4.1. Chemicals

Malachite Green (99%, MW 364.911 Da), Crystal Violet (99%, MW 407.99 Da), and Congo Red (99%, MW 696.69 Da) were purchased from Hadron Scientific (Kielce, Poland). Thiamine hydrochloride (99%, MW 337.27 Da), biotin (>99%, MW 244.31 Da), vitamin B12 (>98%, MW 1355.37 Da), sodium hydroxide (>98%, MW 40.00), hydrochloric acid (37%, MW 36.46), and standard buffered solutions pH 2.0, 7.0, and 10.0 were supplied by Sigma-Aldrich (St. Louis, MO, USA). Hydrogen peroxide (30%, MW 34.01 Da), sodium nitrate (>99%, MW 84.99 Da), sodium dihydrogen phosphate monohydrate (>99%, MW 137.99 Da), sodium molybdate dihydrate (>99%, MW 241.95 Da), manganese (II) chloride tetrahydrate (>99%, MW 197.91 Da), and cobalt (II) chloride hexahydrate (>99%, DW 237.93 Da) were obtained from Chempur^® (Piekary Śląskie, Poland). Zinc sulfate heptahydrate (>99%, MW 287.54 Da), iron (III) chloride hexahydrate (>99%, MW 270.32 Da), EDTA disodium dihydrate (>99%, MW 372.24 Da), and copper (II) sulfate pentahydrate (>99%, MW 249.68 Da) were purchased from Scharlab (Barcelona, Spain). Nonahydrate sodium metasilicate (44–47.5% total solids, MW 284.19 Da) was supplied by Acros Organics, ThermoFisher Scientific (Waltham, MA, USA). The PhosVer^® 3 Phosphate Reagent Powder Pillow, Amino Acid F Reagent Powder Pillow, Citric Acid Powder Pillow, and Molybdate 3 Reagent Solution were provided by HACH-Lange (Loveland, CO, USA). Deionized water was obtained by using a Milli-Q^® purification system (Millipore Co., Bedford, MA, USA).