Desorption with carbon disulfide

Ai r Sorption by HBr-treated activated carbon, desorption with carbon disulfide GC/ECD 0.2 ppm No data LeFevre et al. 1989... 

Air Adsorption onto charcoal desorption with carbon disulfide GC/FID (OSHA Method 05) 0.11 ppm for 10 L sample 96 (8.5% RSD) OSHA 1979... 

Air Adsorption onto charcoal desorption with carbon disulfide, containing internal standard if desired GC/FID (NIOSH method 1003) 0.7 mg/m for 15 L sample 97 at 120-493 mg/m NIOSH 1994... 

OSHA. 1979. Method No. 05. Collection on charcoal adsorbent, desorption with carbon disulfide, analysis by gas chromatography using a flame ionization detector. Organic Methods Evaluation Branch, Occupational Safety and Health Administration Analytical Lab, Salt Lake City, UT. May 1979. 

Analytical methods used are described by Bianchi et al. (1997). Methods 3M 3500 and 3M 3520 involve absorption onto a butadiene-specific activated charcoal, followed by desorption with carbon disulfide or with dichloromethane, respectively, and analysis by direct-injection gas chromatography with flame ionization detection. 

Sample preparation desorption with carbon disulfide... 

Removal of the collected sample from the charcoal tube is accomplished by desorption with carbon disulfide or other solvents appropriate for a desirable desorption efficiency. The capped charcoal tube is scored with a file at both ends and the... 

Air (occupational) Sample trapped on charcoal desorption with carbon disulfide GC/FID (NIOSH Methods 1500 and 1501) 10-100 ppb NR NIOSH 1984... 

Soil air Sample collection on activated charcoal desorption with carbon disulfide GC/FID NR 97-100 Colenutt and Davies 1980... 

Water Purge and trap on activated carbon desorption with carbon disulfide GC/FID conf. by GC/MS NR 96-99 Colenutt and Thorburn 1980... 

Suitable analytical techniques are GC and GC/MS. Air analysis can be performed by charcoal adsorption, desorption with carbon disulfide, and injection onto a GC column. Alternatively, thermal desorption of charcoal instead of solvent elution may be carried out. 

Gas and liquid chromatography, mass spectrometry, and UV and IR spectrophotometry are among the common instrumental techniques applied to analyze aromatic hydrocarbons. Benzene and alkylbenzenes pollutants in water, soils, and solid wastes may be analyzed by various GC or GC/MS methods as specified by the EPA (1984, Methods 602 and 624 1986, Methods 8020, 8024). In general, any mononuclear aromatic in any matrix may be analyzed in a similar way. Analysis of these substances in air may be performed by NIOSH Methods involving adsorption over coconut charcoal, desorption with carbon disulfide, and analysis by GC-FID. 

Analysis of toluene may be performed by GC using photoionization or flame ionization detectors or by GC/MS. The analysis of wastewaters, potable waters, soils, and hazardous wastes may be done by the same EPA Methods as those used for benzene (see Section 26.2). In GC/MS analysis the primary characteristic ion for toluene is m/z 91. Air analysis may be done by charcoal adsorption, followed by desorption with carbon disulfide and injecting into GC-FID (see Section 26.2 and NIOSH Methods 1500 and 1501). 

Many of the charcoal tube methods are based on NIOSH Method P CAM 127 (4) for organic solvents. In this method, a known volume of air is drawn through a charcoal tube to trap organic vapors, the charcoal is transferred to a vial, and the sample is desorbed with carbon disulfide. The sample is analyzed by gas chromatography (GC) with flame ionization detection (FID). Most methods use CS2 as the desorption solvent because it yields good recoveries from charcoal and produces a very low flame response. 

All laboratory work with carbon disulfide should be performed in a hood because of its high toxicity. For complete desorption, the samples should be agitated or periodically shaken for a period of 30 minutes. If the desorbed sample is not analyzed immediately, it should be refrigerated, but no longer than two days. (7)... 

Thermal Desorption Thermal desorption is an alternative GC inlet system particularly used for VOC analysis. However, the analytes subjected to thermal desorption must be thermally stable to achieve successful analysis. Otherwise, decomposition occurs. This technique is mainly used for determination of volatiles in the air. Such a methodology requires sample collection onto sohd sorbents, then desorption of analytes and GC analysis. Traditionally, activated charcoal was used as a sorbent followed by extraction with carbon disulfide. However, solvent desorption involves re-dilution of the VOCs, thus partially negating the enrichment effect. Therefore, the sampling method is to pump a sample of gas (air) through the sorbent tube containing certain sorbents in order to concentrate the VOC. Afterwards, the sample tube is placed in thermal desorber oven and the analytes are released from the sorbent by application of high temperature and a flow of carrier gas. Additionally, desorbed compounds are refocused in a cold trap and then released into the GC column. Such a two-step thermal desorption process provides a narrow chromatographic band at the head of the column. 

Desorption Time. One-half to one hour with good agitation is usually sufficient desorption time for most systems. Once optimum desorption has taken place, the system is generally stable however, some exceptions have been observed Some compounds react or are readsorbed after an optimum desorption time as shown in Fig. 5. The active surface of the sorbent may act as a catalyst. Methanol has been shown to react with carbon disulfide in the presence of charcoal to form polysulfides, mercaptans and polyether-thioether compounds Decanting the solvent from the sorbent usually corrects this problem. 

Samples collected on adsorbents can be desorbed by heat (thermal desorption) or by solvent extraction. Thermal desorption of samples from charcoal is not efficient however, because of the high temperature needed (950°C) to remove hydrocarbons from the charcoal (192). For this reason, most ACS passive headspace procedures use carbon disulfide to extract the adsorbed liquid residues. In 1967 Jennings and Nursten (193) reported concentrating analytes from a large volume of aqueous solution using activated charcoal as the adsorbent and extracting with carbon disulfide. Since then many adaptations of this method have been used to detect accelerants in fire debris, but currently dynamic headspace methods are seldom used because of the inconvenience of sampling and possible contamination issues with equipment. 

Extraction with Organic solvents Caustic soda solution Supercritical gases Extraction with carbon disulfide or other solvents Percolation with caustic soda e.g., extraction with supercritical CO2 Sulfur extraction Sulfosorbon process Phenol-loads activated carbon Organic compounds Desorbate treatment by distillation, steam desorption of solvent Phenol separation with subsequent purging Separation of CO organic compounds... 

We then designed model studies by adsorbing cinchonidine from CCU solution onto a polycrystalline platinum disk, and then rinsing the platinum surface with a solvent. The fate of the adsorbed cinchonidine was monitored by reflection-absorption infrared spectroscopy (RAIRS) that probes the adsorbed cinchonidine on the surface. By trying 54 different solvents, we are able to identify two broad trends (Figure 17) [66]. For the first trend, the cinchonidine initially adsorbed at the CCR-Pt interface is not easily removed by the second solvent such as cyclohexane, n-pentane, n-hexane, carbon tetrachloride, carbon disulfide, toluene, benzene, ethyl ether, chlorobenzene, and formamide. For the second trend, the initially established adsorption-desorption equilibrium at the CCR-Pt interface is obviously perturbed by flushing the system with another solvent such as dichloromethane, ethyl acetate, methanol, ethanol, and acetic acid. These trends can already explain the above-mentioned observations made by catalysis researchers, in the sense that the perturbation of initially established adsorption-desorption equilibrium is related to the nature of the solvent. 

For the study of desorption efficiency, or recovery, of vinyl acetate from the charcoal, known amounts of vinyl acetate, either neat or in solution in cyclohexane, were metered onto 100-mg beds of charcoal. The samples were desorbed with 1 mL of carbon disulfide after 1, 5, or 15 days storage at room temperature. The resulting solutions were analyzed by gas chromatography to determine the amount of vinyl acetate that was desorbed. The desorption efficiencies were then calculated according to the following equation ... 

Figure 2. The relationship between desorption efficiency and loading of vinyl acetate on activated charcoal for different storage periods. The 100-mg beds of charcoal were desorbed with 1.00 mL of (------) carbon disulfide or (---) aceto-...

The collection tubes are prepared for analysis using distilled carbon disulfide as a desorbing agent. The desorption phase is usually complete within thirty minutes. The carbon disulfide solution is then analyzed by a Gas Chromatograph equipped with a flame ionization detector. The separation column specified by NIOSH is a 20 ft. x 1/8 in. stainless steel column packed with 10% FFAP on Chromosorb W. Alternative columns, such as 10% SE-30 on Chromosorb W or Porapak Q can be used depending on separation and peak resolving problems. 

Other corrections that must be considered are the collection efficiency of the charcoal tube and the desorption efficiency of carbon disulfide for this specific solvent. TABLE 1 lists the recommended collection tube for each solvent, flow rate to be used in samplings, and desorption efficiency of many organic compounds. (6) The desorption efficiency of carbon disulfide with the charcoal tubes can be determined by injecting a known amount of solvent onto the charcoal. At least five charcoal tubes are sampled and the 100 mg portion removed and placed in a septum sealed vial. A concentration applicable to the threshold limit value of the organic solvent in question is injected onto the 100 mg of charcoal by piercing the septum cap with a microliter syringe. Several concentrations of solvent should be checked to determine the variation in desorption efficiency with solvent concentration. In like manner, standards are prepared by adding the same amount of solvent to the carbon disulfide solution in the vial. The standards are analyzed with the samples. The percent desorption efficiency (D.E.) is determined as ... 

As mentioned elsewhere a typical DTG plot for exhausted carbon after MM adsorption consists of two peaks [1, 2, 9]. One, low temperature, at about 80 °C, represents desorption of water, and second, with maximum at about 200 °C, represents desorption of dimethyl disulfide. Following the assumption that either H2O or DMDS are adsorbed only in pores smaller than SO A, the data was normalized based on that volume. Figure 2 shows the relationship between the normalized amount of DMDS and water. The correlation coefficient and slope are equal to 0.89 and - 0.99, respectively. The slope represents the density of DMDS (1.06 g/cm ). The small discrepancy is likely related to the hict that not all pores are filled by oxidation products owing to the existence of some physical hindrances (blocked pore entrances). The thin line represents theoretical limit of adsorption assuming real density of DMDS and H2O. The fact that almost all points are located below this line validates our hypothesis about the active" pore volume. It is important to mention here that all points represent equilibrium data, if equilibrium... 

---