Operating the device

The system software of the gas chromatographs CGA21 is based on Windows® . To a large extent self-explanatory, its context sensitive help system allows the device to be operated without using the written documentation a lot. However, basic knowledge of the principles of gas chromatography is indispensible as well as observance of the generally accepted safety rules, in particular if hydrogen is used when operating the FID.

# Device messages during power-on

After turning on the device, different power on messages may appear.

## WLD-Device: Warn ing: Turn on carrier gas

In the heated state, TCD units can be damaged even by minute traces of oxygen. For TCD units to provide trouble-free operation, you must therefore ensure that the supply of carrier gas is sufficient at all times (refer to "Summary of the essential properties of a TCD:") If a TCD unit is turned on, it will issue a corresponding warning message. It is only after you have acknowledged this message with OK that the heating of the TCD is activated; in this manner, you can ensure a sufficient supply of carrier gas without causing any damage to the detector.

## FID-Device: Advice: Measuring gas flow at start up

As a rule, the flame ionisation detector is heated to its minimum temperature of 150°C immediately after the device has been activated, to prevent water from condensing in the detector. At this high temperature, it is no longer possible to measure gas flows; for this reason, the message displayed on the right is issued immediately after the GC has been turned on. If you then select „Measure”, the detector remains unheated until the first measurement has been started. This allows you to dismantle the unheated detector and measure the gas flows first. If you select OK instead, the initial menu of the device is called up. Measuring gas flow is described in chapter 6.

# Main window

Main window

Functional components of the main window:

· Menu bar with temperatures

· Main display

· Peaklist

· Status bar

## Menu bar

The menu bar buttons trigger basic actions. Rollover with mouse cursor pop up hints.

| New Measurement: see chapter „New measurement“
| Open measurement: Opens existing measurement. Supports older binary *.gcd files as well as the current XML format *.gcx.
| Save measurement: Stores existing measurement in XML file format (file extension: .gcx) In general it is recommended to store measurements on USB flash disk and not on the system disk.
| Comparison of chromatograms: Allows you to compare a chromatogram with one or more reference chromatograms. For details see chapter 2.4 “Evaluation of a chromatogram“. This button toggles between two states.
| Print report: Print report as pdf–file. The report includes the temperature program, user data, main display with currently selected section and the peak list. Although possible, we do not recommend using a printer with a CGA21. It is better practice to take measurement files to a PC workstation on an USB flash drive and make printouts there. As an alternative you can make pdf files at the GC, save it to USB flash disk and make printouts at a PC workstation.
| Information about the current measurement: Displays information about the open measurement, such as temperature program, user data etc. User data can be edited.
| Save main display to file:. Saves an image of the main display into a emf –file. This allows for convenient insertion of GC curves into every common office program.
| Help. Access to common help. Important windows contain additional context sensitive help buttons.
| Measuring gas flows Utility for convenient measurement of gas flows using the soap bubble meter.
| Options: Reserved for future use

##

## The main display

The display allows for easy visualization and evaluation of GC measurements. Use the „Open Measurement“ dialog in the usual manner. The chromatogram will be scaled automatically to fit the display area.

Symbol colors:

Red: | Regular GC curve
Blue: | Peaks
Green: | Peaks with a known mass are colored green. They can be used to determine the mass of peaks with unknown mass, provided it is the same compound.
Yellow: | Indicates marked peaks. Marked peaks can be deleted using the „delete peak“ button.

Using the main display (GC Graph):

Pan: simply move the mouse while pressing down the right mouse button. Alternatively use the arrow buttons.

Select zoom area

Enlarged section

Zoom: Draw a rectangle from top-left to bottom-right while holding down the left mouse button as shown above. Mouse gesture in the opposite direction (bottom-down → top, left) restores standard view.

Actions: |
Create a peak: | Peaks can be created by double clicking into the display. The first double click creates a starting point which is indicated by an arrow labeled „start“, the second double click marks the endpoint of a peak. The second double click must be at higher time values than the first.
Mark peak: | Double click into the (blue) peak: Peak will be marked and its color changes to yellow. More than one peak can be marked
Divide Peak: | Peaks can be divided. Left click button „Divide peak“, the mouse cursor turns into a vertical line. The next left click divides the peak under the line cursor.
Delete peak: | A left click onto button „delete peak“ will erase all marked peaks.

## Peaklist

Peaklist

Marked peaks will be added to the peaklist immediately. The entries of the peaklist will be transferred into the measurement file when a „Save“ command is executed. Every line in the peak table represents one peak with its corresponding properties. Fig. 5 shows a mixture of alkanes as an example:

The columns of the peak table:
Nr.: | Peak number in ascending order of their retention times.
Name: | Name of peak given by user. To assign a name to a peak, left click into the peak. The table now shows this peak in the first line highlighted in light yellow. After a double click into the name field a window pops up where the name can be entered.
Max[s]: | Position of maximum: Elapsed time between injection and peak maximum. Time in seconds.
Area: | The Peak area is proportional to mass for a given substance. It is determined automatically by numerical integration in arbitrary units. Please note: The relationship between mass and area of a peak is not trivial, it depends among others from the kind of detector used, the substance and the split ratio. As a consequence these values are only useful for comparison.
Area[%]: | Percentage share of peak area in the sum of all marked peak areas. If only one peak is marked, this percentage is 100%.
Mass and factor: | If the peak has been standardized with a reference measurement, this column shows the mass in [ng] and the factor for conversion of peak area into mass – and vice versa. These columns can be used in two different ways: 1. Let’s assume a reference measurement has been made. In this case the substance and its mass is known. Therefore it is possible to enter the mass of the substance into the table, again by double clicking the mass field in the row of the respecting peak. After having entered the mass, the factor is determined automatically. 2. A measurement like the one mentioned above can be used to determine an unknown portion of the same substance in another measurement by comparing the two measurements via the menu button “measurement compare” This procedure is described in detail in chapter “2.4 Evaluation of a chromatogram” and in an example in chapter “3.3 Benzene in gasoline”.

## Status bar

Displays information about the state of the chromatograph: (from left to right)

· Textual information about the current state of the device

· TCD Thermal Conductivity Detector on/off

· Measurement progress

· Detector type

· Time elapsed since the GC has been turned on.