CGPM recommendations

The CGPM recognizes that some units outside the SI continue to be important and useful in particular applications. An example is the hter as the reference volume in clinical analyses. Liter is the name of the submultiple (cubic decimeter) of the SI unit of volume, the cubic meter. Considering that 1 cubic meter represents some 200 times the blood volume of an adult human, the SI unit of volume is neither a convenient nor a reasonable reference volume in a cHnical context. Nevertheless, the CGPM recommends that such exceptional units as the liter should not be combined with SI units and preferably should be replaced with SI units whenever possible. 

The present 1993 edition is a futher revision of the 1988 edition, incorporating the recent resolutions of the CGPM, the new international standards ISO-31, and new recommendations from IUPAP and from other IUPAC Commissions. Major additions have been made to the sections on Quantum Mechanics and Quantum Chemistry, Electromagnetic Radiation, and Chemical Kinetics, in order to include physical quantities used in the rapidly developing fields of quantum chemical computations, laser physics, and molecular beam scattering. New sections have been added on Dimensionless Quantities, and on Abbreviations and Acrohyms used in chemistry, and a full subject index has been added to the previous symbol index. 

The present volume is a slightly revised and somewhat extended version of the previous edition. The new revisions are based on the recent resolutions of the CGPM [3] the new recommendations by IUPAP [4] the new international standards ISO-31 [5,6] some recommendations published by other IUPAC commissions and numerous comments we have received from chemists throughout the world. 

The international unit itself may eventually be replaced by the SI unit termed the katal, the SI derived unit for catalytic activity (see Chapter 1). It is defined as moles per second. The name katal had been used for this unit for decades, but did not become an official SI derived unit until 1999 with Resolution 12 of the 21st CGPM, on the recommendation of the International Federation of Cfinical chemistry and Laboratory Medicine. Both the International Union of Pure and Applied Chemistry and the lUB now recommend that enzyme activity be expressed in moles per second and that the enzyme concentration be expressed in terms of katals per liter (kat/L). Thus, lU = lO mol/fiOs = 16.7 X 10 mol/s, or l.Onkat/L - 0.06U/L. The formal adoption of the katal is hoped to discourage the use of a non-SI unit called unit, symbol U, defined as micromoles per minute. Units are more commonly used than the katal in practice at present, but their definition lacks coherence with the SI system. 

The CGPM has made several recommendations and standards to represent a quantity including the numerical value, spacing, symbol, and combinations of symbols. A space should follow the numerical value before the unit symbol 454 kg. In the case of exponential notation, the multiplication symbol should be preceded and followed by a space 4.54 x 10 kg. The plane angular symbols... 

The International System of Units (SI) is the modem metric system of measurement. The abbreviation SI is derived from the French Le Systeme International d UniUs. The ll" General Conference on Weights and Measures (CGPM, Confirmee Ginirale des Poids et Mesures) estabhshed the system in 1960. The seven basic units in the SI system are shown in Table 1.2, the recommended prefixes in Table 1.3 and derived units of general character are shown in Table 1.4. Some constants of importance for this book are collected in Table 1.5. These tables are collected at the end of this chapter (see pp. 14ff.). 

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