The BACIS Archives

[ BNB - 00081 ]

Standardisation of methods in olfactometry and psychophysics

H. Boelens, D. de Rijke, P.H. Punter*, T.G.M. Sluijter* and B.Ph.M. Menco*

The main aspects of responses in olfactometry and psychophysics are:

A. In principle quantitative

- detection: odour threshold studies

- intensity: studies of slopes

B. In principle qualitative

- recognition: odour similarity investigations

- preference: studies of hedonics

If we want to standardise the methods in olfactometry and psychophysics it is necessary that we realise the scope and the limitations of the methods. The following remarks can be made concerning scope and limitations.
Stimuli:
- purity (content); nature and concentration of impurities;
- vapour pressures and water solubilities;
- presentation (gasphase or solution, bottles or smelling strip);
- concentration at the receptors (Table I for conversion).
Apparatus:
- conditioning of carrier gases (purification, pressurising);
- flow rates and measurement (turbulent or laminary flow);
- choice of materials (ad/absorption, chemical inertness, flexibility);
- methods of odorizing carrier gases;
- dilution methods;
- velocity of switching between different stimuli and different concentrations;
- stimulus delivery devices;
- calibration methods.

Table I. Concentration conversion factors for vapours and gases

	mm Hg	ppbv	mol/l	mg/l	mg/m3	microg/m3
mm Hg	1	109 ----- 760	1 --------- 760.RT	M.103 --------- 760.RT	M.106 --------- 760.RT	M.109 --------- 760.RT
ppbv	760.10-9	1	10-9 ----- RT	M.10-6 ------- RT	M.10-3 ------- RT	M ----- RT
mol/l	760.RT	109.RT	1	M.103	M.106	M.109
mg/l	760.RT --------- M.103	106.RT --------- M	10-3 ----- M	1	103	106
mg/m3	760.RT --------- M.106	103.RT --------- M	10-6 ----- M	10-3	1	103
microg/m3	760.RT --------- M.109	RT ----- M	10-9 ----- M	10-6	10-3	1

R (gasconstant) = 0.082 (/) (atm) / (mol) (°K)
T = absolute temperature of the vapour in °K
M = molecular weight
ppbv = parts per billion by volume

Receptants:
- number of subjects;
- representativity (e.g. age, sex, occupation);
- elimination of adaption and sensibilisation;
- elimination of conditioning (advanced knowledge);
- effect of concentration intervals;
- reproducibility, variability and reliability.

Evaluation of results:
- psychophysical methods;
- statistical significance;
- interpretation of results.

The purpose of this introduction is to stimulate the discussion of the scientific and critical use of the existing methods, to select and improve the better ones and to discard the poorer ones.