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10.2417/spepro.005145

Measuring the concentration ofphthalate plasticizers inpoly(vinyl chloride)Vadim V. Krongauz, Michael T. K. Ling, and John F. OConnell

A new gas chromatography method was used to analyze phthalate plas-

ticizer concentration after poly(vinyl chloride) sample dissolution with

consequent phthalate extraction and polymer precipitation.

Poly(vinyl chloride) (PVC) became one of the most useful materials

known today after Waldo Lonsbury Semons discovery of plasticiza-

tion in 1926. The use of plasticizers as such, however, began in the

mid-1860s when castor oil was added to soften cellulose nitrate.1, 2

Plasticized PVC is used in food packaging, shoes, furniture, cars, toys,

medical devices, clothing, plumbing, tool handles, and many other ap-

plications. The most popular plasticizer for PVC is di(2-ethylhexyl)

phthalate (DEHP). Like many other materials in consumer use, DEHPwas suspected as possibly causing adverse physiological effects.38 Al-

though the debate over the existence of adverse DEHP effects contin-

ues, the analysis of DEHP and other phthalates present in PVC parts is

required by regulatory agencies. The concentration of tri(2-ethylhexyl)

trimellitate, di(2-ethylhexyl) terephthalate, and other plasticizers cur-

rently replacing DEHP in commercial products is also often examined.

To quantify the amount of phthalate plasticizers in PVC, analyti-

cal methods based on solvent extraction of phthalates from the poly-

mer parts and consequent chromatographic analysis are employed.38

In many cases the solvent of choice does not dissolve PVC, and the

extraction only partitions the phthalate between the polymer part and

the solvent, leaving some amount of plasticizer remaining in the PVC.

Phthalate extraction from the PVC solid is time-consuming, since

molecular diffusion occurring during extraction from polymers is very

slow.912 To reduce measurement uncertainty, and to accelerate and

simplify the extraction of phthalate plasticizers from PVC, the US Con-

sumer Product Safety Commission developed an analytical approach in

which an entire sample of plasticized PVC was used after dissolving it

in tetrahydrofuran (THF).8 The dissolved PVC was then precipitated

from THF by a nonpolar solvent (hexane), while phthalate plastici-

zers remained in the hexane/THF solution.8 Since PVC precipitation

Figure 1.Photographs of the consecutive steps in plasticized poly(vinyl

chloride) (PVC) analysis: 4.0g of methyl ethyl ketone was added to

plasticized PVC (left); 10.0ml of hexane was added in two steps (cen-

ter); 5.0ml of 0.9% saline solution and 1.0g of sodium chloride were

added to precipitate the polymer and salt out the organic solvents from

the aqueous layer, followed by a 1h settling at 4 C (right).

produced a stable PVC suspension, it was recommended that the

solution should be filtered.

We extended the method based on complete PVC dissolution8 by

eliminating the need for solution filtration.13 In our approach we also

dissolved plasticized PVC in a polar solvent, methyl ethyl ketone

(MEK), then precipitated PVC by adding a nonpolar solvent (hexane),

forming a PVC suspension. However, instead of filtration we broke the

PVC suspension and precipitated the PVC by adding an aqueous so-

lution of a strong electrolyte such as sodium chloride. The electrolyte

cleanly precipitated and aggregated the PVC into a water-organic layer

interface (see Figure 1). The salting out effect described quantitatively

by Setschenow and Debye1417 ensured that MEK and hexane formed

an organic layer with a clean boundary where relatively nonpolar ph-

thalate plasticizers were concentrated. The sample of organic layer was

then analyzed using our new gas chromatography (GC) procedure.13

Several gas chromatographic techniques were used for the analysis

of phthalates in the past.38 We developed another straightforward GC

method of phthalate analysis using a Supelcowax 10 capillary column,

designed for solute separation primarily based on molecule polarity.

After injection of the analyte solution, the column was held at 100C

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for 5min, then the temperature was raised to 300

C at 5

C/min, and held

at 300C for 5min. Anisole was used as an internal standard. Our GC

method allowed simultaneous determination of high- and low-boiling

PVC formulation components13 (see Figure 2).

Poly(vinyl chloride) and other polymers may contain a variety of

additives, such as acid and radical scavengers, and antioxidants: for

example, 4-methoxy phenol (monomethyl hydroxyl quinone ester, or

MEHQ) and 3,5-di-tert-butyl-4-hydroxytoluene (butylhydroxytoluene,

or BHT). We used the Supelcowax 10 capillary column and the GC

conditions described above to demonstrate that our developed approach

would allow separation of stabilizers from each other and from the ph-

thalate plasticizers (see Figure 3). The BHT and MEHQ separation dis-

cussed as an example of the capabilities of the GC analysis may require

less preparative work than the corresponding liquid chromatographicmethods.38

We successfully used our approach to find the phthalate plasticizer

concentration in a variety of plasticized PVC samples, such as pellets,

films, and finished parts, both developmental and commercial. We were

also able to quantify the organic stabilizers and radical scavenger addi-

tives present in some PVC samples. The extraction of plasticizers from

PVC by a solvent that does not dissolve PVC may be incomplete and is

definitely slow. Therefore, an approach based on complete dissolution

of the samples reduces the possibility of errors in quantitative analysis.

The precipitation of the PVC colloid using an aqueous electrolyte so-

lution further improved the accuracy and precision of the method. Due

to its robustness, the method could be further modified and optimized

Figure 2. A typical gas chromatogram (GC) of the hexane solu-

tion of the anisole internal standard (retention time (tr ) 1.6min),

di(2-ethylhexyl) phthalate (DEHP) (tr 32.77min), di(2-ethylhexyl)

terephthalate (DOTP) (tr 34.85min), and tri(2-ethylhexyl) trimellitate

(TOTM) (tr 43.75min) obtained using a Supelcowax 10 capillary col-

umn.

Figure 3.A typical chromatogram of the hexane solution of the stabiliz-

ers 3,5-di-tert-butyl-4-hydroxytoluene (butylhydroxytoluene, or BHT)

(tr 11.97min), and 4-methoxy phenol (monomethyl hydroxyl quinone

ester, or MEHQ) (tr 20.49min) obtained using a Supelcowax 10 capil-

lary column with the GC method outlined in this article.

for different tasks, just as we modified the method first presented by

the scientists from the US Consumer Product Safety Commission. For

instance, the type and amount of solvent used to dissolve PVC samples

can be changed, or the thermal regime of the GC oven can be altered.

We would like to thank Baxter Healthcare Corporation for supportingthis work.

Author Information

Vadim V. Krongauz, Michael T. K. Ling, and John F. OConnell

Baxter Healthcare Corporation

Round Lake, IL

Vadim Krongauz is a senior research scientist. He has a BSc/MSc

in chemistry from the Lomonosov Moscow State University, Russia,

and a PhD in physical chemistry from the University of Washington,Seattle.

John OConnell is an engineer specialized in analytical chemistry. He

has a BSc in materials science and engineering (biomaterials) from the

University of Illinois, Champaign-Urbana.

Michael T. K. Ling is the senior director of the materials science di-

vision. He has an MSc in aerospace and mechanical engineering, and

an MEM from Northwestern University.

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c 2013 Society of Plastics Engineers (SPE)