Production of blank water for the analysis of volatile organic compounds in human blood at the low parts-per-trillion level.

Blank water with low levels of volatile organic compounds (VOCs) is of critical importance in many analytical procedures. Because of the increased use of more sophisticated instrumentation, the detection limits for these compounds have dropped dramatically. Consequently, techniques in use in the analytical laboratory to generate blank water may now prove inadequate. The need for blank water with low levels of VOCs was recently underscored by the development of an analytical procedure to analyze 32 VOCs in whole blood; this procedure has detection limits in the tens of parts-per-trillion level for most VOCs. Common sources of blank water in the laboratory such as deionized, cartridge-filtered, and HPLC-grade bottled water are analyzed. These sources contained high concentrations of some VOCs that would interfere with low parts-per-trillion analyses. Well water and bottled water used for human consumption are analyzed, but both prove inadequate for the analysis of VOCs at parts-per-trillion levels. A combination of distillation and purging with helium produced blank water with VOC levels of less than 10 parts-per-trillion for most of the 16 VOCs studied.