In this study, five laboratories, namely, BRML (Romania), TUBITAK UME (Turkey), IMBIH (Bosnia and Herzegovina), BAM (Germany), and DTI (Denmark), developed and validated analytical procedures by ICP-MS, ICP-OES, MWP-AES, WD-XRF, and ID-MS for the determination of inorganic impurities in solid and liquid biofuels, established the budget of uncertainties, and developed the method for determining the amount of ash in the measurement range 0–1.2% with absolute repeatability less than 0.1% and absolute reproducibility of 0.2% (according to EN ISO 18122). In order to create homogeneous certified reference materials, improved methodologies for the measurement and characterization of solid and liquid biofuels were developed. Thus, information regarding the precision, accuracy, and bias of the method, and identifying the factors that intervened in the measurement of uncertainty were experimentally determined, supplementing the information from the existing standards in the field.

Lavandula species are one of the most popular aromatic plants in the world and have a high content of high-quality essential oil (EO). Although there are many species in this genus, only lavandin (Lavandula intermedia Emeric ex Loisel.) and lavender (L. angustifolia Mill.) are highly valued worldwide. The quality and yield of lavandin and lavender depend on genetic factors, environmental conditions and cultivation methods. Therefore, the aim of this paper is to research the effects of the application of biostimulant on the inflorescence yield and the quality of lavandin and lavender. The treatments used in this research consisted of a combination of different species (lavandin and lavender) and biostimulant (applied and unapplied). The research results show that all the research traits significantly depended on the used species and the applied biostimulant. The inflorescence yield, the content of total flavonoids, and the content of EO were higher in the lavandin species (477.3 g plant^-1, 17.21 mg CAE g^-1, 8.57 mL 100 g^-1, respectively) than in the lavender species (180.5 g plant^-1, 13.41 mg CAE g^-1, and 3.69 mL 100 g^-1, respectively). EOs of lavandin and lavender were rich in linalool and linalyl acetate. The use of biostimulators had a positive effect on the inflorescence yield and the content of essential oil. Furthermore, the applied biostimulant increased the linalool content in the essential oil of both researched species, i.e. it positively affected its quality.

Immortelle (Helichrysum italicum) is a perennial Mediterranean plant known for its medicinal and aromatic properties. Various biotic and abiotic factors influence the yield and quality of immortelle. Mulching is a sustainable agricultural practice that conserves soil moisture, prevents weed growth, and regulates soil temperature. The aim of this research was to examine the influence of different types of mulch on the yield and quality of immortelles. The study had three types of mulch (alfalfa, straw, and perennial mulch) and a control (no mulch). The research mulches significantly affected the yield, essential oil (EO) content and content of bioactive compounds. The highest yield of inflorescences was recorded with alfalfa mulch (67.5 g^-¹), while the control had the lowest yield (37.3 g^-¹). The EO content was highest in treatments with straw and control (0.33 mL 100 g^-1), whereas the lowest content was observed with alfalfa mulch (0.28 mL/100 g). The total phenolic content reached its maximum in the control variant (75.1 mg GAE g¹), while perennial mulch resulted in the highest flavonoid content (20.4 mg CAE g^-¹). A total of 63 constituents were identified in the EO. The largest share was: neryl acetate, α-curcumen, italidione, α-pinene and D-limonene, and others in smaller quantities.

This study presents a validation protocol for the atomic emission spectroscopy (AES) method for determining total silicon in biomethane, developed in alignment with ISO 2613-1:2023. The work serves as a practical demonstration, contributing to the forthcoming ISO validation guide for analytical methods assessing impurities in biomethane, prepared within ISO/TC 193 WG 25: Biomethane. The protocol describes the complete analytical process: absorption of volatile siloxane compounds in mineral acid, chemical derivatization into a suitable form for spectroscopy, and measurement of the resulting liquid sample using an optical plasma emission instrument. Method development included optimisation of sampling, derivatization, sample preparation, and quality control procedures. Validation was carried out through rigorous evaluation of linearity, stability, robustness, selectivity, sensitivity, precision, bias, and measurement uncertainty. Results confirmed the method’s reliability for detecting very low mass fractions of silicon (μg/kg range) originating from siloxane species, such as L2, L3, D4, and D5, in biomethane. By demonstrating both methodological robustness and practical applicability, this study provides a model example for ISO’s upcoming guidance on validation of analytical methods, supporting the harmonisation of impurity testing in renewable gases.

Most of the papers that treat the composition of essential oils for this purpose use GCMS or GCMS and GC-FID techniques for the identification and/or quantification of individual compounds. Therewithal, papers usually treat the composition as semi-quantitative (percentage composition as the area of ​​the peak of a particular compound in relation to the total area of ​​the peaks on the chromatogram, given as 100%). At the same time, the quality of the results is not treated in metrological terms. A GCMS method for the quantification of components present Helichrysum italicum hydro-distilled essential oil samples from Bosnia and Herzegovina with a similar composition was developed and optimized. The stability of the method set-up and adequacy of sample storage and manipulation was assessed. Calibration method and assessment of measurement uncertainty was established for neryl acetate, one of the major compounds with known health benefits.