Parts-per notation
The English term parts per million (ppm to German " parts per million ") stands for the number 10-6 and is used in science and technology for the millionth part, as a percentage (% ) for the hundredth part, so 10-2 is.
- 2.1 concentrations
- 2.2 Device accuracy
- 2.3 Chemical shift
- 2.4 Error rates
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 of 1992, the expression to avoid ppm. This is primarily to allow the risk of misunderstanding in the terms analog formed ppb and ppt parts per trillion prevent. Because billion and trillion mean in American parlance 109 ( billion, dt billion ) and 1012 ( trillion, trillion dt ), while they ( Billion ) and 1018 ( for Trillion ) mean in German 1012. Therefore, an entry in one of these units is always to be regarded with caution. In addition, the abbreviation ppt sometimes used in English-speaking countries for parts per thousand.
Conversion
If the Immissionsmenge given as mass fraction per volume, eg in micrograms per cubic meter of air, one refers to the conversion in ppm on the ratio of the number of molecules.
Example: 0.1 micrograms of lead in a cubic meter of air corresponding to ( 0.1 · 10-6 / 207 ) moles of lead in ( 103 / 22.4 ) moles of air. So come on a lead atom approximately 1011 molecules of air ( thus correspond to 0.1 micrograms of lead / m³ air about 10 ppt lead in air). In this calculation were used: Molar mass of lead = 207 g / mol and number of gas particles at 0 ° C per liter = 1 / 22.4 mol ( pV = nRT with ).
Mixing ratios ( ppmv, ppmw, pptv )
Volume mixing ratios ( ppmv for example, ppbv, pptv ) with a suffix "v " by volume or volume parts labeled. For ppmv, the abbreviation is used vpm. vpm is related to vol - % as ppm to %. Here, the statements above are notes must be observed to Verwechselungsmöglichkeiten.
Ppbw stands for parts per billion by weight (weight mixing ratios ) - equivalent to the weight.
Use
Concentrations
A mass fraction can be expressed in milligrams per kilogram, a volume in milliliters per cubic meter, or a mole fraction in micromoles per mole.
Frequent use is ppm for example, to measure the impurities in a pure substance in mass spectrometry. In the certificate of analysis that accompanies a chemical that is ppm refers to the mass of the substance. Thus ppm corresponds to the amount of the impurity in micrograms per gram of the chemical.
Despite the IEC / ISO rejection are the proportions of the gas with gas concentration measuring apparatus or gas detectors in ppm or also measured at higher concentrations, in volume percent or volume fractions in particular in measuring the concentration of gas in air.
In chemistry, ppm is used for concentration data of aqueous solutions with the same density of the solutes. It is meant for the solute of similar density with one ppm = 1,000 ppb, about 1 mg / l. Even when the density of the solute equation ppm = mg / l is not always accurate and should be treated with caution. Nevertheless, the ppm is used in the wrong way with concentration data of aqueous solutions still often.
Instrument accuracy
In geodesy, often the accuracy of equipment is specified for distance measurement in ppm. Here is therefore an indication of a millimeter per kilometer meant.
Chemical shift
In NMR spectroscopy is the use ppm indicating the chemical shift.
Error rates
Especially in the automotive industry failure rates ( error rates ) are expressed in ppm, for example, in the electronics built into the control units. The car manufacturers require strict ppm rates from suppliers. This means, produced one million ECUs must not exceed a certain, relatively small number of defective (see table). The following table should give an example comparing the required error rates on a semiconductor manufacturer that built its processors both in consumer electronics as well as in the automotive industry: