fda三聚氰胺的检测方法
GC-MS Screen for the Prence of Melamine
(Adapted from FDA/ORA Forensic Chemistry Center SOP T015)
Revid April 10, 2007
PURPOSE:
This procedure provides a general guide for the sample preparation and analysis of wheat gluten and pet food matrices for melamine using gas chromatography/mass spectrometry. This procedure is designed to screen the TMS derivative of a methanol extract of the sample and it incorporates instrumental parameters which permit 10.5 minute run times.
SCOPE:
This proc edure is applicable to dry wheat gluten, dry pet food, and wet “cuts and gravy” type pet food. This procedure involves extractions in methanol and therefore prelects compounds which are soluble or partially soluble in methanol. Due to solubility limitations of melamine in methanol, this method is intended to be a qualitative screen only.
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RESPONSIBILITY:
It is the responsibility of the analyst to note any modifications to this procedure in the worksheet.
DEFINITIONS AND ACRONYMS:
TMS – trimethylsilyl
SAFETY CONSIDERATIONS:
Accepted safety measures should be employed when working with chemicals and pressurized gas.
EQUIPMENT:
Agilent 5975 GC-MS system equipped with a 30m DB-5MS column (or equivalent)
Reacti-Vap – Evaporating/Heating Module
REAGENTS:
Methanol: HPLC grade
Pyridine: Certified A.C.S.
BSTFA with 1% TMCS: bis(trimethylsilyl)trifluoroacetamide with 1%
Trimethylchlorosilane (e.g. Sylon BFT, Supelco)
module t at approximately 70°C. Add 200 µl pyridine and 200 µl BSTFA, vortex briefly to mix, and incubate at approximately 70°C for 30 minutes.
C. Sample Fortification:
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This method was successfully applied to detect melamine in wet and dry pet food composites (Figure 2) and dry wheat glutens (Figure 3). Bad on HPLC-UV results, this method was able to detect melamine levels down to 0.01% (by weight) in official FDA samples using ~0.500 g samples with TMS derivatization and splitless injection.
Uncontaminated wheat gluten and pet food composites were spiked with various levels of melamine and taken through the method using ~0.500 g samples and splitless
injection. The method successfully detected melamine (as the 3TMS derivative) at 14 micrograms/g in the wheat gluten and at 7 micrograms/g in the pet food composite. At low spike levels, extracted ion chromatograms were ud to verify the prence of four major ions of the melamine-TMS mass spectrum (m/z=342, 327, 171, and 99). Sample fortification experiments to demonstrate successful detection of melamine in the specific matrix of interest should be performed by the individual laboratories.
D. Standard Preparation:
肉末豆腐怎么做Melamine is sparingly soluble in methanol and slightly more soluble in methanol/water mixtures. Up to ~1.5 mg/mL of melamine standard can be dissolved in a 50/50 mixture of methanol/water with sonication for 30 minutes. If more concentrated solutions of melamine are desired, dimethyl sulfoxide (DMSO) may be ud as a primary solvent followed by methanol or acetonitrile for rial dilutions.
Note: Due to the prence of water in the standard solution, dry down times for
the melamine standard on the Reacti-Vap will be incread.
立体小手工E. Instrument Parameters:
INSTRUMENT: 5975 Agilent GC 6890N Series with 7683B Series
autosampler
DETECTOR: Agilent Mass Selective Detector (MSD) model 5975i
SOFTWARE: Enhanced Chemstation version D.02.00.275; Wiley 7th Edition
and NIST 02 MS Library
COLUMN: J&W Scientific DB-5MS 5% Phenyl Methyl Siloxane with 10M
Duraguard
Part #19091S-433, Serial # US4937937H
ID: 0.25mm Film Thickness: 0.25 microns Length: 30
meters (nominal)
CARRIER GAS: Helium
Flow Rate: 1.3 ml/min
Avg. Linear Velocity: 35 cm/c
Pressure: 17.5 psi (initial)
Mode: constant flow
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INJECTION: Injection Type: Splitless; or Split (1:20)
Injection Volume: 1µl
Injector Temperature: 250ºC
Splitless Injection Purge Flow: 10.0 ml/min at 2.0 minutes
GC PARAMETERS: Start Temperature: 75ºC; Hold: 1.0 min
Ramp Rate: 30ºC/min
Final Temperature: 300ºC; Hold: 2.0 min
Transfer Line Temperature 280ºC
Run Time: 10.5 minutes
MS PARAMETERS: Mass Range: 40-450 amu送给闺蜜的祝福语
Scan Mode: Full (Electron Ionization)
Filament Delay: 4.2 min (splitless); 3.8 min (split)
Threshold: 100
MS Quad: 150ºC
MS Source: 230ºC
友好相处F. Peak Identification:
The mass spectrum of the 3-TMS derivative of melamine (Figure 1) exhibits the molecular ion at m/z=342, a methyl group loss at m/z=327, and significant ions at m/z=171, 99, and 73. The standard of melamine should be prepared (and TMS-derivatized) and analyzed along with the sample preps on the same day to confirm the identification. Figures 2a and 2b are examples of a GC-MS chromatogram of melamine contaminated pet food. Additional peaks prent in the TIC are consistent with TMS derivatives of phosphate and various sugars. Figure 3 is an example of a GC-MS chromatogram of melamine contaminated wheat gluten.
Figure 1
