Studies of climate change increasingly recognize the diverse influences exerted by monoterpenes in the atmosphere, including roles in particulates, ozone formation and oxidizing potential. Measurements of key monoterpenes suggest atmospheric amount-of-substance fractions (concentrations) ranging from low pmol/mol (parts per trillion; ppt) to nmol/mol (parts per billion; ppb), depending on location and compound. To accurately establish concentration trends, assess the role of monoterpenes in atmospheric chemistry, and relate measurement records from many laboratories and researchers, it is essential to have good calibration standards. The feasibility of preparing well characterized, stable gas cylinder standards for monoterpenes at the nmol/mol level was previously tested using treated aluminum gas cylinders at NIST. Results for four of the eleven monoterpenes, monitored versus an internal standard of benzene, indicated stability in these treated aluminum gas cylinders for over six months and projected long term (years) stability. However, the concentration of the key monoterpene ß pinene decreased, while the concentrations of α pinene, d limonene (R (+) limonene), p cymene, and camphene (a terpene not present in the initial gas mixture) increased, indicating a chemical transformation of ß pinene to these species. A similar pattern of decreasing concentration was observed in α pinene where growth of d limonene (R (+) Limonene), p cymene and camphene has been observed in treated gas cylinders prepared with a mixture of just α pinene and benzene as the internal standard. The current research discusses the testing of other cylinders and treatments for the potential of long term stability of monoterpenes in a gas mixture. Both ß pinene and α pinene show somewhat improved short term stability in nickel plated carbon steel cylinders, but excellent stability at over 6 months in aluminum cylinders treated with a different process than used in the original study.
Citation: Analytical Chemistry
Pub Type: Journals
Aculife IV, Carbon steel cylinders, Experis, Degradation, Growth rate, Internal standard, Isomerization, Monoterpenes