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To standardize an analytical method we use standards that contain known amounts of analyte. The accuracy of a standardization, therefore, depends on the quality of the reagents and the glassware we use to prepare these standards.
- 8A Analytical Samples and Methods
- Sample Size
- Real Samples
- 8B Sampling
- 8B-1 Obtaining a Representative Sample
- 8B-2 Sampling Uncertainties
- 8B-3 The Gross Sample
- Sampling Homogeneous Solutions of Liquids and Gases
- Sampling Metals and Alloys
- 8B-4 Preparing a Laboratory Sample
- Number of Laboratory Samples
- 8 C Automated sample handling
- 8D Standardization and calibration
- 8D-1 Comparison with Standards
- Direct Comparison
- Titrations:
- The Least-Squares Method
- (3) Standard deviation about regression
- Transformed Variables
- Minimizing Errors in Analytical Procedures
- Separations
- Saturation, Matrix Modification, and Masking
- Dilution and Matrix Matching
- Internal Standard Methods
- Standard Addition Methods
- 8E Figures of merit for analytical methods
- Quality Assurance of Analytical Results
- Validation
Types of Samples and Methods Quantitative methods are traditionally classified as gravimetric methods, volumetric methods, and instrumental methods. Other methods are based on the size of the sample and the level of the constituents.
Techniques for handling very small samples are quite different from those for treating macro samples.
The analysis of real samples is complicated by the presence of the sample matrix. The matrix can contain species with chemical properties similar to the analyte. If the interferences are caused by extraneous species in the matrix, they are often called matrix effects. Such effects can be induced not only by the sample itself but also by the rea...
The process by which a representative fraction is acquired from a material of interest is termed sampling. ( e.g. a few milliliters of water from a polluted lake) It is often the most difficult aspect of an analysis. Sampling for a chemical analysis necessarily requires the use of statistics because conclusions will be drawn about a much larger a...
The items chosen for analysis are often called sampling units or
Systematic errors can be eliminated by exercising care, by calibration, and by the proper use of standards, blanks, and reference materials. Random errors, which are reflected in the precision of data, can generally be kept at an acceptable level by close control of the variables that influence the measurements. Errors due to invalid sampling are...
Ideally, the gross sample is a miniature replica of the entire mass of material to be analyzed. It is the collection of individual sampling units. It must be representative of the whole in composition and in particle-size distribution. Size of the Gross Sample is determined by the uncertainty that can be tolerated between the composition of the ...
Well-mixed solutions of liquids and gases require only a very small sample because they are homogeneous down to the molecular level. Gases can be sampled by several methods. Ex., a sampling bag is simply opened and filled with the gas or gases can be trapped in a liquid or adsorbed onto the surface of a solid.
Samples of metals and alloys are obtained by sawing, milling, or drilling. It is not safe to assume that chips of the metal removed from the representative of the entire bulk. Solid from the interior must be sampled as well. surface are With some materials, a representative sample can be obtained by sawing across the piece at random interva...
heterogeneous solids, the mass of the gross sample may range from hundreds of grams to kilograms or more. of the gross sample to a finely ground and homogeneous laboratory sample, of at most a few hundred grams, is necessary. process involves a cycle of operations that includes crushing and grinding, sieving, mixing, and dividing the samp...
The number, of samples, depends on the required confidence interval and the desired relative standard deviation of the method. If the sampling standard deviation σs is known, we can use values of z from tables, to get: σ CIfor μ = x ± z s N ts Usually, an estimate of σs is used with t instead of z CIfor μ = x ± s If we divide this term by the...
Automated sample handling can lead to higher throughput (more analyses per unit time), higher reliability, and lower costs than manual sample handling. Discrete (Batch) Methods These often mimic the operations that would be performed manually. Some discrete sample processors automate only the measurement step of the procedure or a few chemical step...
Calibration determines the relationship between the analytical response and the analyte concentration, which is usually determined by the use of chemical standards prepared from purified reagents. To reduce interferences from other constituents in the sample matrix, called concomitants, standards are added to the analyte solution (internal standard...
Two types of comparison methods are: direct comparison techniques titration procedures.
- Some analytical procedures involve comparing a property of the analyte with standards such that the property being tested matches or nearly matches that of the standard. This is called null comparison or isomation methods. -Some modern instruments use a variation of this procedure to determine if an analyte concentration exceeds or is less than s...
Titrations are one of the most accurate of all analytical procedures. In a titration, the analyte reacts with a standardized reagent (the titrant) in a known stoichiometric manner. The amount of titrant is varied until chemical equivalence is reached as indicated by the color change of a chemical indicator or by the change in an instrument resp...
Statistical methods, such as the method of least squares, are routinely used to find the mathematical equation describing the calibration function. Two assumptions are made: There is actually a linear relationship between the measured response y (absorbance) and the standard analyte concentration x. Figure 8-10 The mathematical relationship tha...
The standard deviation about regression, also called the standard error of the estimate or just the standard error, is a rough measure of the magnitude of a typical deviation from the regression line. ∑ N [
Linear least squares gives best estimates of the transformed variables, but these may not be optimal when transformed back to obtain estimates of the original parameters. For the original parameters, nonlinear regression methods may give better estimates. Errors in External Standard Calibration When external standards are used, it is assumed that...
The overall accuracy and precision of an analysis is not limited to the measurement step and might instead be limited by factors such as sampling, sample preparation, and calibration.
Sample cleanup by separation methods is an important way to minimize errors from possible interferences in the sample matrix. Techniques such as filtration, precipitation, dialysis, solvent volatilization, ion exchange, and chromatography can be used. extraction, In most cases, separations may be the only way to eliminate an interfering specime...
*The saturation method involves adding the interfering species to all the samples, standards, and blanks so that the interference effect becomes independent of the original concentration of the interfering species in the sample. *A matrix modifier is a species, not itself an interfering species, added to samples, standards, and blanks in sufficient...
*The dilution method can sometimes be used if the interfering species produces no significant effect below a certain concentration level. *The matrix-matching method attempts to duplicate the sample matrix by adding the major matrix constituents to the standard and blank solutions. *Errors in procedures can be minimized by saturating with inter...
*An internal standard is a reference species, chemically and physically similar to the analyte, that is added to samples, standards, and blanks. *The ratio of the response of the analyte to that of the internal standard is plotted versus the concentration of analyte. *In the internal standard method, a known amount of a reference species is added...
*The method of standard additions is used when it is difficult or impossible to duplicate the sample matrix. *A known amount of a standard solution of analyte is added to one portion of the sample. *The responses before and after the addition are measured and used to obtain the analyte concentration. *Alternatively, multiple additions are mad...
Analytical procedures are characterized by a number of figures of merit such as: - accuracy, precision, sensitivity, detection limit, and dynamic range. 8E-1 Sensitivity and Detection Limit The definition of sensitivity most often used is the calibration sensitivity, or the change in the response signal per unit change in analyte concentration. T...
Validation determines the suitability of an analysis for providing the sought-for information and can apply to samples, to methodologies, and to data. Validation is often done by the analyst, but it can also be done by supervisory personnel. There are several different ways to validate analytical methods. The most common methods include: analys...
Validation determines the suitability of an analysis for providing the sought-for information and can apply to samples, to methodologies, and to data. Validation is often done by the analyst, but it can also be done by supervisory personnel. There are several different ways to validate analytical methods. The most common methods include: analys...
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Sep 12, 2021 · The American Chemical Society’s Committee on Environmental Improvement defines standardization as the process of determining the relationship between the signal and the amount of analyte in a sample. In Chapter 3 we defined this relationship as \[S_{total} = k_A n_A + S_{reag} \text{ or } S_{total} = k_A C_A + S_{reag} \nonumber\]
Jul 20, 2020 · Class 11 Chemistry Notes – Free PDF Download Chapter wise. Chapter 1 Some Basic Concepts of Chemistry Class 11 Notes; Chapter 2 Structure of Atom Class 11 Notes; Chapter 3 Classification of Elements and Periodicity in Properties Class 11 Notes; Chapter 4 Chemical Bonding and Molecular Structure Class 11 Notes
Titrimetric analysis can be carried out for various types of reactions. In this unit you will learn only about neutralisation reactions. These involve titrations of acids and bases. Standard solutions of acids (acidimetry) and bases (alkalimetry) are used in these titrations.
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A primary standard is a substance of known high purity which may be dissolved in a known volume of solvent to give a primary standard solution . If stoichiometry is used to establish the strength of a titrant, it is called a secondary standard solution .
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Jul 29, 2014 · Standardization is the process of determining the accurate concentration of a standard solution by titrating it against a solution of accurate concentration with high degree of purity
