## 4 Why and How to Measure Volatile Organic Compound Emissions from a Material?
### How to Sample and Analyse VOCs  
#### 4.1.1 VOC Sampling  
VOC sampling techniques are diverse. They depend in particular on the matrix being studied, the compounds being sampled, the equipment available, and the cost of the various devices. A distinction is generally made between sampling without preconcentration and sampling with preconcentration [92; 93]. Sampling without preconcentration involves isolating a portion of the air in which the compounds to be studied are present, with no selection of compounds. In this way, all the compounds in the matrix are considered in the analysis. This sampling method is known as \"whole-air sampling\". It can be carried out using  
a bag (made from the following materials: polyvinyl fluoride (tradename: Tedlar), polytetrafluoroethylene and fluorinated ethylene propylene copolymer (tradename: Teflon), polyethyleneterephthalate (tradename: Nalofan), polyvinylidene dilluoride (tradename: Altef)...) offering a wide range of volumes (from a few mL to several dozen liters) and being low-cost but fragile;  
a polished stainless-steel canister, reusable, with a range of volumes from a few mL to several dozen liters, but are expensive;  
a glass vial or ampoule, infinitely reusable after cleaning. The advantage of these collection devices is that several analyses can be carried out on the same sample. However, when sampling \"whole air\", the humidity of the sample is the same as that of the air and can therefore be high. This can lead to artefacts during analysis. It is therefore important to dehumidity the sample when this type of sampling is carried out. [PERSON] et al. [94] highlighted the points that still need to be explored towards the standardization of a suitable procedure, in particular investigations on sorbent combinations and the suitability of chromatography columns. The major challenge is that strong sorbents adsorb water together with very VOCs. Pre-concentration sampling involves the absorption or adsorption of compounds on a substrate in order to extract them from the air. The choice of sorbent depends on the type of compounds to be studied and the sampling method chosen: passive or dynamic. Sampling is considered to be dynamic if the air is pumped through the collection medium to fix the compounds. Dynamic sampling can be carried out using sorbent(s) contained in a cartridge. A multitude of adsorbents are available: graphitized carbons (Carbograph, Carbotrap, Carbopack) for carbon number C3 to C30, carbon molecular sieves (Carbosieves, Anasorb, Carboxen) for carbon number C1 to C9, and porous organic polymers (Tenax, Porapak, Chromosorb) for carbon number C6 to C26 [94]. As each adsorbent has specific properties, it is essential to study them carefully to select the most appropriate one [94; 95]. Adsorbent beds can be built up to extend the range of compounds studied. In contrast, with passive sampling, there is no movement of the matrix, only the diffusion of analytes comes into play. Passive sampling of analytes can be performed with \begin{table}
\begin{tabular}{c c c c c} \hline  & **Compound** & **CAS** & **MW (g mol\({}^{-1}\))** & **Bp (\({}^{\circ}\)C) [90; 91]** & **CMR Classification [14]** \\ \hline \multirow{4}{*}{C\({}_{8}\)} & Ethylbenzene & 100-41-4 & 106 & 136 & Carc. 3 \\  & Styrene & 100-42-5 & 104 & 145 & Carc. 3 \\  & Vanillin & 121-33-5 & 152 & 285 & Carc. 3 \\  & \(m\)-Xylene & 108-38-3 & 106 & 139 & Carc. 3 \\  & \(o\)-Xylene & 95-47-6 & 106 & 144 & Carc. 3 \\  & \(p\)-Xylene & 106-42-3 & 106 & 138 & Carc. 3 \\ \hline \multirow{2}{*}{C\({}_{9}\)} & Syringaldehyde & 134-96-3 & 182 & 192 & Carc. 3 \\  & 1,2,4-Trimethylbenzene & 95-63-6 & 120 & 169 & Carc. 3 \\ \hline \multirow{2}{*}{C\({}_{10}\)} & Naphtalene & 91-20-3 & 128 & 218 & Carc. 2 \\  & Sabinene & 3387-41-5 & 136 & 163 & Carc. 3 \\ \hline \multirow{2}{*}{C\({}_{11}\)} & Undecane & 1120-21-4 & 156 & 196 & Carc. 3 \\ \hline \end{tabular}  
* Bp: boiling point; CMR: carcinogenic, mutagenic, reproductoric.  
\end{table}