIPMENT, TIME AND COST Analytical methods can be compared in terms of their need for equipment, the time required to complete an analysis, and the cost per sample. I. Equipment Methods relying on insrumentation are equipment-intensive and may require significant operator training. II. Time The time needed to complete an analysis for a single sample is often fairly similar from method to method. This is however not completely true, because, much of this time is spent preparing the solutions and equipments are in place, the number of samples that can be analysed per hour differs substantially from method to method. This is a significant factor for laboratories that handle a high volume of sample.
  12. 12. III. Cost The cost of analysis is determined by many factors including the cost of necessary equipments and reagents, the cost of hiring analysts and the number of samples that can be processed per hour. In general methods relying on insruments cost more per sample than other methods.
  13. 13. MAKING THE FINAL CHOICE • Selecting a specific method requires a careful balance among these design criterias. • The most important criteria among these that should be considered during the selection of analytical method is accuracy. For example, In determining the concentration of lead in drinking water, Graphite Furnace Atomic Absorption Spectroscopy is the commonly used method because, it meets all those criterias.
  14. 14. ANALYTICAL CHEMISTRY by B.K. Sharma https://www.brainkart.com https://chem.libretexts.org https://www.asdlib.org

×