Pro EZGC Chromatogram Modeler Help
Table of Contents
- What’s New in the Pro EZGC Modeler?
- The Pro EZGC Interface
- The Compounds Tab
- The Conditions Tab
- The Refine Oven Program Button
- The Model View
- Compound Structure View and Mass Spectrum
- The My EZGC Tab
- Printing Your Model
- See results on other phases, if available.
- Choose compounds directly from our phase libraries.
- Target specific compounds to resolve.
- Change conditions in your model quickly and easily.
- Refine your temperature program automatically.
- View elution temperatures in the peak list.
The Pro EZGC Interface
Your work in the Pro EZGC modeler starts in the Compounds tab.
Search by Name or CAS #
Enter or copy and paste compounds into the Search by Name or CAS # list field, one per line. CAS numbers can be used, as well. Note that the modeler does not currently support language variations on compound names, so use the English spelling when possible. When you have your compounds entered, click the Solve button. The modeler will attempt to find results on multiple phases. If more than one solution is provided, select your phase of choice from the drop-down menu.
To clear your existing selections, click the Clear link beside the Solve button.
If there has been a misspelling of a compound name, the modeler will provide an alternate spelling, if available. To use the alternate spelling, click its link, and it will alter the misspelled name in your list. Hit the Solve button to re-run your search.
Search by Phase
Alternatively, you can click the Search by Phase>> link to get a more targeted results (click Search by Name or CAS #>> to return).
From the Search by Phase view, first choose your phase from the Phase drop-down menu, and then choose your compound class from the Library drop-down menu. A list will appear showing all the compounds available for testing in that compound class.
To select a compound, click on its entry in the list. When you have your selections made, click the Solve button.
If you need to maintain a minimum resolution between particular compounds, click on their rows a second time. You will see your compound row selection change to a darker blue, indicating that that row is “targeted” for resolution. To deselect the compound, click its row once more, and it won’t appear in the modeled result. If no compounds are specifically targeted, the modeler will try to resolve all selected compounds.
Note that run times can vary significantly when you target specific compounds for resolution, and the resolution of other compounds may be sacrificed to gain resolution of your targeted compounds. Because of this, if you are targeting a subset of your full list, be sure to target all the compounds that you wish to resolve.
You can use the Filter Compounds field to quickly filter the list for a compound by name or CAS number. Once you are done, click the “X” in the Filter Compounds field to clear your search and return to the full list. Filtering in this way will not remove any of your existing selections.
Searching by synonym is also supported, so you can quickly find compounds in our libraries.
To clear your existing selections, click the Clear link beside the Solve button, or choose a new phase or compound class from the Phase and Library drop-down menu.
|Rxi-17||Flavors & Fragrances|
|Rxi-17Sil MS||Polycyclic Aromatic Hydrocarbons (PAHs), Flavors & Fragrances|
|Rxi-5Sil MS||Polychlorinated Biphenyls (PCBs), Semivolatile Organic Compounds (SVOCs)|
|Rxi-5ms||Semivolatile Organic Compounds (SVOCs), Pesticides|
|Rxi-624Sil MS||Volatile Organic Compounds (VOCs)|
|Rxi-PAH||Polycyclic Aromatic Hydrocarbons (PAHs)|
|Rxi-XLB||Polychlorinated Biphenyls (PCBs), Pesticides, Polycyclic Aromatic Hydrocarbons (PAHs), Phthalates, Polychlorinated Naphthalenes (PCNs)|
|Rtx-1||Solvents, Flavors & Fragrances, Drugs, Pesticides, Volatile Organic Compounds (VOCs)|
|Rtx-1614||Flame Retardants (FRs)|
|Rtx-35||Drugs, Pesticides, Herbicides, Polychlorinated Biphenyls (PCBs)|
|Rtx-440||Pesticides & Herbicides, Polychlorinated Biphenyls (PCBs)|
|Rtx-5||Drugs, Pesticides, Herbicides, Semivolatile Organic Compounds (SVOCs)|
|Rtx-50||Drugs, Pesticides, Polychlorinated Biphenyls (PCBs)|
|Rtx-502.2||Volatile Organic Compounds (VOCs), Solvents|
|Rtx-624||Volatile Organic Compounds (VOCs)|
|Rtx-OPPesticides||Organophosphorus Pesticides (OPPs)|
|Rtx-OPPesticides2||Organophosphorus Pesticides (OPPs)|
|Rtx-PCB||Polychlorinated Biphenyls (PCBs), Pesticides|
|Rtx-VMS||Volatile Organic Compounds (VOCs)|
|Rtx-VRX||Volatile Organic Compounds (VOCs)|
|Rtx-XLB||Pesticides & Semivolatile Organic Compounds (SVOCs)|
|RT-2330||Fatty Acid Methyl Esters (FAMEs)|
|Stabilwax||Solvents, Flavors & Fragrances, Fatty Acid Methyl Esters (FAMEs)|
Due to the method used to generate our library data, libraries may contain some compounds (alkanes, for example) that are not in the library's compound class.
Once you have solved for your initial modeled result, you can tailor the model to further meet your needs in the Conditions tab.
Your initial view of the Conditions tab allows you to alter a limited subset of parameters. To enable the disabled fields, click the Custom radio button in the Results section at the bottom of the Conditions tab.
The Pro EZGC modeler supports the use of hydrogen, helium, nitrogen, and argon/methane as carrier gases.
In general, hydrogen is the fastest carrier gas with minimal efficiency loss across a range of flow rates. Helium is the next fastest carrier gas and is the most widely used gas for gas chromatography–mass spectrometry (GC-MS) applications. Nitrogen is the slowest carrier gas and optimum separations often require long analysis times.
If you wish to maintain the elution temperature profile after a carrier gas or column dimension change, enter your column dimensions and parameters into the Restek EZGC Method Translator and Flow Calculator.
Most new GC columns are listed with their nominal length on the box (e.g., 30 m). However, like Restek, most vendors usually provide extra column length (from about 0.5 m to even 2 m or more). Accurate column length can be determined by counting the number of column loops on the cage and multiplying that number by pi, then multiplying by the column diameter on the cage (e.g., the column diameter for a Restek GC column on a 7-inch cage is 7.08 inches, or 0.1798 m).Inner Diameter (mm)
Inner diameter (ID) refers to the inner diameter of the GC column fused silica tubing without stationary phase. Restek provides this number on the original GC column box and the column tag.Film Thickness (µm)
Stationary phase film thickness of the GC column is measured in µm. Restek provides this number on the original GC column box and the column tag.
To pick a Restek-supplied column dimension, choose an alternative from the Available Columns list. You can switch to Custom Mode in the Results section to alter the column dimensions directly.
Custom dimensions can be entered manually, but if you wish to order a column with those dimensions, a custom part number may be required.
You may alter any one of the four control parameters, Column Flow, Average Velocity, Holdup Time, or Inlet Pressure, and the other three parameters’ values will then be calculated by the modeler, based upon the parameter you alter.
Note that any change you make on the Conditions tab may take a moment for the server to process. You will see a “spinner” in the Control Parameters bar as the server processes your request.
The volumetric GC column flow rate is in mL/min. The column flow is calculated from the inlet pressure (gauge) of the selected carrier gas, the GC oven/column temperature, and the GC column outlet pressure (abs). The reference temperature and reference pressure used for flow calculation are 22 °C and 1 atm, respectively.Average Velocity (cm/sec)
The average velocity or, more correctly, the average linear velocity of the carrier gas is the average speed of the carrier gas through the column in cm/sec.Holdup Time (min)
The holdup time is the time in minutes that it takes an unretained GC compound to travel the length of the column. Holdup time is sometimes referred to as "dead time" or "void time."Inlet Pressure
Inlet pressure (gauge) is the "head pressure" or pressure on the inlet side of the GC column. The drop-down menu allows choice of psi, kPa, bar, or atm pressure units from the inlet pressure drop-down menu, which are then used for both inlet pressure and outlet pressure (abs).Outlet Pressure (abs)
Outlet pressure (abs) is the pressure on the outlet end of the GC column in psi (or other selected units, such as kPa, bar, atm). The default value is 0.00 (zero), which is the outlet pressure of a GC column installed in a mass spectrometer since it is under vacuum. For detectors that operate at atmospheric pressure (e.g., FID, ECD, TCD, NPD, etc.), it is common to use 14.70 psi, which is the atmospheric pressure at sea level. A simple click on atm or vacuum below the outlet pressure (abs) entry area allows selection of 14.70 or 0.00 psi (or corresponding values for kPa, bar, or atm).
Note: If you want to alter column dimensions or carrier gas while maintaining the value of one of the control parameters, double click on that parameter’s field (Custom mode only). It will then be marked by a blue arrow, indicating that the other parameters will be calculated around it. If you then alter the Carrier Gas or Column Dimensions, that parameter will remain fixed.
For example, you could set the flow of your model to 2 mL/min, and then fix the new hold time by double clicking on the holdup time field. Now, any changes to your carrier gas, column dimensions, or oven program will maintain that holdup time.
Set the pressure units via the drop-down menu beside the inlet pressure field.
Your units selection will persist between sessions. Your outlet pressure of choice will also persist, and will apply to any further searches in the Select tab.
You can change the oven program in this section, and add or remove ramps. To add ramps, change the value in the Number of Ramps field to a value from 1 to 5, or use the radio button to switch to Isothermal.
When adding ramps, add your ramp details starting with the earliest ramp, entering the ramp rate, the temperature, and any hold time.
If a resolution lower than baseline is acceptable, you can change it in the Target Resolution field.
For details on the Refine Oven Program button, see the Refine Oven Program section below.
The modeler supports Constant Flow, Constant Pressure, and Constant Linear Velocity control methods that can be selected from the Control Method drop-down menu. Constant flow is the maintenance of a constant outlet flow of carrier gas during analysis. Constant pressure is a constant inlet pressure (head pressure) on the GC column during analysis. Constant linear velocity mode uses pressure changes to maintain a constant linear velocity.
The Change to Efficiency and Speed radio buttons allow you to quickly alter the model, changing the flow to speed-optimized or efficiency-optimized flow. You can also choose Custom to re-enable the disabled fields in the interface.
To undo any change you have made in the Conditions tab, click the Undo button in the Results section, or press Ctrl-Z on your keyboard. To redo a change, hit the Redo button or press Ctrl-Y on your keyboard.
Re-running a compound list in the Select tab or choosing a different phase from the Multiple Phase Result drop-down menu will reset your Conditions tab, clearing your changes.
The Compounds Separated value shows the numer of compounds that meet or exceed your Target Resolution. (See more on Target Resolution in the Refine Oven Program section below.)
Note that if you have called out specific compounds for targeting (see details in Search by Phase above), the Compounds Separated value will apply only to those targeted compounds.
The Refine Oven Program button is a quick way to refine your model’s oven program for your specific compounds. The button examines a wide range of alternate temperature ramps, and returns a model that meets or bests the previous run time and compounds resolved, if possible. If more refinements may be possible, a circular arrow appears next to the button. The button will disable when no further refinements are available. You can easily undo any changes via the Undo button (or pressing Ctrl-Z).
Warning! When refining the oven program, compounds not already meeting the Target Resolution may be sacrificed to achieve better run times for the compounds that are adequately separated. If the optimization does not resolve all the targeted compounds to the Target Resolution after refinement, undo to the initial starting position, enter a lower value for your Target Resolution, and try again. To maintain the resolution of particular compounds, lower your Target Resolution to match the resolution of those compounds before refining.
The Target Resolution field is defaulted to 1.5, which is full baseline separation. Raising this value may result in longer run times, and lowering this value may decrease the run times (sometimes significantly).
Note that using the Refine Oven Program option may result in a temperature program that exceeds the maximum temperature of your column or the maximum ramp rate of your GC instrument. Please consult your instrument manuals and column documentation to determine these values.
The modeled results appear in the right panel of the interface. You can expand the view (hiding the tabs) via the << arrows beside the My EZGC tab. To collapse the view and re-enable the tabs, click the >> arrows in the upper left corner of the interface.
You can zoom in on the graph by clicking and dragging across a region of the graph with your mouse (or tapping and dragging with your finger if using a tablet). You may zoom in multiple times. To zoom out, double-click (or double-tap) on the graph.
Hovering over a peak’s number (desktop browser version only) will give you its retention time, resolution (to nearest peak), and elution temperature. For coeluting peaks, it will show those values for all coeluters.
The peak list shows retention time, resolution (to nearest peak), peak width, and elution temperature.
Compounds you have specifically targeted to maintain resolution will be highlighted in green.
To view more information on a particular compound, click on the magnifying glass beside the compound name. In the popup that appears, you will see details on the compound, as available, as well as its mass spectrum. The mass spectrum chart can be zoomed in by clicking and dragging over a region of the chart. Mousing over the end point of a bar will give you the relative abundance for that particular ion fraction.
If you are viewing information on a compound that coelutes with another compound in your model, there will be a View Coelutions button below the Mass Spectrum chart. Click it, and the spectra of the coeluting compounds will be overlaid on the chart, for ease of comparison.
The My EZGC tab houses your saved models.
To save a model, simply:
1) Give it a title by clicking on Untitled. Click here to edit. at the top of the modeled result. A title textbox field will become visible. Enter your title, and click OK or hit the Enter key on your keyboard to lock in the new title.
2) Hit the Save button in the top bar of Pro EZGC.
Untitled saves are possible, but not recommended. You can add a title and resave, even after loading the model on a subsequent visit.
If you need to save a variation on a model, make your changes in the Conditions tab, change the model’s title as needed, then click the Save A Copy button. A new entry will appear in your My EZGC list of saved models. You can then compare your models easily by clicking on their entries in the My EZGC list.
You can re-save a model loaded from the My EZGC list by simply clicking the Save button.
To delete a model, simply click the X in the upper right corner of a model’s listing, and click the OK button in the confirmation alert that pops up.
You can print your model by selecting the print button in the toolbar. For models with long compound lists, we suggest expanding the model view first before printing. In the expanded view, long peak lists are split into two columns.