Abstract: Disclosed are methods for quantitatively monitoring components of a cell population, for quantitatively monitoring a difference between components of first and second samples of respective cell populations growing in different conditions, and/or for tagging moieties in biological molecules, and apparatus for performing these methods. Each method and apparatus labels at least a first population of cells with stable isotopes, combines the labeled cells with control cells, and detects isotopic enrichment using an isotope ratio-monitoring detector. The isotope ratio-monitoring can be performed using chemical reaction interface mass spectrometry.

Abstract: Use of nonradioactive tracer technology used to measure DNA synthesis rates. DNA synthesis is determined by administering one or more stable isotope labelled precursors to one or more of DNA molecules and the amount of the stable isotope label in the DNA that is extracted from cells that are of interest is measured.

Abstract: An apparatus and method for measuring the isotope ratio of samples containing carbon and nitrogen compounds. The method includes steps of (a) adding a sample containing carbon or nitrogen compounds to a sample introduction component in which a mixture of analytes is separated into specific molecules, and wherein said sample introduction comprises means for continuous sample introduction into a chemical reaction interface (CRI); wherein said CRI converts intact carbon and nitrogen analytes into new element-specific compounds in an environment comprising fluorine to resolve said compounds; and (b) calculating the isotope ratio of the compounds of said sample with mass spectrometer capable of making precise isotopic measurements. The reactant gas in the reaction chamber is a fluorine gas which allows for better resolution and calculation of the isotope ratio of carbon and nitrogen compounds, with hydrogen, sulfur and oxygen-containing compounds.