Fizzy Extraction of Volatile Organic Compounds Combined with Atmospheric Pressure Chemical Ionization Quadrupole Mass Spectrometry

The overall goal of this extraction procedure is to liberate volatile compounds from a liquid sample and to transfer these compounds to the mass spectrometer for detection. This method can help answer key questions in the field of science or environmental chemistry field such as what volatile compounds are present in beverages or waste water. The main advantage of this technique is that it's fast and conducted online with mass spectrometry detection.

I first had the idea for this method when I opened a bottle of carbonated drink on a sunny day. The bubbles of carbon dioxide released the aroma of the drink. I felt we could easily reproduce this process in the laboratory.

To begin this procedure, prepare a stock solution of limonene in ethanol by mixing 10 microliters of limonene with 990 microliters of ethanol. To prepare the real sample, first squeeze fresh lime fruit on a kitchen squeezer to obtain lime juice. Next, mix two milliliters of lime juice in 500 microliters of ethanol.

Add LC-MS grade water to a final volume of 10 milliliters and shake the volumetric flask thoroughly. Transfer the prepared sample of diluted lime juice to a 20 milliliter screw top head space glass vial with septum cap. Now, prepare a spiked sample by mixing two milliliters of lime juice, 10 microliters of the limonene stock solution, and 490 microliters of ethanol.

Add LC-MS grade water to a final volume of 10 milliliters and shake the volumetric flask thoroughly. Connect a carbon dioxide gas cylinder to the gas supply inlet of a fizzy extraction system. Open the valve in the gas regulator.

Then set the output pressure to 1.5 bar. Following this, connect the extraction chamber outlet to the ion source inlet. Then connect the fizzy extraction system to a 12 volt power supply.

Set up the data acquisition software of a triple quadropole mass spectrometer connected to the fizzy extraction system. Set the desolvation line temperature to 250 degrees Celsius and the flow rate of drying gas to 15 liters per minute. Then select the MS data acquisition method file.

Check that the collision voltage is minus 20 volts, the precursor ion master charge ratio is 137, and the fragment ion master charge ratios are 81 and 95. Then click on the Start Single Run button. Place a sample vial in the fizzy extraction system by using the screw mount.

Press the start button on the LCD shield of the fizzy extraction system. While the automated fizzy extraction process is proceeding, observe development of ion signals on the screen of the triple quadropole mass spectrometer. Carbon dioxide is pressurized in the simple Then the simple chamber is decompressed which leads to effervescence.

After the fizzy extraction process is complete, unscrew the sample vial from the system. Wipe the sample stirring spindle with cellulose tissue. Then wash the spindle with ethanol and wipe it with cellulose tissue.

After switching off the power supply, disconnect the fizzy extraction outlet tube from the ion source. Then close the valve of the gas cylinder and disconnect the gas tubing. Export extracted ion currents for the master charge ratio 81 from the triple quadropole mass spectrometer's data acquisition software to ASCII files.

First, click on Select Folder and choose the data file. Click on the File tab, select Export Data and select Export Data as ASCII. Select Output File, select the file path, and click on Open.

Then select MS Chromatogram(MC)To import the data into the peak integration software and measure the peak areas, select the option Import from the File tab. Open the data file, click on the Yes button, and select the data in the X and Y columns. Then click on OK and select the option Auto Fit Peaks One Residuals.

Now, fit the extraction peak semi-automatically making sure that the fitted curve follows the experimental data points. Select the options List Peak Estimates and then ASCII Editor. Copy the fitting results to clipboard.

To input the peak areas in data analysis software, first input the peak area values in the Y column and the concentration values in the X column. Under the Plot tab, select Symbol and Scatter. Then select Fitting and Fit Linear from the Analysis tab.

The temporal peak areas of extraction events are correlated with concentrations of the analytes in the liquid sample subjected to fizzy extraction which enables quantitative analysis. In this experiment, double standard edition was performed to demonstrate the quantitative capabilities of the technique. A plot relating temporal peaks areas with the concentration of limonene standard added to the diluted lime juice sample is shown here.

Based on the obtained slope and intercept values, the concentration of limonene in the diluted lime juice sample was 8.51 times 10 to the minus five moles per liter. After multiplying by the dilution factor, the concentration of limonene in the original lime juice sample was 4.26 times 10 to the minus four moles per liter. Once mastered, this technique can be done in less than 10 minutes if it is performed properly.

While attempting this procedure, it's important to remember to set the experimental parameters correctly. After watching this video, you should have a good understanding of how to set up fizzy extraction equipment and perform extractions of real samples. Don't forget that working with compressed gas can be extremely hazardous and precautions such as wearing safety goggles should always be taken while performing this procedure.