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www.restekcorp.com

RESTEK Advantage

800-356-1688

Improved Resolution of Dioxins

and Furans by GC-High-

Resolution Mass Spectrometry,

Using an Rtx

-Dioxin Capillary Column

By Frank L. Dorman, Ph.D., Director of Technical Development

✔

Improved separation of dioxin and furan congeners, compared to 5% diphenyl columns.

✔

Greater thermal stability than 5% diphenyl columns or high-cyano confirmation columns.

✔

May eliminate confirmation analysis.

Figure 1 —

Chlorine substitution in the basic

dioxin structure creates 136 congeners.

Temperature program:

Time Rate

Temp.

(min.) (ºC/min.) (ºC)

200

10.2 2.9

235

6.9

300

Injector temp.: 270ºC

Flow: 1.2mL/min. (constant pressure)

Gas chromatographic analysis coupled to high-reso-

lution mass spectrometry is a common method of

evaluating environmental samples for dioxins and

furans. Dioxins and furans are monitored due to the

toxicity of congeners that have chlorine substitution

at positions 2, 3, 7, and/or 8 (Figure 1). In the US,

the most common analysis methods for these com-

pounds are USEPA methods 1613 and 8290, but the

analysis is performed similarly in many countries.

The overall goal of the analysis is to accurately quan-

tify the 17 toxic dioxin and furan congeners by sepa-

rating them from 119 other congeners.

In order to achieve the desired separation, most

methods describe an initial analysis on a 5%

diphenyl/95% dimethyl polysiloxane stationary

phase. If 2-, 3-, 7-, and/or 8-substituted congeners

are detected in this analysis, most methods require a

confirmatory analysis on a stationary phase that sep-

arates these congeners from the less toxic con-

geners. While no single column has been universally

agreed upon as the best confirmation column, most

analysts use a high-cyano stationary phase. While

these columns offer better separation of the 2-, 3-,

7-, 8-substituted congeners, analysts using any of

them must contend with poor thermal stability (max-

imum operating temperatures of approximately

250ºC) and poor column lifetimes, compared to 5%

diphenyl-type columns used for the primary analysis.

The difficulty with using the results from 5%

diphenyl columns is that there are several known

coelutions of environmentally-occurring 2-, 3-, 7-, 8-

substituted congeners with less toxic congeners. This

leads to falsely high values for the toxic congeners

on the 5% diphenyl column, and to unnecessary

confirmatory analysis.

An ideal stationary phase for this application would

combine excellent separation, high thermal stability

and, thereby, long column lifetime. With these goals

in mind, Restek has developed the Rtx

-Dioxin col-

umn. The new, proprietary stationary phase, specifi-

cally developed for dioxins/furans analysis, is stable

to temperatures above 425ºC. When coated onto

high-temperature fused silica tubing, the thermal

limit of the column is a function of the polyimide

outer coating: 380ºC. Not only is this is a major

improvement over the thermal stability of high-cyano

phases, it is an improvement over the capabilities of

5% diphenyl phases as well.

An Rtx

-Dioxin column better separates the dioxin

and furan congeners, compared to 5% diphenyl

columns. Most analysts experienced with dioxin and

furan separations are familiar with the 4-peak tetra-

chlorodibenzodioxin mass pattern from a 5%

diphenyl column, as shown in Figure 2A. An Rtx

Dioxin column separates all five components in the

resolution check mixture for this mass window—a

significant improvement (Figure 2B). Note that

1,2,3,7- TCDD and 1,2,3,8-TCDD are tentatively

identified; reference materials for individual con-

geners are not available.

Because few of the individual dioxin and furan con-

geners are available as reference materials, analysis

of fly ash extracts is the accepted test of whether a

column resolves the toxic congeners from the non-

toxic congeners. In analyses of three fly ash extracts

used in a recent international round-robin study,

data from an Rtx

-Dioxin column agreed to within

±10% of the “true” values for all 2-, 3-, 7-, 8-substi-

tuted congeners, except for one penta- and one

hexa-furan. This also is a significant improvement

over 5% diphenyl column performance for the pri-

mary analysis. Table 1 (page 7) summarizes data for

2,3,7,8-tetrachlorodibenzofuran from an Rtx

Dioxin column, a 5% diphenyl column, and a high-

cyano column, compared to median and mean from

an international round-robin study. Excellent agree-

ment between the median and the mean, and

between the Rtx

-Dioxin column and the study data,

gives confidence in the proximity to the “true” value.

Further work toward optimizing flow and oven tem-

perature is in progress, to determine if the Rtx

Dioxin column could eliminate the need for high-

cyano phases for confirmation.

In summary, the new Rtx

-Dioxin column is a signif-

icant improvement over 5% diphenyl columns com-

monly used in the primary analysis for dioxins and

Figure 2 —

Rtx

-Dioxin column separates all five components in the resolution check mixture.

Chromatography courtesy of Karen MacPherson and Eric Reiner, Ontario Ministry of the Environment, Etobicoke, ON, Canada.

Conditions

Instrument: Micromass Altima high resolution GC/MS

Column: Rtx

-Dioxin, 40m, 0.18mm ID, 0.10µm (cat.# 10756)

Initial temp.: 130ºC

O 1

General structure for dioxin congeners

3Å by 8Å molecule fits PAH receptors,

makes 2,3,7,8-tetrachlorodibenzodioxin

especially toxic

Continued on page 7

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2A) Rtx-5

Column

2B) Rtx-5

Dioxin Column

TCDD-resolution mixture