ANALYTICAL Plasticizers APPROACH in Pacifiers: Direct Determination by FAB-MS
Jackson O. Lay, Jr. Barbara J. Miller National Center for Toxicological Research Jefferson, Ark. 72079
Phthalate esters are widely used plasticizers in flexible polyvinyl chloride (PVC). Of t h e phthalates, dioctyl phthalate has been the most commonly used; in 1979 it represented about 26% of the total phthalate plasticizer consumption in the United States. The dioctyl phthalate isomer used for plasticization, 1,2-benzenedicarboxylic acid bis(2-ethylhexyl)ester, also frequently named di(2-ethylhexyl) phthalate or DEHP, is reported to be an animal carcinogen. DEHP is found in such diverse materials as children's products, clothing, footwear, flooring, home furnishings, housewares, hardware, sporting goods, and personal products. Furthermore, DEHP is typically used in the PVC contained in these products at levels as high as 50% to achieve complete plasticization. Because D E H P is not chemically bound to PVC, significant migration of the plasticizer into the environment is possible. Indeed, DEHP has been detected in air, food, and water samples. These findings, as well as other studies, which have shown that DEHP could be detected in blood that had been stored in plastic bags, have resultThis article not subject to U.S. Copyright Published 1987 American Chemical Society
ed in an increased awareness of the potential for human exposure to DEHP resulting from the use of PVC products. In addition, migration of DEHP from PVC might also lead to human exposure via direct dermal or oral contact. For example, the presence of DEHP in some baby pacifiers may have exposed infants via direct oral uptake of DEHP from PVC. This specific concern has led to a voluntary ban on the use of dioctyl phthalate in baby pacifiers. Attempts to veri-
fy that this or other uses of DEHP have been discontinued require the development of very rapid analytical methods so that large numbers of samples can be examined in a timely manner. We have recently investigated the analysis of PVC pacifiers for D E H P (dioctyl phthalates) at levels of about 30% by weight. Although alternative methods had been developed for the analysis of DEHP in PVC based on lengthy extraction followed by gas chromatogra-
Figure 1. Relative response for DEHP and DDP [MH] + ions. ANALYTICAL CHEMISTRY, VOL. 59, NO. 22, NOVEMBER 15, 1987 • 1323 A
+
Ratio of [MH] ions for DEHP and DDP vs. concentration of DEHP in samples with 10 mg/mL DDP OEHP (mg/mL)
Ratio
0 0 2 2 2 2 5 5 5 5 5 5 5 5 5 5 10 10 10 10 10
0.017 0.005 0.374 0.399 0.413 0.439 1.17 1.09 1.06 1.36 0.99 1.08 1.20 1.17 1.01 1.01 2.23 2.23 2.46 2.47 2.32
phy or gas chromatography/mass spec trometry (GC or GC/MS), we believed a simpler and faster method for the de termination of dioctyl phthalates in PVC could be developed that would re quire neither extraction nor chromato graphic separation. As described be low, we were able to develop a method for the determination of DEHP (dioc tyl phthalate) in PVC at levels typical ly found in consumer products (~30%). This method is based on the addition of a reference material, didecyl phthalate (DDP), to a solution of the pacifier in tetrahydrofuran (THF) with quantita tion by fast atom bombardment mass spectrometry (FAB-MS). Previous reports of quantitative measurements employing FAB-MS suggested to us that this ionization technique might be amenable to our analytical problem, especially if we em ployed an internal standard. We were interested in FAB not for the usual rea sons associated with the analyte being too polar or unstable for the applica tion of an alternative ionization meth od, but rather because of our desire to minimize or eliminate all chromato graphic and extraction steps. We rea soned that it ought to be possible to quantitate the amount of DEHP based on the protonated molecules of DEHP and DDP. Also, we expected that some selective ionization of the analyte and reference standard rather than bulk PVC might occur because of the high molecular weight of the PVC polymer.
Table 1. Concentrations of DEHP in percent by weight of four brands of infant pacifiers as determined by FAB-MS
Pacifier brand A A Β C D
Standard Sample weight Concentration deviation (mg) (%)
