How to Detect Phthalates in Food Contact Materials

Phthalate esters share the same basic structure, and their mass spectra are similar when the electron ionization (EI) method is used, which can make the identification of target phthalate esters difficult. Conventionally, in such cases, the molecular weight is confirmed via the positive chemical ionization (PCI) method, using methane, isobutane, and other flammable, high pressure gases. In contrast, if the use of flammable, high pressure gases is problematic, the molecular weight can be confirmed via the SMCI method using organic solvents.

Here, we present the results of an analysis of phthalate esters using the SMCI method.

Samples and analytical conditions. A standard solution of phthalate esters was prepared to a concentration of 1.0 ng/mL. The solution was measured using the EI and SMCI methods.

EI and SMCI mass spectra. When a similarity search was performed from the EI mass spectrum for Di-n-octyl phthalate, phthalate esters with different molecular weights but with a high degree of similarity were identified. Because compound identification using only the EI mass spectrum was difficult, the number of candidate compounds was narrowed down by confirming the molecular weights using the SMCI mass spectrum.

Additionally, Figure 3 shows the mass spectra for typical phthalate esters using the EI method and SMCI method, respectively, and Table 1 shows the capability of confirmation of molecular derived ions.

The molecular ions for many of the phthalate esters cannot be confirmed using the EI method. In contrast, using the SMCI method, the protonated molecular ions for all the phthalate esters can be confirmed, which provides strong support for compound identification.

For many phthalate esters, confirmation of molecular weight from the EI mass spectrum is difficult. However, pseudo molecular ions can be confirmed using the SMCI method. Accordingly, even if the use of a flammable, high pressure gas is problematic, it is evident that the SMCI method is effective for the confirmation of molecular weights.

Dr. Kuhn is a chromatographer and marketing manager for food and consumer products at Shimadzu Scientific Instruments. Reach him at [email protected].