INTRODUCTION

Polychlorinated biphenyls (PCBs) were extensively used in the past throughout the world, especially as coolants and dielectric fluids, stabilizing additives in PVC and plastic products, flame retardants, sealants etc. These compounds are a class of man-made organic compounds with notable and useful characteristics, such as non-flammability, heat resistance, insulation, and chemical stability. Nevertheless, PCBs are very dangerous chemicals and exposure to them can cause acute and chronic effects (chlorine acne, irritation of mucous membranes, cancer, immunological disturbances etc).

Based on the abovementioned reasons the determination of PCBs inaqueous and solid samples is routinely required. Fast Gas Chromatography (Fast GC) has resulted in a very powerful way to address the demand for increased productivity and reduced costs per analysis. However, when complex samples are to be analyzed the high quantity of very narrow peaks results in a daunting analytical task. Moreover, when positive identifications are mandatory and mass spectrometric detection is needed, conventional quadrupoles or ion trap mass spectrometers do not provide enough information for reliable peak reconstruction of these very narrow peaks over the full mass range. The time of flight mass spectrometer (TOF-MS) is the only system capable of providing high speed acquisition rate to collect a sufficient number of information (15 -20 points/peak), enabling an accurate recognition and quantification of unknown and co-eluting peaks typically present in complex samples. 

In the present work the suitability of a Fast GC/TOF-MS system to fulfill the PCBs determination is investigated. Pure mass spectra are generated and submitted as unknowns to mass spectral library search.

INSTRUMENTATIONAND EXPERIMENTAL CONDITIONS

DANI MASTER GC/TOF-MS equipped with MASTER AS Liquid Autosampler

Sample

A standard mixture of 19 PCB congeners in hexane (Restek, U.S.A.) at different concentrations was analyzed. The congeners are listed in Table 1.

MASTER GC Gas Chromatograph

Injector: Split-Splitless;

Injector Temperature: 320°C

Injector Volume: 0.5  μl

Split Ratio: 1:20

Column: SLB 5ms, 5m x 0.1mm x 0.1μm

Carrier gas (He) flow rate: 0.5 mL/min

Oven Temperature Program: from 120°C to 200°C at 35°C/min to 300°C at 30°C/min (hold 2 min)

MASTER TOF-MS

Transfer line temperature: 250°C

Acquisition Rate: 50 spectra/sec

Start-end mass: 50 –550 amu

Ion source temperature: 240°C

Acquisition time: 5 min

Solvent delay: 30 sec

RESULTS AND DISCUSSION

The standard mixture of 19 PCB congeners was analyzed using FastGC conditions, applying the method previously indicated : Figure 1shows the chromatogram acquired with a 5 meter column: although the analysis time is very short (5 minutes) the 19 compounds maintain a good separation.

In Table 1retention time, library searches matching and coefficients of determination (r2) are reported. The calibration responses were evaluated in a range from 2.5 to 500 pg in column. In Figure 2a calibration plot example is reported.

Figure 3presents the comparison between the mass spectrum of 2,2',5-Trichlorobiphenyl, obtained during analysis, and spectrum stored in the NIST Library: the matching is 928 and the reverse matching is 979. In addition, the spectra acquired with the TOF-MS are fully comparable with spectra contained in the NIST®MS Library.

CONCLUSIONS

This investigation regards the application of Fast GC-Time of Flight Mass Spectrometry for PCB analysis. The application of Fast GC has drastically reducedanalysis time and the use of the TOF-MS enabled to obtain distinguishable signals for the PCBs, providing their identification and allowing their quantification over several orders of magnitude of concentration.