Coupling a Knudsen reactor with the short lived radioactive tracer (13)N for atmospheric chemistry studies.

A Knudsen cell flow reactor was coupled to an online gas phase source of the short-lived radioactive tracer (13)N to study the adsorption of nitrogen oxides on ice at temperatures relevant for the upper troposphere. This novel approach has several benefits over the conventional coupling of a Knudsen cell with a mass spectrometer. Experiments at lower partial pressures close to atmospheric conditions are possible. The uptake to the substrate is a direct observable of the experiment. Operation of the experiment in continuous or pulse mode allows to retrieve steady state uptake kinetics and more details of adsorption and desorption kinetics.

Uptake measurements of ethanol on ice surfaces and on supercooled aqueous solutions doped with nitric acid between 213 and 243 K.

Uptake of ethanol either on pure frozen ice surfaces or supercooled solutions doped with HNO3 (0.63 and 2.49 wt %) has been investigated using a coated wall flow tube coupled to a mass spectrometric detection. The experiments were conducted over the temperature range of 213-243 K. Uptake of ethanol on these surfaces was always found to be totally reversible whatever were the experimental conditions. The number of ethanol molecules adsorbed per surface unit was conventionally plotted as a function of ethanol concentration in the gas phase and subsequently analyzed using Langmuir's model. The amount of ethanol molecules taken up on nitric acid doped-ice surfaces was found to increase largely with increasing nitric acid concentrations. For example at 223 K, and for an ethanol gas-phase concentration of 1x10(13) molecules cm3, the number of adsorbed molecules are (in units of molecules cm-2): approximately 1.3x10(14) on pure ice; approximately 1.4x10(15) on ice doped with HNO3 0.63 wt %; approximately 7.5x10(15) on ice doped with HNO3, 2.49 wt %, i.e. 60 times larger than on pure ice. Since, according to the shape of the isotherms, the adsorption did not proceed beyond monolayer coverage, the enormous increase of ethanol uptake was explained by considering its dissolution in either a supercooled liquid layer (T<230 K) or a liquid solution (T>230 K). The formation of both was indeed favored by the presence of the HNO3. Our experimental results suggest that the amount of ethanol dissolved in such supercooled solutions follows Henry's law and that the Henry's law constants at low temperatures, i.e., 223-243 K, can be estimated by extrapolation from higher temperatures. Such supercooled solutions which exist in the troposphere either in deep convective clouds or in mixed clouds for temperature above 233 K, might be responsible for the scavenging of large amounts of soluble species, such as nitric and sulfuric acids, oxygenated VOCs including alcohols, carboxylic acids, and formaldehyde.

[Bone marrow allograft: value of erythrocyte enzyme phenotypes in the biological monitoring]. / Allogreffe de moelle osseuse: intérêt des phénotypes des enzymes érythrocytaires dans la surveillance biologique.

Differences in erythrocyte isoenzyme patterns may be used as biologic markers to monitor allogenic bone marrow transplants. In 19 patients, these markers proved useful for confirming engraftment, although they failed to predict any of the recurrences observed.

[Use of monoclonal antibodies for the immunoenzymological determination of alpha-fetoprotein in amniotic fluid]. / Utilisation des anticorps monoclonaux pour la détermination immunoenzymologique de l'alpha-foetoprotéine dans le liquide amniotique.

A two site immunoenzymatic assay using monoclonal antibodies for alpha-fetoprotein in amniotic fluid has been evaluated. Results obtained with monoclonal antibodies correlated well with those obtained by electroimmunodiffusion assay. The evaluation of this method has shown rapidity, accuracy and a better sensitivity than electroimmunodiffusion assay. Further more the measurements of both maternal serum and amniotic fluid alpha-fetoprotein can be associated.

[Prenatal diagnosis of abnormalities of the neuroectodermal tube. Limitations of the assay of amniotic alpha fetoprotein and acetylcholinesterase and value of the qualitative study of cholinesterases. Apropos of 6 cases of anencephaly]. / Diagnostic anténatal des anomalies de la gouttière neuroectodermique. Limites du dosage de l'alpha-foetoprotéine et de l'acétylcholinestérase amniotiques et intérêt de l'étude qualitative des cholinestérases. A propos de six cas d'anencéphalie reconnus.

Measurement of amniotic fluid alpha-foetoprotein and acetylcholinesterase for the detection of neural tube defects has been used in 285 normal or neural tube defects affected pregnancies: 18 false positive results (with non neural tube defects fetal malformations) have been reported. A qualitative polyacrylamide gel electrophoresis technique has been used to identify the acetylcholinesterase isoenzyme derived from foetal cerebrospinal fluid. Results illustrate the value of amniotic fluid acetylcholinesterase electrophoresis. Amniotic cholinesterase presence may serve as a valuable marker for the detection of neural tube defects.