Standard Mixtures of Volatile Organic Compounds
Multi-component gas mixtures are the quickest and easiest way to calibrate measurements of volatile organic compounds (VOCs) in ambient air and to help identify ambient VOC species.
Mixtures routinely available include:
- 30 component EU Directive ozone precursor mixture
- BTEX (benzene, toluene, ethylbenzene and xylenes) mixture
plus 1,3-butadiene upon special request
- Spiked ambient air mixture (ozone precursors in whole air)
- Terpene mixtures
- Oxygenated (methanol, ethanol, acetone and n-hexane) mixture
- Deuterated toluene standards
Development into new standards includes:
- VOC mixtures of oxygenates and halogenated species
- Parts per million to sub-parts per billion amount fraction
NPL is also able to provide custom mixtures to meet the requirements of the customer.
Click here to download User Guide for NPL VOC Gas Standards (65 KB)
World Meteorological Organisation (WMO) Primary Standard
NPL is proud to announce that the 30 component EU Directive ozone precursor gas standard is now recognised by the World Meteorological Organisation (WMO) as their primary standard.
These standards are used as primary standards for the assessment of global ambient levels of VOCs. This is part of the Global Atmospheric Watch (GAW) international global programme that provides the technical basis for the assessment of the chemical composition of the atmosphere.
This mixture contains all the hydrocarbon species listed within the EU Directive covering ambient ozone measurements (2002/3/EC) as being ozone precursors requiring monitoring. These are:
|Standard gas mixtures are currently available with the following components:|
|ethyne (acetylene)||2-methylbutane (i-pentane)||toluene|
|propene (propylene)||trans-pent-2-ene (trans-2-pentene)||m-xylene|
Amount fractions are close to 4 nmol/mol (also called molar parts per billion, ppb).
These mixtures have recently been used in an international comparison, EUROMET 886. As part of the study a comprehensive stability assessment has proven the excellent integrity of these mixtures.
This mixture replaces NPL's older 30-component hydrocarbon mixture as the Primary Reference Gas Mixture for multi-component VOCs.
This mixture contains benzene, toluene, ethylbenzene, m-xylene, p-xylene and o-xylene at amount fractions of around 4-10 nmol/mol (also called molar parts per billion, ppb).
We can also offer BTEX mixtures that contain lower amounts of m-xylene and p-xylene, so that when combined their total concentration is equal to the other individual components. For example, a 10 ppb mixture of benzene, toluene, ethylbenzene and o-xylene, with m-xylene and p-xylene at 5 ppb each. Please contact us directly for further information.
Please contact us directly for further information regarding these mixtures.
This newly available mixture contains the following monoterpenes and terpenoids:
|Standard gas mixtures are currently available with the following components:|
Amount fractions are close to 2 nmol/mol (also called molar parts per billion, ppb).
NPL's range of terpene standards is a subject of novel research. Please contact us directly for a variety of other terpene standards including (+/-)-ß-pinene, ß-myrcene, (+/-)-camphor, cis-ocimene, (+/-)-ß-pinene and p-cymene.
NPL is pleased to be able to offer this new oxygenated mixture containing methanol, ethanol, acetone and n-hexane at 5 μmol/mol (also called parts per million, ppm). Please contact us for further details.
This newly available standard contains deuterated toluene in nitrogen. This standard can be used as an internal standard in gas chromatography. It is is avaliable at at 5 μmol/mol (also called parts per million, ppm) and also other concentrations. Please contact us for further details.
About NPL's volatile organic compounds mixtures
NPL manufactures primary standards of all volatile organic compounds (VOCs) at accurately known concentrations using an internationally agreed method that combines known weights of gases and volatile liquids into specially passivated gas cylinders. At each stage in the process the highest level of QA and QC are implemented including a thorough purity analysis of each compound before and after manufacture. Our primary standards are maintained at NPL and used to certify secondary standards. Both standards are supplied to customers to give traceability and international comparability to their measurements.
VOC standards made by NPL have been used for worldwide comparisons between major laboratories performing VOC analyses. The stability and accuracy of NPL VOC standards have been characterised over extended periods as part of several international research programmes.
The carefully defined methods and extensive quality control used at NPL ensure that all standards have values traceable to the international SI system of units and measurements.
NPL specialises in producing custom gas mixtures with guaranteed uncertainties for complex gas analysis.
NPL has been developing accurate and stable multi-component mixtures of Volatile Organic Compounds (VOCs) since the early 1980s in response to customer needs and regulation on precursors to tropospheric ozone formation.
Examples of mixtures prepared during the 1980s and early 1990s include:
The NPL 30-component mixture
In 1997, a 30-component mixture replaced the 26-component mixture with the following compounds:
|ethane||trans-but-2-ene (trans-2-butene)||2-methylpentane (i-hexane)|
|ethene (ethylene)||cis-but-2-ene (cis-2-butene)||3-methylpentane|
|propene (propylene)||2-methylbutane (i-pentane)||toluene|
|prop-1-yne (propyne)||2-methyl-1,3-butadiene (isoprene)||ethylbenzene|
|2-methylpropane (i-butane)||cis-pent-2-ene (cis-2-pentene)||o-xylene|
This mixture was used by participants in the Accurate Measurements of Hydrocarbons in the Atmosphere (AMOHA) project. The results of this project have been published as follows: Slemr, J., F. Slemr, R. Partridge, H. D'Souza, and N. Schmidbauer, Accurate Measurements of Hydrocarbons in the Atmosphere (AMOHA): Three European intercomparisons, J. Geophys. Res., 107(D19), 4409, doi:10.1029/2001JD001357, 2002.
The NPL O3P mixture
In 2005, NPL developed the first in the series of Ozone Precursor (O3P) VOC mixtures containing all of the VOCs listed in the EU directive (2002/3/EC) concerning the monitoring of the most important pre-cursor compounds for the formation of tropospheric ozone. This required the removal of five species from the NPL 30 component list (propyne, i-butene, cis-2-pentene, cyclohexane and 3-methylpentane) with the addition of 5 other species (1-pentene, iso-octane*, n-octane, p-xylene and 1,2,3-trimethylbenzene):
* Iso-octane was interpreted as 2,2,4-trimethylpentane after consultation with various expert groups. IUPAC names are used on all O3P certificates to avoid ambiguity with component identification.
This hierarchy of NPL O3P mixtures now underpins and provides traceability for ambient VOC measurements in the UK and worldwide.
The O3P hierarchy has been maintained with a suite of in-house standards at concentrations ranging from 2μmol/mol (ppm) to 2nmol/mol (ppb).
Since 2005, NPL has sold O3P Primary Reference Gas Mixtures (PRGMs) to monitoring stations, research institutes, NMIs, etc.
The O3P hierarchy formed the basis for the EURAMET 886 comparison exercise. The full report of the EURAMET 886 exercise is downloadable from the NPL website via this link: AS29, where extensive data on the stability of these mixtures can be found. This work has also recently been published: R J P Grenfell, M J T Milton, A M Harling, G M Vargha, C Brookes, P G Quincey and P T Woods, Standard mixtures of ambient voltaile organic compounds in synthetic and whole air with stable reference values, J Geophys Res, 115, D14302, 2010, doi:10.1029/2009JD012933.
O3P MkII hierarchy
In 2008, NPL began the process of re-making the ozone precursor hierarchy and the O3P MkII hierarchy forms the basis of PRGMs for customers from May 2009. On these certificates a note will be found referring to the O3P hierarchy (If this note is not present on an ozone precursor PRGM certificate then this mixture originated from the original O3P hierarchy). New technologies applied to the preparation of these multi-component VOC mixtures have led to improvements in the introduction of low vapour pressure, high molecular weight species.
In light of this improvement, a correction factor of -1.8% should be used to convert the gravimetric value of ethylbenzene on original O3P PRGM certificates dated prior to 1 May 2009 to provide equivalence to O3P MkII standards. Equivalence is within the quoted measurement uncertainty of ± 2% (95% confidence level).
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