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

Summary

Fizzy extraction is a new laboratory technique for analysis of volatile and semivolatile compounds. A carrier gas is dissolved in the liquid sample by applying overpressure and stirring the sample. The sample chamber is then decompressed. The analyte species are liberated to the gas phase due to effervescence.

Abstract

Chemical analysis of volatile and semivolatile compounds dissolved in liquid samples can be challenging. The dissolved components need to be brought to the gas phase, and efficiently transferred to a detection system. Fizzy extraction takes advantage of the effervescence phenomenon. First, a carrier gas (here, carbon dioxide) is dissolved in the sample by applying overpressure and stirring the sample. Second, the sample chamber is decompressed abruptly. Decompression leads to the formation of numerous carrier gas bubbles in the sample liquid. These bubbles assist the release of the dissolved analyte species from the liquid to the gas phase. The released analytes are immediately transferred to the atmospheric pressure chemical ionization interface of a triple quadrupole mass spectrometer. The ionizable analyte species give rise to mass spectrometric signals in the time domain. Because the release of the analyte species occurs over short periods of time (a few seconds), the temporal signals have high amplitudes and high signal-to-noise ratios. The amplitudes and areas of the temporal peaks can then be correlated with concentrations of the analytes in the liquid samples subjected to fizzy extraction, which enables quantitative analysis. The advantages of fizzy extraction include: simplicity, speed, and limited use of chemicals (solvents).

Introduction

Various phenomena observed in nature and daily life are linked to gas-liquid phase equilibriums. Carbon dioxide is dissolved in soft and alcoholic drinks under elevated pressure. When a bottle of such a fizzy drink is opened, the pressure drops down, and gas bubbles rush to the liquid surface. In this case, effervescence improves organoleptic properties of beverages. The release of gas bubbles is also the main cause of decompression sickness ("the bends")¹. Due to sudden decompression, bubbles form in divers' bodies. The persons suffering from the decompression sickness are treated in hyperbaric chambers.

Gas bubbles....

Protocol

This protocol assumes that all the steps are performed according to the relevant laboratory safety regulations. Some of the steps use commercial instruments - in those cases, manufacturer guidelines need to be followed. When handling toxic chemicals, MSDS guidelines need to be followed. The custom-made equipment⁴ must be operated cautiously; especially, when handling pressurized gases and live electric wiring.

1. Preparation of Standard Solution

1. Prepare 6.2 x 10^-2 M stock solution of limonene in ethanol by mixing 10 µL limonene with 990 µL ethanol.
2. Prepare 10 mL of 6.2 x 10^-5

Results

At the beginning, the fizzy extraction system is tested with a standard solution. Subsequently, the real sample and real sample spiked with standard are analyzed. The areas of the temporal peaks of extraction events are correlated with concentrations of the analytes in the liquid samples subjected to fizzy extraction, which enables quantitative analysis. Here, we performed double standard addition to demonstrate quantitative capabilities of the technique (Figure 7

Discussion

Several smart ways to deliver samples to a mass spectrometer were developed in the studies conducted during the past three decades (e.g., references^{8,9,10,11,12,13,14}). One of the goals of those studies was to simplify preparation of samples for analysis. To achieve that goal, vario.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Water	Fisher	W6212	Diluent
Ethanol	Sigma-Aldrich	32221-2.5L	Diluent
(R)-(+)-Limonene	Sigma-Aldrich	183164-100ML	Standard
Carbon dioxide	ChiaLung	n/a	Carrier gas
Cellulose tissue, Kimwipes Kimtech	Kimberly-Clark	34120	Used for cleaning
Triple quadrupole mass spectrometer	Shimadzu	LCMS-8030	Detection system
Atmospheric pressure chemical ionization interface	Shimadzu	Duis	Ion source
20-mL screw top headspace glass vial with septum cap	Thermo Fisher Scientific	D-52379	Sample vial
LabSolutions software	Shimadzu	n/a	version 5.82
PeakFit software	Systat Software	n/a	version 4.12
OriginPro software	OriginLab	n/a	version 8