Mass spectrometry emerges as a central analytical framework in 1929-1935, propelled by the advent of a new mass spectrograph and early isotope work that enable direct mass and isotopic analyses across chemistry and biology. In parallel, micro-methods and spectrophotometric approaches expand the analytical toolkit for trace analysis in clinical chemistry, lipid studies, and biomolecule quantification, illustrating how mass spectrometry complemented traditional methods. The period also shows a shift toward quantitative mass measurements in electrochemical and biochemical contexts, with isotope separation and interpretation establishing MS as a practical analytic method. Historical Significance: The instrumental innovations and interpretive frameworks codified the mass-to-charge paradigm, enabling direct mass measurements of elemental species and isotopes and catalyzing rapid advances in isotope analysis across disciplines. Foundational works documented mass spectra and isotopes, provided interpretive rules, and demonstrated hydrogen isotope discovery, electrolyte ion mass determination, and systematic mass analysis that shaped future research directions.