Previously we wrote about esters of phthalic acid that are mainly used as plasticizers (substances added to plastics to increase their flexibility, transparency, durability, and longevity). Phthalate esters are the main plasticizers used as softening agents in the production of PVC, and there have been reports that certain beverages, particularly fruit juices, contain high levels of phthalates.
If you are tasked with determining phthalate esters in soft drinks using gas chromatography coupled with mass spectrometry, here are some tips for your sample preparation.
Sample Prep Tips
The standards and extracts need to be prepared in scrupulously clean glassware. Avoiding any contact with plastic is vital as phthalates can contaminate glassware and blank samples very easily. Glass analytical syringes, glass pipettes, and pesticide grade solvents should be used for preparing samples.
Glassware needs to be scrupulously cleaned by rinsing first with water and then with acetone and hexane. For accuracy, the calibration samples should be prepared using a digital dispenser that accurately and reproducibly performs a wide variety of liquid handling procedures – as well as one that has a glass syringe barrel and stainless steel dispensing needle. This avoids the use of plastic pipettes; any plastic containers need to be avoided to reduce potential phthalate contamination in the sample preparation.
To prepare the spiked soft drink samples, 300 ng/mL and 1000 ng/mL of phthalate should be prepared in acetone spiked into 5 mL of soft drink followed by the addition of 5 mL of dichloromethane containing 1000 ng/mL internal standard. Shake the solution mixture vigorously. An aliquot of organic layer will be transferred to the gas chromotography vial.
Use a high injector temperature (320 °C) to release the high MW phthalates or any absorbing phthalates in the injector head.
To read about an analysis done to demonstrate the quantitative analysis of phthalate esters in soft drinks, which includes the sample preparation details and other experiment notes, read the Determination of Phthalate Esters in Soft Drinks By GC-MS application note.