However, there is no consensus on an analytical procedure to detect them in food and water.
The European Union Reference Laboratory (EURL) for Dioxins and PCBs in Feed and Food in Freiburg is developing a harmonised approach for use in EU official control laboratories.
Persistent organic pollutants (POPs) pose a threat to health and the environment. The most commonly encountered POPs are organochlorine pesticides, such as dichlorodiphenyltrichloroethane (DDT) and industrial chemicals, most notably polychlorinated biphenyls (PCB).
About chlorinated paraffins
A lesser known category of POPs, chlorinated paraffins (CPs), are commonly used in coolants and lubricants for metal processing and as plasticizers and flame retardants in rubber, plastics, paints and sealants.
Manufactured continuously since the 1930s, the production volume is estimated to exceed one million tonnes per annum.
CPs are a group of synthetic polychlorinated alkanes, with a wide range of carbon chain lengths and varying degrees of chlorination. This creates the possibility of thousands of isomers and homologues, characterized by short-chain (SCCPs, C10-13), medium-chain (MCCPs, C14-17) and long-chain (LCCPs, C>17) CPs.
It is not well understood how CPs get into the environment, though one probable avenue is by leaching out of plastic and rubber products. Once in the environment, SCCPs bind to sediments and aquatic organisms, eventually ending up in the food chain.
Despite evidence of extensive exposure, there are few studies on the pervasiveness and toxicity of SCCPs, particularly in food and food contact materials (FCMs), arising from the inherent difficultly to detect and analyse CPs.
Even so, regulations are in place to monitor their circulation. Regulation 2015/2030 and the Water Framework Directive 200/60/EC in the EU and the Significant New Use Rule under the Toxic Substances Control Act in the US severely limit the manufacture and use of SCCPs, restricting their concentration and allowing agencies to prohibit use.
Outside specific exemptions, only the production, placing on the market and use of articles with less than 1500 mg/kg SCCPs is allowed.
‘SCCPs have been listed in Annex A of the Stockholm Convention POPs list in April/May 2017. Apart from specific exemptions the result equates to a near worldwide ban on production and use’.
The chlorinated paraffin challenge
Even though there is a need to test for such contaminants, the broad complexity among their structures makes accurate analysis challenging.
A number of methods using gas chromatography-mass spectrometry (GC-MS), gas chromatography-electron capture detector (GC-ECD) and gas chromatography-negative chemical ionization-mass spectrometry (GC-NCI-MS) are available, but none have been robust enough to develop into a standard method for food safety testing labs, due to limitations in sensitivity and selectivity, low resolution and high interference.
The primary challenge in quantifying CPs in food stems from the difficultly to separate a large population of isomers and homologues with similar physiochemical properties, causing mass overlap of CPs with the same nominal mass. The low target levels of CPs in FCMs and the resulting complex chromatograms highlight the need of a highly selective and sensitive method.
Effective Chlorinated Paraffin Detection
High resolution accurate mass gas-chromatography mass spectrometry (HRAM GC-MS) technology advances SCCP analysis in addition to the opportunity for MCCP and LCCP analysis.
The HRAM accuracy enables superior selectivity and sensitivity and improves detection of group separation and quantification.
These features are important for SCCP analysis where background noise can interfere with target masses. Mass accuracy is also maintained across compound concentrations, which is essential for correct identification and quantification.
Both GC-MS with electron ionization (EI) and GC-MS with NCI approaches can be applied to SCCP analysis. EI allows low levels of total SCCPs to be detected and quantified but because of high fragmentation, it is difficult to distinguish between homologue specific ions and between SCCPs and MCCPs.
NCI provides higher selectivity for homologue groups and even between homologues. It also exhibits excellent compound linearity for chlorinated homologues and peak area repeatability.
HRAM GC-MS with NCI is the method preferred by many labs for detection and quantification of SCCPs because it allows for sensitive detection using ions characteristic for various homologue groups in a mixture.
Using NCI, SCCP congeners can be easily separated based on the number of chlorine substitutes for a certain carbon chain length and according to the number of carbon and chlorine atoms for various carbon chain lengths.
The high resolving power of HRAM GC-MS helps detection at high and low concentrations of CPs, which is crucial for achieving enough selectivity to confidently separate SCCP specific low mass ions.
- Khalil Divan is senior director of global marketing, Food and Beverage, Chromatography and Mass Spectrometry at Thermo Fisher Scientific