Humidity and M o i s t u r e I t s Measure-ment and Control in Science and Industry

Abstract Experiments were carried out to study the feasibility of using a gas-liquid chromatograph for measuring humidity of small samples. The system employed a thermal conductivity cell for detection and a digital integrator to measure the peak areas. A number of column packings were tried, and 2% Carbowax on Haloport F was selected because i t caused relatively little tailing. Water peak areas were found to vary almost linearly with humidity level. Air and water peak areas varied with sample size; both decreased markedly with increased carrier gas flow rate, and both decreased with a decrease in filament current. Accuracy ranged from about 2 1 1 4 C deg dew-point at 21°C dew-point temperature to &1 C deg a t -18°C dew-point temperature for sample sizes ranging from 4.9 to 15.9 cm3. Because of the small amounts of water involved, sorption on tubing walls can constitute an important source of error. Gas liquid chromatography has been used to measure the moisture content of a variety of liquids (1-4) and of air (5,6). I t affords a method of measuring small quantities of moisture and is of interest in the present case because it constitutes a possible method of determining the properties of small samples of moist air withdrawn from spaces in building components or laboratory specimens and equipment. The literature contains little detailed information about the use of GLC for hygrometric work. Experiments were undertaken, therefore, to determine the character of the air and water signals as affected by 15.9, 8.2 and 4.9 cm3 were used. The volumes of the sample chambers were measured by determining the amount of water required to fill them. The additional volume contributed by the Beckman valve was estimated to be 0.2 cm3. The entire Beckman valve was heated to about 110°C because sorption on the metering chamber walls at room temperature was sufficient to produce a marked effect on the results. A number of column packings were tried. These included calcium carbide to produce acetylene, which could then be detected, Poropak R@, (Waters Assoc., Framingham, Mass.), Ucon 550 on Haloport, Chromosorb W, and Carbowax on Haloport F. On the basis of the observed reproducibility and tailing, 2% Carbowax on Haloport F was selected as the most suitable for work in the range of interest. The packing material was chilled to -30°C to simplify loading, and the column (stainless steel tube, 1/4 in., i.d., and 9 ft 6 in. long) was vibrated to improve the uniformity of packing. The column was operated at approximately 90°C. The sensing element was a thermal conductivity cell with a four-filament bridge in a system similar to that discussed by Lawson and Miller ( 8 ) . Results appeared to be more reproducible when a constant current was supplied to the bridge, and this procedure was employed in the tests. The electrical output from the thermal conductivity cell was transmitted to an Aerograph 470 digital integrator, which gave the areas of the air and water peaks separately in digital form, the units being millivoltseconds (mV-sec) . The water peak areas at low dewpoint temperatwes were so small that it was not -sample size, humidity level, sensor current, carrier gas flow rate and column temperature, and to evaluate the attainable accuracy and sensitivity of the method. Method During the initial stages of the investigation samples of moist air were introduced into a chromatograph by means of a syringe with a volume of less than 5 cm3. Reproducibility was poor, possibly owing to the effects of sorption on the walls of the syringe, and the method was abandoned in favor of a system that would avoid this difficulty. Room air was pumped through a saturator, which produced a humidity level known to within 0.1 C deg dew-point ( 7 ) , to a Beckman valve that allowed air samples of known volume to be metered into the carrier gas stream and analysed. Sample chambers of 1. Casazza, W. T., and Steltenkamp, R

IgE and mast cells in host defense against parasites and venoms.

IgE-dependent mast cell activation is a major effector mechanism underlying the pathology associated with allergic disorders. The most dramatic of these IgE-associated disorders is the fatal anaphylaxis which can occur in some people who have developed IgE antibodies to otherwise innocuous antigens, such as those contained in certain foods and medicines. Why would such a highly "maladaptive" immune response develop in evolution and be retained to the present day? Host defense against parasites has long been considered the only beneficial function that might be conferred by IgE and mast cells. However, recent studies have provided evidence that, in addition to participating in host resistance to certain parasites, mast cells and IgE are critical components of innate (mast cells) and adaptive (mast cells and IgE) immune responses that can enhance host defense against the toxicity of certain arthropod and animal venoms, including enhancing the survival of mice injected with such venoms. Yet, in some people, developing IgE antibodies to insect or snake venoms puts them at risk for having a potentially fatal anaphylactic reaction upon subsequent exposure to such venoms. Delineating the mechanisms underlying beneficial versus detrimental innate and adaptive immune responses associated with mast cell activation and IgE is likely to enhance our ability to identify potential therapeutic targets in such settings, not only for reducing the pathology associated with allergic disorders but perhaps also for enhancing immune protection against pathogens and animal venoms