The method describes how to determine the iron content of water photometrically with a cuvette test.
Iron(II) ions form a rust-colored complex with 1,10-phenanthroline. Iron(III) ions are reduced to iron(II) ions.
The method describes how to determine the iron content of water using a phenanthroline solution.
Iron(II) ions react with 1,10-phenanthroline, forming a rust-colored complex; ferric iron is reduced to ferrous iron prior to complex formation by hydroxyl ammonium chloride. The color of the solution is visually compared to a color disk using a comparator.
The cations in beer and wort are determined with this analysis.
This method is suitable for both wort and beer.
Inductively coupled plasma optical emission spectroscopy (ICP-OES) is a fast and reliable method for the laboratory analysis of metals. Inductively coupled plasma (ICP), a high frequency field of ionized gas, serves as a medium for atomizing and exciting the substances found in samples. Liquid, dissolved or aerosol samples are injected into the ionized gas stream. In emission spectroscopy, ICP can be used in conjunction with a number of optical and electronic systems either simultaneously or sequentially in multi-element spectrometers. In the plasma, the atoms and ions are excited to a higher energy state bringing about the emission of electromagnetic radiation (light), primarily in the ultraviolet and visible region of the spectrum. Metals ordinarily occur as ions in the temperature range typical for ICP of 6000 to 10000 K; however, non-metals and metalloids are only partially ionized.
ICP-OES operates within a very wide range. This usually encompasses six orders of magnitude in concentrations smaller than μg/l up to g/l, depending upon the element and the concentrations used for the set of analysis data. With ICP-OES, beer and wort can also be analyzed without prior processing of the samples, in contrast to AAS. Methods for determining the following in beer and wort will be described below: Al, B, Ba, Ca, Co, Cu, Fe, K, Mg, Mn, Mo, Na, P, Si, Sr, Sn and Zn.
Determination of the steam-volatile acids by means of titration
This method serves as a means for determining the titratable steam-volatile acids in beverages and concentrates
Volatile acids are distilled using steam, and the distillate is analyzed through titration. Sulfurous acid present in the distillate is determined iodometrically and subtracted from the total.
Determination of formic acid by enzymatic means
This analysis is suitable for wort, beer, beer-based beverages and NAB.
Formic acid can be found in beer in small quantities, and it is also formed by contaminating bacteria, for example, by lactic acid bacteria (rods).
In the presence of the enzyme formate dehydrogenase (FDH), the formic acid created in this reaction is quantitatively oxidized to bicarbonate by nicotinamide adenine dinucleotide (NAD):
HCOO- + NAD+ + H2O \(^{\underrightarrow{FDH}}\) HCO3- + NADH + H+
The amount of NADH formed during the reaction is equivalent to the amount of formic acid and can be determined photometrically based on its absorbance at 334, 340 or 365 nm.
Oxalic acid (oxalate) is transformed into formic acid and CO2 in this reaction catalyzed by the enzyme oxalate decarboxylase (Ox-DC):
Oxalic acid \(^{\underrightarrow{Ox-DC}}\) formic acid + CO2
The quantity of NADH produced during the reaction is equivalent to the amount of formic acid and is determined photometrically owing to its absorption at 334, 340 or 365 nm. In preparation for this test, the free formic acid present in the solution is determined along with the oxalic acid. Each are accounted for in the blank.