The open access instruments are located in B208B Stanley Hall and are available to authorized users 24 hours a day, seven days a week. Authorized users may sign up for time using the calendars provided in B208B Stanley Hall. A 3-hour time limit applies from 9 a.m. to 5 p.m. Monday through Friday. There is no limit during off hours. Overnight runs must be completed by 9 a.m.
Groups that are interested in using the open access mass spectrometers should appoint a group operator for each instrument they wish to use (this can be the same person). Group operators are expected to train other members of their group who wish to use the instruments. Graduate students who are assigned the responsibility of being a group operator are expected to complete CHEM268 as part of their training or have equivalent prior experience. CHEM268 (Chemical and Biological Mass Spectrometry) is offered in the spring semester each year. Exceptions to this requirement will be made on a case-by-case basis by the facility manager. For more information about the open access instruments, training, and group operator responsibilities, please contact Dr. Ulla Andersen (email: norklit AT berkeley DOT edu).
The LC/MS instrument consists of a time-of-flight mass spectrometer and a liquid chromatography system. The mass spectrometer has a mass range up to m/z 30,000 and is equipped with an electrospray ion source. The recommended flow rate is 0.3 mL/min or less. Groups that are interested in using the LC/MS instrument should appoint a group operator as described above. Each research group is responsible for supplying their own chromatography columns. The following mobile phases are available from the facility: water, water + 0.1% formic acid + 5% acetonitrile, methanol, and acetonitrile + 0.1% formic acid. Users may bring other LC-compatible solvents as long as they have been filtered (0.2 µm filter).
In many cases, buffers and/or additives are necessary in the mobile phase to modify chromatography. All commonly used LC/MS techniques require the use of volatile additives. Use of non-volatile additives will cause blockages as the additive crystallizes out in the LC/MS interface and/or will suppress ionization. Acceptable buffers/additives include formic acid, ammonium hydroxide, ammonium acetate, and trifluoroacetic acid. Unacceptable buffers/additives include non-volatile salts, e.g., phosphates, surfactants/detergents, and inorganic acids (e.g., sulfuric acid, nitric acid, phosphoric acid, and hydrochloric acid). Inorganic acids must be avoided because they can corrode metal parts within the ion source.
In matrix-assisted laser desorption ionization (MALDI), the sample is embedded in a low molecular weight, UV-absorbing matrix that enhances desorption and ionization of the analyte. Sample preparation is crucial for successful MALDI. It is important to choose the correct matrix for your sample and to use suitable concentrations of both the sample and the matrix. CHEM 268 covers the basic principles of the MALDI techniques and attendees will be given comprehensive material and instructions on how to successfully prepare and clean-up MALDI samples. Groups that are interested in using the MALDI instrument should appoint a group operator. Each group is responsible for supplying their own sample plates, matrixes and other supplies necessary for sample preparation (micropipettor, microcentrifuge tubes, and solvents).