Minimizing Phthalate Interferences Using the Rtx-CLPesticides/Rtx-CLPesticides2 Columns

Dan Li, Chris English, Jack Cochran, Jason Thomas, and Rebecca Stevens

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The alkyl and aryl esters of 1,2-benzenedicarboxylic acid, better known as phthalates, are widely used as plasticizers. Mainly added to polyvinyl chloride (PVC), phthalates make plastic products more durable and flexible. Phthalates are everywhere: plastic toys, PVC water pipes, wallpaper, artificial leather, electrical wire insulation, glue, nail polish, lipsticks, hair spray, plastic water bottles, paints and printing ink are all formulated using phthalate additives. These seemingly endless applications create a big marketplace. Health concerns bubbled up more than a decade ago over their potential to disrupt endocrine signaling [1].

Aside from health concerns, their ubiquity can cause frustration for chromatographers. Phthalates leached from laboratory consumables, such as rubber tubing, plastic syringes, pipette tips, plastic filters, plastic beakers, plastic stir bars, plastic vials, 96-well plates or other plastic labware can interfere with a lot of chromatographic analysis (both GC and LC). Common lab interference phthalates include diethylhexyl phthalate, diisononyl phthalate, di-n-butyl phthalate (from polytetrafluoroethylene), butyl benzyl phthalate, di-n-octyl phthalate and dimethyl phthalate (from cellulose acetate and Parafilm) [2]. In addition, lab gloves used in sample handling processes are another source for phthalates contamination.

The Rtx-CLPesticides/Rtx-CLPesticides2 GC column set provides unique selectivity and rapid determination of pesticides by GC- μECD (micro Electron Capture Detector) in the low pg range. The advantages of the μECD are clear; low detection of halogenated compounds with minimal interference from hydrocarbons and a variety of other sample matrix. The conjugate electrophore gives phthalate molecule good sensitivity on ECD detector as well. EPA methods 8061A and 606 also recommended ECD for phthalate analysis. Therefore, phthalates can interfere with target compound identification and quantification. This study was designed to determine where the phthalates elute on these pesticide columns relative to the US EPA 8081 chlorinated pesticides.

A significant number of phthalates were observed interfering with pesticides analysis (see the chromatogram and the table). Among contaminants, di-n-butyl phthalate and diethylhexyl phthalate are the most notorious in envirionment due to their low molecular weight, easy partition from polymer matrix, solubility in water, and high usage in polyvinyl chloride production.

Need suggestions to avoid phthalate contaminants? Sometimes avoiding the problem is better than solving the problem. Plastic is the most common source of phthalates. Use glass labware instead of plastic. Although micropipette tips and centrifuge tubes are made from polypropylene, which should be phthalate-free, phthalates can still leach from plastic pipette box, plastic pakage or plastic caps. When using glass, baking-out is a simple way to remove contaminants. In addition, rinsing glassware with redistilled solvents was found to be effective in eliminating phthalates contamination during sample preparation.

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Columns: Rtx®-CLPesticides 30 m, 0.32 mm ID, 0.32 μm (cat.# 11141) and Rtx®-CLPesticides2 30 m, 0.32 mm ID, 0.25 μm (cat.# 11324) using Rxi® guard column 5 m, 0.32 mm ID (cat.# 10039) with deactivated universal “Y” Press-Tight® connector (cat.# 20405-261); Sample: Organochlorine pesticide mix AB #2 (cat.# 32292), Pesticide surrogate mix, EPA 8080, 8081 (cat.# 32000); Injection: Inj. Vol.: 2 μL splitless (hold 0.3 min), Liner: Splitless taper (4 mm) (cat.# 20799), Inj. Temp.: 250 °C; Oven: Oven Temp: 120 °C to 200 °C at 45 °C/min to 230 °C at 15 °C/min to 330 °C at 30 °C/min (hold 2 min); Carrier Gas: He; Detector: μ-ECD @ 330 °C; Notes: Instrument was operated in constant flow mode. Linear velocity: 60 cm/sec @ 120 °C. This chromatogram was obtained using an Agilent μ-ECD. To obtain comparable results, you will need to employ a μ-ECD in addition to dual columns connected to a 5-meter guard column using a “Y” Press-Tight® connector. Concentrations are 8-80 ppb for pesticides and 10 ppm for phthalates.

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References:

[1] J. Annamalai, V. Namasivayam. Endocrine disrupting chemicals in the atmosphere: their effects on humans and wildlife. Environ. Int. 76 (2015),78-97.

[2] A. Reid, C. Brougham, A. Fogarty and J. Roche. An investigation into possible sources of phthalate contamination in the environmental analytical laboratory. Intern. J. Environ. Anal. Chem. 87 (2007) 125-133.

 

One Response to “Minimizing Phthalate Interferences Using the Rtx-CLPesticides/Rtx-CLPesticides2 Columns”

  1. […] her recent ChromaBLOGraphy posts, Minimizing Phthalate Interferences Using the Rtx-CLPesticides/Rtx-CLPesticides2 Columns and EPA Regulated Phthalates FREE?, my colleague Dan Li pointed out the ubiquitous nature of […]

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