How Can PCBs Be Isolated and Recovered from Serum, Plasma, or Organ for Trace Enviro-health QA?

Figure 3.10 (introduced earlier) is a flowchart that summarizes this author’s attempt to use RP-SPE as part of a combination of sample prep techniques that isolate and recover AR 1248 with nearly 100% recoveries.¹⁰³ PCBs are easily released from a serum, plasma, or tissue homogenate via probe sonification (PC), coagulation using acetonitrile, or other water-miscible organic solvent or salt. The supernatant aqueous phase is easily separated from the coagulated protein via mini-centrifugation. RP-SPE serves in this case, similar to the situation when an environmental water sample is passed through, as an on-off or digital extraction step. The dilute of the aqueous supernatant serves to decrease the analyte-matrix interaction, as discussed earlier, which in turn strengthens the analyte-sorbent interaction. In this case, the combination of PS-RP-SPE with C-GC-ECD as the determinative technique eliminated the need for further cleanup. Such might not be the case if C-GC-MS or another universal determinative technique is used. Cleanup techniques might then need to be considered. Table 3.26 lists the excellent % recoveries obtained from the author’s method development study.

TABLE 3.26

% Recoveries for the Isolation and Recovery of AR 1248 Comparing Spiked Acetonitrile to Spiked Rat Liver Homogenate

FIGURE 3.49A

Janak and coworkers have discussed a similar approach to the isolation and recovery of PCBs from whole blood.¹⁰⁴ Details of their approach are outlined via a flowchart in Figure 3.49A and Figure 3.49B. Referring to Figure 3.49A, formic acid dissolved in isopropyl alcohol (IPA) was used to coagulate protein from 5 g of whole blood prior to bath sonication. After passing the supernatant through a conditioned RP-SPE cartridge, the sorbent is washed with 5% IPA dissolved in water, followed by 10% methanol in water. The sorbent is then washed again with a series of solutions as indicated and dried. Referring to Figure 3.49B, the sorbent is eluted with methylene chloride (dichloromethane), then evaporated down to 10 pL, and finally reconstituted with enough heptane to yield ~100 pL. This heptane eluent is transferred to a Pasteur pipette filled with mixed adsorbents and previously rinsed with heptane. The cleaned-up PCBs are subsequently eluted with a binary solvent eluent consisting of 4:1 heptane to methylene chloride. Mean percent recoveries reported from spiked whole-blood specimens were 78 ± 8%.¹¹⁾⁴

FIGURE 3.49В

Readers can refer to the numerous logical flow chart diagrams shown in Appendix D that describe many innovative approaches to conduct sample prep for both enviro-chemical and enviro-health TEQA.

PBDEs, Used as Flame Retardants, Are More Contemporary Pollutants. Have These Organic Compounds Been Studied by RP-SPE Sample Prep Techniques?

Within the first decade of the 21st century, a class of organic compounds very similar in its chemistry was making headlines. Polybrominated diphenyl ethers, PBDEs, whose molecular structures are closely related to the polybrominated biphenyls, PBBs. There exists 209 distinct PBDE congeners as is found for both PBBs and PCBs. Scheter and coworkers reported that dioxin, dibenzofuran, and PCB levels in human blood are much lower in 2003 when compared to 1973 levels; however, the opposite is true for PBDEs. Unlike dioxin, dibenzofuran, and PCBs, they found no significant correlation between PBDE levels and age.¹⁰⁵ A comprehensive study of the most common PBDE congeners: BDEs 28, 47, 77,100, 99, 85, 154, 153, 183 that compared

% recoveries from human and sheep serum using both LLE and reversed-phase solid-phase disk extraction (RP-SPDE) sample prep techniques brought unique insights."¹⁶

RP-SPE as a sample prep technique is low cost, effective, and continues to gain popularity as regulatory restrictions lift over time. For enviro-chemical QA considerations, Font et al. have reviewed developments in water pollution analysis for PCBs and earlier published a review applicable to multiresidue pesticide analysis of water.¹⁰⁷¹⁰⁸ For enviro-health QA considerations, a comprehensive RP-SPE study involving bovine and human serum conducted by Brock and colleagues at the National Center for Environmental Health (NECH), Centers for Disease Control and Prevention (CDC) is noteworthy.¹⁰⁹ A plethora of analytical papers utilizing RP-SPE techniques as a viable alternative to LLE continue to be seen in the primary analytical chemistry literature. Over the last decade, advances in the technology for SPE have added the so-called 96-well plate with accompanying sample prep automation to the analytical chemist’s arsenal. We now consider a sample prep technique developed during the late 1980s that relates to SPE, yet is applicable to solid matrices, in particular biological tissue specimens. It is called matrix solid-phase dispersion.