Appendix II: Procedure for F-900 Validation Using Fruit
The following methods should be run consecutively on a given replicate and repeated for each new replicate (new specimen). At least 5 replicates for pre-climacteric (un-gassed or still green) apples, bananas, or avocados should be run. The data from method 1 and 2 can be combined into a table. The results from method 3 can be graphed, as a figure, to show the trend over time.
Method 1: Sampling with No Filtration/Trapping
The purpose of this method is to determine what response the sensor has without trapping of interfering gases. This can be thought of as the baseline response
Procedure:
Turn on the F-900, verify chambers are set to off and flow is set to 200 ml/min.
Connect experimental setup as shown in Figure 25.
Load the sample specimen into the fruit chamber.
Start measuring the fruit headspace with the F-900.
After sampling the headspace for 5 minutes, or a set period of time of your choosing, take a syringe sample and run it in the GC (gas chromatograph). Record result in spreadsheet program, such as Microsoft Excel.
Vent the fruit chamber, record the result in Microsoft Excel and start Method 2. The fruit chamber should be well vented to flush out any plant gases between measurements.
Method 2: Sampling with Filtration/Trapping
The purpose of this method is to determine what response the sensor has with trapping of interfering gases by H₂O. This can be thought of as the effect to the instantaneous measurement.
Procedure:
Fill conditioning Chamber In with distilled water and clean the water using potassium permanganate in an in-line column connected to the intake port of the F-900, until the background signal is below 20ppb.
Load the sample specimen into the fruit chamber.
Start measuring the fruit headspace with the F-900.
After sampling the headspace for exactly 5 minutes, take a syringe sample and run it in the GC (gas chromatograph). Record result in spreadsheet program, such as Microsoft Excel.
Vent the fruit chamber, record the result in Microsoft Excel and start Method 3.
Method 3: Long-Term Monitoring with Filtration
The purpose of this method is to determine the effectiveness of the PolarCept filter for long term measurements. This will require the trap to self-regenerate between consecutive measurements. The regeneration time is defaulted to 6 minutes; however for some species a greater time may be needed. By keeping the default value for avocados, we can better compare results and will demonstrate the weakness of the method and how to realize if the “cleaning” period should be extended.
Procedure:
Fill conditioning Chamber In with distilled water and clean the water using potassium permanganate in an in-line column connected to the intake port of the F-900, until the background signal is below 40ppb.
Verify that Chamber In is set to “Special” with a sufficient cleaning period for the produce being monitored.
Load the sample specimen into the fruit chamber.
Start measuring the fruit headspace with the F-900.
Allow the system to run for 5 measurement and cleaning cycles.
Vent the chamber and load the data file to a computer.
Switch to the next replicate and begin at Method 1 again.
Figure 25: Set-up for fruit chamber using (KMnO₄) to scrub ethylene from the outside air.