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focusjrceceuropaeu

By Gail Ward,2014-06-20 11:43
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focusjrceceuropaeu

USER GUIDANCE

    FOCUS PARENT DEGRADATION KINETICS_VERSION1.0.XLS

    RELEASED ON XXX

An Excel file was provided by the FOCUS workgroup on degradation kinetics to facilitate

    kinetic analysis for parent compounds. The file consists of 9 worksheets. . Note that only

    worksheets for datasets without replicates and datasets with 2 replicates have been created. Chi2 statistics for datasets with more than 2 replicates can be calculated by entering the average value for each sampling time in the sheet “chi2 all models”.

    FOCUS Degradation Kinetics Workgroup Parent Degradation Kinetics.xls Version 1.0 (released xxx 2004)

    Use this worksheet toUser must enterName of worksheetWarning

    Calculate chi2 statistics and create graphs (conc. vs. time plot and Observed data and SFO parameters

    residual plot) for datasets without replicates and SFO kinetics(M0, k) derived elsewhereSFO no reps

    Calculate chi2 statistics and create graphs (conc. vs. time plot and Observed data and SFO parameters

    residual plot) for datasets with 2 replicates and SFO kinetics(M0, k) derived elsewhereSFO 2 reps

    Fit SFO kinetics to datasets without replicates, calculate chi2 Observed data and starting values for

    statistics and create graphs (conc. vs. time plot and residual plot) SFO parameters (M0, k)SFO no reps with fit

    Fit SFO kinetics to datasets with 2 replicates, calculate chi2 Observed data and starting values for

    statistics and create graphs (conc. vs. time plot and residual plot) SFO parameters (M0, k)SFO 2 reps with fit

    Calculate chi2 statistics and create graphs (conc. vs. time plot and Observed data and FOMC parameters

    residual plot) for datasets without replicates and FOMC kinetics(M0, alpha, beta) derived elsewhereFOMC no reps

    Calculate chi2 statistics and create graphs (conc. vs. time plot and Observed data and FOMC parameters

    residual plot) for datasets with 2 replicates and FOMC kinetics(M0, alpha, beta) derived elsewhereFOMC 2 reps

    EXCEL IS NOT A ROBUST TOOL FOR FITTING

    FOMC KINETICS AND THIS WORKSHEET SHOULD

    ONLY BE USED IN COMBINATION WITH OTHER

    Fit FOMC kinetics to datasets without replicates, calculate chi2 Observed data and starting values for OPTIMISATION TOOLS, ALWAYS TEST DIFFERENT

    statistics and create graphs (conc. vs. time plot and residual plot) FOMC parameters (M0, alpha, beta)STARTING VALUES AND CHECK VISUAL FITFOMC no reps with fit

    EXCEL IS NOT A ROBUST TOOL FOR FITTING

    FOMC KINETICS AND THIS WORKSHEET SHOULD

    ONLY BE USED IN COMBINATION WITH OTHER

    Fit FOMC kinetics to datasets with 2 replicates, calculate chi2 Observed data and starting values for OPTIMISATION TOOLS, ALWAYS TEST DIFFERENT

    statistics and create graphs (conc. vs. time plot and residual plot) FOMC parameters (M0, alpha, beta)STARTING VALUES AND CHECK VISUAL FITFOMC 2 reps with fit

    Observed and calculated data and

    Calculate chi2 statistics (observed data and concentrations number of parameters (average

    calculated with any model must be entered)replicate values)Chi2 all models

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GETTING STARTED

    The file contains macros. To be able to load files with macros, the security settings on your machine may have to be changed. In order to do this, start Excel, go to Tools - Macro - Security and select the medium level.

    The macros use the Excel Solver Add-In. Prior to using the file for the first time, the Solver must be activated. Go to Tools Add-Ins and click the Solver Add-In box.

    If the macros do not run, a reference to the file Solver.xla may be missing. Locate the file Solver.xla on your computer and make a note of the path. This could be, for example:

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c:/program files/microsoft office/Office/library/solver/solver.xla. With the Excel file parent

    degradation kinetics.xls open, go to Tools Macro Visual basic editor. Then go to Tools

     References. Click on browse and navigate to the location of the file solver.xla. Note that “Files of type” must be set to “all types (*.*)” to display files with the ending .xla. Select the file solver.xla and click on open.

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USING THE SPREADSHEETS

    Load the provided Excel file. In each sheet, the user must enter text or values in the blue cells. All other cells will be automatically updated.

    Two Excel macros have been created which allow the automatic fitting of either SFO or FOMC kinetics to the data. Once the measured data have been entered, appropriate starting values have to be specified (i.e. for M0 and k when fitting SFO kinetics and M0, alpha and beta when fitting FOMC kinetics). Excel may not be able to obtain a good fit unless adequate starting values are provided. First, the plot of concentrations versus time should be investigated. If the calculated curve is very different from the measured concentrations, the starting values must be changed. Modify the values for M0 and k (SFO kinetics) or M0, alpha and beta (FOMC kinetics) manually until the curve is close to the measured concentrations. This may be difficult for FOMC kinetics as alpha and beta can vary over a wide range. Both values are usually very large (>1000) where degradation is close to first-order kinetics and much smaller (often between 0 and 5, but other combinations are possible) where degradation is clearly bi-phasic.

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Once appropriate starting values have been found, click on the button “Optimise SFO

    parameters” or “Optimise FOMC parameters” This will run the Excel Solver and find that

    combination of the parameter values that minimises the residual sum of squares (RSS). Check the visual fit. If the curve is not close to the measured data, try again with different starting values.

    Different optimised parameters may be returned by the Excel Solver routine for different starting values. A number of starting values should, thus, be tested. The combination that gives the smallest RSS should be used, provided the visual fit is acceptable. If degradation is close to SFO kinetics, the FOMC model will result in a very similar curve for very different combinations of alpha and beta. Therefore, different starting values will provide a different answer. In this case, the influence of the starting values on the DT50 and DT90 value should be investigated. If the influence on the endpoints is small, use the answer which gives the smallest RSS.

    Visual plots are automatically created. Although the worksheets are protected, the appearance of the graphs can be modified. Chi2 statistics are also calculated. The error level is set to the smallest error value for which the Chi2 test is passed by solving the equation:

    21CO;;err100 22tabulatedO

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