chemistry

Analytical Chemistry - Calibration Home > Analytical Chemistry > Calibration CALIBRATION What is calibration? Calibrated instruments|Analytical Chemistry Calibrating a pH meter using buffers Quantitative Analysis by Atomic Absorption Performance Verification of Analytical Balances according to ISO/IEC 17025 Calibration and Outliers - Statistical Analysis Calibration of an instrument in Analytical Chemistry is the operation that determines the functional relationship between measured values (signal intensities S at certain signal positions zi) and analytical quantities characterizing types of analytes qi and their amount ( content , concentration ) n. Calibration includes the selection of the model (its functional form), the estimation of the model parameters as well as the errors, and their validation. During calibration , the in...

Quantitative Analysis by Atomic Absorption Home > Analytical Chemistry > Analytical Chemistry - Atomic Absorption > Atomic Absorption Spectrometry (AAS) > Light Sources for Atomic Absorption > Quantitative Analysis by Atomic Absorption   Quantitative Analysis by Atomic Absorption   The capability of an atom to absorb very specific wavelengths of light is utilized in atomic absorption spectrometry . Light of a specific wavelength and of initial intensity I o is focused on the flame cell containing ground state atoms. The initial light intensity is decreased by an amount determined by the atom concentration in the flame cell. The light is then directed to the detector where the reduced intensity, I t , is measured. The amount of light absorbed is determined by comparing I t   to I o and according to Beer’s law :   A = log I o / I t = α * c * d         (1)   Abso...

Why calibration is such a common and important step in analytical methods? How is defined? Calibration is the process of assigning a value, usually in concentration units, to an instrument response. For example, you might calibrate the response of an analytical device – such as a spectrophotometer - by analyzing different “known” concentrations of an analyte (i.e. solution of a metal ion such as Zn +2 ) and establish the instrument’s response per unit concentration of the metal (Fig. 1). Then, an unknown concentration of a test sample of the same analyte can be estimated from the graph by extrapolating the observed absorbance (y-axis) over to the analyte concentration (x-axis) (yellow line in Fig. 1). In the graph shown in Fig. 1, the calibration function is established based on points in Table I.1:                       Table I.1: Instrument Response for different analyte A   co...