Solventless sample preparation techniques based on solid- and vapour-phase extraction

Catalytic Oxygenation-Mediated Extraction as a Facile and Green Way to Analyze Volatile Solutes

Sparging-based methods have long been used to liberate volatile organic compounds (VOCs) from liquid sample matrices prior to analysis. In these methods, a carrier gas is delivered from an external source. Here, we demonstrate "catalytic oxygenation-mediated extraction" (COME), which relies on biocatalytic production of oxygen occurring directly in the sample matrix. The newly formed oxygen (micro)bubbles extract the dissolved VOCs. The gaseous extract is immediately transferred to a separation or detection system for analysis. To start COME, dilute hydrogen peroxide is injected into the sample supplemented with catalase enzyme. The entire procedure is performed automatically-after pressing a "start" button, making a clapping sound, or triggering from a smartphone. The pump, valves, and detection system are controlled by a microcontroller board. For quality control and safety purposes, the reaction chamber is monitored by a camera linked to a single-board computer, which follows the enzymatic reaction progress by analyzing images of foam in real time. The data are instantly uploaded to the internet cloud for retrieval. The COME apparatus has been coupled on-line with the gas chromatography electron ionization mass spectrometry (MS) system, atmospheric pressure chemical ionization (APCI) MS system, and APCI ion-mobility spectrometry system. The three hyphenated variants have been tested in analyses of complex matrices (e.g., fruit-based drinks, whiskey, urine, and stored wastewater). In addition to the use of catalase, COME variants using crude potato pulp or manganese(IV) dioxide have been demonstrated. The technique is inexpensive, fast, reliable, and green: it uses low-toxicity chemicals and emits oxygen.

Rapid Extraction and Analysis of Volatile Solutes with an Effervescent Tablet

Extraction of volatile compounds from complex liquid matrices is a critical step in volatile compound analysis workflows. Recently, green chemistry principles are increasingly implemented in extraction processes. Some of the available approaches are solvent-free but still require concentration or trapping of analytes. Here, we propose effervescent tablet-induced extraction (ETIE) as a method of transferring volatile/semivolatile compounds from liquid matrices to the gas phase for analysis. This technique relies on the release of carbon dioxide produced in situ during a neutralization reaction, which occurs when a tablet is inserted into an aqueous sample matrix. In this process, many bubbles of carbon dioxide are instantly formed in the sample matrix. The bubbles rapidly extract and liberate volatile compounds from the sample. The gaseous effluent is then immediately transferred to a detector (atmospheric pressure chemical ionization mass spectrometry (MS) or gas chromatography (GC) hyphenated with MS). ETIE-GC-MS can be used for analysis of volatile compounds present in real samples. The method was validated for analysis of selected ethyl esters present in a yogurt drink. The calibration data set was linear over a range from 5 × 10^-7 to 1 × 10^-5 M. The limits of detection ranged from 1.51 × 10^-7 to 6.82 × 10^-7 M, while the recoveries ranged from 71 to 118%. Inter- and intraday precision of selected ethyl esters in aqueous solution was satisfactory (relative standard deviation, 3.6-18.3%). Furthermore, it is shown that ETIE improves the performance of headspace solid-phase microextraction while eliminating the need for heating and shaking samples.

Reagent-free analytical flow methods for the soft drink industry: Efforts for environmentally friendly chemical analysis

The evolution of an entirely green analytical system for industrial quality control of carbonated drinks is described. The developed flow system is capable of providing analytical data of the dissolved CO2, sucrose, and color of a sample consecutively in real-time. The system has been carefully designed on the basis of “reagent-free”, meaning that no added chemicals are required for the analysis. The system first vaporizes CO2 from the soft drink in a gas–liquid separation chamber, with a channel for a flow of pure water as the CO2 acceptor. The dissolved CO2 alters the conductivity of the water stream, which is directly related to the concentration of CO2 in the soft drink. The sucrose content is measured based on the “schlieren effect”, the sample plug flows out of the vaporization chamber into a colorimeter with a near-infrared/light-emitting diode (NIR/LED) as light source. The schlieren effect arises at the boundary of pure water and soft drink with refraction of light in proportion to the sugar concentration. The system also measures the absorbance of the sample using an RGB-LED. The related principles and preliminary experiments as proof of concept are described as well as the construction of the flow system for this completely reagent-free analyzer. A simple flow injection system using the schlieren effect was also developed for rapid quantitative analysis of sugar in noncarbonated soft drinks.

Microextraction techniques combined with capillary electrophoresis in bioanalysis

Over the past two decades, many environmentally sustainable sample-preparation techniques have been proposed, with the objective of reducing the use of toxic organic solvents or substituting these with environmentally friendly alternatives. Microextraction techniques (MEs), in which only a small amount of organic solvent is used, have several advantages, including reduced sample volume, analysis time, and operating costs. Thus, MEs are well adapted in bioanalysis, in which sample preparation is mandatory because of the complexity of a sample that is available in small quantities (mL or even μL only). Capillary electrophoresis (CE) is a powerful and efficient separation technique in which no organic solvents are required for analysis. Combination of CE with MEs is regarded as a very attractive environmentally sustainable analytical tool, and numerous applications have been reported over the last few decades for bioanalysis of low-molecular-weight compounds or for peptide analysis. In this paper we review the use of MEs combined with CE in bioanalysis. The review is divided into two sections: liquid and solid-based MEs. A brief practical and theoretical description of each ME is given, and the techniques are illustrated by relevant applications.

Measurement of benzene concentration in urban air using passive sampling

The concentration of benzene in urban air in the Tri-City area of Poland (Gdańsk-Sopot-Gdynia, and Tczew) was assessed using diffusive passive samplers (Radiello). Samples were collected during a four-year monitoring campaign (2007-2010) at selected monitoring stations managed by the Agency of Regional Air Quality Monitoring in the Gdańsk Metropolitan Area (ARMAAG) Foundation. The performance of the passive samplers was investigated in a field study that measured the benzene concentration in urban air. The results obtained by the Radiello samplers were compared with the results obtained using an on-line monitor (Chrompack CP 7001). Statistical analysis of the results obtained by the two different techniques (passive and on-line) was performed by a linear regression method (Student's t-test). The influence of temperature fluctuations on the uptake rate behavior of the passive samplers was also investigated.