Blaženka Šebečić

Spectrofluorometric method for determination of the total mercury content in environmental samples — Waste waters

A highly selective spectrofluorometric method for the determination of total mercury (Hg) in waste waters is described. Fluorescence quenching of rhodamine B with Hg(II) in the presence of iodide, after a concentration step, is the basis of this sensitive method. All forms of mercury, including organic compounds, are pre-oxidized to ionic mercury by acidic potassium permanganate. The final and complete oxidation is achieved by adding potassium persulphate and heating. Hg(II) was reduced by tin(II) chloride and Hg vapour driven by an air stream into an absorption solution containing potassium permanganate and sulphuric acid, using a closed, recirculating air stream. In this solution fluorescence quenching of rhodamine B at an excitation wavelength of 485 nm and emission wavelength of 586 nm was measured. The recoveries were done by adding 3.0 μg Hg/100 ml to each sample before the digestion. It was indicated that the recoveries for determining mercury in waste waters were 98.3%–102.7%. The method gives reliable results down to a concentration of 10 ng Hg/ml waste water.

Dynamics of the accumulation of thiamine during maturation of soybean seeds

Summary The dynamics of the accumulation of thiamine were followed in developing seeds of four genotypes of soybean under defined climatic and constant topographical and agrotechnical conditions in the course of three consecutive vegetation years. Tests were carried out at weekly intervals until the seeds were completely mature and had a moisture content of about 14%. Thiamine content was determined fluorometrically by measuring the intensity of thiocrome fluorescence. It was found that the greatest accumulation of the dry matter took place during the seed development stages III and IV whereas thiamine accumulation is more or less linear during the development. Maximal concentrations of thiamine were found in mature seeds. Although the dynamics of accumulation, regardless of the year of investigation, were the same in all the genotypes, the analysis of the impact of climatic factors showed that higher precipitation during the period of seed development, along with moderate air temperature, affected thiamine accumulation of some soybean genotypes more than others.

Effect of frozen storage on the degree of vitamin B6 degradation in different foods

ZusammenfassungAus den Ergebnissen der Untersuchung des Gefriervorgangs und der fünfmonatigen Lagerung bei -18°C auf die Stabilität des Gesamtvitamin B6 bei Lebensmitteln verschiedener Herkunft kann geschlossen werden, daß die Verluste des Vitamins Bß von 18,92% bis 60,26% betragen und daß der Verlust bei den Lebensmitteln tierischer Herkunft (ca. 55,0%) bedeutsam höher ist. Es ist offensichtlich, daß die Biostruktur, beziehungsweise die chemische Zusammensetzung, einer der wesentlichen Gründe ist, die die Höhe des Verlustes des Vitamins B6 bei den Lebensmitteln, die bei -18 °C gelagert werden, beeinflussen. Wenn man aber den biologischen Wert des Lebensmittels betrachtet, auch bei einigen Lebensmitteln pflanzlicher Herkunft, ist der Verlust des biologischen Wertes schon nach fünf Monaten verhältnismäßig hoch, jedoch nach der Deklaration kann tiefgefrorenes Gemüse bis zu 12 bzw. 24 Monaten gelagert werden.AbstractInvestigation of the effect of freezing and storage at-18° C for 5 months on the stability of total vitamin B6 in foods of different origin leads to the conclusion that the decrease in vitamin B6 content ranged from 18.92% to 60.26% and that the loss is significantly greater in food of animal origin (an average of 55.0%). Obviously, biostructure, that is chemical composition, is one of the basic factors affecting the degradation degree of vitamin B6 in foods preserved by freezing. However, in relation of their biological value and with reference to the declaration allowing deep-frozen vegetables to be stored for 12–24 months, some foods of vegetable origin preserved by freezing exhibit a relatively high loss of biological value in terms of vitamin B6 as early as after 5 months of storage.

Fluorometric method for determination of vitamin B6 in soya bean

ZusammenfassungDie einfache fluorometrische Methode zur Bestimmung von zugegebenem Pyridoxin in angereicherten Lebensmitteln basiert auf der Oxidation des Pyridoxins mit Kaliumpermanganat zur 4-Pyridoxinsäure und wurde für die Bestimmung des gesamten Vitamin B6 in Soja modifiziert. Im Vergleich mit anderen fluorometrischen Methoden ist die vorgeschlagene, einfach, schnell und leicht durchzuführen. Diese Methode braucht nur wenig Zeit für die Oxidation und verwendet ungiftige Chemikalien (KMnO4 statt KCN). Die gute Wiederfindung, die geringe relative Standardabweichung und der geringe Gesamtfehler reiht das vorgeschlagene Verfahren in die Gruppe der ausgezeichneten Methoden ein.SummaryThe simple fluorometric method for determination of added pyridoxine-HCl in enriched food, based on oxidation of pyridoxine to 4-pyridoxic acid by means of KMnO4, has been modified for determination of total B6 in soya bean. In comparison to the other fluorometric procedures, the proposed method is the simplest one, rapid and easy to perform, demanding the least time for oxidation and not using hazardous chemicals (KMnO4 instead of KCN). Good recovery, low relative standard deviation and low total error allow the proposed procedure to be included into the group of excellent methods.

Modified lumiflavin procedure for determination of riboflavin in soyabean

ZusammenfassungDurch Prüfen der Anwendungsmöglichkeit verschiedener Methoden zur Bestimmung von Riboflavin wurde festgestellt, daß die Lumiflavin-methode von Hausheer u. Mitarb. [1] die geeigneste zur Bestimmung von Riboflavin in Stoffen komplexer Zusammensetzung wie Soja ist. Infolge der nicht angemessenen Vorbereitung der Blindprobe wird die Methode durch einen positiven Resultatfehler belastet. Durch die Modifizierung der Blindprobe und des Verfahrens wurden genauere Resultate, eine größere Geschwindigkeit und eine einfachere Methode erzielt. Die Soja-Muster, die nach diesem modifizierten Verfahren analysiert wurden, haben eine Wiederfindung des Riboflavins und einen Standardfehler von 102,9±2,1SummaryInvestigation of the application of different methods for riboflavin determination proved the lumiflavin method recommended by Hausheer et al. [1] to be the most suitable one for determining riboflavin in materials of complex composition, such as soyabean. However, due to inadequate preparation of the blank sample, the method is burdened by a positive error. By modifying the blank sample and certain modifications in the procedure, more precise results, greater speed and simplification of the method were achieved. The soyabean sample analysed by this modified procedure gave a mean recovery and standard error of 102.9±2.1 for added riboflavin, which is very satisfactory.