## 1 Introduction  
In recent years, there has been increased interest in medicinal and aromatic plants since they are sources of many bioactive compounds with diverse pharmacological activities and medicinal applications [1]. Particularly interesting for pharmacy and the cosmetic industry, due to their diverse therapeutic and cosmeceutical properties, are essential oils (EOs), mixtures of volatile organic compounds (VOCs) that are obtained by different distillation methods from plant-based raw materials [2]. Dried rhizomes of various _Iris_ L. species (mainly _Iris pallida_ Lam, _I. \(\times\) germanica_ L., and _I. florentina_ L.), also known as orris roots,are resources of a semi-solid essential oil (EO), i.e., \"orris oil\" or \"orris butter\", which is especially valued in perfumery but is also used by the food industry to flavor soft and alcoholic beverages (e.g., rum, gin, and vermouth) and sweets [3; 4]. This is not only because of the pleasant violet-like smell coming from its volatile constituents [3] but also because of their powerful fixative properties [4]. The name \"orris butter\" comes from the fact that the EO has a high share of myristic (tetradanoic, C\({}_{14}\)H\({}_{28}\)O\({}_{2}\)) acid (around 65%) and other saturated fatty acids, such as lauric (dodecanoic, C\({}_{12}\)H\({}_{24}\)O\({}_{2}\)) acid and palmitic (hexadecanoic, C\({}_{16}\)H\({}_{32}\)O\({}_{2}\)) acid [3], the melting points of which are above the human body temperature [5]. However, the characteristic smell of the oil is mainly not due to the presence of fatty acids but to the presence of irones, C\({}_{14}\) monocyclic ketones, which are believed to be formed by oxidative degradation from their triterpen precursors iridals during rhizome maturation (aging) and are not present in fresh plant material. A storage period of about 2-to-5 years is believed to be required for rhizomes of irises to achieve their maximum iron content and fullness of the scent, resulting in high-quality EO [3; 4]. The determined amounts (yields) and chemical composition of VOCs may vary depending on the used isolation technique. Hydrodistillation (HD) is one of the most frequently used techniques for the extraction of VOCs from plant material [6], which is environmentally friendly [7]. On the other hand, headspace solid-phase microextraction (HS-SPME) represents a relatively novel, easy, effective, and convenient technique, which allows the extraction of VOCs on the fiber coating depending on their concentrations in the sample headspace and can be used for rapid isolation of VOCs from plant material [8; 9]. HS-SPME has been extensively used for the extraction of VOCs, without the need for the sample pre-treatment [9; 10]. The genus _Iris_ (Iridaceae) has about 300 species distributed worldwide, with the majority of endemic species located in Asia and the Mediterranean area [11]. Many of these species are used in traditional medicine, e.g., _I. germuica_ to reduce the activity of smooth muscles, _I. dichotomous_ Pall. to treat respiratory and rheumatic disorders, and _I. fomentina_ for digestive and metabolic disorders [12; 13; 14]. Moreover, dried rhizomes of various _Iris_ species were utilized collectively in order to create toothpowders and ease children's teething pain [15]. Due to the presence of different bioactive compounds, such as flavones, isoflav, benzophenones, and xanthones, _Iris_ extracts have been reported to have many biological activities [12; 14; 15; 16]. These include antioxidative, anticancer, antibacterial, anti-inflammatory, antifungal, antiviral, anthelmintic, antidiabetic, neuroprotective, hepatoprotective, hypolipidemic, and other activities [14; 15; 16; 17; 18; 19]. Nevertheless, species from the genus _Iris_ are rich sources of EOs, which can be found in a variety of plant parts, mostly in the rhizomes, but also in the roots, seeds, leaves and flowers, and may be used in aromotherapy for their sedative properties [14; 20].