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Volatile Organic Compounds: Organic compounds that have a relatively high Vapor pressure at room temperature.

PTR-ToF-MS Coupled with an Automated Sampling System and Tailored Data Analysis for Food Studies: Bioprocess Monitoring, Screening and Nose-space Analysis

1Department of Food Quality and Nutrition, Research and Innovation Centre, Fondazione Edmund Mach (FEM), 2Faculty of Science and Technology, Free University of Bolzano, 3Department of Agriculture, Food and Environmental Sciences, University of Foggia, 4Institute of Analytical Chemistry & Radiochemistry, Leopold-Franzens Universität Innsbruck, 5Institut für Ionenphysik und Angewandte Physik, Leopold-Franzens Universität Innsbruck

JoVE 54075


Development of Sulfidogenic Sludge from Marine Sediments and Trichloroethylene Reduction in an Upflow Anaerobic Sludge Blanket Reactor

1Bioprocesses Department, Laboratory of Environmental Biotechnology, Unidad Profesional Interdisciplinaria de Biotecnología, Instituto Politécnico Nacional, 2Laboratory of Molecular Biology, Escuela Superior de Medicina, Instituto Politécnico Nacional

JoVE 52956


Preparing Anhydrous Reagents and Equipment

JoVE 10227

Source: Laboratory of Dr. Dana Lashley - College of William and Mary
Demonstrated by: Timothy Beck and Lucas Arney

Many reactions in organic chemistry are moisture-sensitive and must be carried out under careful exclusion of water. In these cases the reagents have a high affinity to react with water from the atmosphere and if left exposed the desired reaction will not take place or give poor yields, because the reactants are chemically altered. In order to prevent undesired reactions with H2O these reactions have to be carried out under an inert atmosphere. An inert atmosphere is generated by running the reaction under nitrogen gas, or in more sensitive cases, under a noble gas such as argon. Every component in such a reaction must be completely anhydrous, or free of water. This includes all reagents and solvents used as well as all glassware and equipment that will come into contact with the reagents. Extremely water-sensitive reactions must be carried out inside of a glovebox which provides a completely sealed off anhydrous environment to work under via a pair of gloves which protrudes out to one of the sides of the chamber.

 Organic Chemistry

Schlenk Lines Transfer of Solvents

JoVE 5679

Source: Hsin-Chun Chiu and Tyler J. Morin, laboratory of Dr. Ian Tonks—University of Minnesota Twin Cities

Schlenk lines and high vacuum lines are both used to exclude moisture and oxygen from reactions by running reactions under a slight overpressure of inert gas (usually N2 or Ar) or under vacuum. Vacuum transfer has been developed as a method separate solvents (other volatile reagents) from drying agents (or other nonvolatile agents) and dispense them to reaction or storage vessels while maintaining an air-free environment. Similar to thermal distillations, vacuum transfer separates solvents by vaporizing and condensing them in another receiving vessel; however, vacuum transfers utilize the low pressure in the manifolds of Schlenk and high vacuum lines to lower boiling points to room temperature or below, allowing for cryogenic distillations. This technique can provide a safer alternative to thermal distillation for the collection of air- and moisture-free solvents. After the vacuum transfer, the water content of the collected solvent can be tested quantitatively by Karl Fischer titration, qualitatively by titration with a Na/Ph2CO solution, or by 1H NMR spectroscopy.

 Organic Chemistry

Determination Of NOx in Automobile Exhaust Using UV-VIS Spectroscopy

JoVE 10076

Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University

In the troposphere, ozone is naturally formed when sunlight splits nitrogen dioxide (NO2):

NO2 + sunlight → NO + O

O + O2 O3 Ozone (O3) can go on to react with nitric oxide (NO) to form nitrogen dioxide (NO2) and oxygen: NO + O3 → NO2 + O2 This results in no net gain of ozone (O3). However, with the anthropogenic production of ozone forming precursors (NO, NO2, and volatile organic compounds) through the combustion of fossil fuels, elevated levels of ozone in the troposphere have been found. Motor vehicle exhaust is a significant source of these ozone forming precursors: NO, NO2, and volatile organic compounds (VOCs). For example, mobile sources make up nearly 60% of NO + NO2 emissions. At the high temperatures found in a car’s combustion chamber, nitrogen and oxygen from the air react to form nitric oxide (NO) and nitrogen dioxide (NO2):

 Environmental Science

Freezing-Point Depression to Determine an Unknown Compound

JoVE 10137

Source: Laboratory of Lynne O' Connell — Boston College

When a solid compound is dissolved in a solvent, the freezing point of the resulting solution is lower than that of the pure solvent. This phenomenon is known as freezing-point depression, and the change in temperature is directly related to the molecular weight of the solute. This experiment is designed to find the identity of an unknown compound by using the phenomenon of freezing-point depression to determine its molecular weight. The compound will be dissolved in cyclohexane, and the freezing point of this solution, as well as that of pure cyclohexane, will be measured. The difference between these two temperatures allows for the calculation of the molecular weight of the unknown substance.

 General Chemistry

Performing 1D Thin Layer Chromatography

JoVE 5499

Source: Laboratory of Dr. Yuri Bolshan — University of Ontario Institute of Technology

Thin layer chromatography (TLC) is a chromatographic method used to separate mixtures of non-volatile compounds. A TLC plate consists of a thin layer of adsorbent material (the stationary phase) fixed to an appropriate solid support such as plastic, aluminum, or glass1. The sample(s) and reference compound(s) are dissolved in an appropriate solvent and applied near the bottom edge of the TLC plate in small spots. The TLC plate is developed by immersing the bottom edge in the developing solvent consisting of an appropriate mobile phase. Capillary action allows the mobile phase to move up the adsorbent layer. As the solvent moves up the TLC plate, it carries with it the components of each spot and separates them based on their physical interactions with the mobile and stationary phases.

 Organic Chemistry

Fractional Distillation

JoVE 5700

Source: Laboratory of Dr. Nicholas Leadbeater — University of Connecticut 

Distillation is perhaps the most common laboratory technique employed by chemists for the purification of organic liquids. Compounds in a mixture with different boiling points separate into individual components when the mixture is carefully distilled. The two main types of distillation are "simple distillation" and "fractional distillation", and both are widely used in organic chemistry laboratories. Simple distillation is used when the liquid is (a) relatively pure (containing no more than 10% liquid contaminants), (b) has a non-volatile component, such as a solid contaminant, or (c) is mixed with another liquid with a boiling point that differs by at least 25 °C. Fractional distillation is used when separating mixtures of liquids whose boiling points are more similar (separated by less than 25 °C). This video will detail the fractional distillation of a mixture of two common organic solvents, cyclohexane and toluene.

 Organic Chemistry

High-Performance Liquid Chromatography (HPLC)

JoVE 10156

Source: Dr. Paul Bower - Purdue University

High-performance liquid chromatography (HPLC) is an important analytical method commonly used to separate and quantify components of liquid samples. In this technique, a solution (first phase) is pumped through a column that contains a packing of small porous particles with a second phase bound to the surface. The different solubilities of the sample components in the two phases cause the components to move through the column with different average velocities, thus creating a separation of these components. The pumped solution is called the mobile phase, while the phase in the column is called the stationary phase. There are several modes of liquid chromatography, depending upon the type of stationary and/or mobile phase employed. This experiment uses reversed-phase chromatography, where the stationary phase is non-polar, and the mobile phase is polar. The stationary phase to be employed is C18 hydrocarbon groups bonded to 3-µm silica particles, while the mobile phase is an aqueous buffer with a polar organic modifier (acetonitrile) added to vary its eluting strength. In this form, the silica can be used for samples that are water-soluble, providing a broad range of applications. In this experiment, the mixtures of three components frequently found

 Analytical Chemistry

Gas Chromatography (GC) with Flame-Ionization Detection

JoVE 10187

Source: Laboratory of Dr. B. Jill Venton - University of Virginia

Gas chromatography (GC) is used to separate and detect small molecular weight compounds in the gas phase. The sample is either a gas or a liquid that is vaporized in the injection port. Typically, the compounds analyzed are less than 1,000 Da, because it is difficult to vaporize larger compounds. GC is popular for environmental monitoring and industrial applications because it is very reliable and can be run nearly continuously. GC is typically used in applications where small, volatile molecules are detected and with non-aqueous solutions. Liquid chromatography is more popular for measurements in aqueous samples and can be used to study larger molecules, because the molecules do not need to vaporize. GC is favored for nonpolar molecules while LC is more common for separating polar analytes. The mobile phase for gas chromatography is a carrier gas, typically helium because of its low molecular weight and being chemically inert. Pressure is applied and the mobile phase moves the analyte through the column. The separation is accomplished using a column coated with a stationary phase. Open tubular capillary columns are the most popular columns and have the stationary phase coated on the walls of the capillary. Stationary phases a

 Analytical Chemistry

Sonication Extraction of Lipid Biomarkers from Sediment

JoVE 10055

Source: Laboratory of Jeff Salacup - University of Massachusetts Amherst

The material comprising the living "organic" share of any ecosystem (leaves, fungi, bark, tissue; Figure 1) differs fundamentally from the material of the non-living "inorganic" share (rocks and their constituent minerals, oxygen, water, metals). Organic material contains carbon linked to a series of other carbon and hydrogen molecules (Figure 2), which distinguishes it from inorganic material. Carbon's wide valency range (-4 to +4) allows it to form up to four separate covalent bonds with neighboring atoms, usually C, H, O, N, S, and P. It can also share up to three covalent bonds with a single other atom, such as the triple bond in the often-poisonous cyanide, or nitrile, group. Over the past 4.6 billion years, this flexibility has led to an amazing array of chemical structures, which vary in size, complexity, polarity, shape, and function. The scientific field of organic geochemistry is concerned with the identification and characterization of the whole range of detectable organic compounds, called biomarkers, produced by life on this planet, as we

 Earth Science

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