Precipitation collectors

Fig. 14-9. Wet/dry precipitation collector and flow chart for analysis of samples. (DI HjO distilled water). Source "NADP Quality Assurance Report," Central Analytical Laboratory, Illinois Institute of Nafural Resources, Champaign, 111., March 1980.

Cloud Water and Precipitation Collectors. Several methods have been developed for collecting cloud water samples (24-26). Probably the device most commonly used in warm clouds is the slotted rod collector developed by the Atmospheric Science Research Center at the State University of New York (SUNY) at Albany. Commonly known as the ASRC collector (25), this collector consists of an array of rods constructed from Delrin (a form of nylon). Each rod is hollow and has a slot located at its forward stagnation line. The rod radius determines the collection efficiency as a function of particle size, the rods are sized to collect cloud droplets but not submicrometer aerosol particles, and the 50% cutoff is calculated to be at about 3 xm. 

Field Operations. Each si e had four automatic precipitation collectors (Aerochem Metrics) and a Universal Recording Weighing Bucket Rain Gauge (Belfort) with an eight-day spring powered clock and strip chart recorder. An event pen marker was interfaced with the samplers and noted the sampler lid open and close times on the rain gauge strip chart. 

The collocation data were used to determine concentration means and medians of daily and weekly sampling and to obtain the bias between the measured weekly and the derived weekly values, composited from the corresponding daily results. All derived weekly concentrations were calculated separately for each collector as the precipitation-weighted mean, C = icipi/i i where C- and Pi are the daily concentration and sample weight. For derived weekly precipitation, the sum of the daily volumes for the week was taken for each precipitation collector. 

The performance of various precipitate collectors are discussed and compared in the following sections. 

These are the type of precipitate collectors reported most often [3-9,12-14]. Such filters were originally used as cleaning devices in high performance liquid chromatography. The constructions of two different designs of stainless-steel filters are shown in Rg. 

The advantages of the knotted reactor precipitate collector may be summarized as follows ... 

The foregoing list included almost all the required features of an ideal precipitate collector mentioned in Sec. 7.2.1, except at the moment it may not be applicable to all forms of precipitate, particularly those with a hydrophylic nature. However, much remains to explored in the material of the reactor, and in the types of precipitate which are applicable with the present design. Even during the preparation of this manuscript, dithizone and APDC were added to the list of complexing agents which produced precipitates suitable to be processed in coprecipitation procedures using the knotted reactor... 

Some general guidelines may be proposed for the choice of the proper type of precipitate collector to serve the purpose of different applications. 

Fig.7 Schematic diagram of a FI filterless on-line precipitation system with precipitate dissolution using a knoned reactor (KR) as precipitate collector, a. sample loading (precipitate collection) sequence b, precipitate dissolution sequence. Pi. P2. peristaltic pumps V. 4 5 channel injector valve PR. precipitant S. sample R. buffer reagent (optional) DS, dissolution solvent KR, knoned reactor precipitate collector and W, waste [21].

The impedance of the on-line precipitate collector. This is particularly im] when the collection of a relatively large amount of precipitate is inteh befoit dissolution, or when a small capacity Altering device is used to limit dispersion. Thus, with a nylon membrane filter of 0.45-/xm pore and 5 mm diameter the highest tolerable flow-rate was found to be only 0.3 ml min in the collection [ of a calcium oxalate precipitate [10]. 

In principle, all effective FI continuous precipitation systems with dissolution may be used to achieve some degree of analyte preconcentration. The only prerequisite is that enough sample is available. Within limits defined by the capacity of the precipitate collector, the enrichment factors EF will be proportional to the amount of sample processed. The efficiencies of different preconcentration systems, however, may be quite different. A quantitative evaluation of the efficiencies of the systems may be made using the criteria originally proposed for on-line column preconcentration methods. i.e., in terms of CE and CL These are calculated for the various methods collected in Tables... 

Figure 3, Total gross beta In precipitation, F-1 and F-il combined July 1976 through June 1977 (F-1 and F-H were the sample locations for two large precipitation collector funnels).

The D0E-MAP3S Refrigerated Precipitation Collector (Photo Courtesy of C. Hakkarinen)... 

Yebra et al. [83] used a continuous-flow procedure for the indirect determination of sodium cyclamate by flame atomic absorption spectrometry (FAAS). This method is based on oxidation of the sulfamic group derived from cyclamate to sulfate in acidic conditions and in the presence of sodium nitrite. The procedure is adapted to a flow system with precipitate dissolution (Figure 24.11), where sulfate formed is continuously precipitated with lead ion. The lead sulfate formed is retained on a filter, washed with diluted ethanol, and dissolved in ammonium acetate (because of the formation of soluble lead acetate) for online FAAS determination of lead, the amount of which in the precipitate is proportional to that of cyclamate in the sample. In this work a home-made filtration device was used made of a Teflon tubing packed with a cotton pulp and the ends of the filter column were plugged with filter paper (chamber inner volume 141 J,L). This precipitate collector was effective in retaining the precipitate and did not produce excessive back-pressure if the precipitate was dissolved following each precipitation cycle. 

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