4.19  Determination of persistent organic pollutants (pesticides and PCBs)

4.19.1    Principle

This method covers the following groups of components:

Chlororganic pesticides: 

Polychlorinated biphenyls,

These components may be determined in air samples, described in chapter, 3.13. Filter and PUF plugs are extracted separately with a hexane/diethylether 9:1 mixture in a soxhlet extractor. The extracts are concentrated and then cleaned by using adsorption chromatography (silica). After the concentration to the appropriate volume and addition of the recovery standard, the components are separated and quantified by using gas chromatography combined with mass spectrometry (MS).


4.19.2  Materials and equipment

4.19.2.1  Glassware

4.19.2.2  Other equipment

4.19.2.3  Analytical equipment and accessories

4.19.2.4  Chemicals and gases

Organic solvents

All solvents, except diethyl ether can be used without cleaning.

Inorganic chemicals, adsorbents and various accessories

Gases


4.19.3  Cleaning and pre-treatment

4.19.3.1  Cleaning of the sampler

See chapter 3.16.3.1

4.19.3.2  Cleaning of PUF-plugs

See chapter 3.16.3.2

4.19.3.3  Cleaning of glass equipment

See chapter 3.16.3.3

4.19.3.4  Cleaning of other equipment

See chapter 3.16.3.4

4.19.3.5  Check and pre-treatment of solvents and chemicals

All solvents must be of "pesticide grade" or equivalent quality. The solvent must give chromatograms free from interfering peaks (S/N < 3) in the elution range from a-HCH to OCN. Performing a complete method blank test may also check this.

4.19.3.6  Cleaning of diethyl ether

The diethyl ether must be cleaned because it contains an inhibitor to prevent formation of peroxides: 250 ml diethyl ether is filtered using a chromatography column (diam. 20 mm) packed with 20 cm basic aluminiumoxide. Diethyl ether without inhibitor may, with time, form peroxides, which represents an explosion hazard, especially by pre-concentrating samples using a rotary evaporator. Therefore not more than an amount sufficient for one month’s consumption is cleaned. The solvent is stored in the dark at a temperature <5°C.

4.19.3.7  Pre-treatment of sodium sulphate

Sodium sulphate is put in a porcelain dish and heated to 600°C for 8 hours in an oven. Let cool to room temperature in a desiccator. Store in a stoppered glass bottle. The bottle must be labelled with the expiry date of the sodium sulphate. Maximum storage time is one month. After the expiry date the sodium sulphate is discarded.

4.19.3.8  Pre-treatment of silica

Ca. 400 g silica is put in a porcelain dish and heated at 600°C for at least 8 hours in an oven. After heating the silica is left to cool in a desiccator and shall not be used before it has reached room temperature. The silica is stored in a glass bottle with a glass stopper. The bottle must be labelled with the expiry date of the silica. Maximum storage time is one month

4.19.3.9  Cleaning of soxhlet thimbles

Soxhlet thimbles are cleaned by soxhlet extraction using n-hexane for 8 hours. The thimbles are dried in a fume hood at room temperature overnight and wrapped individually in aluminium foil.

4.19.3.10  Cleaning of cotton wool

Cotton wool is soxhlet extracted with 500 ml – 2500 ml (depending of amount of cotton) n-hexane or dichloromethane for 24 hours. The cotton is dried in a vacuum desiccator at 60°C.


4.19.4  Gas cleaning

4.19.4.1  Gas bottle exchange

  1. Gas bottles must be replaced when the pressure approach 20 bar. The bottle pressure should never be lower than 15 bar.
  2. Before exchanging GC-carrier gas bottles, set GC-oven temperature below 50°C.
  3. Bottle exchange should be performed rapidly. Collect the new bottle before disconnecting the old one.
  4. If only one spare bottle is in the storage room, order a new batch.
  5. Flush the bottle valve on the new bottle twice (ear protection) before connecting the pressure reduction valve.
  6. Connect pressure reduction valve firmly and open it.
  7. Check for leaks with leak detector (Ion Sciences: Gas Check B4 or Supelco: Snoop leak detector).
  8. Mount valve protection cap on the empty bottle and transport the bottle to the storage room.
  9. All bottles must be secured against falling over.


4.19.5  Special procedures

Helium GC carrier gas cleaning:

  1. Chrompack Gas Clean Oxygen Filter (with charcoal) and Chrompack Gas Clean Moisture Filter are connected in series after the pressure reduction valve. Exchange the units after exchanging 5 bottles or once a year.
  2. Two metal cartridges are mounted in series on the gas line before each GC inlet. The first is filled with active carbon, the second is filled with molecular sieves. Exchange adsorbents each 3 years and after irregularities (empty gas bottle).

Nitrogen used for final sample blow-down/pre-concentration is cleaned using a metal cartridge filled with active carbon. Exchange adsorbent when exchanging the gas bottle.


4.19.6   Treatment of adsorbents

Chrompack filters are discarded after use.

Re-activation of molecular sieves: Fill molecular sieves in a metal cartridge and activate at 300°C (3 h) in an oven, flushing the cartridge with 20 ml/min. pre-filtered helium.

Active carbon is discarded after use.


4.19.7  Sample preparation

Sample pre-treatment, e.g. weighing of filters and extraction, is discussed in chapter 3.17.5

4.19.7.1  Principle

Small amounts of interfering substances may be removed from the sample with one single method. Depending on the components to be measured different cleaning procedures can be selected; treatment of the extract with sulphuric acid for acid-stable components, or with alkaline hydrolysis for acid-labile substances. Both treatments are followed by adsorption chromatography. When both acid-stable and -labile substances are measured and their relative amounts unknown, the concentrate should be divided into two equal parts before further treatment. After cleaning, the sample should be concentrated once more followed by addition of a recovery standard (TCN or OCN) in order to determine the amount of internal standard before the sample is ready for analysis by GC/MS.

4.19.7.2  Sulphuric acid treatment of acid-stable substances

The concentrated sample (0.5–1 ml volume) is transferred to a 10–15 ml centrifuge tube, 8-10 ml conc. sulphuric acid added, and placed in a rack until the next day. The hexane fraction is transferred to a new centrifuge tube and 1 ml MilliQ water added drop by drop. The water phase is removed and the hexane phase dried with ½ teaspoon Na2SO4.

4.19.7.3  Alkaline hydrolysis of acid-labile substances

To 1 ml concentrated sample is added a solution of 0.2 g KOH in 1 ml ethanol and 0.1 ml MilliQ water. The mix is heated on a water bath at 50°C for 30 min. Add 5 ml MilliQ water, shake the sample, separate by a centrifuge, concentrate the organic phase by evaporation, and add a recovery standard before the GS/MS analysis. If the hydrolysed sample is strongly coloured after evaporation, the sample may be cleaned using silica-chromatography (next Section).

4.19.7.4  Silica chromatography

Cotton is put at the bottom end of a glass column (20 cm x 1.5 cm) and the column is filled with 4 g silica activated at 600°C. A layer of 1g Na2SO4 is added on top. Use a vibrator when filling. The column is washed with 30 ml 10 % diethyl ether in hexane. The column should never be allowed to run dry! The sample (0.5–1 ml volume) is transferred to the column after washing, and the sample container rinsed with additionally 2–3 ml diethyl ether/hexane mixture which is transferred to the column. Elute the column with 30 ml of diethyl ether/hexane mixture and the sample is collected in a TurboVap glass with 20 ml nonane as a keeper. The sample volume is carefully reduced with the TurboVap until 0.5 ml, and transferred to a sample glass with conical insert. The TurboVap vessel is rinsed three times with 0.15 ml hexane, and the liquid volumes added to the sample. The sample volume is reduced to the desired volume (0.1–0.5 ml) in a slow nitrogen stream. Recovery standard is added and the sample vessel sealed with a screw cap or a crimp cap with auto-injector septum. This sample is now ready for a GS/MS analysis. If the sample is not analysed at once (same day) it must be kept dark in a freezer at -20°C. If the sample is stored for more than 1 month, this should be noted in the data report.

4.19.7.5  If the sample contains silica particles

Flush a pasteur pipette with a piece of cotton wool at the bottom with hexane. Pass the sample through the pipette and collect the sample. Wash with a small amount hexane before volume reduction to 0.1–0.5 ml.


4.19.8  Standards

A standard mixture containing known concentrations of components of interest is used for identification/quantification. Standard components should preferably be provided as crystalline solids with purity better than 99 per cent. If they can be provided in solutions only, the solutions must be certified or calibrated against certified standards from an international standardisation bureau as NIST or BCR.

Concentrated standards containing only one, or a small number of components are prepared and checked by GC/MS in full scan mode before further use. If impurities are discovered, their concentrations should correspond to less than 3% of the main components area. The other standards; calibration standards, internal standards, and recovery standards, are all prepared as different diluted mixtures based on the concentrated standards.

Weighing the proper amounts of crystalline substance of the standards should be performed with great care. Use disposable gloves and a mask. Weighing ships and spatulas should be rinsed in toluene and hexane before use and (air) dried. The tare of the ship is set to zero and the standard component transferred to the ship by a thin spatula in an amount as close to the estimated one as possible. The spatula must be rinsed and dried between each weighing in order to avoid contamination. When all components have been weighed, the content of the ship is transferred to a volumetric flask with n-hexane or iso-octane. The flask is filled with n-hexane or iso-octane to the correct volume and placed in an ultrasonic bath until all solids are dissolved. The concentrated standard is transferred to a flask equipped with screw cap and a teflon seal.

The weighed amounts and standard concentrations, a standard number, and the weight of the standard flask must be recorded in the standards logbook. The concentrated standards should be kept in a refrigerator at 4°C. When preparing the more diluted solutions, the concentrated standards should be removed from the fridge two hours before use. The concentrated standard should be sonicated for 5 min. in order to dissolve any solid substance. This is of particular importance for heavily soluble components e.g. b-HCH. In order to maintain a high accuracy in the final concentration, the dilution should be less than 1:100 in all steps, i.e. at most 100 ml in a 10 ml graduated flask. When more diluted solutions are needed, secondary standards should be prepared. The flask containing the concentrated standard should be weighed before and after removing a volume for dilution, and the weights recorded in the logbook.

Diluted solutions are prepared by using volumetric flasks and pipettes or syringes. Disposable pipettes are preferred to syringes used for different standards because of a possibility for contamination. The entire dilution process must be checked by weighing.

4.19.8.1  Concentrated standard

The following components may be included in a set of standards:

Pesticides

Abbreviation

Polychlorinated biphenyls

IUPAC no.

Hexachlorobenzene

HCB

2,2',5-TriCB

  18

a-Hexachlorocyclohexane

a-HCH

2,4,4'-TriCB

  28

b-Hexachlorocyclohexane

b-HCH

2,4',5-TriCB

  31

 

 

2’,3,4-TriCB

  33

 

 

3,4,4’-TriCB

  37

g- Hexachlorocyclohexane

g-HCH

2,2',4,4'-TetCB

  47

Trifluralin

Trifl

2,2',5,5'-TetCB

  52

Chlordene

CDen

2,3,4,4'-TetCB

  60

Heptachlor

HepC

2,3',4,4'-TetCB

  66

Oxy-Chlordane

oxy-CD

2,4,4',5-TetCB

  74

Cis-Heptachlorepoxide

cis-Hepex

2,2',4,4',5-PenCB

  99

Trans-Chlordane

tr-CD

2,2',4,5,5'-PenCB

101

Cis- Chlordane

cis-CD

2,3,3',4,4'-PenCB

105

trans-Nonachlor

tr-NO

2,3,4,4',5-PenCB

114

cis-Nonachlor

cis-NO

2,3',4,4',5-PenCB

118

Pesticides

Abbreviation

Polychlorinated biphenyls

IUPAC no.

 

 

2’,3,3’,4,5-PenCB

122

a-Endosulfan

a-Endo

2',3,4,4',5-PenCB

123

Dieldrin

Diel

2,2',3,3',4,4'-HexCB

128

Aldrin

Ald

2,2',3,4,4',5'-HexCB

138

 

 

2,2’,3,4,5,5’-HexCBC

141

Endrin

End

2,2',3,4',5',6-HexCB

149

o,p’-Dichlorodiphenyldichloroethane

op-DDD

2,2',4,4',5,5'-HexCB

153

p,p'-Dichlorodiphenyldichloroethane

pp-DDD

2,3,3',4,4',5-HexCB

156

o,p'-Dichlorodiphenyldichloroethylene

op-DDE

2,3,3',4,4',5'-HexCB

157

p,p'- Dichlorodiphenyldichloroethylene

pp-DDE

2,3',4,4',5,5'-HexCB

167

 

 

 

 

Pesticides

Abbreviation

Polychlorinated biphenyls

IUPAC no.

o,p'-Diklorodifenyltrikloroehtane

op-DDT

2,2',3,3',4,4',5-HepCB

170

p,p'-Diklorodifenyltrikloroethane

pp-DDT

2,2',3,4,4',5,5'-HepCB

180

 

 

2,2’,3,4,4’,5’,6-HepCB

183

 

 

2,2',3,4',5,5',6-HepCB

187

 

 

2,3,3',4,4',5,5'-HepCB

189

 

 

2,2’,3,3’,4,4’,5,5’-OctCB

194

 

 

2,2’,3,3’,4,4’,5,5’,6-NonCB

206

 

 

2,2’,3,3’,4,4’,5,5’,6,6’-DecaCB

209

 

 

 

 

Internal standard pesticides

Abbreviation

Internal standards PCB

IUPAC no.

13C-p,p’- Dichlorodiphenyldichloroethylene

13C-p,p’-DDE

13C-2,4,4'-Trichlorobiphenyl

13C-PCB-28

13C-g-Heksachlorosyklohexane

13C-2D-g-HCH

13C-2,2',5,5'-Tetrachlorobiphenyl

13C-PCB-52

13C-a-Heksachlorosyklohexane

13C-a-HCH

13C-2,2',4,5,5'-Pentachlorobiphenyl

13C-PCB-101

 

 

13C-2,3',4,4',5-Pentachlorobiphenyl

13C-PCB-118

 

 

13C-2,2',4,4',5,5'-Hexachlorobiphenyl

13C-PCB-153

13C4-Aldrin

 

 

 

13C4-Dieldrin

 

 

 

13C4-Heptachlor

 

 

 

13C-Hexachlorobenzene

13C-HCB

13C-2,2',3,4,4',5,5'-Heptachlorobiphenyl

13C-PCB-180

Recovery standards

 

 

 

1,2,3,4-Tetrachloronaphtalene

TCN

 

 

Octachloronaphtalene

OCN

 

 


4.19.8.2  Calibration standard

A standard for GC/MS should have concentrations similar to the expected concentrations of the components to be measured

4.19.8.3  Internal standard (ISTD)

The internal standard may be a solution with pesticides and/or PCBs which contains labelled isotopes.

4.19.8.4  Recovery standard (RSTD)

A solution containing tetrachloronaphtalene is used for this purpose. The recovery standard is added to the sample as the last step before quantification.

4.19.8.5  Standard addition

Amounts of standards added before extraction (ISTD) and after the sample preparation (RSTD) should be similar to the expected concentrations in the sample.

4.19.8.6  Quality assurance of standards

The purity of the standards is checked in the GC/MS full scan mode before acceptance. If impurities are discovered in the concentrated standard, the amounts as expressed by its area in the chromatogram must be less than 3 % of the main component’s area. When concentrated standards are stored dark in a refrigerator, their stability will be very good. In order to document the stability, the full scan mode check is repeated at intervals not longer than 3 years. Normally this will be carried out when preparing a working standard after 2 years. The working standards are stored dark in a refrigerator, but new standards should be prepared every two years at most. Working standards kept in sample flasks with capillary tubes are not checked for weight loss (1 mg in 6 months when closed). The stability of working standards stored as described above is considered to be 2 years.

A newly prepared series of standards must always be compared with the previously used ones before use. Only differences considered to be less than the reproducibility of the analytical method are accepted. The working standards should be compared with certified reference material; NIST SRM 1492 “Chlorinated pesticides in hexane” and BCR CRM 365 “Polychlorinated biphenyls in iso-octane”, at least once every year. Standards from laboratory comparisons may also be used. The standards should be stored in a refrigerator.


4.19.9  Separation and quantification

4.19.9.1  Principle

The cleaned samples are analysed by gas chromatography/mass spectrometry (GC/MS). Standard mixtures are used for identification and quantification.

The individual components are identified by their GC retention and their mass fragments.

The quantification of the components is made by using internal standard. A calibration is performed with a standard mixture containing known concentrations of the components to be measured and one or more components not contained in the sample (internal standards). The calibration is followed by injection of the sample containing known amounts of internal standards. Quantification is relative to the internal standard. In this way, the sample extract volume will not be included in the calculations, and it is not necessary to accurately determine the final sample volume after evaporation or the injection volume.

4.19.9.2  Gas chromatographic conditions

The GC-parameters given are approximate and must be fine-tuned for each column, since equal columns may separate the actual compounds slightly differently.

Capillary column: Rtx-5, 60 m x 0.25 mm x 0.10 mm:
Carrier gas: He, 185 kPa (1.85 bar, 27 psi)
GC-temperature program:
1µl injected splitless (autoinjector or "hot needle" injection) at 60°C, 2 min. at 60°C, 60–190°C with 20°/min., 190-230°C with 3°/min., 230–280°C and 280°C for 15 min. isothermally.

Capillary column: Rtx-5 or equivalent, 30 m x 0.25 mm x 0.10 mm:
Carrier gas: He, 75 kPa (0.75 bar, 11.5 psi)
GC-temperature program:
1 ml injected splitless (autoinjector or "hot needle" injection) at 60°C, 2 min. at 60°C, 60–150°C with 20 °/min., 150–280°C with 1 °/min. and 280°C for 10 min. isothermally.

Capillary column: Rtx-2330 or equivalent, 30 m x 0.25 mm x 0.10 mm:
Carrier gas: He, 83 kPa (0.83 bar, 12 psi)
GC-temperature program:
1 ml injected splitless (autoinjector or "hot needle" injection) at 60 or 100°C (depending on solvent), 2 min. at 60 or 100°C (depending on solvent), to 170°C with 20 °/min., 170–230°C with 3 °/min., 230–270°C and 270°C for 6.5 min. isothermally.

Capillary column: HP Ultra-2, 25 m x 0.20 mm x 0.11 mm:
Carrier gas: He, 110 kPa (1.1 bar, 15 psi)
GC-temperature program:
1 ml injected splitless (autoinjector or "hot needle" injection) at 60°C, 2 min. at 60°C, 60–150°C with 20 °/min., 150–230°C with 4 °/min. and 230–280 with 25 C/min and 275°C for 5 min. isothermally.

In addition the following parameters are used:

Split gas flow: 40 ± 10 ml/min
Septum purge flow: 3 ml/min
Injector temperature: 260°C
GC/MS-interface temperature: 260°C–280°C

To save carrier gas, the split gas flow is reduced to <5 ml/min when the instrument is not used.

Autoinjector conditions (approximate):
Solvent A: toluene
Solvent B: n-hexane
Sample wash: 0
Sample pumps: 5
Sample volume: 1 µl
Solvent A washes: 8
Solvent B washes: 8

Solvents A and B for syringe cleaning must be exchanged each day. The solvent vials are cleaned when necessary.

The injector septum is exchanged after ca. 50 injections or once a week. The cleanness of the glass liner is checked after ca. 100 injections or if the GC-separation is poor.

4.19.9.3  GC/MS-analysis

For quantification GC/MS with either EI or NCI ionisation is used. To check the stability of the GC/MS-system, a calibration standard is injected before and after each sample batch.

Operation of the GC/MS-system is described in the instrument manuals.

Calibration- and detection conditions for EI (VG-AUTOSPEC GC/MS)
Gas chromatograph
GC/MS-interface: 260°C
Ion source:
Electron impact (EI) ion source
Ion source temperature: 260-300°C
Max. acceleration voltage: 8000 V
Electron energy: 30 eV-40 eV
Lock substance: Perfluorokerosene (PFK)

By mounting the capillary column, 1-2 mm of the exit of the column (on the MS-side) should extend into the ion source.

Using mass fragment m/z = 330,97 from perfluorokerosene (PFK, boiling point range 70°–240°C) the instrument is optimised manually for ion gain and mass resolution. At resolution 10,000 (defined as m/Dm = 10,000 at 5% valley) the signal/noise ratio for 500 fg of g-HCH should be S/N ³3.

The mass scale for each SIM-function (single ion monitoring) is calibrated automatically if possible. Optimisation of ion source and mass resolution and calibration of mass scale is controlled for each single PFK-mass in each SIM-function.

To reduce the risk of false identification further, two masses in each fragment cluster are detected (see table SIM-program for pesticides).

The SIM-program described is sufficient for a semi-quantitative analysis. If a higher accuracy is desired, a 13C-labelled internal standard must be added to each SIM-group in order to compensate for differences in sensitivity between the different SIM-functions.

Since the mass spectrometer has a large linear range, injection of one calibration standard before a series of samples is sufficient.

Calibration
The response factor, Rfi, for each compound, i, relative to the internal standard (ISTD) is determined from an analysis of a calibration standard with known concentrations:

         

Rfi :

Response factor of compound i

AmountISTD:

Amount of internal standard injected

Amounti :

Amount of compound i injected

Areai :

Peak area of compound i

AreaISTD:

Peak area of internal standard

Quantification
Using the response factors, Rfi, determined during the calibration, a known amount of internal standard and the peak areas detected during the quantitative analysis, the amount of each compound i is calculated.

         

Amounti:

Amount of compound i in the sample

AmountISTD:

Amount of internal standard added to the sample

Areai :

Area of compound i

Rfi :

Response factor of compound i

AreaISTD:

Area of internal standard

Recovery of internal standard (added before sample clean-up) is computed relative to amount of recovery standard (RSTD) added before the quantification. Relative response factors based on the recovery standard (RRFg) is calculated for each ISTD-compound from the quantification standard analysis.

         

          

Amt.ISTD           :    Amount internal standard added before extraction
Amt.RSTD          :    Amount of recovery standard added before quantification
AreaISTD           :    Peak area of internal standard
AreaRSTD          :    Peak area of recovery standard


SIM-program for PCB-compounds

SIM-function

Isomer group

12C-Mass 1

12C-Mass 2

13C-Mass 1

13C-Mass 2

1

HCB
PFK

283,8102
292,9825

285,8072

293,8244

295,8214

2

TCN
TrCB
TeCB
PFK

263,9067
255,9613
289,9224
280,9825

265,9038
257,9584
291,9194


268,0016
301,9226


269,9986
303,9597

3

TeCB
PeCB
PFK

289,9224
325,8804
342,9792

291,9194
327,8775


337,9207


339,9177

4

PeCB
HxCB
HpCB
PFK

325,8804
359,8415
393,8025
342,9792

327,8775
361,8385
395,7995

337,9207
371,8817

339,9177
373,8788

5

HxCB
HpCB
PFK

359,8415
393,8025
380,9760

361,8385
395,7995


405,8428


407,8398

 

SIM-program for DDT-compounds

SIM-function

Isomer group

12C-Mass 1

12C-Mass 2

13C-Mass 1

13C-Mass 2

1

TCN
PFTBA
DDE
DDD
DDT
DDT(control)

263,907
218,986
246,000
235,008
235,008
246,000

 265,904

247,997
237,005
237,005
247,997



258,041



260,038

 

All mass fragmentograms and area lists are printed after the analysis. Mass fragmentograms must be evaluated on the following properties:

Calibration- detection conditions for NCI (HP 5989 GC/MS)

The instrument parameters are optimised using perfluortributylamine (PFTBA) either with automatic or manual tuning. To reduce the risk of false identification further, two masses (M and M+2) in each fragment cluster are detected (see table for SIM-program).

Since the mass spectrometer has a large linear range, injection of one calibration standard before a series of samples is sufficient. The analysis is performed using the same procedures described for EI GC/MS.

All mass fragmentograms and area lists are printed after the analysis.


SIM-program for POP (for guidance)

SIM-function

Isomer group

Mass 1

Mass 2

1

HCH
13C-HCH
Chlordene
13C-2D-HCH
HCB
13C-HCB
Trifluralin
Heptachlor

252.9
262.9
263.9
264.9
282.8
295.8
335.1
299.8

254.9
264.9
265.9
266.9
284.8
297.8
336.1
301.8

2

TCN
Aldrin
Oksychlordane
Heptachlorepoxide
Trans-Chlordane

263.9
329.9
349.8
387.8
407.8

265.9
331.9
351.8
389.8
409.8

3

o,p-DDE
PCB 101, PCB-118
13C-PCB-118
Dieldrin, Endrin
a-Endosulfane
cis-Chlordane
trans-Nonachlor

245.9
325.9
337.9
379.9
405.8
407.8
441.8

247.9
327.9
339.9
381.9
407.8
409.8
443.8

4

o,p-DDD
p,p-DDE
PCB 105
PCB-153
13C-PCB 153
cis-Nonachlor

245.9
315.9
325.9
359.8
371.8
441.8

247.9
317.9
327.9
361.8
373.8
443.8

5

p,p-DDT
PCB 138
PCB 156

280.9
359.8
359.8

282.9
361.8
361.8

6

PCB 156
PCB 180
OCN
13
C-PCB 180

359.8
393.8
401.7
405.8

361.8
395.8
403.7
407.8

 

4.19.10  Calibration of instruments

The GC/MS-instrument should be calibrated every day. The sensitivity of the mass spectrometer can, for instance, be controlled daily by determining the signal-to-noise ratio for a given amount of a chosen component (one such component could be PCB-101).

4.19.10.1  Control of concentrations of standards

Every new working standard should be compared to the existing standard before it is taken into use. Deviations within the reproducibility of the procedure are acceptable. At least once a year, the working standards should be controlled against a reference standard from an intercomparison or which has been certified from an international reference laboratory.

The accuracy should be within the uncertainty of the procedure (± 20 %). Measures to assure constant standard concentration is described in chapter 4.19.8.2 under “Quality assurance of standards”.

4.19.10.2  Frequency of GC injections of quantification standard

The quantification standard should be injected at the beginning of the GC-run of every series of samples. A maximum of 10 samples should be analysed before a new injection of the quantification standard is carried out. If the sample series consists of less than 10 samples, the quantification standard should be injected after the last sample. A control standard should also be injected with every sample series.

4.19.10.3  Analysis of control samples

At the moment there is no certified reference material available that can be utilised for determination of organic compounds in air samples. It is therefore necessary for the laboratory to establish a control sample. This sample should be large enough to correspond to about 40 real air samples. The sample is extracted in the usual way. The extract is homogenised and split into 40 separate samples that are stored in suitable flasks at -20°C. Each year, at least 4 of these control samples should be analysed. The results for at least one component from each component group (for instance g-HCH, tr-CD and PCB-153) should be plotted on a quality control chart (QCC, Vogelsang, 1991). This quality control chart gives a good overview of the long time stability of the measurement results.


4.19.11  Recovery test

An internal standard (ISTD) should be added at the beginning of the procedure and a recovery standard (e.g. octachloronaphtalene) should be added just before the quantification step. In addition to this, recovery tests with spiked (including C12-components) samples or solvents should be carried out for every 100 sample of a certain type. In this work, analysis of control samples and blank samples are also important parts. The recovery of the internal standard should be between 40% and 120%, while the spiked C12-components should have a recovery that corresponds to the uncertainty of the procedure (for instance ± 20 %) relative to the theoretically added amount of each component. For volatile components, for instance HCB or HCH, which are prone to losses during the volume reducing steps, the lower recovery limit for the corresponding C13-spiked components are 20%.


4.19.12  Quality assurance

4.19.12.1  General principles

The aim of quality assurance (QA) is to ascertain that the established results have the necessary accuracy and traceability.

The methods used for determination of organic compounds in environmental samples at very low concentrations may include a number of possibilities for errors:

To eliminate as many as possible of these error sources, the following demands should be fulfilled:

  1. The laboratory personnel must have adequate competence and everyone involved must be familiar with the detailed routines
  2. Equipment, chemicals and other materials should be well suited for their purpose. The quality should be regularly controlled and documented
  3. The operating procedures should fit the purpose, be validated and adequately documented
  4. Every working step and routine should be described
  5. The results should be completely traceable

4.19.12.2  Administrative routines

Operating procedures
The operating procedures are the fundament for every quality assurance measure taken. The procedures assure continuity and dependability in every working step carried out in the laboratory. They are also an important part of the education and training of new operators and of the continuous training of all personnel involved. The operating procedures should include descriptions and specifications of the following:

4.19.12.3  Sample journal

As soon as the laboratory receives a sample, the sample should be registered in the sample journal or sample logbook. The journal should include information about sample type, sampling site, sampling date, sample amount, and, if necessary, place of storage. Every sample should be given a unique sample number, for instance year/serial number (99/102).

4.19.12.4  Sample handling form

When the sample is registered in the sample journal a sample handling form for the sample should be established. In addition to information about sample type, sample number and so on, details of the important steps in the sample handling should be written on the form, especially deviations from the procedures. Amounts of added standards and name and location of electronic data files should also be specified. All notes in the form should be signed (initials) and dated.

4.19.12.5  Instrument logbook

Every analysis instrument should have an instrument logbook. In this journal every sample run should be registered together with method used, temperature program or other vital instrument parameters. Instrument deviations, for instance poor separation or “tailing”, should be registered. In addition, instrument sensitivity and simple maintenance of the instrument, e.g. change of septum or cleaning of the glass liner, should be registered.

4.19.12.6  Standard journal

Every standard should be given a unique identification. The standards should be registered in the standard journal. Concentration, solvent, date of preparation and weight of the container should be specified. A container should be weighed at room temperature before and after removal of an amount of standard. Weight and date should be registered in the journal. It is not necessary to weigh a working standard in a glass container with capillary outlet.

4.19.12.7  Acceptance of results

The following criteria should be fulfilled in order to achieve a necessary degree of certainty in the identification and quantification of organic compounds:

4.19.12.8  Reporting of results

The report should include:

4.19.12.9  Storage

The following should be stored:

It is not necessary to store paper copies of chromatograms or fragmentograms

4.19.12.10  Validation of the method

There are always a number of possible errors that may affect the quality of the results. It is not possible to eliminate all these errors because samples are different due to a number of factors and because every step in the procedure has inherent possibilities for errors. Validation of a method must therefore be a continuous process.

The following is a list of some of the more important possible errors with measures or control routines:

  1. Loss after sampling: Every sample should be wrapped adequately, for instance in aluminium foil and plastic bags with zip locks, and transported to the laboratory as soon as possible. If samples must be stored, they should be kept in the dark. Air samples should be stored at -20°C.
  2. Loss during sample preparation and clean-up
  3. Contamination during sampling, storing or sample preparation and clean-up: See chapter 4.19.10. “Testing of blank values”.
  4. A large number of partially unidentified organic compounds (sample matrix) are complicating the determination of organic compounds in air samples. It is not always possible to remove these organic compounds (or sample matrix) completely and in some cases this may give rise to interferences or faulty identifications (see chapter 5.3.2).

4.19.12.11  Testing of blank values

An important part of the quality control of the results is the comparison of the measured sample concentration with the blank values of the method (calculated on the basis of the sample amount). Before the preparation and clean-up of every new series of samples or new sample type is started, a blank sample should be run through the procedure. The result for this sample will represent the blank value of the method.

In the case of larger series of the same type of samples, it will be enough to run a blank sample (filter and PUFs) for every 30 real sample unless there are other considerations that make it necessary with more frequent blank samples. One such consideration is the analysis of a sample with unexpected high concentration (more than 100 times above the normal level). A blank field sample (representing the blank value of the whole process including sampling, transport and preparation and clean-up) should be run 2 to 3 times a year for each sampling site.

Criteria for acceptance of blank values
The results of a blank sample is accepted if the blank values for every component to be quantified is lower than the limit of detection (signal-to-noise ratio larger than 3:1) or at lower than 1/10 of the lowest expected concentration level. For a larger blank sample series (more than 5 blank samples) the limit of quantification may be utilised. This level of quantification is defined as the average of the blank value (for a component) plus 3 standard deviations.

4.19.12.12  Participation in laboratory intercomparisons

Intercomparisons are an important tool for validating the operating procedure. The laboratory should try to achieve participation in at least one intercomparison a year for each sample type (air, precipitation, sediment and biological samples).


4.19.13  Reference

Vogelsang, J. (1991) The quality control chart principle: Application to the routine analysis of pesticide residues in air. Fresenius J. Anal. Chem., 340, 384-388.


Last revision: November 2001