Mass Spectrometry

Step 1: Understanding the techniques.
MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization Time of Flight) mass spectrometry is a powerful technique used for determining the molecular weight of molecules, including polypeptides. It ionizes the sample and measures the time it takes for ions to travel through a flight tube, providing accurate molecular weight measurements.
Step 2: Analyzing the options.
(1) Gel permeation chromatography: This method separates molecules based on size but does not provide precise molecular weight measurements. It is useful for estimating size but not for accurate molecular weight determination.
(2) SDS-PAGE: SDS-PAGE (Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis) separates proteins based on their size, but it does not directly measure molecular weight. The results need to be compared to a molecular weight standard.
(3) Analytical ultracentrifugation: This technique measures the sedimentation rate of particles in a centrifugal field but is less commonly used than MALDI-TOF for precise molecular weight determination.
(4) MALDI-TOF mass spectrometry: Correct — MALDI-TOF is the most accurate and widely used method for determining the molecular weight of polypeptides, as it directly measures the molecular ions and provides precise data.
Step 3: Conclusion.
The correct answer is (4) MALDI-TOF mass spectrometry, as it offers the most accurate molecular weight determination for polypeptides.