What is PPM

parts per million

The English expression parts per million (ppm, in German "parts of a million") stands for the number 10−6 and is used in science and technology for the millionth part, as well as percent (%) for the hundredth part, i.e. 10-2, stands.

Basics

parts per million (ppm) and parts per trillion (ppt)

The IEC recommended in 1978 as well as the international standard ISO 31-0 Quantities and units - Part 0: General principles from 1992 to avoid the term ppm. Above all, in order to avoid the risk of misunderstandings with the analogously formed terms ppb and ppt parts per trillion to prevent. Because trillion and trillion in American usage mean 109 (billion) and 1012 (trillion, German trillion), while in the German 1012 (for trillion) and 1018 (for trillion) mean. Therefore, any information in one of these units must always be viewed with caution. In addition, the abbreviation ppt is sometimes used in English-speaking countries for parts per thousand used.

conversion

  • 1 percent = 10 −2 = 10,000 ppm = 1 part per hundred = 1%
  • 1 Per mille = 10−3 = 1,000 ppm = 1 part per thousand = 0.1% = 1 ‰
  • 1 bp (base point / permyriad ) = 10−4 = 100 ppm = 1 part per ten thousand = 0.01% = 1 ‱
  • 1 pcm (per cent mille) =10−5 = 10 ppm = 1 part per hundred thousand = 0.001%
  • 1 ppm = 10−6 = 1 part per million = 0.0001%
  • 1 ppb (parts per billion) = 10−9 = 1 part per billion
  • 1 ppt (parts per trillion) = 10−12 = 1 part per trillion
  • 1 ppq (parts per quadrillion) = 10−15 = 1 part per quadrillion

If the immission quantity is given as a mass fraction per volume, e.g. B. in µg per m³ of air, the conversion to ppm refers to the ratio of the number of molecules.

Example: 0.1 µg of lead in one m³ of air corresponds to (0.1 * 10−6 / 207) mol of lead in (103 / 22.4) mol air. So there are about 10 for one lead atom11 Air molecules (thus 0.1 µg lead / m³ air corresponds to about 10 ppt lead in air). The following were used for this calculation: molar mass of lead = 207 g / mol and number of gas particles at 0 ° C per liter = 1 / 22.4 mol (with pV = nRT).

Mixing ratios (ppmv, ppmw, pptv)

Volume mixing ratios are followed by a "v" by volume or. volume parts (for example ppmv, ppbv, pptv). The abbreviation vpm is also used for ppmv. vpm is related to% by volume like ppm to%. Please note the information given above regarding the possibility of confusion.

ppbw stands for parts per billion by weight (Weight mixing ratios) - this corresponds to the weight percent.

use

Concentrations

A mass fraction can be specified in milligrams per kilogram, a volume concentration in milliliters per cubic meter or a molar fraction in micromoles per mol.

Frequently used ppm in mass spectrometry to z. B. to measure the impurities in a pure substance. In the case of the certificate of analysis that is enclosed with a chemical, ppm refers to the mass of the substance. Thus, ppm corresponds to the amount of contamination in μg per g of the chemical.

Despite the IEC / ISO rejection, especially when measuring the concentration of natural gas in air, the proportions of the gas are measured with gas concentration measuring devices or gas detection devices in ppm or, in the case of higher concentrations, in percentages or proportions by volume.

In chemistry, the ppm is used when specifying the concentration of aqueous solutions with the same density of the dissolved substances. For dissolved substances of similar density, 1 ppm = 1,000 ppb means approx. 1 mg / l. Even with the same density of dissolved substances, the equation ppm = mg / l is not always accurate and should be used with caution. Nevertheless, the ppm is still often used incorrectly when specifying the concentration of aqueous solutions.

Device accuracy

In geodesy, the accuracy of devices for measuring distances is often given in ppm. So here is an indication of Millimeters per kilometer meant.

Chemical shift

In NMR spectroscopy, the ppm is used to indicate the chemical shift.

Error rates

In the automotive industry in particular, failure frequencies (error rates) are expressed in ppm, for example in the case of the electronics in the built-in control units. The automakers are demanding ppm rates from the suppliers. This means that out of a million control units produced, a maximum of a certain, relatively small number may be defective (see table). The following table is intended to provide an exemplary comparison of the required error rates for a semiconductor manufacturer that uses its processors in both consumer electronics and the automotive industry:

Consumer electronics 1000 ppm
Automotive industry 20 ppm

See also