Semi-Continuous Determination of Ambient Air Quality

Combustion of fossil fuels for energy production pollutes the environment with large quantities of unsafe substances in the form of aerosols or gases. These emissions cause damage, at their source, as well as miles away from it. The physical and chemical properties of the emissions from anthropogenic as well as natural sources are very relevant to the environment and the climate.

Flow diagram for Particle Into Liquid Sampler combined with ion chromatography (PILS-IC)

Flow diagram for Particle Into Liquid Sampler combined with ion chromatography (PILS-IC).

PILS Mode of Operation

The PILS places aerosols into a supersaturated water vapor phase, where they rapidly grow into droplets. These droplets are isolated on the basis of their inertia and pumped on with a carrier fluid, which contains an internal standard to allow basic quantification. Air bubbles that occur are removed in a so-called debubbler, and the aqueous phase is moved to an ion chromatograph, for example, for analysis.

The Particle Into Liquid Sampler (PILS)1 samples aerosol particles from an air flow and brings them into the aqueous phase. Then, they can be tested using ion chromatography or voltammetry. So as to examine the gas phase, it is recommended that the 920 Absorber Module or a MARGA2 system, available from Metrohm Applikon can be employed.

The size of the aerosol particles to be established is restricted by an impactor or a cyclone at the inlet. This makes it possible, for instance, to test particles smaller than 1 µm, 2.5 µm or 10 µm (PM1, PM2.5, PM10). To stop interferences, the gases are absorbed by denuder systems. A vacuum pump creates an air flow in the system with a flow rate of 1 m3/h.

The time resolution for the determination of aerosols that can be achieved with this simple technique is far superior to that possible with filter samples.

Advantages of the PILS

  • Direct on-site sample analysis
  • Determination of ions in aerosols with high temporal resolution
  • High sampling rate
  • Simple interfacing to an ion chromatography and voltammetry system
  • Diurnal variation analysis with high time resolution
  • Contamination-free aerosol collection technique (particles PM1, PM2.5, PM10)
  • Direct analysis without any additional sample preparation
  • Sample storage is not required

Application Areas

The PILS can be instantly coupled with many analytical methods. With ion chromatography, water-soluble anions and cations can be determined simultaneously. Heavy metals can be established using a voltammetric measuring stand. The PILS can also be employed for offline sampling with an autosampler. Other examples are the determination of total organic carbon (along with a TOC Analyzer) or interfacing with ICP methods.

Application areas for PILS – IC:

  • Monitoring of outside air
  • Monitoring of pollutants inside buildings
  • Measurements of tunnel air
  • Emission control at the workplace for worker protection
  • Mobile use, for example on aircraft
  • Determination of stack emissions

Anion and cation chromatogram for outside air determination and aerosol particles smaller than 2.5 µm (PM2.5). Lithium bromide was used as an internal standard

Anion and cation chromatogram for outside air determination and aerosol particles smaller than 2.5 µm (PM2.5). Lithium bromide was used as an internal standard.

Heavy Metal Determination Using PILS-VA

Integrating a PILS with a 884 Professional VA allows semi-continuous determination of a range of heavy metals (Ni, Pb, Zn, Cd, Cu, Co, etc.) in particulate matter. The high time resolution records even the slightest changes in the chemical composition of aerosols. In the example analysis below, the cadmium and copper concentrations in the air rise continually over several days, up to the point where the rain that sets in washes the majority of the cadmium and copper out of the air (wet deposition).

Semi-continuous voltammetric determination of heavy metal content (Cd, Pb, and Cu) in outside air samples from Herisau (Switzerland), using a PILS sampling system

Figure 6. Semi-continuous voltammetric determination of heavy metal content (Cd, Pb, and Cu) in outside air samples from Herisau (Switzerland), using a PILS sampling system.

Standard Ion and Heavy Metal Determination Using PILS-IC-VA

Coupling with a number of analyzers simultaneously is also possible. In the case of PILS-IC-VA, particles brought into solution are conveyed in three streams to a dual channel ion chromatograph for anion and cation analysis, and to a voltammetric measuring stand for heavy metal cation determination.

Semi-continuous ion chromatographic determination of anion and cation content, and voltammetric determination of heavy metal content in outside air samples from Herisau (Switzerland). To simulate contamination events, sparklers that had previously been immersed in heavy metal salt solutions were burned

Semi-continuous ion chromatographic determination of anion and cation content, and voltammetric determination of heavy metal content in outside air samples from Herisau (Switzerland). To simulate contamination events, sparklers that had previously been immersed in heavy metal salt solutions were burned.

The 920 Absorber Module – an Automatic Gas Sampler

The 920 Absorber Module can also be applied as a semionline sampler. Here, the gaseous compounds (HNO2, NH3, HCl, HNO3, SO2) are absorbed directly in a solution over a defined period of time. An external gas flow meter maintains the gas flow constant through this period. The absorbent chosen should have a high level of solubility for the gas flow and also be reasonably priced. Usually, ultrapure water is used.

The Liquid Handling regulated by the MagIC Net software includes sample preparation, as well as all rinsing processes. The collected sample can then be conveyed directly to an ion chromatograph for analysis.

Furthermore, the analytical system can be calibrated automatically from a single multi-ion standard using Metrohm intelligent Partial Loop Technique (MiPT). Since MiPT allows for flexible injection volumes (4-200 µL), it includes a broad range of concentrations.

A 10 port valve, a six port valve and two 800 Dosinos are available for the whole Liquid Handling.

Consequently, the 920 Absorber Module can be used to track volatile organic acids in process exhaust gases, for example, or in the ambient air at workplaces.

The 920 Absorber Module (right) is able to collect samples fully automatically and transfer them to the 930 Compact IC Flex (left), for example, for ion chromatographic determination.

The 920 Absorber Module (right) is able to collect samples fully automatically and transfer them to the 930 Compact IC Flex (left), for example, for ion chromatographic determination.

Features and Benefits of PILS-IC-VA

Fully automated analysis

Once the sample table has been developed in the MagIC Net software, the PILS-IC-VA system functions totally automatically. The voltammetric determination is synchronized and the measuring results are conveyed directly to the MagIC Net database.

No time-consuming sample preparation

The samples are straightaway brought into solution by the Particle Into Liquid Sampler. The following step is straightforward analysis by ion chromatography or voltammetry without any ensuing time-consuming sample preparation or storage, something that would be needed with filter samples, for instance.

Analyzes at hourly intervals

The samples are gathered and tested completely automatically at hourly intervals. Semi-continuous analysis enables significantly higher time resolution than conventional methods, predominantly those involving filters.

Multi-parameter monitoring

With this combination, standard cations and anions as well as heavy metals can be established in a single analysis. The software automatically measures the corresponding concentrations in the air.

High flexibility

The PILS is very flexible. It can also be applied for determinations along with mass spectrometry or water soluble organic carbon analyzers, for instance. Alternatively, the samples can be gathered in sample vessels for offline determination, using an autosampler.

Unattended measuring

Because of the use of supply bottles and rinsing canisters, automated measurements are possible even over an extended period of time. Standardized, automated sampling and analysis guarantee excellent reproducibility.

References

1 PILS is a coproduction of Metrohm Applikon and Metrohm.

2 Monitor for Aerosols & Gases in ambient Air.

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

For more information on this source, please visit Metrohm AG.

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