The aim of the present work is the modification of the standard indophenol blue method in order to be feasible the determination of ammonium in geothermal water samples with high mineral content. Several pretreatment techniques were studied and evaluated in order to neutralise the pH of all solutions (blank, sample, standards) and minimise the interferences from salts. The Ultrasonic bath followed by mechanical stirring and vacuum filtration seems to be the most efficient pretreatment technique with almost 100% recovery of . Also there was an optimisation in the main procedure of the method in order to gain in sensitivity. The proposed method was compared with the standard ion chromatography and spectrophotometric indophenol blue methods and a t-test was performed. The RSD% values (n = 4) of the proposed spectrophotometric method were below 3.5% and the LOD of was 0.026 mg L⁻¹. The proposed method was applied to several geothermal water samples from regions of Greece.

Metal–organic frameworks (MOFs) are crystalline porous materials composed of metal ions or clusters coordinated with organic linkers. Due to their extraordinary properties such as high porosity with homogeneous and tunable in size pores/cages, as well as high thermal and chemical stability, MOFs have gained attention in diverse analytical applications. MOFs have been coupled with a wide variety of extraction techniques including solid-phase extraction (SPE), dispersive solid-phase extraction (d-SPE), and magnetic solid-phase extraction (MSPE) for the extraction and preconcentration of metal ions from complex matrices. The low concentration levels of metal ions in real samples including food samples, environmental samples, and biological samples, as well as the increased number of potentially interfering ions, make the determination of trace levels of metal ions still challenging. A wide variety of MOF materials have been employed for the extraction of metals from sample matrices prior to their determination with spectrometric techniques.