1. What is the International System of Units (SI)?

In chemistry, the SI unit of "Amount of Matter" is the mole. Recently defined, it is still not widely used in laboratories, but above all, the standards that enable it to be used are tricky or even sometimes inaccessible to conventional laboratories. What's more, no metrology organization certifies a reference mole. In fact, it is common practice in laboratories to express a concentration as a mass (kg) or a relative mass (kg.kg - ¹ or kg.L - ¹ ). As a relative concentration is dimensionless, a rather deplorable habit is also to express it as a fraction, such as %, ppm (parts per million) or ppb (parts per billion).

Given these difficulties in ensuring traceability of measurements made by physico-chemical or biochemical analysis laboratories, specific solutions had to be...