Atmospheric particles that can be natural or anthropogenic, are defined as a suspension of fine solid or liquid particles in air. They are either emitted or formed in the atmosphere and their particle sizes affect their transport and deposition. Their most important impacts, such as respiratory health hazards, visibility reduction, and climate effects are dependent upon the particle size that ranges from a few nanometers to a few hundred micrometers. Chemical composition of aerosol particles is generally determined by gas- and liquid-chromatographic techniques, mostly with mass spectrometric detection. Use of liquid chromatography (LC) has increased in atmospheric analysis due to the recently recognized importance of highly oxidized compounds in aerosol formation and growth, improved separation efficiency of the columns, and high-resolution mass spectrometric detection.

Sampling and Sample Preparation

Sample preparation techniques used for solid samples, such as extraction, clean-up, and concentration, are also suitable for aerosol samples, in general. The analysis mode (target, nontarget) and analysis technique determine the choice of sample preparation method. Liquid extraction, assisted with temperature, pressure, ultrasound, or microwaves, is frequently used (Table 1). Soxhlet extraction, which gives the best recoveries, is less used, because of long extraction time and high solvent consumption. Sonication, instead, is the most popular due to cheap instrumentation, low solvent consumption, and short extraction time. 

Off-Line Techniques

1. Organic Acids

Organic acids have been widely studied in atmospheric aerosols by LC. Fast analyses have been obtained for the acids by utilizing UHPLC using column packed with small 1.7 μm particles, anion exchange column with completely inorganic eluents, or by short rapid resolution C18 HPLC column.

2. Organosulfates (OS)

Generally, RPLC separation with detection in negative ion mode are utilized for the determination of OS. High-pressure liquid chromatography-electrospray ionization-quadrupole time-of-flight-mass spectrometry (HPLC-ESI-QTOF-MS) is employed to investigate the influence of anthropogenic emissions on the formation of SOA and specifically OS.

3. Ammonia and Amines

A sensitive method for atmospheric ammonia was developed by Huang et al. where in-line derivatization with o-phthalaldehyde (OPA) and n-acetyl-cysteine (NAC) was utilized to form highly fluorescent sulfonatoisoindole derivatives for HPLC with fluorescence detection. Ion chromatography with cation exchange column (IonPac CS 12 A, 4 mm i.d. × 25 cm) has been utilized for the analysis of dodecyl-dimethylammonium chloride (DDAC, disinfectant used in hospitals) in indoor atmosphere.

4. Amino Acids

Hydrophilic interaction chromatography (HILIC) is an attractive alternative to conventional RP separation, and it has recently become popular for the analysis of amino acids.

5. Lipids

Hydrophobic compounds from primary biological sources are relatively easy to analyze from aerosols, because conventional C18 columns can provide excellent selectivity and resolution. However, majority of studies rely on GC-based method, even when derivatization is required. The reason might be a relatively long analysis time needed for LC of fatty acids. It can be reduced dramatically, if for example, chloroform is added to an eluent. However, no application to aerosol particles are published yet.

6. Polycyclic Aromatic Hydrocarbons

Because of the diversity of PAHs (over 10,000 compounds), GC has been used for the analysis in the majority of publication. The reason lies in high chromatographic resolution achieved in GC and especially in two-dimensional GC compared to that in LC. However, UPLC coupled to MS is an excellent alternative to the traditional GC approach and has been widely utilized in atmospheric aerosol studies. Since PAHs are aromatic compounds, they are easily detected with UV or FLD, but then selective sample preparation is recommended. Column choice is quite simple, since traditional C18 can be utilized, because of the nonpolar nature of PAHs and their derivatives. High-elution-strength gradients are usually required to minimize analysis time.

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