2.3.3. GC/MS Instrumental Analysis Setup

Adsorbent cartridges were thermally desorbed and analyzed on a thermal desorber (UNITY 1™, Markes International Ltd.) coupled to a gas chromatograph (Agilent GC-6890) and a mass selective detector (Agilent MS-5973N). For quality assurance, adsorbent cartridges were conditioned before each use at 310 ◦C for 30 min and analyzed to verify the blank level. The chamber air background was also evaluated before each experiment. VOCs were thermally desorbed at 300 ◦C for 10 min and refocused onto the cold trap at −10 ◦C. The cold trap was then flash-heated at 300 ◦C, and VOCs were transferred via the heated transfer line (180 ◦C) to the GC column. The GC column was a 30 m × 250 μm × 0.25 μm film thickness with (5%-phenyl)-methylpolysiloxane stationary phase (J&W HP5-MS, Agilent Technologies). Carrier gas (helium) flow was controlled by constant pressure mode and equal to 1.3 mL min<sup>−</sup>1. The GC oven program used for optimal VOC separation was: 40 ◦C for 1 min, ramp 1: 8 ◦C min−<sup>1</sup> up to 80 ◦C, ramp 2: 20 ◦C min−<sup>1</sup> up to 270 ◦C. A mass spectrometer was operated in

electron impact (EI) ionization mode (70eV) in the mass range 25–250 m/z (SCAN acquisition mode, TIC chromatogram). Valves, transfer lines and ion source were kept at 280 ◦C. Single-target ions were extracted in selected ion monitoring (SIM) mode for compound identification and quantification. One quantifier ion and one qualifier ion were selected for each compound on the basis of their selectivity and abundance (Table 1). Six standard solutions with concentration levels 10, 20, 50, 100, 200 and 400 μg/mL were prepared by successive dilution in ethanol of a certified VOC standard mixture (ULTRA Scientific Italia s.r.l, Bologna, Italy). Six-point calibration curves were constructed by syringe injection of 1 μL of VOC standard solutions onto Carbograph 4 cartridges. Identification of VOCs was based on comparison of the obtained mass spectra with those included in the National Institute of Standards and Technology (NIST) library and considered positive by library search match > 800 for both forward and reverse matching. Further criteria for compound identification were: (i) the matching of relative retention times (tR) with those of the authentic standards within the allowed deviation of ±0.05 min; (ii) the matching of ion ratios collected with those of the authentic standards within a tolerance of ± 20%. Only VOCs of particular concern due to potential adverse effects on human health and with a chamber air concentration approximately equal to or higher than 1 μg/m<sup>3</sup> were taken into account for further discussion. The list of VOCs (common for the three different investigated items) and related information (molecular formula, CAS number, quantifier and qualifier ions), as well as the performances of the analytical methodology in terms of Limit of Detection (LOD), Limit of Quantification (LOQ) and correlation coefficients (R2), are reported in Table 1.

**Table 1.** Volatile Organic Compounds (VOCs) emitted by the heating bag: molecular formula, CAS number, retention time (tR), quantifier and qualifier ions (m/z), Limit of Detection (LOD) (μg/m3), Limit of Quantification (LOQ) (μg/m3) and correlation coefficient (R2).


2.3.4. Test Chamber Experiments: Emission Rates (ERs) and Estimation of Reference Room Indoor Concentrations (Ci,ref)

The primary objective of emission testing is the determination of VOC specific emission rates (SERs), enabling description of the emission behavior of the material/product regardless of air exchange rate and loading factor. According to ISO standards and most of the existing health-related evaluation schemes at EU level, VOC specific emission rates are calculated at fixed sampling times, e.g., 3 and 28 days after the introduction of the material inside the test emission chamber [27]. The determination of specific emission rates for any individual VOC detected is addressed to model the exposure scenario and to estimate indoor air concentrations that an occupant of a real-scale room could be exposed to. More specifically, VOC specific emission rates derived at 3 days allow the estimation of indoor concentrations representative of short-term exposure. In the present study, the emission rate for compound *i* (ER*i*) emitted by the electric heating bag at 72 h in the test chamber experiment was calculated on the basis of the mass conservation Equation (1):

$$ERi = Ci \ltimes V \times n \tag{1}$$

where *Ci* is the chamber concentration of compound *i* in the air sampled at 72 h (expressed as μg/m3 or ng/m3); *V* is the chamber volume (m3); and *n* is the air exchange rate (h−1). Starting from *ERi*, individual VOC indoor concentrations resulting from the presence or use of the investigated item inside the 30 m<sup>3</sup> reference room (*Ci,ref*) may be estimated via the following formula:

$$\text{Ci},ref = \frac{ERi}{n \times V} \tag{2}$$

with *n* and *V* representing the air exchange rate (0.5 h−1) and volume (30 m3) of the reference room, respectively.
