Calibration of a GC955

Transcription

1 Calibration of a GC955 1

2 Contents of the power point instructions Standard calibration Automatic validation methods and calibration of multi component mixes Autolinearisation: test of the linearity of a system with one concentration of a calibration gas 2

3 Introduction Three kinds of calibrations are done: a basic calibration, to determine the functioning of the instrument. Formally with a calibration of at least 5 points. At producer at start of work with a system a basic calibration by the customer with his own calibration gas: here zero-air and at least two, better three different concentrations of the calibration gas should be determined. For every concentration at least two (better three samples) should be analyzed. After major repairs this is advised lastly a control calibration (validation) to check if the instrument sensitivity is stable. Here one concentration (span) can be determined. Standard on site 3

4 Before starting To calibrate the GC a calibration mixture is needed, that contains at least the components of interest, for instance benzene, toluene and a xylene isomer for the environmental BTX-measurements. Pure air is also needed, to determine the zero-point and to dilute the calibration mixture. The highest concentration should be in the region where the maximum concentration is expected. The other concentration in the normal air range. Deviation of linearity mostly occurs in the upper and lower range of a usable concentration range. 4

5 Preparing for calibration Connect a calibration gas pressure free to the instrument Measure the overflow at the moment when the sample pump or the sample cylinder is running. you have two possibilities to connect the calibration gas to an instrument with preconcentration unit: Directly to the 10-port-valve -inlet (only the sample cylinder sucks the sample) or over the T together with the sample pump (bypass pump) 5

6 Preparing for calibration Before starting the calibration you should set the peak windows. This must be done on a file in data file, load data file. (load the file with calibration mixture) Go to options edit peak windows or edit the peak windows in graphical mode (see manual chapter 4.2.2) 6

7 Start calibration In view mode, actual run, options, set calibration mode you find 3 possibilities 7

8 Start calibration Start new calibration (starts a new calibration, the old calculated calibration lines for each component will be lost, the old chromatograms are still saved on the hard disk) Add data to current calibration (the old and the new calibration points can be used to calculate the calibration line) Normal data mode (no calibration) (switches off the calibration mode) 8

9 Start calibration After activating one of the calibration Option automatically opens the window edit sample concentration. (it is the same you can open in edit sample concentrations under options in actual run) The massage CALIBRATION on the screen in actual run appears 9

10 Edit concentrations During the run you can already select the components present in the bottle add 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 %. 10

11 Edit concentrations Now you have to repeat two (better three) runs for this first concentration. The values edited are used as default After each run the software switches into the dialog window view mode, calibration. If you change the gas concentration of the calibrator after a few runs you have to open the edit calibration window again,to activate the used components and edit the concentration(s). 11

12 Edit concentrations If you have not given the values during the calibration you can do this afterwards add the concentration values of your calibrating mixture in the dialog window edit sample concentrations under options in data mode. This is only possible with binary files present in the subdirectory calibration. 12

13 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 choose the options you want You can use a different unit 13

14 Select the calibration points You can remove files from the calculation set, if you have clear outliers(view mode, calibration, options, data selection calibration files) 14

15 Calculate the calibration line Open the dialog box Calculate calibration line under view mode, calibration, options Chose the regression you want (for ambient best option is linear regression with fixed base point) 15

16 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 5.4 to 21.3 ppb 16