The Background and Implications of the "New SI" for Analytical Chemists

D Thorburn Burnsa and EH Korteb

(a) School of Chemistry and Chemical Engineering, The Queen’s University of Belfast, Belfast, BT9 5AG, UK
(b) Formerly at Institut für Spektrochemie, Dortmund and Berlin, Germany


The International System of Units (SI) is not in itself a complete philosophical system; it has been developed over time to deal with practical needs. It started during the French revolution with units of unified length and mass. By the mid-1800’s three base units were in place, for measuring distance, mass and time (centimetre, gram and second, the CGS system). These base units evolved into the metre, kilogram and second (the MKS system). The ampere became the fourth base unit in 1946. In 1954 the kelvin and the candela were added as new base units. Finally, in 1971, the mole became the seventh base unit, for the amount of substance1,2. The definitions of each base unit have undergone continuous evolution to deal with improvements in measuring capabilities and following the realisation of any shortcomings in the prior definitions.

The revision presently on the way will lead to the “New SI” that again comprises of seven base units, namely the second, s; the metre, m; the kilogram, kg; the ampere, A; the kelvin, K; the mole, mol and the candela, cd 3.

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