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Internal Quality Assurance Requirements for the Analysis of Dioxins in Environmental Samples

Section 4: Sample Preparation and Processing

  1. All glassware should be washed thoroughly with lab-grade detergent and high purity solvents. Following this, analysis of a composite glassware proof rinse (hexane and dichloromethane) sample for PCDDs/PCDFs and potential interferences is recommended.

  2. All solvents and reagents should be verified to be free of contamination that might interfere with the analysis of target compounds.

  3. Solid samples should be homogenized to ensure that any aliquot used for analysis is representative of the whole sample. Splitting of aqueous samples is not recommended.

  4. Sample size is dictated by the method in use and to some extent it is selected on the basis of desired detection limits. Recommended sample size, final volume, and achievable detection limits for various matrices are provided in Table 1.

  5. Extraction and cleanup procedures for use with various matrices can be selected by the laboratory. The lab must demonstrate, however, that these procedures can yield acceptable results for accuracy and surrogate recovery (Section 3).

  6. If possible, samples expected to be similar in analyte concentration range should be processed together in order to minimize the possibility of cross-contamination.

  7. Pertinent sample processing details should be recorded and made available for review if required.

  8. Unused portions of samples and sample extracts must be preserved in a refrigerator or freezer for tissue samples (Subsection 2.3c) for possible reanalysis if required. Samples and extracts must not be discarded without the permission of the client.

  9. Before processing, each sample must be spiked with known amounts of the carbon-13-labelled dioxin/furan surrogates shown in Table 2. The degree of analyte loss during sample workup is reflected in the percentage recovery of the spiked surrogates.

    If any surrogate recovery is outside the range indicated in Table 2, the sample should be reprocessed and reanalyzed, if possible. These ranges reflect the practical experiences of several government and commercial laboratories.

    Although individual surrogate recoveries as low as 30 or 40% will be considered acceptable, consistently low or highly variable recoveries may indicate that one or more of the sample processing procedures, or the GC/MS instrumentation, is not being effectively controlled.

    Method performance tests (see Section 3) should be repeated as the starting point of any investigation, and all investigative work should be fully documented.

  10. A method blank consisting of blank media (e.g., reagent water, filter, solvents) spiked with surrogates should be processed along with each batch of up to 10 test samples to demonstrate freedom from PCDD/PCDF cross-contamination and freedom from contaminants that would interfere with PCDD/PCDF analysis.

  11. One sample in every 10 test samples should be processed and analyzed in duplicate (supplied by laboratory QA/QC personnel as blind samples if possible) to assess reproducibility. Duplicate sample analysis can be replaced or supplemented by the analysis of a control sample (certified or uncertified reference material whose PCDD/PCDF content is well characterized). Analytical precision can then be assessed on a continuing basis. Control samples should also be submitted by QA/QC personnel as blind samples if possible.
Table 1: Recommended Sample Size, Final Volume, and Achievable Method Detection Limits for Various Matrices
 TissueSediment, Soil, Sludge, AshPulp Mill EffluentPulpDrinking WaterOilAmbient Air
Sample Size10 g
(wet)
5 g
(dry)
1 L12 g
(dry)
12 L1 g1000 m3
Final
Volume
(μL)
20202020202020
Target
Detection
Limit
LRMS
(HRMS)
pg/g
LRMS
(HRMS)
pg/g
LRMS
(HRMS)
pg/L
LRMS
(HRMS)
pg/g
LRMS
(HRMS)
pg/L
LRMS
(HRMS)
pg/g
LRMS
(HRMS)
pg/m3
T4CDD/F2
(0.5)
12
(1)
60
(5)
5
(0.4)
5
(0.4)
60
(5)
0.06
(0.005)
P5CDD/F5
(1)
24
(2)
120
(10)
10
(0.8)
10
(0.8)
120
(10)
0.12
(0.01)
H6CDD/F5
(1)
24
(2)
120
(10)
10
(0.8)
10
(0.8)
120
(10)
0.12
(0.01)
H7CDD/F15
(1.5)
36
(3)
180
(15)
15
(1.2)
15
(1.2)
180
(15)
0.18
(0.015)
OCDD/F20
(2.0)
48
(4)
240
(24)
20
(1.6)
20
(1.6)
240
(20)
0.24
(0.02)

Note : These method detection limit (MDL) values are bases on assumption of low processing losses (high recovery) and final extracts that are free from significant levels of matrix background interference. - (March 1992)

Table 2: Suggested Surrogate Standard Spike and Recovery Criteria
Surrogate StandardAmount Spiked (ng/sample)Acceptable Recovery(%)
LRMSHRMSTissueAll Other Matrices
13C12-2,3,7,8-TCDD2140 to 12030 to 130
13C12-2,3,7,8-TCDF2140 to 12030 to 130
13C12-1,2,3,7,8-P5CDD4140 to 12030 to 130
13C12-1,2,3,7,8-P5CDF*0140 to 12030 to 130
13C12-1,2,3,6,7,8-H6CDD4140 to 12030 to 130
13C12-1,2,3,4,7,8-H6CDF*0140 to 12030 to 130
13C12-1,2,3,4,6,7,8-H7CDD4140 to 12030 to 130
13C12-1,2,3,4,6,7,8-H7CDF*0140 to 12030 to 130
13C12-OCDD8240 to 12030 to 130
* Optional but desirable - (March 1992)
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