Teflon sample problem

In most cases the sample bottle has a wide mouth, making it easy to fill and remove the sample. A narrow-mouth sample bottle is used when exposing the sample to the container cap or to the outside environment is undesirable. Unless exposure to plastic is a problem, caps for sample bottles are manufactured from polyethylene. When polyethylene must be avoided, the container cap includes an inert interior liner of neoprene or Teflon. 

The first case is the most likely to be a problem with new plastic samplers. Although there is little in the literature to substantiate the belief, folklore has it that aging most plastic samplers in seawater markedly reduces the subsequent leaching of plasticisers. The second case is known to be a problem in fact, the effect is used in the various Teflon surface film samplers already mentioned. This problem alone would seem to militate against the use of Teflon for any sampling of organic materials, unless a solvent wash of the sampler in included routinely. With such a solvent wash, we introduce all of the problems of impurities in the reagents. 

The mercury values obtained by the Teflon-piston sampler were high at 0.21 0.2 nmol/kg due to malfunction with incomplete filling and previous contamination, as indicated by the very low salinity in this set. The values inside the bag were higher than those outside, measured about one month after intercomparison to be 0.02,0.03, and 0.04 nmol/kg. There was a subsampling problem. The first and second draw of the sampling bottle usually showed a very wide spread of values, as much as 0.07 nmol/kg, e.g., between 0.05 and... 

In static method a known amount of contaminant is introduced into a fixed volume of air in devices such as teflon bags, gas sampling bulbs and gas cylinders, etc. Dynamic methods involve continuous introduction of contaminant (at a controlled rate) into a stream of air. Static methods are generally much simpler to construct and use, however, these suffer from a number of problems. Dynamic methods, while more elaborate and relatively more expensive, offer greater flexibility in concentration range, sample volume and are also less affected by adsorption losses. 

We have used both the horizontally and vertically configured impactors to sample coal-combustion aerosols in elevated plumes and in plumes at ground level near Deep Creek Lake in western Maryland. Few problems were encountered in this study however, particle bounce could not be evaluated for ambient samples because the individual submicrometer particles could not be discerned. Marple and Rubow (8) have performed extensive calibrations with monodisperse aerosols these show that impaction plates covered with aluminium foil have slightly larger D50S than plates covered with Teflon-fiber filters. 

The greatest advantage of on-line digestion methods over batch methods is that they minimize the problem of acid fumes produced during the digestion of biological samples in the traditional Teflon vessels used in batch treatments. Gas evolution in the on-line methods, however, can lead to problems resulting in pressure build-up and disturbances... 

Common problems with GC analysis include septum leaks and adsorption of components from the sample onto the septum durmg injection. In addition, because the septum is heated, decomposition products often form and bleed into the column. This results in spurious peaks, termed ghost peaks, appearing in the chi omatogram. Septum bleed is greater at higher injection-port temperatures. To minimize this problem, a Teflon-coated, low-bleed septum is used. The inner surface of the septum is purged continuously with the carrier gas that is vented before... 

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