Hello Sarah! I will try to answer two of your queries in as simple terms as possible!

1) Tandem Mass Spectrometry:

Mass spectrometer analyses the sample based on the mass and charge on the protein or the polypeptide. Upon injection, the masses of the polypeptides are matched with previously known sequence databases or calculated masses of all theoretically possible peptides. This method is also called peptide mass fingureprinting. Now, since this approach compares only masses in the experimental sample with that of theoretical sequences, for a given mass resulting from a specific theoretical sequence, the arrangement of amino acids in the theoretical sequence will not affect the calculated mass. This means that unless you are certain what protein you are using, it is fairly difficult to determine what is the sequence of the protein.

To resolve this problem and determine the exact sequence present in a peptide, tandem mass spectrometry is used. In simple terms, there are two mass spectrometers installed in the instriment. In the first one, you can determine which peptides are of interest to you and the second one allows determination of sequences.

The mechanism of sequence determination in the second MS is quite interesting. The selected peptide (they like to call it ions) is choped into two and the masses are determined. At any given time, there will be large number of peptides with the same sequence available for chopping. Secondly, the chopping occurs at different sites in the sequence. The masses of all the sequences are compared and compared with theoretical sequences. The information from all these matches is compiled to determine very accurate information about the sequence of the peptide.

Hope that has helped you understand what tandem MS means!

2) MALDI-TOF

This is a type of Mass Spectrometer! There are two major types of these instruments that are most commonly used! ESI-TOF and MALDI-TOF. The basic difference is the way the sample is activated (Ionized).

In MALDI- MS the sample is embedded in a matrix which can be easily vapourized. High energy pulses of a laser are applied on to the matrix which evaporates also vapourising the sample. The sample then goes for analysis into the instrument. In ESI-MS the sample is ionized by a spray of electrons on to the sample.

The TOF refers to the type of detector used in the instrument and is based on the time reqired by the sample to reach the detector. Heavier peptides and/or with less charge on them will migrate slower than smaller peptides with charged functional groups.

hope this answer is useful!

Regards,

Anant Dave

Hello Sarah! I will try to answer two of your queries in as simple terms as possible!

1) Tandem Mass Spectrometry:

Mass spectrometer analyses the sample based on the mass and charge on the protein or the polypeptide. Upon injection, the masses of the polypeptides are matched with previously known sequence databases or calculated masses of all theoretically possible peptides. This method is also called peptide mass fingureprinting. Now, since this approach compares only masses in the experimental sample with that of theoretical sequences, for a given mass resulting from a specific theoretical sequence, the arrangement of amino acids in the theoretical sequence will not affect the calculated mass. This means that unless you are certain what protein you are using, it is fairly difficult to determine what is the sequence of the protein.

To resolve this problem and determine the exact sequence present in a peptide, tandem mass spectrometry is used. In simple terms, there are two mass spectrometers installed in the instriment. In the first one, you can determine which peptides are of interest to you and the second one allows determination of sequences.

The mechanism of sequence determination in the second MS is quite interesting. The selected peptide (they like to call it ions) is choped into two and the masses are determined. At any given time, there will be large number of peptides with the same sequence available for chopping. Secondly, the chopping occurs at different sites in the sequence. The masses of all the sequences are compared and compared with theoretical sequences. The information from all these matches is compiled to determine very accurate information about the sequence of the peptide.

Hope that has helped you understand what tandem MS means!

2) MALDI-TOF

This is a type of Mass Spectrometer! There are two major types of these instruments that are most commonly used! ESI-TOF and MALDI-TOF. The basic difference is the way the sample is activated (Ionized).

In MALDI- MS the sample is embedded in a matrix which can be easily vapourized. High energy pulses of a laser are applied on to the matrix which evaporates also vapourising the sample. The sample then goes for analysis into the instrument. In ESI-MS the sample is ionized by a spray of electrons on to the sample.

The TOF refers to the type of detector used in the instrument and is based on the time reqired by the sample to reach the detector. Heavier peptides and/or with less charge on them will migrate slower than smaller peptides with charged functional groups.

hope this answer is useful!

Regards,

Anant Dave