Collection media

Collecting media articles on similar incidents to those outlined in the exercise. 

The application of various antibiotics such as rifampicin/tetracycline (63), cefatoxime/trimethoprim (64), or bacteriostatic compounds such as Micropur (Roth, Karlsruhe, Germany) (65) used for root pretreatment or added to collection media is another strategy to prevent biodegradation during root exudate collection. However, depending on dosage and plant species, also phytotoxic effects of antibiotics have been reported (Table 3). Antibiotics in the soil environment... 

Phosphine and hydrogen sulfide create highly acidic conditions that degrade GB on the collection media. Recovery of GB showed a steady decline as analytical holding time increased. 

Table I summarizes the sampling media used in the last three years of the study. Previously, we have developed validated sampling and analytical methods for many of the common organic solvents that could be collected on charcoal, desorbed with carbon disulfide, and analyzed by gas chromatography. These procedures are usually nearly identical with the NIOSH method P CAM 127. Likewise, methods for substances that give well-behaved particulates both in collection and analysis had been validated. The substances summarized in Table I represent a wide variety of problems in sampling and analysis. Consequently, many of the samplers were charged with unusual collection media.

To achieve optimal sensitivity and selectivity, it was necessary to develop three totally separate methods, one for each compound. Initially, it was necessary to develop, optimize, and calibrate a procedure for quantitating each analyte. With these steps successfully completed, candidate collection media were screened in tests designed to find a material with three attributes (1) an acceptable sorption capacity for the appropriate... 

Selection of Collection Media. The methods developed for HCCP, HCBD, and 1,2-DCP involve the collection of the analytes from air on solid sorbent materials in small Pyrex tubes. Each tube is 7 cm long by 6 mm o.d. and 4 mm i.d. The recommended sampling tubes contain two beds of sorbent material—one layer for sorption and a second, smaller, backup layer to monitor breakthrough if the capacity of the sorbing layer is exceeded. 

Table IV. Collection Media Selected for the Three Analytes HCCP HCBD...

This overall study of acid mists began with the development of a sampling and analytical method for hydrogen chloride ((>,7). Various solid sorbents and filters, both treated and untreated, were evaluated as collection media and for compatibility with ion chromatography. The sorbent of choice was silica gel which had been washed with deionized water to remove inorganic impurities. 

Worker exposure to toxic vapors is monitored by collecting samples in the breathing zone of the worker. These samples are usually returned to a laboratory for analysis. A suitable sampling pump and collection device are required. Lightweight, battery-operated pumps are available in a variety of flowrates. Collection devices are usually sorbent tubes or bubblers or impingers, but bags and evacuated containers have also been used. This discussion will focus on solid sorbents as collection media. 

Again, we tried to standardize on sampling media and sample treatment, using MCE filters followed by Chromosorb 102 sorbent tubes and extraction of the sample from the collection media with toluene. In the case of demeton, poor recoveries were noted from Chromosorb 102 this was also found by other investigators (13). XAD-2 was demonstrated to be satisfactory. 

Accurate estimates of worker exposure to organoarsenicals have not been possible because l) extensive studies of collection media for sampling organoarsenicals in air have not been performed and... 

We have found that rigorous sorbent pretreatment procedures (e.g., Soxhlet extraction and thermal desorption) in concert with a well-established quality control program will successfully control potential contamination effects arising from the sample collection media. Furthermore, a well-executed quality control program will permit identification of spurious data points attributable to media contamination when and if they do occur. 

The precision and accuracy of the analytical methods depends strongly on the desorption efficiency which is the percent removal of contaminent from the collection media. An Electron Capture detector will definitely increase the accuracy of chlorinated species. Precision is increased by using the solvent flush technique of sample injection. 

Copper like vanadium has a separate OSHA standard for dust and fumes resulting in some confusion for the industrial hygienist in selecting collection media. The 0.2 mg Cu/cu m fume standard is one-fifth the dust standard. The distinction between fumes and mist is somewhat ambiguous. Both methods for copper use nitric acid wet ashing however, S-186 uses an analyte matrix of hydrochloric acid for AAS aspiration. 

Insects are spectacular not only in their biological diversity but also in their collection media. When possible insects should be pinned dry. This technique is convenient, requires fairly low maintenance, and is much lighter than liquid storage. Tliey are, however, frequently interred in ethanol, as well as collected in ethanol, and later dried out and pinned. Fortunately, both pinned and ethanol-preserved samples yield usable DNA. 

Another way of considering the effect of particle bounce is shown in Fig. 7.6. A plot of collection efficiency versus substrate loading indicates efficiencies which never reach 100 percent Particle bounce can be minimized by using collection media coated with such materials as Vaseline, L and H high-vacuum greases, stopcock grease, oil, or Apiezon (Moss and Kencyer, 1986). 

In every analytical problem a unified approach must be taken to obtain results of satisfactory accuracy. Considerations of interferences due to contamination are of the utmost importance in the analysis of trace elements from air samples. In many cases attention must be given to selection of high-purity acids and other reagents, and particularly to the purity requirements for collection media such as filters. 

At 72 h, harvest cells. Use media to dislodge the cells. Collect media and cells and centrifnge at 1,000 x g, for lOmin at 4°C to pellet the cells. Discard the media. Resnspend pellet in PBS to wash the pellet. Centrifuge at 1,000 x g, for lOmin at 4°C. Discard PBS and freeze pellet. Frozen pellets can be stored at -20°C for processing at a later time. 

The collection media in this type of filter can be composed of various materials including hair, spun glass, wool, paper and asbestos. (In the past, asbestos has been used in the manufacturing of all types of filters. Since asbestos is cancer causing, be sure to specify a non-asbestos fiber). The ex-Tended surface media filter consists of folds of material woven back and forth. Corrogated aluminum or paper separators are inserted perpendicularly to the filter face and separate the folds to help direct airflow in an even, parallel fashion. 

Filters for use as collection media are saturated with sodium bisulfate as described in Section 3.2.2.2. 

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