Mass spectrometry

Atheris Labs uses a complementary set of high technology instruments of the latest generation to offer a wide range of MS analyses: from routine ESI-MS or MALDI-TOF-MS analyses, via identification of proteins isolated from 2D SDS-PAGE gels, de novo nanoLC-MS/MS sequencing, characterisation of post-translational modifications, complex structural investigations to quantitative pharmacological analyses. We like efficiency, provide high quality data very quickly and willingly discuss the results.

Our team of specialists accumulates several decades of experience in MS-based investigations. Whatever your analytical issue is, we are able to define the best strategy for each project and design the experiments to be performed on the best-suited instrument, depending on the sample and analytical requirements. Mass spectrometers used include single quadrupole ESI-MS, MALDI-TOF-MS with PSD, triple quadrupole ESI-MS/MS, ESI-TOF-MS, MALDI-TOF-TOF and hybrid Q-TOF ESI-MS/MS.

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Electrospray MS - In positive or negative ionisation mode

Electrospray ionisation mass spectrometry (ESI-MS) is widely used for the characterisation, purity and quality control of a wide range of samples. Molecular masses from 50 to 100’000 Da can be measured with a typical accuracy of 20 ppm (± 0.2 Da for a 10 kDa compound). The samples are introduced in the mass spectrometer in solution and ionised at atmospheric pressure, which is ideal for fragile samples and well adapted to non-covalent interaction studies.

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MALDI-TOF-MS - In linear or reflectron mode

MALDI-TOF-MS is the method of choice for sensitive high throughput analysis of mixtures of peptides, crude extracts or large proteins. The samples are mixed to a matrix and loaded onto a sample plate were they are allowed to dry prior to analysis. While the more sensitive linear mode is adapted to biopolymers from 3 to 500 kDa, the more accurate and resolving reflectron mode is used for the analysis of smaller compounds in the 300-5000 Da range.

In a typical proteomics experiment, proteins isolated by 2D-PAGE are digested in-gel by a specific enzyme such as trypsin. A MALDI-TOF-MS analysis of the proteolytic digest will allow fast protein identification by peptide mass mapping. If necessary, additional investigation by tandem MS/MS fragmentation will generate complementary sequence information for automated searches in specialised gene or protein databases.

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On-line LC-ESI-MS - From nano-bore to preparative scale

A reversed phase HPLC system can be coupled on-line to an ESI-MS instrument, and mass spectra of the eluate can be obtained during the whole chromatographic process. Ion current and UV chromatograms are acquired and fractions can be collected in most cases. This is usually by far the best way to analyse complex mixtures, such as enzymatically digested proteins or to rapidly develop an efficient purification protocol. In some cases, however, the best results are obtained by off-line ESI-MS or MALDI-TOF-MS analysis of fractions collected from an HPLC run.

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MS/MS structural investigation - Tandem mass spectrometry

Tandem mass spectrometers are usually made of two mass analysers separated by a collision cell. The first analyser is used as a mass-filter to isolate one single molecular ion that will enter the collision cell in which its fragmentation will be induced. The resulting fragments are directly analysed in the second mass analyser, where their molecular mass is measured, leading to highly valuable structural information, such as amino acid sequences.

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Protein characterisation - MS/MS de novo sequencing

Finally, the most challenging and promising area is probably the MS/MS-based automated de novo peptide sequencing, which can be extremely fast and efficient in most cases, even if the results are sometimes incomplete or difficult to interpret (leucine can not be distinguished from isoleucine). This technique is an excellent complement to the Edman degradation, and remains a method of choice for the sequencing of peptides, even directly from crude extracts.

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