PCDFs cleanup

Y. Zebuehr, C. Naef, D. Broman, K. Lexen, A. Colmsjo and C. Oestman, Sampling techniques and cleanup procedures for some complex environmental samples with respect to PCDDs and PCDFs and other organic contaminants , Chemosphere 19 39-44(1989). 

Chang RR, Jarman WM, King CC, et al. 1990. Bioaccumulation of PCDDs and PCDFs in food animals III. A rapid cleanup of biological materials using reverse phase adsorbent columns. Chemosphere 20 881-886. 

The relative ion abundance criteria for PCDDs/PCDFs listed in Table 6 must be met for all PCDD/PCDF peaks, including the labeled internal and recovery standards in all solutions. The lower and upper limits of the ion abundance ratios represent a 15 percent window around the theoretical abundance ratio for each pair of selected ions. The 13Ci2-2,3,7,8-TCDD cleanup standard contains no 35C1, thus the ion abundance ratio criterion does not apply to this compound. 

All of the specified ions listed in Table 5 for each PCDD/PCDF homologue and labeled standards must be present in the SICP. The ion current response for the two quantitation ions and the M-[COCl]+ ions for the analytes must maximize simultaneously ( 2 seconds). This requirement also applies to the internal standards and recovery standards. For the cleanup standard, only one ion is monitored. 

In addition to chlorocymenes and chlorocymenenes, four groups of persistent alkylaromatk chlorohydrocarbons have been detected and characterized from chlorobleaching of pulp. They were assumed to be planar aromatic chlorocom-pounds (PLAC) because they were found in cleanup fractions of PCDDs and PCDFs after reversed elution with toluene from a carbon column [39]. PLAC groups were alkyl-polychloronaphthalenes (RPCN), alkyl-polychlorobibenzyls (RPCBB), alkyl-polychlorofluorenes (RPCFL), and alkyl-polychlorophenan-threnes (RPCPH). Among the latter, chlororetenes are most abundant [40]. 

Koistinen et al. [98], who studied the induction of EROD activity of 29 PCDE congeners in vitro using H4IIE rat hepatoma cells, have reported that PCDEs are inactive as inducers of EROD. A similar type of activity as that reported by Howie et al. [88] was only seen with PCDE congeners before cleanup by Florisil column chromatography. After the removal of PCDD and PCDF impurities using Florisil the activity was lost, except for PCDE 156 which was a weak inducer (TEF 1.2 x 10-5). It is possible that effects such as chloroacne reported for higher chlorinated PCDEs [12], could be due to toxic PCDF impurities. 2,3,7,8-Substituted PCDFs have been measured at ng ml-1 levels in 10 pg ml-1 PCDE solutions [98]. 

The cleanup methods used for analyses of PCDEs have been developed simultaneously with the cleanup methods of PCDDs and PCDFs. Since PCDEs may interfere in the GC-MS determination of PCDFs [38, 68], the sample preparation procedures for analyses of PCDDs and PCDFs have been developed aiming to isolate PCDEs from these compounds. 

During extraction and cleanup, concentration of sample extracts can be performed using similar techniques as in the analysis of organochlorines, PCDDs, and PCDFs [1, 111]. Vacuum evaporation and evaporation under nitrogen flow are also typical concentration techniques in PCDE analyses. 

Kuehl et al. [116] have used Celite-545 coated with concentrated sulfuric acid for lipid removal. They eluted fish extract using hexane through this column to a cesium silicate column. Acid treated silica gel is a common material for lipid removal of biota and abiota samples for PCDD/PCDF analyses [111, 112] and has been applied to human adipose tissue extracts for analysis of PCDE [132]. Silica impregnated with concentrated sulfuric acid packed on silica gel in a column has been applied as a second cleanup step [43,120,132]. A multi-silica gel column consisting of layers of silica (silica gel 60), silica impregnated with sulfuric acid (44%), silica, silica impregnated with sodium hydroxide (1 mol 1 ), silica, silica with silver nitrate (10%), and silica has been used for fish extracts by Birkholz et al. [120], The extract was eluted with 2% dichloromethane in hexane and was further purified on Florisil. 

In addition to lipid removal, Florisil column chromatography can be used for chromatographic cleanup and to separate PCDEs from other compounds such as PCBs, PCDDs, and PCDFs. Florisil has been used activated and after deactivation with water. An activated Florisil column has been reported to separate PCDEs... 

Koistinen et al. [58] have applied a Florisil cleanup which uses a partially deactivated (1.25%) Florisil microcolumn (1 g) to separate PCDEs from PCDDs and PCDFs in abiota and biota extracts [33,57,113,114,123-125]. After sulfuric acid cleanup, PCDEs are eluted through a Florisil column together with PCBs using hexane (15 ml). PCDDs and PCDFs are retained in the column and can be eluted with dichloromethane (12 ml). 

Alumina column chromatography has been a common cleanup method in PCDD/PCDF analyses [111, 112], Activated basic aluminum oxide has been used to isolate PCDEs from PCDDs and PCDFs [37, 43, 67], as well as from PCBs [120]. 

Activated alumina (260 °C) column has been used for isolation of PCDEs, PCDDs, and PCDFs from chlorophenol extracts [37,38]. Four fractions were collected from an alumina column (50 g) petroleum ether (400 ml), 5% ethyl ether in petroleum ether (200 ml), 25% ethyl ether in petroleum ether (400 ml), and ethyl ether (400 ml). PCDEs, PCDDs, and PCDFs were determined in the third and fourth fractions after sulfuric acid cleanup. 

A carbon column was initially presented by Jensen and Sundstrom [137] for separation of non-planar and planar PCBs. It is often applied in the cleanup of PCDDs and PCDFs as presented by Smith et al. [138], Kuehl et al. [116] used a carbon-glass column to separate non-planar and planar compounds. They prepared the column by blending AMOCO PX-21 carbon (50 mg) with a shredded glass filter pad (600 mg) in dichloromethane and packed this slurry into a glass column. The sample was fractionated by eluting with dichloromethane (50 ml), dichloromethane benzene (1 1 50 ml), and finally in reverse with toluene (50 ml). Non-planar compounds, loosely bound planar compounds, and tightly bound planar compounds were isolated in these three fractions. PCDEs have been reported to elute in the same fraction as PCDDs and PCDFs on activated carbon [36]. 

Carbon fiber column cleanup has been successfully used for separation of PCDEs from PCDDs and PCDFs in a HPLC system [129]. The separation can be achieved using three solvent system, in which dichloromethanexyclohexane (1 1 v/v) is the first eluent, ethyl acetate benzene (1 1 v/v) the second, and toluene the third. PCDEs are eluted in the first fraction and PCDDs and PCDFs in the third, which is collected using reversed elution. 

The use of isotope-labeled internal standards, which is recommended in the mass spectrometric analysis of PCDDs and PCDFs, to monitor the efficiency of extraction and cleanup has not been common in PCDE analyses due to the limited number of commercially available labeled standards. A D5-labeled pentaCDE has been used as an internal standard in Finnish studies [33,113,114, 123-125,139] and 13Cl2-labeled PCDEs have been used only in few studies [120, 131]. Labeled compounds behave hke the corresponding endogenous compounds during cleanup steps and would be the best internal standards for reliable results in PCDE analysis. 

It is difficult to conclude what the best analytical method is for PCDEs but, based on the literature, microcolumns such as Florisil [57] seem to be effective in separation of PCDEs from PCDDs and PCDFs. Furthermore they are fast and inexpensive. Before PCDEs can be analyzed by MS, however, an additional cleanup step is needed. This has been performed using column chromatography on carbon, since silica gel and neutral alumina microcolumns have not worked well with fish extracts for this purpose [57]. Activated silica and alumina microcolumns, however, could possibly be alternatives for a carbon column. An activated silica column has been used an additional cleanup step after Florisil and carbon column chromatography in the case of mussel extracts [123]. It is not necessary to separate PCBs from PCDEs, since PCBs have been reported not to interfere in the MS analysis of PCDEs [57,130],... 

Reiger and Ballschmiter [43] described a multistep method for PCA analysis in sewage sludge by cyclohexane-isopropanol extraction and cleanup on silica gel column chromatography. Fractionation on silica gel was achieved by eluting with hexane (FI), which desorbed hexachlorobenzene, 4,4 -DDE, PCB, PCDD, and PCDF. PCAs were then desorbed from the column with (90 10) hexane/di-ethyl ether. The recovery of PCAs by this method was 86%. These authors also noted that cleanup chromatography on activated alumina should be avoided because PCAs were either totally or partially destroyed by dehydrochlorination during the adsorption process. 

Liability for possession and production of persistent toxic chemicals, particularly PCDD and PCDF is going to increase. In Ontario the recent promulgation of the "Spills Bill" has placed the liability for immediate cleanup and damages for a spill of toxic chemicals directly on the transporter and producer. This bill will eventually increase the cost of transportation of waste and promote on-site destruction devices. 

Analytical costs can be reduced significantly through the use of composites. In situations where large samples are required (1 m for PCDD/PCDF), four 0.25 m samples can be composited from a surface or an individual room. Composite sampling results of this type are often accepted by regulatory agencies in determining the effectiveness of cleanup. 

Reagent technology adapted from the PCB treatment industry is now being applied to decontaminate concrete surfaces. The technique has been successfully applied in Europe to several spill cleanups involving PCB, dibenzofuran (PCDF) and dibenzodioxin (PCDD). In all cases, the technique met or exceeded the performance of other removal techniques at a significantly lower cost. Table 3 illustrates one example of reagent effectiveness on concrete (Nobile, et al., 1986). 

Purification of the raw extract is always necessary in order to remove interfering compounds and prepare the sample for the chromatographic separation and final instrumental assessment. In many of the cleanup procedures, extracts are treated with concentrated sulfuric acid the planarity and aromaticity of PCDDs and PCDFs are often used to selectively adsorb them on the surface of carbonaceous materials such as activated or graphitized carbon. The raw extract may be spiked with a cleanup standard in order to check the efficiency of purification steps. The instrumental analysis is carried out by HRGC/HRMS. 

Generally, procedures devised for purification of extracts from biological or environmental matrices were eventually adapted to water matrices. For this reason we will describe the most frequently used cleanup procedures to assess PCDDs and PCDFs, with particular attention to those actually employed in water analysis. It should be stressed that contaminant determination at concentrations lower than ng/kg level requires the use of both highly selective cleanup procedures and very specific and sensitive detection systems. 

Despite the extensive cleanup procedures used for PCDDs and PCDFs, compounds with gas chromatographic properties similar to those of the analytes may interfere with the assessment of the latter when LRMS is employed. In some cases, the difference between the molecular ion exact mass of the analyte and that of the interfering species is so small that their resolution is difficult to be achieved even when HRMS is used. 

---