A mass spectrometer is a scientific instrument used to analyze the mass of individual molecules or atoms within a sample. It does this by ionizing the sample, sorting the ions based on their mass-to-charge ratio, and then measuring the abundance of each ion. Mass spectrometry can be used to identify unknown compounds, determine their chemical structure, quantify the amount of a particular substance in a sample, and study the isotopic composition of elements. It is commonly used in fields such as chemistry, biochemistry, environmental science, and forensics.