ATP (adenosine triphosphate) measurement is a key technique for assessing cleanliness and hygiene in various environments. ATP-meter the amount of ATP in a sample into light intensity, which is measured in Relative Light Units (RLU). But how can you convert a given amount of ATP in SI units—in femtomoles (fmol)—to the corresponding RLU value? Here, we show you how to use linear equations to perform this conversion for different types of ATP-meter.
Step 1: Understanding linear equations
Each ATP-meter a specific linear equation that describes the relationship between ATP concentration (x, in fmol) and RLU (y). The formula is as follows:
y = kx + m
- y is the RLU value.
- x is ATP in fmol.
- k is the slope (the sensitivity of the meter).
- m is the point of intersection with the y-axis (background RLU).
Step 2: Equations for different meters
The equations below have been compiled from various AOAC(based on analyses of pure ATP directly onto swabs). The reports provide the following equations for the four most common ATP:
Neogen AccuPoint Advanced):
y = 5.91x + 7.77
Example: For 10 fmol ATP y = 5.91*(10) + 7.77 = 66.87 RLU.Neogen 3M Clean-Trace ):
y = 4.05x + 17.94
Example: For 10 fmol ATP y = 4.05*(10) + 17.94 = 58.44 RLU.Hygiena EnSURE):
y = 2.13x – 0.68
Example: For 10 fmol ATP y = 2.13*(10) – 0.68 = 19.62 RLU.Kikkoman Lumitester):
y = 1.65x + 9.37
Example: For 10 fmol ATP y = 1.65*(10) + 9.37 = 25.87 RLU.
Step 3: Apply the formula
To convert any ATP to RLU for a specific meter, simply substitute the value of x into the corresponding linear equation. You can also use this to perform the reverse calculation—from RLU to ATP by solving the equation for x:
x = (y – m) / k
(Note that negative values may occur at very low ATP, as the lines do not pass through the origin.)
Why is this important?
Understanding the conversion between ATP RLU is essential for interpreting measurement results and ensuring accuracy in hygiene monitoring. By using linear equations, you can better compare different systems and better understand limit values. Common ATP limit values ATP in standards (e.g., SS8760014, DS2451-10) or described in the research literature are25–100 femtomoles ATP.
For Clean-trace ,if you calculate as describedabove for25–100 femtomoles, the result is 119–423 RLU. This is close to the threshold levels recommended by the manufacturer for critical surfaces in food safety (150–300 RLU) and healthcare hygiene (250–500 RLU), but itis not exact. The explanation is that, for a long time,the calculation has been simplified (rounded) to harmonize different meters. Our conclusion from all of this is that if you useATP-meter Clean-trace ATP-meter consider your ATP threshold levels and whether you need to adjust them.
Please contact us if you would like to learn more about ATP and how this technology can be used for cleaning inspections.