EPA Regulated Phthalates FREE?

Dan Li, Rebecca Stevens, and Chris English

BLOG impurity

Phthalates are a class of compounds that have gained global notoriety. Most investigations focus on determination of phthalates in environmental matrices, baby products or demonstrate the adverse effect on human health. However, the presence of EPA regulated phthalates as impurities in technical phthalate mixtures is underestimated. Regulated phthalate impurities are formed as byproducts of synthesis and are difficult to separate from the technical materials.

The use of non-regulated phthalates should take into consideration regulated phthalate impurities. There are few reports on the analysis of technical-grade phthalate mixtures, indicating that the level of regulated phthalates may be underestimated. In this study, non-regulated technical-grade phthalates from different vendors were investigated using gas chromatography-mass spectrometry (GC-MS). Relatively high levels of regulated phthalates were found as impurities in non-regulated phthalates.

The standard EPA Method 8061A Phthalates Mixture (cat.#: 33227) consists of 15 components, each at a concentration of 1,000 μg/mL. Benzyl benzoate (cat.#: 31847) was used as the internal standard. Technical-grade phthalates (Table 1) were purchased from two vendors.

Table 1

The GC-MS analysis was performed on a Shimadzu GC-MS QP2010 Plus instrument. An Rtx®-440 capillary column of 30 m x 0.25 mm x 0.25 μm dimension (cat.# 12923) and 3.5 mm Precision Liner w/wool (cat. # 23320.1) were employed for analysis. See Table 2 for experimental details.

Table 2

Standard solutions were prepared in a concentration range of 1-80 μg/mL (2-100 μg/mL for di-n-octyl phthalate) for calibration curves. The final concentration of the internal standard (benzyl benzoate) in both calibration curves and standards is 20 μg/mL. The technical-grade standards were prepared at 200 μg/mL, except for benzyl 2-ethylhexyl phthalate from Vendor 1, which was prepared at 300 μg/mL to get the impurities in the range of the calibration curve. All standards and tested samples were dissolved and diluted with methylene chloride. During sample preparation plastics were strictly avoided; all preparation work was done using glassware (volumetric flask, syringe, vial, etc).

The Rtx®-440 column (cat.# 12923) provides excellent separation and quantification of the EPA method 8061A phthalate targets (Figure 1). In this mixture, only five components (bis(2-ethylhexyl) phthalate, di-n-butyl phthalate, di-n-hexyl phthalate, dicyclohexyl phthalate and di-n-octyl phthalate) were calibrated since they were present as impurities in technical-grade phthalates. A seven-point internal standard calibration was conducted for each monitored phthalate. The calibration curves were obtained by linear regression of the peak area ratio against concentration ratio of analytes to internal standard. Each sample was injected twice. The linearity (R2) was greater than 0.999 for all five components calibrated (Table 3).

Figure 1

table 3

Basically, there are two types of technical-grade phthalates. One type of mixture, such as diisononyl phthalate and diisodecyl phthate, consists of different isomers. The quantification of this type is difficult because the total amount is spread out across many isomer peaks [1]. The other type contains synthetic byproducts that are not removed from main products. For instance, two impurities were detected from hexyl 2-ethylhexyl phthalate, including di-n-hexyl phthalate and bis(2-ethylhexyl) phthalate, which are obviously yielded from synthesis due to the structural relationship (Figure 2).

Figure 2

Among the impurities, only EPA regulated phthalates were measured. The obtained results are shown in Table 1. Impurities levels from two different vendors are consistent with each other except for benzyl 2-ethylhexyl phthalate (highlighted in Table 1), where the concentration is lower for Vendor 1 (1.1%) compared with Vendor 2 (18.1%). This suggests that Vendor 1 and 2 may have a different synthesis process or a different raw material was purchased for this compound. The concentration of regulated phthalate as impurities ranges from 1% to 25%.

The non-regulated technical-grade phthalates are commonly found in industry. Butyl benzyl phthalate, butyl cyclohexyl phthalate and butyl octyl phthalate are widely used as plasticizer, because they are highly compatible or share similar solubility with various polymers, such as polyvinyl acetate, polyvinyl chloride, cellulose nitrate, epoxy, urethane, polyamide, acrylic and so on [2].

Bis(2-ethylhexyl) phthalate is present in a variety of technical-grade phthalates at relatively high concentrations. Therefore, the actual concentration of bis(2-ethylhexyl) phthalate in plastic products may exceed the regulation limit, even if the manufacturer only uses non-regulated phthalates.

In summary, the quantification of technical-grade phthalate mixtures revealed regulated phthalates as impurities and underscores the importance of this study. The Rtx®-440 column (cat.# 12923) is a good choice for phthalate separation and quantification. Impurity levels in phthalates provided by two different vendors were consistent, except for benzyl 2-ethylhexyl phthalate. The use of these technical mixtures tested in this study for manufacturing of plastics may be cause for concern.

Acknowledgements: The authors would like to thank Shimadzu Corporation for their consultation with the operation of the QP2010 Plus GC-MS Instrument.

References

[1] Lin, Z.-P., M. G. Ikonomou, H. Jing, C. Mackintosh, F. A. P. C. Gobas, Determination of phthalate ester congeners and mixtures by LC/ESI-MS in sediments and biota of an urbanized marine inlet. Environ. Sci. Technol. 37, 2100-2108 (2003)

[2] Lokensgard E, Industrial Plastics: Theory and applications. 5-th Edition, 112-113.

2 Responses to “EPA Regulated Phthalates FREE?”

  1. Kyle D'Silva says:

    Nice application and blog guys.

  2. […] dual column set for the analysis of regulated phthalates using µECD. As shown in my previous blog , the Rtx-440 column (cat. # 12923) is a perfect choice for fast phthalate separation and […]

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