Migrant identification

Headspace GC-MS is the preferred method for the analysis of very volatile migrants. Practically the same GC conditions can be used as for GC-MS. Due to the coupling to MS, identification is also relatively easy. The heating time and temperature are the main experimental variables. The major drawback of headspace GC-MS is quantification. As a result of the principle of headspace GC-MS, i.e., partitioning of compounds between gas phase and liquid phase, the chemical properties will have a significant influence on the partition of each molecule between gas phase and liquid phase. Therefore, quantification is almost solely possible by using external standards of the same compound (Grob and Barry 2004). 

Fig. 5.6 Possible identification strategy for nnknown migrants using GC-MS.

GRAMSHAW, J.W., VANDENBURG, HJ. and LAKIN, R.A., 1995, Identification of potential migrants from samples of dual-ovenable plastics. Food Additives and Contaminants, 12, 211-222. 

WAKUi c, KAWAMURA Y and MAiTANi T, Migrants and acrylonitrile from disposable gloves , Journal of the Food Hygienics Society of Japan, 2001 42 322-328. MUTSUGA M, WAKUI c, KAWAMURA Y and MAITANI T, Isolation and identification of some unknown substances in disposable nitrile-butadiene rubber gloves used for food handling , Food Additives and Contaminants, 2002 19(11) 1097-1103). 

Kim-Kang, H. Gilbert, S.G. Isolation and identification of potential migrants in gaimna-irradiated plastic laminates by using GC/MS and GC/IR. Appl. Spectrosc. 1991, 45, 572-580. 

Identification and concentrations of migrants were determimed by both gas chromatography with a mass selective detector (GC-MS) (Agilent 6890 equipped with... 

It can be seen that the GC-MS method would be likely to fail to properly detect potential migratable species such as low volatility monomers, higher MW oligomers and possibly miss out on certain compounds that decomposed during the analysis. These considerations explain why Lin and co-workers [6] utilised the non-destructive LC-MS method for detection and identification of the potential migrants from UV/EB curable, acrylate type formulations. 

Volatile migrants pose a different sort of challenge. The usual evaporative concentration techniques will result in the loss of analyte. The analyte may be partitioned into a small volume of non-volatile solvent for subsequent analysis, but identification of a useful combination of solvent miscibility and analyte solubility is often impossible. Solid phase extraction and solid phase micro-extraction are often very useful for aqueous/ethanolic matrices. Here, a large volume of matrix is brought into contact with a small amount of solid material for which the analyte has a high affinity. The analyte is then desorbed from the solid phase with an appropriate solvent for subsequent analysis. 

GC/FT-IR can be used for amino acid profiling with tert-butyldimethylsilyl derivatization, for the investigation of food-packaging materials, the analysis of biologically active wheat straw extracts with allopathic activity, that of cis- and traws-octadecanoic acids in margarines and of sugar units in disaccharides, for the identification of small molecular migrants extracted from y-irradiated plastic laminates or the radiolysis products of y-irradiated medazepam solution. 

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