Organic Contamination Monitoring and Control in the Lunar Receiving Laboratory

The assessment of the indigenous organic matter in returned lunar samples has been a primary scientific goal of the Apollo program. The levels of such indigenous organic material were expected to be and found to be small. The pristine integrity of the lunar samples, however, could only be realized by carefully controlling the collection, processing, and analyzing of lunar samples so they might remain free of any significant levels (average laboratory detection limit of 10⁻⁹ g/g) of terrestrial contamination.

The primary purpose of this paper is to describe the contamination control procedures adopted to meet these requirements, to present briefly the analytical evidence obtained throughout the program on potential contamination sources, and to summarize the types and levels of organic contaminants actually found in the lunar samples.

The control of potential organic contamination of the lunar samples has consisted of: (a) severe limitations on materials which “see” or contact the lunar samples, (b) isolation of the sample in controlled environments at all times, (c) development of procedures to clean all surfaces which come into direct contact or may “see” the samples, and (d) strict controls on fabrication, processing, and handling of all lunar sample hardware. Materials actually contacting the lunar sample have been limited to stainless steel, aluminum alloy, and Teflon. Samples were handled under clean vacuum or nitrogen environments whenever possible. Cleaning methods capable of achieving total organic contamination levels on surfaces of less than 10⁻⁹ g/cm² were implemented for all surfaces contacting lunar samples.

A contamination monitoring scheme was put into effect to assist in the evaluation of cleaning procedures and to assess the quantity and type of organic contamination that finds its way into the samples despite the controls discussed. This consisted of the analysis of: (1) York mesh samples or aluminum foil processed with the flight Apollo lunar sample return containers (ALSRC); (2) the analysis of solvent wash samples used to clean all Lunar Receiving Laboratory (LRL) sample processing tools, cabinets, equipment, and containers; (3) the analysis of lunar module (LM) exhaust gas products; and (4) the analysis of sintered samples of Ottawa sand exposed to the various processing cabinets in the LRL.

Monitoring of the processing activities in the Lunar Receiving Laboratory during simulations prior to Apollo 11 indicated that organic contamination levels as high as 1000 ppm might be introduced to the lunar samples. Procedural and handling improvements reduced this level to less than 1 ppm during processing of Apollo 11 lunar material. Further controls, more thorough cleaning and greater attention to potential sources of contamination reduced the level to less than 0.1 ppm during Apollo 12 sample processing. Preliminary data indicate the levels for the Apollo 14 and 15 sample processing were also less than 0.1 ppm. The major contaminants found in the lunar samples (mainly, Apollo 11 and 12) consisted mainly of hydrocarbons, phthalate esters, LM exhaust products, plastics-Teflon, Mylar, etc., and some silicones.

It can be concluded that a contamination control plan has been successfully developed and implemented, providing investigators with lunar samples containing less than 0.1-ppm total organic contamination, which is as low or lower than the experimental blanks obtained in organic geochemical research laboratories.