Reprocessing data files

Reprocessing data files

This new power point on reprocessing contains the following sections: Reprocessing procedure Information about optimisation of peak window settings Calibrating in the demo program

Introduction The data binary files are in fact chromatograms, i.e. files containing detector-output data and data from other sensors in the instrument. During the actual run, the instrument settings, like peak windows and calibration are used to interpret the chromatogram. The results of this interpretation, like peak labeling, retention times, and concentration, are saved in RUNDATA.TXT. This data is not saved with the data file (*.BIN-file). This makes it possible to reinterpret (reprocess) the data, without changing the original data files. For instance: a peak arises in the chromatogram, which could only be assigned after the measuring period had finished. Reprocessing makes it possible to give accurate information on this newly identified peak, even though it is not appearing in the original RUNDATA.TXT.

Procedure for reprocessing: 1. To do a reprocessing, the data files must be transferred to a PC. Make a suitable subdirectory and copy the data. No name longer then 8 characters in the directories! Files to copy: Make a copy of all the files directly in the directory GC955_1 and GC955_2. See that you have an update of: The data files in the monthly subdirectories that have to be reprocessed Act_run.prg contains the settings for peak windows Act_calib.dat contains the actual calibration GC855id.txt or GC955id.txt contains the names of the peak windows autolins3.dat

Making a file list Then a list must be made, which files are to be reprocessed. The names and path of these data files, are placed in a text file. For this open the DOS mode and type the line: dir C:\path\path\D_yymm\*.bin/b/s >filename.txt, where path\path\d_yymm is the list of the subdirectories from C, *.bin/b/s means all the binary files including subdirectories.

Example:the DOS command line for making a text file named januar.txt for the data from january 2006

The list file that results (here for instance reprocessing data for GC nr. 1538 for January 2006)

Now go to the submenu for reprocessing in data mode\options

Check of settings Then the demo program must be started by double clicking on the GC955.exe file. Load one of the files in data mode to check if the settings for the reprocessing are as you want them. The following list is an overview of settings, which are important in reprocessing: Peak window settings must be over the peaks Integration attributes can be optimised (see section 2) Calibration must be a calibration from the period the measurements were made (A simulation of a calibration can be done on the PC, see section 3 for that.) Optional extra peaks that have been identified later can be put in a peak window.

Start reprocessing Now go to the options \ reprocessing in data mode and select the input file name you have just created. Also give a name in report file name to be used for the result file.

The process Now click on START. The program starts loading the first data file and re-integrates this file with the current settings. The time needed depends on your processor and the amount of files. As it uses a lot of processor power laptops may get too hot and close down (at least my former laptop liked to do that...). The status line indicates the total number of files to be processed with a slow processor and the number of the actual processed file, giving an idea on how long the processing will take. It is possible to stop the processing by pressing the stop button. 1. The results of the reprocessing are placed in an output file. The format of this file is like RUNDATA.TXT s. All output files are placed in the directory GRAPHDAT, a subdirectory of the directory where GC955.EXE is located. The data files themselves remain unchanged. To evaluate the result open the file in excel.

The resulting text file

Differences between the reprocessed file and the rundata file The reprocessed file had the names of the peak windows (if the name is shorter than 12 characters, extra nonsense characters will be added) The reprocessed file has the sample information at the start, the rundata has them at the end. Alas we have a software bug: when you open in Excel, the headers are shifted by 3 cels too far left The rundata files have one column with the day and one with the hour time, the reprocessed file has the name of the file at the start of the line, like M_060315.bin The reprocessed file has one extra parameter for each column: the hitrate

Section 2: optimising integration settings Each peak has a default setting for calculation of start and end of peak. Typical problems are: incomplete separation leading to shoulders, or even to two maxima in one peak, and baseline changes in a peak window.

Settings can be optimised in Peak window editor in data mode\options

Integrate with [forced] horizontal baseline from start of peak: in this case a strict horizontal baseline is integrated, independent of possible drift.

Integrate down to detector values = 0 (Virtual baseline): this can be used if there is an peak in front of the peak of interest and the detector signal had not yet gone down to baseline before the start of the peak.

Integrate with [forced] horizontal baseline from end of peak: in this case a strict horizontal baseline is integrated, independent of possible drift.

Include possible shoulders: this is useful in the presence of small peaks under the main peak or if there is a sloping peak

Integrate highest peak in window: this prevents smaller peaks nearer to the center of the window to be mistaken for the peak of interest. If this is not active, then the peak with the lowest hit rate, i.e. the peak nearest to the center of the window, is integrated.

Saving the optimised settings To save these settings you must go from data mode to program edit mode Save the changed program setting under its own name. You may copy this.prg file also back to the GC and use it there

Calibrating later using the datafiles from a calibration test in the demo program Make a copy of the existing act_calib.dat to have a back-up. Make in the subdirectory calibdat a new subdirectory named C_yymmdd for today, like c_060316. Now go to Windows explorer mode, select the binary files that belong to the suitable calibration runs. Copy these files to the subdirectory C_yymmdd.

Edit concentrations Notate the concentration values of your calibrating mixture in the dialog window edit sample concentrations under options in actual run. Values can be given as mg/m 3 or µg/m 3,as vppm, vppb or %. Save the data file after giving the values and continue for the next file you want to use until all are done.

Desactivate the old calibration Go to actual run Under options \ start new calibration select: Start new calibration The screen for editing values comes up, just click ok Now you can go to the window calibration

Settings for the calibration line The measured calibration values are used to make a calibration line. The correlation coefficient of the line will be calculated, to indicate the linearity. This is done in the calibration mode of view mode. At first go to settings and chose the options you want

Select the calibration points You have to add for each compound you want to calibrate the files you will use. Click on Add file and select the files from the list box If you click a file that has no value for this compound a message will appear, just click ok

Calculate the calibration line Open the dialog box Calculate calibration line under view mode, calibration, options Chose the regression you want (the best option is linear regression with fixed base point)

Calculate the calibration line After clicking ok, the calibration line is calculated for the component you have chose in the dialog box data selection calibration files A calibration line for benzene from a permeation tube source, diluted to a range from 1.2 to 11 ppb

Now back to reprocessing With the peak windows set as you want and with the calibration in, you can do the reprocessing. Any questions: please ask first Huang Xiaodong of Dadi (huang.xiaodong@encon.com.cn) If he cannot solve the question, he will contact Synspec Please send with your question the rd200607.txt, some binfiles, the act_run.prg and the act_calib.dat