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    Calibration Curve

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    Ankan Datta
    Calibration curve is one approach to the problem of instrument calibration. Other approaches may mix the standard into the unknown, giving an internal standard. Calibration curve is a plot of how the (LOQ), dynamic range, and limit of linearity instrumental response, the so-called (LOL), changes with the concentration of the analyte.

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    Calibration Curve

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    Ankan Datta
    413 views3 pages
    Calibration curve is one approach to the problem of instrument calibration. Other approaches may mix the standard into the unknown, giving an internal standard. Calibration curve is a plot of how the (LOQ), dynamic range, and limit of linearity instrumental response, the so-called (LOL), changes with the concentration of the analyte.

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    Calibration curve is one approach to the problem of instrument calibration. Other approaches may mix the standard into the unknown, giving an internal standard. Calibration curve is a plot of how the (LOQ), dynamic range, and limit of linearity instrumental response, the so-called (LOL), changes with the concentration of the analyte.

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    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    413 views3 pages

    Calibration Curve

    Uploaded by

    Ankan Datta
    Calibration curve is one approach to the problem of instrument calibration. Other approaches may mix the standard into the unknown, giving an internal standard. Calibration curve is a plot of how the (LOQ), dynamic range, and limit of linearity instrumental response, the so-called (LOL), changes with the concentration of the analyte.

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    of 3

    Calibration curve - Wikipedia, the free encyclopedia http://en.wikipedia.

    org/wiki/Calibration_curve

    Calibration curve
    From Wikipedia, the free encyclopedia

    In analytical chemistry, a calibration


    curve is a general method for
    determining the concentration of a
    substance in an unknown sample by
    comparing the unknown to a set of
    standard samples of known
    concentration.[1] A calibration curve is
    one approach to the problem of
    instrument calibration; other approaches
    may mix the standard into the unknown,
    giving an internal standard.
    A calibration curve plot showing limit of
    The calibration curve is a plot of how the detection (LOD), limit of quantification
    instrumental response, the so-called (LOQ), dynamic range, and limit of linearity
    analytical signal, changes with the (LOL).
    concentration of the analyte (the
    substance to be measured). The operator prepares a series of standards across a range
    of concentrations near the expected concentration of analyte in the unknown. The
    concentrations of the standards must lie within the working range of the technique
    (instrumentation) they are using (see figure).[2] Analyzing each of these standards using
    the chosen technique will produce a series of measurements. For most analyses a plot of
    instrument response vs. analyte concentration will show a linear relationship. The
    operator can measure the response of the unknown and, using the calibration curve, can
    interpolate to find the concentration of analyte.

    Contents
    1 How to create a calibration curve
    2 Error in Calibration Curve Results
    3 Applications
    4 Notes
    5 Bibliography

    How to create a calibration curve


    The data - the concentrations of the analyte and the instrument response for each
    standard - can be fit to a straight line, using linear regression analysis. This yields a model
    described by the equation y = mx + y0, where y is the instrument response, m
    represents the sensitivity, and y0 is a constant that describes the background. The
    analyte concentration (x) of unknown samples may be calculated from this equation.

    1 of 3 10/24/2010 12:07 AM
    Calibration curve - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Calibration_curve

    Many different variables can be used as the analytical signal. For instance, chromium (III)
    might be measured using a chemiluminescence method, in an instrument that contains a
    photomultiplier tube (PMT) as the detector. The detector converts the light produced by
    the sample into a voltage, which increases with intensity of light. The amount of light
    measured is the analytical signal.

    Most analytical techniques use a calibration curve. There are a number of advantages to
    this approach. First, the calibration curve provides a reliable way to calculate the
    uncertainty of the concentration calculated from the calibration curve (using the statistics
    of the least squares line fit to the data). [3]

    Second, the calibration curve provides data on an empirical relationship. The mechanism
    for the instrument's response to the analyte may be predicted or understood according to
    some theoretical model, but most such models have limited value for real samples.
    (Instrumental response is usually highly dependent on the condition of the analyte,
    solvents used and impurities it may contain; it could also be affected by external factors
    such as pressure and temperature.)

    Many theoretical relationships, such as fluorescence, require the determination of an


    instrumental constant anyway, by analysis of one or more reference standards; a
    calibration curve is a convenient extension of this approach. The calibration curve for a
    particular analyte in a particular (type of) sample provides the empirical relationship
    needed for those particular measurements.

    The chief disadvantages are that the standards require a supply of the analyte material,
    preferably of high purity and in known concentration. (Some analytes - e.g., particular
    proteins - are extremely difficult to obtain pure in sufficient quantity.)

    Error in Calibration Curve Results


    As expected, the concentration of the unknown will have some error which can be
    calculated from the formula below.[4][5] This formula assumes that a linear relationship is
    observed for all the standards. It is important to note that the error in the concentration
    will be minimal if the signal from the unknown lies in the middle of the signals of all the
    standards (the term goes to zero if )

    sy is the standard deviation in the residuals Linear least squares#Residual values

    and correlation

    m is the slope of the line


    b is the y-intercept of the line
    n is the number standards

    2 of 3 10/24/2010 12:07 AM
    Calibration curve - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Calibration_curve

    k is the number of replicate unknowns


    yunknown is the measurement of the unknown
    is the average measurement of the standards
    xi are the concentrations of the standards
    is the average concentration of the standards

    Applications
    Analysis of concentration
    Verifying the proper functioning of an analytical instrument or a sensor device such
    as an ion selective electrode
    Determining the basic effects of a control treatment (such as a dose-survival curve in
    clonogenic assay)

    Notes
    1. ^ http://terpconnect.umd.edu/~toh/models/CalibrationCurve.html
    2. ^ http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation
    /Guidances/UCM070107.pdf
    3. ^ The details for this procedure may be found in D. A. Skoog et al. (2006). Principles of
    Instrumental Analysis., as well as many other textbooks.
    4. ^ http://www.chem.utoronto.ca/coursenotes/analsci/StatsTutorial/ConcCalib.html
    5. ^ http://alpha.chem.umb.edu/chemistry/ch361/Salter%20jchem%20ed%201.pdf

    Bibliography
    Harris, Daniel Charles (2003). Quantitative chemical analysis. San Francisco: W.H.
    Freeman. ISBN 0-7167-4464-3.
    Crouch, Stanley; Skoog, Douglas A. (2007). Principles of Instrumental Analysis. Pacific
    Grove: Brooks Cole. ISBN 0-495-01201-7.
    Lavagnini I, Magno F (2007). "A statistical overview on univariate calibration, inverse
    regression, and detection limits: Application to gas chromatography/mass spectrometry
    technique". Mass spectrometry reviews 26 (1): 1–18. doi:10.1002/mas.20100
    (http://dx.doi.org/10.1002%2Fmas.20100) . PMID 16788893
    (http://www.ncbi.nlm.nih.gov/pubmed/16788893) .
    Retrieved from "http://en.wikipedia.org/wiki/Calibration_curve"
    Categories: Analytical chemistry

    This page was last modified on 11 April 2010 at 21:53.


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