Detecting Dioxin and Furans in Flyash Using a Gas Chromatography-Based Electronic Nose

The need to measure dioxin/furans in real or near real time in flyash matrices from incinerators in order to meet the Environmental Agency’s (EA) Standards has been identified by a Japanese Company.  Flyash samples were sent to Electronic Sensor Technology for evaluation using a GC/SAW as part of a preliminary evaluation of promising technologies such as fast chromatography.

This article presents a description of the GC/SAW measurement system, sample analysis procedures, calibration procedures, values obtained and minimum detection levels.

Evaluation Protocol

Unknown concentrations of furans and dioxins were contained in the flyash samples. Flyash samples were first extracted using a solvent mixture of methanol and hexane. After centrifuging to separate solids samples of the hexane were extracted into vials.

Microliter quantities of the sample extract were injected into an open-tubular desorber attached to the inlet of a GC/SAW vapor analyzer to carry out the evaluation. For each sample, the concentration of individual furans and dioxins were recorded and referenced to calibration standards of similar concentration.

The fundamental steps of the extraction procedure are displayed in the following pictures. Special attempt was not made to perform any type of clean up procedures such as silica column filtering or acid washing in this preliminary evaluation.

Steps used in solvent extraction of flyash samples.

Figure 1. Steps used in solvent extraction of flyash samples.

Description of GC/SAW Technology

Electronic Sensor Technology manufactures fast chromatographs in two different models. Surface acoustic wave (SAW) integrating detectors are used by both these models. The model 4100 features a handheld GC and sampling preconcentrator fixed to a support case with the help of a 6 foot umbilical cable.

The model 7100 is designed for portable or laboratory use and the vapor preconcentrator and chromatograph are integrated into a benchtop case. Both systems use an RS232 connection to interface with a Pentium laptop running proprietary control software. A complete range of post processing analysis and communications software is provided by links to features inherent in Microsoft Office and Windows 95.

Handheld Model 4100 GC/SAW vapor Analyzer.

Figure 2. Handheld Model 4100 GC/SAW vapor Analyzer.

Benchtop Model 7100 GC/SAW Vapor Analyzer.

Figure 3. Benchtop Model 7100 GC/SAW Vapor Analyzer.

It is possible to configure these instruments to rapidly analyze a wide variety of volatile and semi-volatile compounds using the patented integrating SAW detector. The GC/SAW typically can speciate and quantify furans and dioxins at the picogram level within a 10 second chromatogram using a temperature ramped DB-5 column.

A 4100 system was used together with a model 3100 open-tubular desorber fixed to the inlet of the system in order to evaluate the Japanese Company samples. Liquid injections are thermally vaporized by this accessory, and the GC/SAW measurement system is then used to sample these vapors.

Block diagram of GC/SAW vapor measurement system.

Figure 4. Block diagram of GC/SAW vapor measurement system.

Sample Preparation and Injection

Two additional dilutions were carried out and standard calibration solutions were used in hexane. A 50 to 1 dilution was prepared by injecting 20 µliters of stock solution into 1 milliliter of hexane. A 1000 to 1 dilution was prepared by injecting 1 µliter of stock into 1 milliliter of hexane.

Attachment of Open-Tubular sample desorber attached in inlet of GC/SAW Vapor Analyzer.

Figure 5. Attachment of Open-Tubular sample desorber attached in inlet of GC/SAW Vapor Analyzer.

A 10 µliter glass syringe was used to inject all samples extracts and calibration standards. The sample injection and measurement was carried out in two steps:

Step 1 - 1-10 µliters of sample is injected into middle of glass wool wick within a six inch long desorbtion tube fixed to the inlet of the GC/SAW vapor analyzer.

Step 2 - A desorbtion tube heater (280 °C) is placed over the glass desorbtion tube and the operator initiates vapor sampling (measurement cycle) by the GC/SAW.

The remainder of the measurement process was automatic and additional operator actions were not required besides annotating notes which identified the actions being taken or other related sample identification information.

Calibration Standards

Two calibration standards were purchased from AccuStandard Inc. (25 Science Park, New Haven CT 06511). Each kit comprised of five furans (M8280B) and five dioxins (M8280A) as required by EPA 8280 Method. The concentration of each analyte within the mixture was 5.0 nanograms per µliter of toluene. A 10-to-1 dilution was used as a calibration level of 0.5 ng/µliter. The following table provides the full analyte specifications as well as their TEQ rating.

Analyte C CAS No. TEQ*
2,3,7,8-tetrachlorodibenzo-p-dioxin 51207-31-9 1.00
1,2,3,7,8-Pentachlorodibenzo-p-dioxin 40321-76-4 0.50
1,2,3,4,7,8-Hexachlorodibenzo-p-dioxin 39227-28-6 0.10
1,2,3,4,6,7,8-Heptachlorodibenzo-p-dioxin 35822-46-9 0.01
Octachlorodibenzodioxin 3268-87-9 0.001
2,3,7,8-Tetrachlorodibenzofuran 1746-01-6 0.1
1,2,3,7,8-Pentachlorodibenzofuran 40321-76-4 0.05
1,2,3,4,7,8-Hexachlorodibenzofuran 55684-94-1 0.10
1,2,3,4,6,7,8-Heptachlorodibenzofuran 35822-46-9 0.01
Octachlorodibenzofuran 39001-01-0 0.001

Figure 6. Analyte Standards Used in Sample Evaluation.

No other standards were available for comparison with the Japanese Company samples. Hence, in this article any quantification of isomers lower than tetra is based upon an estimated response factor and not upon a calibration standard.

Selection of GC Method

The GC/SAW vapor analyzer can perform dioxin analysis and quantification at slower speeds such as 20, 50, or more seconds and also within a 10 second chromatogram. There is a trade-off in resolving power with improved resolution being achieved at longer and slower chromatograms (Figure 5).

Resolution vs speed displayed for 18 °C / sec, 7 °C /sec, and 3 °C /sec column ramping rates.

Figure 7. Resolution vs speed displayed for 18 °C / sec, 7 °C /sec, and 3 °C /sec column ramping rates.

A 20 second chromatogram was achieved with a linear increase of column temperature from 60 °C to 200 °C within 20 seconds for quantification of the Japanese Company sample. The complete GC method was constructed using a graphical method as shown in Figure 7. The GC method steps are developed by dragging placeholders from the vertical toolbar into a horizontal line at the bottom of the dialog screen of Figure 7.

Law Enforcement Applications and Requirements

The GC method steps are developed by dragging placeholders from the vertical Figure 6. Each placeholder corresponds to a step or action with parameters set by the operator. This method starts with a 30 second sample (preconcentrate) time, move valve to inject position, inject sample, ramping of the column temperature and taking of data for 20 seconds following the injection.

The method ends with the activation of a 15 second bake cycle to ‘clean’ the crystal detector and the column temperature is returned to 60 °C.

GC Method dialog screen showing method used to evaluate MSE samples.

Figure 8. GC Method dialog screen showing method used to evaluate MSE samples.

Analysis Time Requirements

In automatic mode, it is essential for each analysis to contain the following basic steps with their minimum values. The values used for the Japanese Company samples are shown for comparison.

  Minimum (Sec) BHK Sample (Sec)
Inject Sample into Desorber 2 5
Preconcentrate Vapor Sample 15 30
GC Analyze 10 20
Recovery of Column & Detector 15 30
Total Cycle Time 42 85

 

Calibration Procedures

Instrument calibration involved injecting standards of known concentration. A response factor specific to each analyte was produced by division of SAW detector ‘counts’ by the concentration. The response factor (Hz/pg), retention time, peak name, and percentage variation allowed in retention time (Percent spread) were entered into a calibration table and this completed calibration (Single point). The other features available within the software include multiple point calibration and interpolation. Proper calibration was regularly checked by injecting dioxin or furan mixtures of known concentration.

Operator entry of retention time windows, peak labels, and response factors completes system software calibration.

Figure 9. Operator entry of retention time windows, peak labels, and response factors completes system software calibration.

Chromatogram of furan standards after entry of proper response factors and retention times into peak identification file.

Figure 10. Chromatogram of furan standards after entry of proper response factors and retention times into peak identification file.

Minimum Detection Limit

For instruments’ detection limits, the GC/SAW is determined by signal to noise, and the noise and detected peak amplitudes acquired with a blank injection of pure hexane into the GC/SAW are specified to be less than 1 picogram. Operating the system at a signal to noise ratio of 3 would then provide a 3 picogram minimum detection level, and a minimum detection level of 10 picograms will be provided while operating at a higher signal-to-noise ratio of 10.

Blank injection chromatogram of 10 uliters of hexane compared with 2 uliter dioxin standard (0.5 ng/uliter).

Figure 10. Blank injection chromatogram of 10 uliters of hexane compared with 2 uliter dioxin standard (0.5 ng/uliter).

Multiplication of the standard deviation of seven replicate measurements by 3.14 helped evaluate EPA Method detection limits. Method detection limits differed between 10 and 30 picograms using this method with 10 picogram injections. RSD values for manual injections were typically 20% or less.

Quality Control/Assurance Procedures

ISO9000 procedures are utilized by Electronic Sensor Technology throughout the manufacture and testing of all GC/SAW instruments. The company also maintains an on-site calibration laboratory where EPA quality control and quality assurance methods for all performance tests are practiced.

The laboratory director logged and maintained samples obtained from the Japanese Company. The laboratory operators controlled the quality of calibration standards throughout the testing of the Japanese Company samples.

The company server was used to log and archive all GC data taken on the Japanese Company samples. Each data record was labeled and time-stamped based on the laboratory’s Quality Assurance procedures of the laboratory.

The EST Quality team tests and certifies the performance of each and every system before it is delivered the customer

Figure 11. The EST Quality team tests and certifies the performance of each and every system before it is delivered the customer

Evaluation Results

At this time, only preliminary results on isolated samples have been done and a comprehensive evaluation of the extraction method has not been performed. Extract chromatograms were compared with chromatograms attained from standard solutions. An example of a 4 microliter flyash extract chromatogram is shown in Figure 12.

The three background traces correspond to (top to bottom) a standard mix of furans (1 nanogram per isomer), a mix of dioxins (1 nanogram per isomer), and a standard mix of furans and dioxins (0.5 ng per isomer).

Comparison with individual and mixed dioxin furan standards

Figure 12. Comparison with individual and mixed dioxin furan standards

The amount of each isomer detected as well as its recorded retention time is displayed by the inset table. The following table summarizes the measurement results as total di, tri, tetra, penta, hexa, hepta, and octa dioxins and furans detected. Identification was based upon a retention time which matched the standard’s retention time within 5%, and quantification was based upon response factors as determined from calibration standards.

  Measured pg Flyash ng/g
Di/Tri DF 599 48
Tetra DF 518 41
Penta DF 482 39
Hexa DF 947 76
Hepta DF 871 70
Octa DF 1227 98
Total DF 4644 372

 

Quantities of each isomer detected in this sample ranged from 500 pg to 1.3 ng. Since the 4 microliter sample represented only 1/80 of the total amount extracted, these results indicate the sample contained 40 to 104 ng/g of furan or dioxin isomers.

The fastest analysis time available is represented by ten second chromatograms. A useful detection of compounds can be achieved even though peak separation is not complete. Slowing the column temperature program of the GC method helped obtain improved resolution.

An example performed on the same extract but with a slower temperature ramp is shown in Figure 13. For comparison, a mixed furan/dioxin standard (1 nanogram per isomer) is shown in the background of this figure. As expected, the peak separation is significantly improved in a 20 second chromatogram.

Comparison with mixed standards

Figure 13. Comparison with mixed standards

Quantitatively, the amount of furan/dioxin isomers detected was quite similar. In this case, the concentrations again ranged from 500 pg to 2 ng for the isomers detected.

A concentration of furans and dioxins in the flyash sample from 40 to 160 ng/g was predicted. The total amount of dioxins furans was approximately 500 ng/g.

  Measured pg Flyash ng/g
Di/Tri DF 123 10
Tetra DF 1352 108
Penta DF 944 76
Hexa DF 625 50
Hepta DF 1700 136
Octa DF 1290 103
Total DF 6034 483

 

Comparison with Laboratory Results

Not all flyash samples gave the same result as indicated by the result shown in Figure 14. A 150 second analysis time was produced by a very slow temperature ramp and the resolution achieved illustrates perhaps the best separation which can be attained with the length of column used.

The amount of furan/ dioxin isomers detected in this flyash sample was relatively low spanning a range of 100 to 300 picograms. Thus, this extract had a normalized concentration of from 8 to 24 ng/g. For comparison, a mixed standard (1 nanogram per isomer) is shown in the background.

Increased resolution with slower ramp and lower temperature.

Figure 14. Increased resolution with slower ramp and lower temperature.

  Measured pg Flyash ng/g
Tetra DF 171 14
Penta DF - -
Hexa DF 282 23
Hepta DF 123 10
Octa DF - -
Total DF 576 46

 

Japanese Company supplied independent laboratory results of GC/MS analysis upon the flyash samples; a sample chromatogram as well as the analytical results are shown in Figure 15. The concentration of furan/dioxin isomers is detected ranged from 96 to as high as 1100 ng/g.

These results seem to be quiet similar to that reported with the GC/SAW; however, the analysis time is approximately 30 minutes. A much longer column was used in this case and the resolution is greatly improved.

Laboratory results supplied by BHK

Figure 15. Laboratory results supplied by BHK

Comparing the average of GC/ SAW measurements with the Japanese Company laboratory results provides an estimate of the recovery of the simple extraction method as follows.

  Measured pg Laboratory ng/g Estimated Recovery %
Di/Tri DF 29 - -
Tetra DF 75 96 78%
Penta DF 57 182 31%
Hexa DF 63 271 23%
Hepta DF 103 210 49%
Octa DF 101 217 46%
Total DF 427 1100 39%

 

Recommendations

The simple extraction method used in these preliminary evaluations was designed to provide an initial field method for rapidly screening flyash samples. It is necessary to perform accurate recovery and MDL testing on this method. A Soxhlet extraction will be used as a baseline measurement for comparison. To accomplish this, the Soxhlet extraction apparatus pictured in Figure 16 was purchased and is available.

Soxhlet extraction apparatus.

Figure 16. Soxhlet extraction apparatus.

The preliminary results proved the existence of a significant amount of background compounds which might produce false alarms. An application of some cleanup method is needed in order to reduce this probability. In the future, an evaluation of solid phase extraction (SPE) and solid phase micro extraction SPME as a means for filtering and reducing the number of compounds which might interfere with dioxin/furan detection will be tested.

This information has been sourced, reviewed and adapted from materials provided by Electronic Sensor Technology.

For more information on this source, please visit Electronic Sensor Technology.

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