ASTM D7687-17

5.1 This test method measures the concentration of cellular-ATP present in the sample. ATP is a constituent of all living cells, including bacteria and fungi. Consequently, the presence of cellular-ATP is an indicator of total metabolically active microbial contamination in fuels. ATP is not associated with matter of non-biological origin.

5.2 This test method is similar to Test Method E2694 except for the volumes sampled.

5.3 This test method differs from Test Method D4012 in that it utilizes filtration and wash steps designed to eliminate interferences that have historically rendered ATP testing unusable with complex organic fluids such as fuel and fuel-associated water.

5.4 This test method differs from Test Method D7463 in several regards:

5.5 This test method can be used with all fuels specified in Specifications D396, D975, D1655, D2069, D2880, D3699, D6751, and D7467 and other fuels with nominal viscosities ≤75 cSt at 20° ± 2°.

5.6 The ATP test provides rapid test results that reflect the total bioburden in the sample. It thereby reduces the delay between test initiation and data capture, from the 36 h to 48 h (or longer) required for culturable colonies to become visible, to approximately 5 min.

5.7 Although ATP data generally covary with culture data in fuel and fuel-associated water, different factors affect ATP concentration than those that affect culturability.

5.8 As explained in Test Method D7978, there are inherent difficulties in assessing precision of microbiological procedures for fuels on account of the inherent variability of the determinant and various determinable and indeterminable sources of inaccuracy (see Guide D7847).

1.1 This test method covers a protocol for capturing, extracting and quantifying the cellular adenosine triphosphate (cellular-ATP) content associated with microorganisms found in fuels and fuel-associated water.

1.2 The ATP is measured using a bioluminescence enzyme assay, whereby light is generated in amounts proportional to the concentration of cellular-ATP in the samples. The light is produced and measured quantitatively as relative light units (RLU) which are converted by comparison with an ATP standard, computation to pg ATP/mL and optional further transformation to Log_{1.3 This test method is equally suitable for use as a laboratory or portable method.}

1.4 This test method is limited to fuels with a nominal viscosity ≤75 cSt at test temperature.

1.5 This test method detects ATP concentrations in the range of 5.0 pg ATP/mL (≈0.699 log₁₀[pg ATP/mL]) to 100 000 pg ATP/mL (≈5.000 log₁₀[pg ATP/mL]) for 20 mL samples of fuel and 20 pg ATP/mL (≈1.301 log_{Note 1: These ranges were calculated with the formula for calculating sample ATP in pg/mL provided in 12.1 based on the minimum recommended RLU for a 1 ng/mL ATP standard when using the reagents specified in Section 7 and the luminometer specified in 6.4 and corrected with a reagent-method blank as determined in Appendix X5.}

1.6 Providing interferences can be overcome, bioluminescence is a reliable and proven method for qualifying and quantifying ATP. This test method does not differentiate between ATP from different sources, for example: from different types of microorganisms, such as bacteria and fungi.

1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.