Environmental monitoring

Addressing the challenges of microplastic characterisation using thermal desorption

In this application note, we demonstrate the quantitative analysis of microplastics using direct thermal desorption (TD) combined with gas chromatography-mass spectrometry (GC-MS). Direct desorption of filtrates containing microplastics provides a simple and streamlined sample preparation step while GC-MS analysis produces informationrich volatile organic compound (VOC) profiles. The VOC profiles contain marker compounds to identify and quantify the plastic, along with other chemical signatures that could prove useful in source apportionment, toxicity assessment and regional profiling. 

Simple and reliable quantitation of ppt-level PAHs in air by TD-GC-MS

This study describes the performance of a sorbent tube and optimised analytical protocol dedicated to the detection of ppt-level polycyclic aromatic hydrocarbons (PAHs) in ambient air. Using active (pumped) sampling with analysis by TD-GC, this innovative approach completely avoids the labour-intensive solvent-extraction protocol employed in many standardised methods. The optimised analytical method also offers increased sensitivity due to increased extraction efficiency, absence of a dilution stage, and efficient transfer of compounds to the GC.

Passive monitoring of benzene and other hazardous air pollutants at refinery perimeters in accordance with US EPA Method 325

This study describes a stepwise approach to complying with US EPA Method 325 for monitoring volatile organic compounds (VOCs) at refinery perimeters. A range of equipment from Markes International is outlined that allows fully method-compliant deployment of tube-based passive samplers, sample analysis and tube cleaning. All these stages are underpinned by a radio-frequency identification tagging system to ensure a robust chain of custody from field to lab.

Continuous on-line monitoring of hazardous air pollutants by TD-GC-FID

This study shows how the TT24-7 thermal desorber can be used for the continuous on-line detection of hazardous air pollutants, and how the time profiles and concentration data obtained can be of value for source apportionment. If the system was applied to more polluted environments, it would be possible to speed up sampling and reduce cycle times still further, provided the TT24-7 was used in conjunction with an appropriately fast GC method.

Monitoring trace greenhouse gases in air using cryogen-free TD-GC-MS

This document shows how Markes’ thermal desorption (TD) technology for analysing ‘air toxics’ can also be applied to the detection of the most challenging ultra-volatile greenhouse gases, including tetrafluoromethane, hexafluoroethane, sulfur hexafluoride and nitrous oxide. Detection limits below 1 ppt are demonstrated for sulfur hexafluoride and hexafluoroethane, with excellent peak shape and linearity also being obtained.

Automated cryogen-free monitoring of ‘air toxics’ in ambient air using TD-GC-MS in accordance with US EPA Method TO-17

This study demonstrates the performance of Markes’ thermal desorption instruments for the tube-based analysis of 65 ‘air toxic’ compounds in accordance with US EPA Method TO-17. Analytical precision, linearity and method detection limits are shown to be within the requirements of the method, and we additionally illustrate the capability of Markes’ instruments to split, re-collect and re-analyse samples without analytical bias.

Innovative cryogen-free ambient air monitoring in compliance with US EPA Method TO-15

This study describes the GC-MS analysis of humidified canister ‘air toxics’ samples at various relative humidities, using cryogen-free systems for thermal desorption preconcentration. Detection of 65 target compounds ranging in volatility from propene to naphthalene is demonstrated with excellent peak shape and performance well within the criteria set out in US EPA Method TO-15, including method detection limits as low as 4 pptv.

Evaluation of a ‘soil gas’ sorbent tube for improving the measurement of volatile and semi-volatile fuel vapours in contaminated land

This Application Note describes the development of a two-bed sorbent tube in conjunction with Markes’ Micro-Chamber/Thermal Extractor™ for the sampling of petroleum, diesel and kerosene vapours collected from soil gas. Both lighter and heavier (polyaromatic, longer-chain) hydrocarbons were detected, and quantitative recovery is demonstrated for even the heaviest fuel components.

Air monitoring - The advantages and applications of canisters and tubes

This study discusses the application areas of canister-based and sorbent-tube-based sampling for volatile organic compounds (VOCs), and the advantgaes and limitations of each approach. Cryogen-free, method-compliant thermal desorption technology is now available, offering high sensitivity measurement of air toxics in both canisters and tubes on a single analytical platform.

Using thermal desorption for industrial (stack) emissions testing

This study covers selection of the appropriate organic vapour sampler for the analytes of interest in stack gas sampling, and optimisation of the subsequent sampling and thermal desorption (TD)-GC analytical process. Also discussed are the benefits of thermal desorption against solvent extraction.

Diffusive (passive) monitoring and TD-GC analysis of hazardous air pollutants in industrial and urban locations

This Application Note describes the monitoring of benzene and other vapour-phase organic compounds in urban or industrial air using diffusive (passive) sampling onto sorbent tubes with subsequent analysis by thermal desorption (TD) with gas chromatography (GC). It summarises how this robust and cost-effective air monitoring technique should be applied to monitoring airborne VOCs around the perimeter of oil refineries and other industrial facilities. Topics covered include advice on sorbent selection, determination of uptake rates, deployment of samplers, method sensitivity and application/interpretation of data.

Rapid and reliable screening of landfill gas for priority and odorous compounds by TD-GC-MS 

This Application Note describes the use of sorbent tubes to sample landfill gas, with analysis by thermal desorption (TD) and GC-MS detection. In particular, we describe the use of optimised sampling and analytical conditions for the detection of toxic and priority VOCs, and for effective water management. Combined with automated detection of target compounds using library-matching TargetView software, this approach offers the ability to greatly speed up the screening of complex landfill gas profiles 

Measuring PFAS pollution in ambient air using TD-GC-MS/MS 

Markes International’s TD100-xr™ thermal desorption instrument coupled to a gas chromatograph and a triple quadrupole mass spectrometer enables measurement of per- and polyfluoroalkyl substances (PFAS) in air at concentrations as low as 2pg/m³. 

Addressing multiple challenges of microplastics analysis using versatile TD-GC-MS

Evaluation of salt samples 

Volatile organic compounds (VOCs) from polymer standards were analysed to establish marker compounds for microplastics analysis using direct thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). The marker compounds enabled quantitation of multiple types of microplastics in a variety of salt samples. Sample introduction into the GC-MS was automated using the TD100-xr™ thermal desorber, which increases the throughput of large sample volumes. 

Identification of impurities in hydrogen fuel supplies using Multi-Gas on-line TD-GC-MS systems 

A Multi-Gas thermal desorber from Markes International was used to analyse impurities in hydrogen fuel. Performance criteria and detection limits were exceeded for a range of target compounds, complying with ISO-14687-2, ISO-21087 and ASTM D7892 standard methods.