## 4 Characterization of VOC Emissions
### Sampling Methods
#### 4.1.2 Sampling Devices
Further developments include thin-film solid-phase microextraction (TF-SPME). This method uses a sorbent on a carbon mesh strip, which has a larger surface area compared to traditional SPME fibre, increasing the collection volume and extraction rate. In addition, it is suitable for a wider range of volatiles, making it suitable for analysing VVOCs and trace-level compounds [94; 95]. Similarly to SPME fibre, the Magic Chemisorber (r) (Frontier Lab, Fukushima, Japan) PDMS is made by a thin film of 500 \(\upmu\)m of PDMS on a titanium tube used mainly for the trace analysis of volatile compounds in air or solutions. The sampling device is then introduced into a pyrolyzer to thermally desorb the extract components followed by GC-MS analysis [96]. For sampling SVOCs, **polyurethane foam** (PUF) is most commonly used [97; 98], in both active and passive sampling modes, although it has recently been used primarily for passive sampling [99]. It has a large surface area characterized by a porous structure capable of collecting a wide range of volatiles over long periods of time. Moreover, they are relatively inexpensive, easy to use and compatible with a variety of sampling setups [100]. **Sorbent tubes**[16] can be used passively by exposing an open end directly to bulk air, or actively when combined with an air pump. The advantages are their versatility, as they can be tailored to increase specificity, as well as their high sensitivity and detection limit. However, their limitation lies in their limited capacity for high-volume sampling [16]. Several types of sorbents are available depending on the compounds of interest, and more than one sorbent can be used in a series or as multiple beds in the same tube [62; 71; 101]. Typical sorbent materials are charcoal, graphitized carbon, silica gel, porous organic polymers (Polarpak, Tenax(r), Chromosorb), quartz wood and coconut charcoal. Several of these sorbents can be used for a wide range of applications, such as silica gel tubes used for sampling polar hydrocarbons, low MW thiols, amines and inorganic acids. Charcoal tubes are applied for the collection of non-polar compounds. Sorbent tubes filled with Tenax(r) are used to collect high boiling compounds: Tenax(r) TA is typically used for high boiling T compounds at low concentration, while Tenax(r) GR (Tenax/graphite) has a wider collection of analytes reaching low boiling compounds. Other sorbent materials are compound-specific, such as sulfur tubes to sample volatile sulfur compounds and Porapak(r) tubes specific for the analysis of volatile nitriles. In heritage science, Tenax(r) TA sorbent tubes are most commonly used due to their broad range of high volatile compounds collected [26; 27; 40; 43; 56]. Similar to sorbent tubes, gas detection tubes such as **Drager tubes(r)** can be used in active and passive mode and directly provide quantitative data [102]. These consist of glass tubes filled with a specific chemical reagent reacting with the compound or family of compounds of interest, such as aldehydes, acetic acid and formic acid [102]. The main advantages of Drager sampling tubes are their low cost and speed of analysis, with a wide range available for accurate measurements. The **Radiello(r) sampler** is a passive sampling device for VOCs consisting of a cartridge of graphitized charcoal inserted into a radial diffusive sampler. After sampling, the cartridge is thermally desorbed and analysed by gas chromatography. The advantage of a radial diffusive sampler is the large diffusion area parallel to the cartridge and the tortuous diffusion path, which means that the uptake rate is not affected by wind and air currents [68; 103; 104]. Another type of diffusion tubes is **Palmes(tm) tubes**, which were originally developed for nitrogen dioxide sampling. These are now commonly used for passive sampling in heritage environments to measure the concentration of formic and acetic acid, normally followed by ion chromatography [22; 99].