To avoid phthalates contamination, all glassware wash with acetone and rinse with dichloromethane before dried at 120 oC for overnight.Also O-rings can be damaged by

high temperatures.

If you're using PEEK tubing, maybe have a set just for phthalates, it accumulates in the PEEK tubing, I have found.

Avoid any plastic material contact

water double disitilled only on glass,

There is a wide range You can do: phthalates are ubiquitous (especially dibutyl-, diisobutyl and diethylhexylphthalate) and therefore You have to avoid contamination.

High impact sources are soft PVC (like vinyl gloves, flooring, PVC tubing) and recycling paper. Avoid such materials in Your phthalate lab. Redistil solvents, they are also an important source. Use clean phthalate-free water (HPLC grade, tap water may work also in some regions). All glassware has to be rinsed with clean (distilled) solvents. Dust has to be avoided.

Furthermore keep an eye on the storage of Your samples. Wrap samples in alumina foil during storage to avoid contamination through recycled paper and cardboard.

Some literature with respect to these problems:

Zimmermann S, Gruber L, Schlummer M, Smolic S, Fromme H. Determination of phthalic acid diesters in human milk at low ppb levels. Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2012;29(11):1780-90. doi: 10.1080/19440049.2012.704529.

Fankhauser-Noti, A., Grob, K., Blank problems in trace analysis of diethylhexyl and dibutylphthalate: Investigation of the sources, tips and tricks. Anal. Chim. Acta 2007, 582, 353-360. DOI: 10.1016/j.aca.2006.09.012

Thanks for all replaying and support. The following article (My recent article) link is given to those who are still looking newly for how to avoid phthalates contamination during phthalates analysis.

Article Rapid determination of phthalate esters in edible oils with ...

Here you can find literature about phthalates contamination in analysis of food and food contact materials:

Van Holderbeke M, Geerts L, Vanermen G, Servaes K, Sioen I, De Henauw S, Fierens T.:Determination of contamination pathways of phthalates in food products sold on the Belgian market.Environ Res. 2014 Sep 5;134C:345-352. doi: 10.1016/j.envres.2014.08.012. 

Fierens T, Servaes K, Van Holderbeke M, Geerts L, De Henauw S, Sioen I, Vanermen G.:Analysis of phthalates in food products and packaging materials sold on the Belgian market.,Chem Toxicol. 2012 Jul;50(7):2575-83. doi: 10.1016/j.fct.2012.04.029.

https://www.researchgate.net/publication/272788973_Distribution_of_phthalate_esters_in_Egyptian_edible_oil

Article Distribution of phthalate esters in Egyptian edible oil

Microtips also plastic.so how can we avoid such..