ProductListing
The target analytes are eluted from the cartridgewith two
additions of 40mLmethyl-
tert
-butyl ether. The two fractions are
combined and evaporated to about 1mLon a rotary evaporator
under vacuum at 50°C. The extracts are then redissolved in1mL
ofmethanol forGC analysis.
Procedure#2, Liquid/LiquidExtraction
The chemically-reduced sample alsomaybe concentratedby
liquid/liquid extraction.The aqueous sample first is adjusted
with sodiumhydroxide to apHgreater than10. Sodium chloride
is addeduntil saturation. The sample then is extracted twicewith
25mLofmethyl-
tert
-butyl-ether.The ether fractions are com-
bined and evaporated todryness. Finally, the extract is reconsti-
tuted in2mLofmethanol forGC/MS analysis.
YourChromatographicProblems Solved
Problem:PrimingEffects
Analysts commonly seepriming effects in this analysis.While
standard sleeve,wool, and columndeactivationsworkwell to
decrease this inmost situations, theydonot performwellwith
amines in splitless injections at low concentrations.
Solution:AmineDeactivation
Restekhas developed the idealGCproducts to eliminate the
resultingpriming effects in the analysis of azodye. The use of
Restek’sproprietaryamine-deactivated sleeves, amine-deacti-
vatedwool, and anRtx
®
-5Amine columnwill ensure the highest
level of system inertness and excellent reproducibility. The
priming effectwhenusing standarddeactivatedproductswas
evaluatedby comparing the response factors during repetitive
runs. The results indicated that the response factors for the first
injectionwere up to10% lower than the tenth injection.How-
ever, the comparison analysis that used aminedeactivation
showednopriming effect. The aminedeactivations also im-
proved repeatability and lowered standarddeviations to<5%.
Problem:CalibrationStandards
A lackof accurate, stable calibration standards presents another
obstacle to the analysis of azodyes.Manyof the target com-
pounds arenot commercially available in apure, stable form.
Some areonly available as thehydrochloric, carbonate, or sulfate
salts of the free base.While these salts have better stability as a
neatmaterial, theydonotmake good rawmaterials forGC
calibration standards. Standards prepared from the salt forms of
azodyeswill yieldpoor response andpeak shapewhen analyzed
usingGC.The salt forms alsowill cause difficulty in assigning
the actualweight/weight purity. The best standards forGC
analysis are prepared from the free base forms of the azodye
target analytes.
Solution:CalibrationStandardPurity
To ensure accuratepreparationof calibration standards, these
target compoundsmust be tested and re-purified.Oneof thebest
methods for final purificationof the freebase is sublimation.
Whenperformedunder an inert atmosphere, this produces avery
purematerial for final preparationof a calibration standard.
Usingmultiplepurity assays is required todetect impurities.
WhileGCwill detect onlyorganic impurities, differential
scanning calorimetry (DSC)will detect bothorganic and
inorganic impurities.All of the rawmaterials forRestek’s azo
dyemixes are carefully tested andpurified toprovide themost
accurate and stable calibration standards available.
Conclusion
Whenusing theGerman azodyemethod andRestek’s amine-
deactivated column, sleeve, andwool, analysts can achieve
reproducible and accurate results.
References
1. German Consumers Goods Act of July 15, 1994, Lebensmittel-und
Bedarfsgegenständegesetz §35 LMBG
2. BgVV, Bundesgesundhbl. 2/96
Restek Trademarks:
Rtx.
Other Trademarks:
Extrelut (E. Merck).
4mmGooseneckBase-Deactivated Inlet Sleeves
PackedwithBase-DeactivatedWool
GC
each
5-pk.
25-pk.
HP
20798-211.1
20799-211.5 20800-211.25
Varian
20904-211.1
20905-211.5 20906-211.25
CE*
20945-211.1
20946-211.5 20947-211.25
Base-DeactivatedFusedSilicaGuardColumns
5m, 0.25mm ID cat.# 10000, ea.
cat.# 10000-600, 6-pk.
Rtx
®
-5AmineColumn
30m, 0.25mm ID, 0.25µm, cat.# 12323
*5mmGooseneck base-deactivated inlet sleeve.
AzoDyeMix#1
Compounds 1-24 fromFigure 1 chromatogram
10µg/mL ea. in ethyl acetate, 1mL/ampul
Each
5-pk.
10-pk.
31466
31466-510
w/data pack
31466-500
31466-520
31566
Internal Standard forAzoDyeMethod
3,3',5,5'-tetramethylbenzidine mix
1000µg/mL in ethyl acetate, 1mL/ampul
Each
5-pk.
10-pk.
31467
31467-510
w/data pack
31467-500
31467-520
31567
