Flow-through samplers

The independence from a power supply makes PASs popular options for measurements of POCs in the remote alpine atmosphere, but they also limit the temporal resolution that can be achieved. Trying to combine the advantages of both PAS and active samplers, a flow-through sampler (FTS) was recently designed, which requires no external power source, but can sample large volumes of air in fairly short periods of time [18, 19] by rotating into the wind and have it blow through a series of PUF disks. The volume of air sampled can be estimated from wind speed records. The FTS will trap particles, but they cannot be analyzed separately from the gas phase POCs. 

Note 2—A suitable sampling chamber may be devised from a polyethylene wash bottle of nominal SOO-mL (I6-oz) or 1-L (32-oz) size. The wi bottle s internal delivery tube provides for delivery of the sample gas to the bottom of the bottle. A l2.S-mm ( A-in.) hole cut in the bottle s cap provides access for the detector tube and vent for the purge gas (Fig. I). (An alternate flow-through sampler may be fashioned using a I-gal Ziploc-type food storage bag. The flexible line enters one comer of the bag s open end and extends to the bottom of the bag. The opposite comer of the open end is used for tube access and sample vent. The remainder of the bag s top is sealed shut. The basic procedure for the sampler in Fig. 1 applies.)... 

As we have seen so far, libraries of hydrogenation catalysts are never composed of more than a few dozen members, up to 100 to 200 at the most. Consequently, modern analytical equipment such as gas chromatography (GC) or high-performance liquid chromatography (HPLC) equipped with an auto-sampler or even flow-through NMR systems are sufficient to handle the analysis of the entire library. Nevertheless, a few groups have initiated research towards the development of fast, sometimes parallel, analytical procedures. A few reviews have appeared on this subject [59]. Here, we will concentrate on the methods developed to analyze hydrogenation reactions, or methods that could likely be applied. 

FIA star 5010 Modular, semi- or fully automatic operation. May be operated with process controller microprocessor. Can be set up in various combinations with 5017 sampler and superflow software which is designed to run on IBM PC/XT computer 60-180 samples h Dialysis for in-line sample preparation and in-line solvent extraction.Thermostat to speed up reactions. Spectrophotometer (400-700nm) or photometer can be connected to any flow through detector, e.g. UV/visible, inductively coupled plasma, atomic absorption spectrometer and ion-selective electrodes... 

In the purge-and-trap procedure, vials filled to the brim with the water samples are loaded into an auto-sampler, and then when the unit is operating, samples are drawn, one by one, into a tube where helium sparging occurs. Because the THMs are volatile, the helium sparging draws them out of the samples. The helium-THM gaseous mixture then flows through a trap in which the THMs are adsorbed and concentrated. This is followed by a desorption step in which the desorbed THMs are guided to the GC column. A Hall detector is used. 

A simple positive-displacement sampler system is shown in Figure 3. The basic system contains a battery and motor connected to a positive-displacement pump mechanism and provides an efficient means for moving air through the sampler. In order to provide feedback flow control the system must be expanded to include the means to monitor air flow through the pump to compensate for flow variations. 

In the ideal case the resistance to mass transfer of a diffusive sampler is confined to the stagnant air gap between the sampling face of the device and the surface of the collecting sorbent material (Van den Hoed and Van Asselen, 1991). Then the mass flow through the sampler can be described by Fick s first law of diffusion... 

LDPE membranes were prefouled for one month in water collected from a park fountain. Membranes became heavily fouled with a thick algal and bacterial film. The fouled membranes were used for the construction of Chemcatcher samplers fitted with sorption phases previously spiked with several PRCs. Samplers fitted with either fouled or unfouled membranes were simultaneously exposed (rotation speed 40 rpm and water temperature 11°C) in a laboratory flow through a calibration system... 

FIGURE 3.4 Biofouling reduces the exchange kinetics of PRCs (deuterated acenaphthene and fluorene) between the nonpolar Chemcatcher sampler (fitted with either fouled or unfouled LDPE membranes) and water. The experiment was performed in a laboratory flow-through calibration system at a water temperature of 11°C with simulated water turbulence of 40 rpm. MD(t)/MD(0) is the fraction of the PRC remaining in the sampler during exposure. 

IBAD The interim biological agent detector (IBAD) is composed of a particle-size sorter/counter, a wet cyclone sampler, a manual identifier, and a flow-through colorimetric ticket assay. Agent identification occurs within 20 minutes. 

The gas flow through the sampler should not exceed the whole gas flow in the plasma, as only well defined zones of the plasma (namely those with the highest analyte concentrations) should be sampled. 

Fig. 130. Complementary module for glucose for the automatic flow stream analyzer ADM 300 (VEB Prflfgerfite-Werk Medingen, GDR) consisting of the automatic sampler APS 4, electronic amplifier AMV 3 with flow-through cell (left), peristaltic pump, and recorder.

Automated samplers function without the need for an operator, giving the possibility of selection of a sampling regime arranged in dependence on time or flow-through quantity. One of these is the sampler shown in Fig. 3.66 [7]. The system has a simple battery-driven peristaltic pump, which can take samples heavily polluted with suspensions of solid material using a suction basket immersed in water. The pump feeds the sample into a 5 1 bottle at the required times determined by the timing unit. 

Fig. la-d. Rigid Whole-Air Samplers, a Evacuated Bulb b Flow-Through Sample Bulb c Displacement Sample Bottle and d Evacuated Metal Cylinder... 

---