Speciation of methylcyclopentadienyl manganese tricarbonyl by high-performance liquid chromatography-diode laser atomic absorption spectrometry

Methylcyclopentadienyl manganese tricarbonyl (MMT) is a fuel additive that has been marketed for use in unleaded gasoline since December 1995, The wid espread use of this additive has been suggested to cause health risks, but limitations in data regarding its degradation products and their toxicity p revent an accurate evaluation. To monitor the organomanganese compounds, it is clearly advantageous to employ low-cost, high-sensitivity, manganese-sp ecific instrumentation to perform speciation, In this work, instrumentation fitting these criteria was obtained by the combination of high-performance liquid chromatography (HPLC) with diode laser atomic absorption spectromet ry (DLAAS) and was used to determine MMT, its nonmethylated derivative, cyc lopentadienyl manganese tricarbonyl (CMT), and inorganic manganese. DLAAS w as shown to be a versatile analytical technique for total Mn determination, with a detection limit of 1 ng/mL and a Linear dynamic range (LDR) of almo st 5 orders of magnitude. Analytical figures of merit for HPLC-DLAAS includ ed a detection limit of 2 ng(as Mn)/mL, a LDR of 3 orders of magnitude, and an analysis time of three minutes. The organometallic compounds are charac terized by rapid photolysis in sunlight, and hence, experiments were perfor med to evaluate whether normal laboratory lighting is suitable for their de termination. Our results showed that normal laboratory protocols may be emp loyed except that the organomanganese compounds should be stored away from light except during sample introduction procedures. The ability of the inst rumentation to selectively preconcentrate organomanganese compounds while r emoving inorganic manganese was demonstrated. Sufficient resolution was obt ained to determine a 20-fold excess of CMT compared with MMT. The ability o f the system to do practical analysis was demonstrated by the accurate dete rmination of MMT in spiked samples of gasoline, human urine, and tap water. These results demonstrate the suitability of HPLC-DLAAS for the speciation of MMT and its derivatives in industrial, toxicological, and environmental samples.