GB 5009.190-2014 PDF English
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National Food Safety Standard -- Determination of Indicator Polychlorinated Biphenyls in Foods
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Determination of indicator polychlorinated biphenyls in foods
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GB 5009.190-2014: National Food Safety Standard -- Determination of Indicator Polychlorinated Biphenyls in Foods
---This is an excerpt. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.), auto-downloaded/delivered in 9 seconds, can be purchased online: https://www.ChineseStandard.net/PDF.aspx/GB5009.190-2014
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
National Food Safety Standard - Determination of Indicator
Polychlorinated Biphenyls in Foods
ISSUED ON: DECEMBER 1, 2014
IMPLEMENTED ON: MAY 1, 2015
Issued by: National Health and Family Planning Commission of the People’s
Republic of China
Table of Contents
Foreword ... 3
1 Scope ... 4
Method I Stable Isotope Diluted Gas Chromatography-mass Spectrometry ... 4
2 Principle ... 4
3 Reagents and Materials ... 4
4 Instruments and Equipment ... 6
5 Analytical Procedure ... 7
6 Quality Control and Assurance ... 13
7 Others ... 14
Method II Gas-chromatographic Method ... 14
8 Principle ... 14
9 Reagents and Materials ... 15
10 Instruments and Equipment ... 15
11 Analysis Procedure ... 16
12 Determination ... 17
13 Precision ... 19
14 Others ... 19
Appendix A Standard Solution for Indicator Polychlorinated Biphenyl ... 20
Appendix B Characteristic Ion and Isotopic Abundance Ratio ... 23
Appendix C PCBs Mass Chromatogram and Mass Spectrogram through GC-MS
Determination ... 25
Appendix D Purification Flow Diagram ... 33
National Food Safety Standard - Determination of Indicator
Polychlorinated Biphenyls in Foods
1 Scope
Method I in this standard specifies the determination methods for polychlorinated biphenyls
(PCBs), including indicator PCBs (PCB28, PCB52, PCB101, PCB118, PCB138, PCB153 and
PCB180) as well as PCB18, PCB33, PCB44, PCB70, PCB105, PCB128, PCB170, PCB187,
PCB194, PCB195, PCB199 and PCB206 in foods specified in the Global Environmental
Monitoring System/Food Planning Part. Method II specifies the determination methods of
PCB28, PCB52, PCB101, PCB118, PCB138, PCB153 and PCB180.
This standard is applicable to the determination of indicator PCBs in animal-based foods (like
fish, shellfish, egg, meat, milk and their products) and oil and fat samples.
Method I Stable Isotope Diluted Gas
Chromatography-mass Spectrometry
2 Principle
Adopt stable isotope dilution technology; add 13C12 labeled PCBs in the sample as the
quantitative standard; carry out Soxhlet extraction; carry out chromatography purification,
separation and concentration for the extracted sample solution with column chromatography,
and then add it into the internal recovery standard; adopt gas chromatography - low-resolution
gas chromatograph-mass spectrometer, analyze through quadrupole mass spectrum selected
ion monitoring (SIM) or ion trap tandem mass spectrum multi-response monitoring (MRM),
and then quantify through internal standard method.
3 Reagents and Materials
3.1 Reagents
3.1.1 N-hexane (C6H14): pesticide residue.
3.1.2 Dichloromethane (CH2Cl2): pesticide residue.
3.1.3 Acetone (C3H6O): pesticide residue.
3.1.4 Methanol (CH3OH): pesticide residue.
3.1.5 Isooctane (C8H18): pesticide residue.
3.1.6 Anhydrous sodium sulfate (Na2SO4): guaranteed reagent. Put the commercially
available anhydrous sodium sulfate into the chromatographic column, and successively elute
it twice with n-hexane and dichloromethane; the volume of solvent used for each elution is
about twice the volume of anhydrous sodium sulfate. After elution, transfer the anhydrous
sodium sulfate into a flask; bake it to dry at 50℃ and then bake it for 8~12h at 225℃; cool it
and then store it in a dryer.
3.1.7 Sulfuric acid (H2SO4): with content of 95%~98%, guaranteed reagent.
3.1.8 Sodium hydroxide (NaOH): guaranteed reagent.
3.1.9 Silver nitrate (AgNO3): guaranteed reagent.
3.1.10 Chromatographic silica gel (75~250μm). Put the commercially available silica gel
into the glass chromatographic column, and successively elute it twice with n-hexane and
dichloromethane; the volume of solvent used for each elution is about twice the volume of
silica gel. After elution, transfer the silica gel into flask, and cover the flask mouth with
aluminum foil; put it into the oven, and bake at 50℃ to dry; then heat up to 180℃ and bake
for 8~12h; cool it and then put it into a reagent bottle with ground stopper; store it in the
dryer.
3.1.11 44% acid silica gel: weigh 100g of activated silica gel, dropwise add 78.6g of
sulfuric acid and shake until it is free of cake; put in into the reagent bottle with ground
stopper and store it in dryer.
3.1.12 33% alkaline silica gel: weigh 100g of activated silica gel, dropwise add 49.2g of
1mol/L sodium hydroxide solution and shake until it is free of cake; put in into the reagent
bottle with ground stopper and store it in dryer.
3.1.13 10% silver nitrate silica gel: dissolve 5.6g of silver nitrate into 21.5mL of deionized
water, dropwise add it into 50g of activated silica gel, and shake until it is free of cake; put in
into the brown reagent bottle with ground stopper and store it in dryer.
3.1.14 Alkaline aluminum oxide: adopt alkaline aluminum oxide for chromatogram
chromatography, and bake it at 660℃ for 6h; put it into the reagent bottle with ground stopper
and store it in dryer.
3.2 Standard solutions
3.2.1 Standard solution for the determination of the time window: composed of cognate
can lead to a good cleaning effect. Where brush is adopted for cleaning, special attention shall
be paid to that the brush shall not damage the internal surface of glass ware.
5 Analytical Procedure
5.1 Sample preparation
5.1.1 Pretreatment
5.1.1.1 Pack the site-collected sample with lucifugal material like aluminum foil and brown
bottle, put it in small refrigerator and then transport it to the laboratory; store it in a cryogenic
refrigerator below -10℃.
5.1.1.2 Solid sample like fish and meat may be dried by freezing or anhydrous sodium
sulfate, and shall be mixed uniformly. Oil and fat may be directly dissolved in n-hexane for
purification treatment.
5.1.2 Extraction
5.1.2.1 Before extraction, put an empty cellulose or glass fiber extraction sleeve into the
Soxhlet extractor; use n-hexane + dichloromethane (50+50) as extraction solvent, pre-extract
for 8h, and then take it out for air drying.
5.1.2.2 Put 5.0g~10.0g of pretreated sample into the extraction sleeve treated according to
Article 5.1.2.1, add 13C12 labeled quantitative internal standard (Article 3.2.2); cover the
sample with glass wool, balance for 30min and then put into Soxhlet extractor; use proper
amount of n-hexane + dichloromethane (50+50) as extraction solvent and extract for 18~24h;
control the back flow speed within 3~4 times/h.
5.1.2.3 After extraction, transfer the extraction solution into a round-bottom flask,
concentrate it with rotary evaporator to nearly dry. Where the analysis result is calculated
according to fat, the fat content of sample shall be determined.
5.1.2.4 Fat determination: exactly weigh the mass of round-bottom flask before
concentration, and then exactly weigh the mass of the round-bottom flask again after the
solvent is concentrated to dry; the difference of two weighed results is regarded as the fat
content of the sample. After the fat content determination, add a small amount of n-hexane to
dissolve the residue in flask.
5.1.3 Purification
5.1.3.1 Acidic silica gel column purification
Purification column filling: plug the bottom of glass column with glass wool, and then
successively fill in 4g of activated silica gel, 10g of acid silica gel, 2g of activated silica gel
and 4g of anhydrous sodium sulfate (see Figure D.1 in Appendix D) from bottom to top. Elute
with 100mL of n-hexane in advance.
Purification: completely transfer the concentrated extraction solution to the column; wash the
round-bottom flask for 3~4 times with 5mL of n-hexane, and transfer the washing liquid to
the column. Where the liquid level falls to the anhydrous sodium sulfate layer, add 180mL of
n-hexane to elute, and concentrate the eluent to about 1mL.
Where the complete acid silica gel layer is discolored, it indicates that the fat content in the
sample exceeds the load limit of column. After the eluent concentration, prepare a stick of
new acidic silica gel purification column, and repeat above operation until the sulfuric acid
silica gel is not completely discolored.
5.1.3.2 Composite silica gel column purification
Purification column filling: plug the bottom of glass column with glass wool, and then
successively fill in 1.5g of silver nitrate silica gel, 1g of activated silica gel, 2g of alkaline
silica gel, 1g of activated silica gel, 4g of acid silica gel, 2g of activated silica gel and 2g of
anhydrous sodium sulfate (see Figure D.1 in Appendix D) from bottom to top. Then, elute
with 30mL of n-hexane + dichloromethane (97+3) in advance.
Purification: completely transfer the concentrated eluent after being purified according to
Article 5.1.3.1 to the column; wash the round-bottom flask for 3~4 times with 5mL of
n-hexane, and transfer the washing liquid to the column. Where the liquid level falls to the
anhydrous sodium sulfate layer, add 50mL of n-hexane + dichloromethane (97+3) to elute,
and concentrate the eluent to about 1mL.
5.1.3.3 Alkaline aluminum oxide column purification
Purification column filling: plug the bottom of glass column with glass wool, and then
successively fill in 2.5g of baked alkaline aluminum oxide and 2g of anhydrous sodium
sulfate (see Figure D.1 in Appendix D) from bottom to top. Elute with 15mL of n-hexane in
advance.
Purification: completely transfer the eluent concentrated after being purified according to
Article 5.1.3.2 to the column, wash the round-bottom flask for 3~4 times with 5mL of
n-hexane, and then transfer the washing liquid to the column. Where the liquid level falls to
the anhydrous sodium sulfate layer, add 30mL of n-hexane (2×15mL) to elute the column;
where the liquid level falls to the anhydrous sodium sulfate layer, use 25mL of
dichloromethane + n-hexane (5+95) for elution. Concentrate the eluent to nearly dry.
5.1.4 Treatment before machine analysis
Transfer the purified sample solution into small injection tube, and concentrate it under
nitrogen flow; wash the round-bottom flask for 3~4 times with a small amount of n-hexane,
ratio for the detected ion of each compound replaced by trichlorine to heptachlor shall be
greater than 3; otherwise, instrument tuning shall be repeated until meeting the relevant
requirements.
5.4 Qualification and quantification of PCBs
5.4.1 Confirmation requirements of PCBs chromatographic peak: the signal to noise ratio of
the detected chromatographic peak shall be greater than 3 (see Figure C.1 or Figure C.3 in
Appendix C).
5.4.2 The abundance ratio of two monitored characteristic ions shall be within the
theoretical range, respectively see Table B.1 and Table B.2 in Appendix B.
5.4.3 Inspect the mass spectrogram corresponding to chromatographic peak (see Figure C.2
or Figure C.4 in Appendix C); where the concentration is sufficiently large, the fragment ion
(M-70) discarding 2 chlorine atoms shall exist, see Table B.1 in Appendix B.
5.4.4 Inspect the mass spectrogram corresponding to chromatographic peak (see Figure C.2
or Figure C.4 in Appendix C); for chromatographic peak of trichlorinated biphenyl to
heptachlor biphenyl, fragment ion (M+70) added with 2 chlorine atoms cannot exist, see
Table B.1 in Appendix B.
5.4.5 The retention time of confirmed PCBs shall be within the time window predetermined
through analyzing the standard solution for the determination of the time window. Standard
solution for the determination of the time window is composed of cognate compounds of the
first and last peaks of chloride-replaced PCBs on DB-5ms chromatographic column. Analyze
the standard solution of window determination (1μL) by adopting determined
chromatographic condition and full-scan mass spectrum collection mode, and determine the
time window according to the retention time section of each PCBs family. The retention time
sections of three PCBs families are overlapped on DB-5ms chromatographic column, thus,
the characteristic ion of each PCBs family shall be detected within the same time window. To
guarantee the selectivity and sensitivity of analysis, the detected characteristic ions in the
same window shall be as little as possible during the time window determination.
5.5 Expression of analysis result
5.5.1 In this standard, isotope dilution technology is adopted for the quantification of
PCB28, PCB52, PCB118, PCB153, PCB180, PCB206 and PCB209; internal standard method
is adopted for the quantification of other target compounds and the recovery calculation of
quantitative internal standard. 20 target compounds determined in this standard covers a
majority of PCBs industrial products, including 3 compounds from each family from
trichlorinated biphenyl to Octa-PCB, and respectively one from nonachlor biphenyl and
decachlorobiphenyl; see Table A.4 in Appendix A. A 13C12 labeled compound is adopted as the
quantitative internal standard of each family, see Table A.2 in Appendix A. There are two
internal recovery standards to calculate the recovery of quantitative internal standard, see
ms - the quantity of added quantitative internal standard, ng;
H - the peak height of quantitative internal standard;
RRFn - the relative response factor of target compound to quantitative internal standard;
m - the sample quantity, g.
Since sample matrix, sampling quantity, injection volume, recovery of quantitative internal
standard, chromatographic separation condition, electrical noise level and instrument
sensitivity may affect the detection limit of sample, the noise level shall be obtained from
actual sample spectrogram. Where the result of certain target compound is reported as not
detected, the detection limit of sample shall be simultaneously reported.
6 Quality Control and Assurance
6.1 Initial precision and accuracy test
Before analyzing the actual sample, the laboratory shall reach acceptable precision and
accuracy level. Verify the reliability of analysis method through analyzing the labeled sample.
Take at least 3 portions of blank sample with matrix similar to that of the actual sample, and
respectively add standard solution of precision and accuracy test, see Table A.5 in Appendix A;
respectively add quantitative internal standard solution. Analyze the prepared labeled sample
through the method same as that of the actual sample, calculate the recovery of target
compound and quantitative internal standard. The determined value of target PCBs of each
portion shall be within 75%~120% of the adding quantity, RSD< 30%. The average recovery
of quantitative internal standard shall be within 50%~120%, and the recovery of quantitative
internal standard shall be within 30%~130%.
The above standard shall be reached before analyzing the actual sample. Where the extraction
or purification method of the sample is modified and the analysis operator is changed, the
above test shall be repeated until reaching the above standard. The above test shall be carried
out for the laboratory every 6 months until reaching the above standard requirements.
Where the standard reference substance with matrix similar to that of the sample is available,
the quantitative internal standard solution may be replaced by standard reference substance in
precision and accuracy test.
6.2 Recovery of quantitative internal standard
Before sample extraction, add quantitative internal standard to calibrate the loss of target
compound in sample extraction and purification process. The recovery of quantitative internal
standard shall be within 30%~130%. Where the recovery of quantitative internal standard of
sample analysis result fails to meet the above requirements, the extraction, purification and
machine analysis of sample shall be repeated.
6.3 Method blank
For each batch, a method blank test shall be carried out for each 15 samples at most.
6.4 Quality-controlled sample
For each batch, a quality-controlled sample shall be provided for each 15 samples at most.
The quality-controlled sample may be standard reference substance or labeled sample with
given concentration. The determined value of the target compound shall be within 75%~125%
of the standard value.
6.5 Retention time window
Analyze the standard solution for the determination of the time window weekly to determine
the accuracy of the retention time window. Where the chromatographic column is changed or
cut, or the chromatographic parameter is changed, the retention time window shall be
calibrated with standard solution for the determination of the time window.
6.6 Standard calibration solution
5 concentration levels of standard calibration solution are used for initial calibration. Where
the RSD of RRF is less than 20%, it indicates that the calibration is successful. During the
analysis process, a confirmatory test shall be carried out every 12h. Where machine analysis
is carried out with CS3 in standard calibration solution, the analysis result shall be within
±20% of its fixed value, and the recovery of quantitative internal standard shall be within
75%~125%.
7 Others
The quantitation limit of each target compound is 0.5μg/kg.
Method II Gas-chromatographic Method
8 Principle
In this standard, take PCB198 as quantitative internal standard; add PCB198 into the sample,
and carry out oscillating extraction through heating in water bath; then determine through gas
chromatography-electron capture detector method after sulfuric acid treatment and
chromatographic column chromatography purification; qualify according to retention time
while quantify according to internal standard method.
10.9 Analytical balance.
10.10 Water bath oscillator.
10.11 Centrifuger.
10.12 Chromatographic column.
11 Analysis Procedure
11.1 Sample extraction
11.1.1 Solid sample: weigh 5~10g of sample (accurate to 0.1g), and put it into a conical
flask with plug; add quantitative internal standard PCB198, and then extract for 2h on water
bath oscillator with proper amount of n-hexane + dichloromethane (50+50) as extraction
solution; the water bath temperature is 40℃, and the oscillating speed is 200r/min.
11.1.2 Liquid sample (except oil and fat sample): weigh 10g of sample (accurate to 0.1g),
and put it into a centrifuge tube with plug; add quantitative internal standard PCB198 and
0.5g of sodium oxalate; add 10mL of methanol and shake well; add 20mL of ethyl ether +
n-hexane (25+75) and extract for 20min through oscillation; centrifuge for 5min at 3000r/min;
take supernatant and pass it through the glass column filled with 5g of anhydrous sodium
sulfate; add 20mL of ethyl ether + n-hexane (25+75) to the residue; repeat the above
procedure, and then combine the extraction solution.
11.1.3 Transfer the extraction solution into a round-bottom flask, concentrate it with rotary
evaporator to nearly dry. Where the analysis result is calculated according to fat, the fat
content of sample shall be determined.
11.1.4 Sample fat determination: exactly weigh the weight of round-bottom flask before
concentration, and then exactly weigh the weight of the round-bottom flask and residue after
the solvent is concentrated to dry; the difference of two weighed results is regarded as the fat
content of the sample.
11.2 Purification
11.2.1 Sulfuric acid purification
Transfer the concentrated extraction solution into a 10mL test tube; wash the round-bottom
flask for 3~4 times with about 5mL of n-hexane, and then combine the washing liquid into a
concentrated solution; scale the volume to the scale with n-hexane, add 0.5mL of
concentrated sulfuric acid, and shake for 1min; centrifuge for 5min at a rotation speed of
3000r/min to separate the sulfuric acid layer and organic layer. If the upper-layer solution still
has color, it indicates that the fat is not completely removed; then add certain amount of
concentrated sulfuric acid and repeat the above operation until the upper-layer solution is
colorless.
11.2.2 Alkaline aluminum oxide column purification
Purification column filling: add a small amount of glass wool into the bottom of glass column,
and then successively add 2.5g of baked alkaline aluminum oxide and 2g of anhydrous
sodium sulfate from the bottom; elute with 15mL of n-hexane in advance.
Purification: transfer the concentrated solution (Article 11.2.1) into the chromatographic
column; wash the round-bottom flask for 3~4 times with 5mL of n-hexane, and transfer the
washing liquid into the chromatographic column. When the liquid level falls to the anhydrous
sodium sulfate layer, add 30mL of n-hexane (2×15mL) for elution; where the liquid level falls
to the anhydrous sodium sulfate layer, use 25mL of dichloromethane + n-hexane (5+95) for
elution. Concentrate the eluent with rotary evaporator to nearly dry.
11.3 Sample solution concentration
Transfer the sample solution (11.2.2) into a sample injection bottle, wash the round-bottom
flask for 3~4 times with a small amount of n-hexane, and combine the washing liquid into the
sample injection bottle; concentrate it to 1mL under nitrogen flow and maintain it for GC
analysis.
12 Determination
12.1 Chromatographic conditions
12.1.1 Chromatographic column: DB-5ms column, 30m×0.25mm×0.25μm or equivalent
chromatographic column.
12.1.2 Injection port temperature: 290℃.
12.1.3 Temperature programming: adopt a start temperature of 90℃ and maintain for
0.5min; heat up to 200℃ at a speed of 15℃/min, and maintain for 5 min; heat up to 250 ℃ at
a speed of 2.5℃/min, and maintain for 2min; and then heat up to 265℃ at a speed of
20℃/min, and maintain for 5 min.
12.1.4 Carrier gas: high-purity nitrogen (with purity >99.999%); the column pressure is
67kPa (equivalent to 10psi).
12.1.5 Injection volume: splitless injection of 1μL.
12.1.6 Chromatographic analysis: qualify according to retention time while quantify based
on the comparison between the sample and the standard peak height or peak area.
12.2 Qualitative analysis of PCBs
......
Source: Above contents are excerpted from the full-copy PDF -- translated/reviewed by: www.ChineseStandard.net / Wayne Zheng et al.
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