Desorption efficiency

Substance Expected concentration range (ppm) (mg/m ) Recommended sampling - (ml/min) 2 hr 4 hr 8 hr Recommended maximum tube load (mg) Approximate desorption efficiency " (%) Eluent ... 

The desorption efficiencies given are directly related to the eluent used. All data in the desorption efficiency column correspond to the specific eluent listed ... 

Recommended sampling21 (ml/min) 2 hr 4hr Recommended maximum tube load31 (mg) 8 hr Approximate desorption efficiency (%> Eluent... 

In the investigation of methods for measurement of personal exposure, a method for measuring hydroquinone in air was evaluated, both in the laboratory and in the workplace. The method involved sampling the inhalable fraction onto a filter contained in a multi-holed sampler with a back-up of Tenax TA, followed by desorption into acetonitrile and analysis by HPLC. Desorption efficiency was shown to be effectively 100%. 13 refs. 

Performance of the system is not Umited by inorganic waste content of the soil, but the process does not remediate inorganic wastes. Desorption efficiency is affected by the composition of the contaminated soil (i.e., clay content). Moisture content and organic waste concentrations affect treatment efficiency and treatment rate. 

Freon 113 desorbs hydrocarbons from charcoal at consistent % recoveries, however, does not meet the minimum desorption efficiency of >75% recommended by NIOSH (1 ). However, a mixture of perchloroethylene and Freon 113 does provide a desorption efficiency >80% and can be analyzed by this IR method. 

Recovery Studies. As can be seen from Table I, Freon 113 desorbed both hydrocarbons with consistency, however, at levels less than 75% recovery. The desorption efficiency was the same, whether the sample was allowed 30 minutes or 24 hours for desorption. One surprising fact was that the NIOSH approved gas chromatographic technique for PD-680 also showed a desorption recovery at less than 75% this was rechecked several times... 

Determination of Desorption Efficiencies in the 3M 3500 Organic Vapor Monitor," presented at American Industrial Hygiene Conference, Houston, Texas, May 20, 1980. 

DCP were subjected to two types of preliminary tests— capacity tests and desorption efficiency tests. On the basis of these tests, a sorbent material was tentatively selected for each analyte the selection was confirmed only after the overall sampling and analysis method was validated. 

In some desorption efficiency tests, the sorbent materials that had yielded the most promising results in the capacity tests were spiked with solutions of HCCP in hexane, HCBD in hexane, or... 

DCP in 15% (v/v) acetone in cyclohexane. In other tests, desorption efficiency was determined prior to capacity tests. 

A series of experiments was also performed to determine the sample blank and the optimum extraction time. When required, several solvents were evaluated to obtain optimal extraction efficiencies. A desorption efficiency of at least 0.8 was required. 

The sorbent materials that performed best in the capacity and desorption efficiency tests were investigated further with respect to the stability of the sorbed analyte. Preliminary tests of analyte stability were conducted by a procedure similar to that in the desorption efficiency tests the procedure differed in that samples were stored 7 d prior to analysis rather than Id. To be acceptable, a sorbent material had to exhibit no statistically significant loss of analyte at the 0.05 significance level by a two-tailed t test. 

The selections are presented in Table IV along with the breakthrough times, breakthrough volumes, breakthrough capacities, and desorption efficiencies under the specified sampling conditions. 

The procedure for these tests was similar to that described for the desorption efficiency tests. The spiked samples were stored overnight and extracted, and the extracts were analyzed. 

Determination of Accuracy and Precision of the Analytical Procedure. The desorption efficiency was determined for each method at widely separated analyte quantities to establish the average recovery to be expected. The spiking and analysis procedures for these tests were similar to those described earlier for the preliminary desorption efficiency tests. For HCCP and... 

The desorption efficiency was averaged for levels ranging from near the LAQL to 1000 X LAQL. 

Analytical Recovery. Mean recoveries from spiked silica gel samples indicated that the desorption efficiencies for each of the acids studied is essentially complete. Table III lists the mean recoveries and precision for each of the acids. 

Percent recovery is the percent of the chemical collected under actual sampling conditions which is recovered for analysis. The major contributing factor to low recovery is often the desorption efficiency, i.e., the partitioning of a chemical, at equilibrium, between a specific kind and volume of solvent and a specific batch and amount of solid sorbent. Recovery and desorption efficiency are not always... 

Once the desorption efficiency is determined, the effects of other factors can be examined by laboratory experimentation and field validation. 

The most common technique in determining desorption efficiency is to inject the compound or a solution of the compound directly into the solid sorbent (13). The mixture is allowed to stand overnight and then desorbed and analyzed. Gases and highly volatile compounds are usually introduced as a mixture in air or nitrogen from a SARAN film bag or a cylinder. 

Phase Equilibrium. An equation has been derived (14) which relates the desorption efficiency to the volume of solvent and the amount of sorbent. The equation assumes the system is in equilibrium and can be approached from either direction. That is, the same desorption efficiency should be obtained when the compound is initially in the solvent or the solid phase. This has been shown to apply to most organic compounds in the concentration range of interest in Industrial Hygiene analyses. The equations below can be used to optimize the solid/liquid ratio when developing an analytical procedure ... 

DESORPTION EFFICIENCY OF AROMATIC COMPOUNDS Sorbent Coconut Base Carbon 0.5 grams Solvent Carbon Disulfide 5 mL... 

Once is determined, the desorption efficiency can be calculated for any solid and liquid ratio. Another equation... 

Another useful equation ( 15) has been derived which can be used to determine the ratio n necessary to obtain a desired desorption efficiency Z ... 

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