Quantitative NMR is a valuable method because the measured signals represent a direct measurement of the composition if correct inter-pulse delay are adequately chosen.2 Therefore, in presence of an internal reference of known purity, the composition of a sample can be determined accurately using a single spectrum/ integration sequence (so-called absolute quantification). For this purpose, we used 3-(trimethylsilyl)-1-propanesulfonic acid di sodium salt (TSPA, CAS: 2039-96-5, 97% purity) as standard (also used as chemical shift reference) and D2O for NMR solvent.

After proper weighting of the standard and the gel, the masses of ethanol or isopropanol contained in the samples are calculated by equations 1:

Masse= [ 15 X 0.97 X M(Alc) X SIntAlc X m(Std) ]/[ 218.3 X n1H(Alc) X SInt(Std) ]

= [ 0.06665 X M(Alc) X SIntAlc X m(Std) ]/[ n1H(Alc) X SInt(Std) ] Eq.1

Where M(Alc), n1H(Alc) and m(Std) are respectively the molecular mass, the number of integrated proton and the weighted masse of the chosen alcohol; SInt(Alc) and SInt(Std) being the sum of the integrals for the chosen alcohol and the standard; 15 and 218 and 0.97 being the total number of proton, the molecular mass and the purity of the standard.

For ethanol and isopropanol respectively, the equation resumes to:

Mass(ethanol)=[ 0.615 X SInt(Alc) x m(Std) ]/ SInt(Std) Eq. 2

Mass(isopropanol)=[ 0.572 X SInt(Alc) x m(Std) ]/ SInt(Std) Eq. 3

We found 75% and 68% for handrub solutions produced according to the WHO protocols. The weighted masses were TSPA, 18.14mg, ethanolic gel: 34.69mg (Figure 1) and TSPA: 41.85mg, isopropanol gel: 25.95mg (Figure 2).