ABSTRACT
The reports prepared by Messrs HARTUNG, VOORBURG and HANGARTNER concerning the analysis : ’’european standards and guidelines in the field of olfactometry are commented ; explanations and further information are supplied”.
INTERPRETATION OF THE FRENCH STANDARD BY J.H. HARTUNG
Paragraph ’’Recommendations for sampling in the guidelines” :
static sampling has not been abandoned. It is used very often (tedlar bags). The comment “abandoned because of adsorption problems” applies to the apparatus (olfactometers), cf. french standard 3.3.2, p. 2.
Answers to the questions asked in the conclusion (p. 4 of J.H. HARTUNG
Type of sampling and procedure
dynamic sampling : direct introduction of the gas to be studied into the olfactometer,
static sampling, in 10–50 1 tedlar bags. The bags are introduced into a stainless steel carboy of a convenient size and filled thanks to the slight underpressure created in the carboy (the bac is made passive by successive filling and evacuating operations).
Material of the sampling device
bags : tedlar bags
connecting tubes : stainless steel and/or PTFE.
Sample size : 10–50 1.
Sampling time : varying between 15 and 30 min.
Storage and temperature time : varying between a few minutes and 3–4 days ; ambient temperature.
In order to prevent condensations, an equipment is used, dynamically allowing the dilution of a known flow of the odorous gas in a known flow of an inodorous gas ; the temperature of the dilution gas must be that of the gas to be diluted if it is a hot gas ; ideally a heat exchanger should be set as much upstream the olfactometer (or sampling bag) as possible.
The dilution gas humidity must be as low as possible (nitrogen and oxygen) when dealing with a humidity saturated gas at ambient temperature.
To prevent dusts from clogging the olfactometer tubes, a glass filter (with low retention of odorous molecules) is set upstream the apparatus. In case of dusts in the analyzed gas, it is better to make a 79bag sampling without filtering ; the dusts likely to have trapped the odorous compounds are sedimented in the bag, are not re-suspended when the gas is introduced into the olfactometer, and eventually desorb the odorous compounds in the bag.
INTERPRETATION OF A FRENCH STANDARD BY J.H. VOORBURG
Paragraph “olfactometer”, p. 1
The static olfactometer have not been abandoned on account by the “consumation of considerable quantities of gas” but because of adsorption phenomena and, as mentioned in the report, because of the time needed for change of concentration.
Paragraph “Range of concentration”, p. 2
The possible dilution factor, sampling between 10 and 10000, makes it possible to utilize a series of 7 regularly spaced dilutions (corresponding to a geometrical progression of ✓l0, viz approximately 03 ; 0.1 ; 0.3 ; 1 ; 3 ; 10 ; 30). In the practie, as soons as dilution equals or exceeds 3000, the threshold value is obtained with greater accuray by performing pre-dilution of the gas analyzed in order to set this threshold value between the dilution factors 10 and 1000.
Paragraph “calibration”, p. 3
In this paragraph, “calibration” and “olfactometer cleaning” should be distinguished.
The french standard makes no reference concerning the olfactometer calibration. Calibration will certainly be carried out with methane analyzed by a flame ionization detector.
INTERPRETATION OF THE FRENCH STANDARD BY H. HANGARTNER
Comments on the tables
“General conditions”
time needed to determine a threshold (for one individual) : about 20 min,
duration of breaks : 20 min,
time needed to determine two thresholds by the panel : 400 min, e. about 7 hours.
“Detection methods”
“Factor of dilution series” : 3 instead of 1.8 (1.8 being the lowest flow of the odorous and inodorous gases, in m3/h, at the outlet of the olfactometer, at the time of “sniffing”, cf. french standard, para. 4.1).
“Evaluation of threshold values” No comment.
“Selection of panelists”
“Sensitivity” : selection of panelists as a function of their individual thresholds of perception on 5 pure products. Interindividual differences ranging between 1 and 1000 are accepted, as it really occurs.
“Honesty” : the question is eliminated by the forced choice answer.
“Physical condition” : for routine measurements the answer to a questionnaire does not seem important, but may be valuable in the case of intercomparaisons (that interpretation of such questionnaires is difficult, …).
“Panel size”
changes brought in the french standar : 10 individuals instead of 20,
meaning of “comparative m.” ?
80“Selection of panelists”
“Sensitivity” : selection des sujets en fonction de leur seuils individuels de perception pour 5 produits purs. On accepte des différences interindividuelles comprises entre 1 et 1 000, comme cela est le cas dans 1a réalité.
“Honesty” : la réponse à choix forcé élimine la question.
“Physical condition” : la réponse à un questionnaire ne semble pas essentielle pour des mesures de routine, mais peut être valable dans le cas d’essais circulaires (à noter la difficulté d’exploitation d’un questionnaire…).
“Panel size”
modification apportée dans la norme française : 10 sujets et non 20,
signification de “comparative m.” ?
