Know thy carbs! Safer carbohydrate detection methods for school labs. Part 1

In experimental chemistry lessons, historical wet lab detection reactions are particularly popular, above all, Fehling’s test from 1848 and the slightly better Benedict test from 1909. In modern analytical laboratories, these methods have become largely obsolete due to more specific and faster technologies. However, modern detection methods (e.g., gas chromatography and high-performance liquid chromatography or HPLC) are almost exclusively “black box” methods. Due to their didactical merits and monetary advantages over “black box” analytical technology, current chemistry teaching materials still rely on classic test reactions for carbohydrates. However, due to their historical context, these methods frequently use chemicals that should be avoided, substituted, or abandoned altogether from a modern lab safety perspective. Outdated compounds in contemporary lab activities with students include 1-naphthol when performing Molisch’s test, ammonia in the classroom (Woehlk test), and copper ions (Fehling, Benedict) or silver fulminates in the lab waste following the use of Tollens’ reagent. Here, we examine the most frequently applied carbohydrate tests in secondary education chemistry labs and present safer alternatives and procedures. In this part, we will look at historical carbohydrate detection reactions and a novel method for wet lab lactose detection. The second part will deal with improved detection reactions for carbohydrates. (DIPF/Orig.)Im experimentellen Chemieunterricht sind historische nass-chemische Nachweisreaktionen besonders beliebt, vor allem der Fehling-Test von 1848 und der etwas bessere Benedict-Test von 1909. In modernen analytischen Labors sind diese Methoden durch spezifischere und schnellere Technologien weitgehend überholt. Moderne Nachweismethoden (z. B. Gaschromatographie und Hochleistungsflüssigkeitschromatographie oder HPLC) sind jedoch fast ausschließlich "Black Box"-Methoden. Aufgrund ihrer didaktischen Vorzüge und der monetären Vorteile gegenüber der "Black Box"-Analysetechnik wird in den aktuellen Chemie-Lehrmaterialien immer noch auf die klassischen Testreaktionen für Kohlenhydrate zurückgegriffen. Wegen ihres historischen Kontextes verwenden diese Methoden jedoch häufig Chemikalien, die aus Sicht der modernen Laborsicherheit vermieden, ersetzt oder ganz aufgegeben werden sollten. Zu den veralteten Verbindungen, die in heutigen Labortätigkeiten mit Schülern verwendet werden, gehören 1-Naphthol bei der Durchführung des Molisch-Tests, Ammoniak im Klassenzimmer (Wöhlk-Test) und Kupferionen (Fehling, Benedict) oder Silberfulminate im Laborabfall nach der Verwendung des Tollens\u27schen Reagenzes. Im Folgenden werden die in den Chemielabors der Sekundarstufe am häufigsten verwendeten Kohlenhydrattests untersucht und sicherere Alternativen und Verfahren vorgestellt. In diesem Teil befassen wir uns mit historischen Kohlenhydrat-Nachweisreaktionen und einer neuartigen Methode zum Nachweis von Laktose im Nasslabor. Der zweite Teil wird sich mit verbesserten Nachweisreaktionen für Kohlenhydrate befassen. (Autor

Test your knowledge with challenges from the International ChemistryOlympiad! Urea - From Friedrich Woehler to AdBlue(R)

Der Artikel erläutert die umfangreiche Bedeutung des Harnstoffs - angefangen bei der Entgiftung des körperlichen Stoffwechsels über die Verwendung als Frostschutzmittel bis zur Abgasreinigung in modernen Dieselfahrzeugen

Know thy carbs! Safer carbohydrate detection methods for school labs. Part 2

In experimental chemistry lessons, historical wet lab detection reactions are particularly popular, above all, Fehling’s test from 1848 and the slightly better Benedict test from 1909. In modern analytical laboratories, these methods have become largely obsolete due to more specific and faster technologies. However, modern detection methods (e.g., gas chromatography and high-performance liquid chromatography or HPLC) are almost exclusively “black box” methods. Due to their didactical merits and monetary advantages over “black box” analytical technology, current chemistry teaching materials still rely on classic test reactions for carbohydrates. However, due to their historical context, these methods frequently use chemicals that should be avoided, substituted, or abandoned altogether from a modern lab safety perspective. Outdated compounds in contemporary lab activities with students include 1-naphthol when performing Molisch’s test, ammonia in the classroom (Woehlk test), and copper ions (Fehling, Benedict) or silver fulminates in the lab waste following the use of Tollens’ reagent. Here, we examine the most frequently applied carbohydrate tests in secondary education chemistry labs and present safer alternatives and procedures. In part 1, we looked at historical carbohydrate detection reactions and a novel method for wet lab lactose detection. Part 2 deals with improved detection reactions for further carbohydrates. (DIPF/Orig.)Im experimentellen Chemieunterricht sind historische nass-chemische Nachweisreaktionen besonders beliebt, vor allem der Fehling-Test von 1848 und der etwas bessere Benedict-Test von 1909. In modernen analytischen Labors sind diese Methoden durch spezifischere und schnellere Technologien weitgehend überholt. Moderne Nachweismethoden (z. B. Gaschromatographie und Hochleistungsflüssigkeitschromatographie oder HPLC) sind jedoch fast ausschließlich "Black Box"-Methoden. Aufgrund ihrer didaktischen Vorzüge und der monetären Vorteile gegenüber der "Black Box"-Analysetechnik wird in den aktuellen Chemie-Lehrmaterialien immer noch auf die klassischen Testreaktionen für Kohlenhydrate zurückgegriffen. Aufgrund ihres historischen Kontextes verwenden diese Methoden jedoch häufig Chemikalien, die aus Sicht der modernen Laborsicherheit vermieden, ersetzt oder ganz aufgegeben werden sollten. Zu den veralteten Verbindungen, die in heutigen Labortätigkeiten mit Schülern verwendet werden, gehören 1-Naphthol bei der Durchführung des Molisch-Tests, Ammoniak im Klassenzimmer (Woehlk-Test) und Kupferionen (Fehling, Benedict) oder Silberfulminate im Laborabfall nach der Verwendung des Tollens-Reagenzes. Hier untersuchen wir die am häufigsten verwendeten Kohlenhydrat-Tests in Chemielabors der Sekundarstufe und stellen sicherere Alternativen und Verfahren vor. In Teil 1 haben wir uns mit historischen Kohlenhydrat-Nachweisreaktionen und einer neuartigen Methode zum Nachweis von Laktose beschäftigt. Teil 2 beschäftigt sich mit verbesserten Nachweisreaktionen für weitere Kohlenhydrate. (Autor

Teste dein Wissen mit Aufgaben aus der ChemieOlympiade! Enantiomere - gibt es eine bessere Hälfte? (Teil II)

The article explains the phenomenon of right- and left-rotating solutions and the consequences of the fact that many molecules have mirror image isomerisms. The aim is to inspire pupils to participate in the chemistry olympiad

When experiments fail... accidents in chemistry lessons and their legal consequences

Unfälle im Chemieunterricht sind so selten, dass sie sich gegenüber anderen Schulunfällen prozentual nicht erfassen lassen. Passiert aber etwas, so steht es meist groß in der Zeitung; nicht selten wird das Vorgefallene auch noch gerichtlich und dienstrechtlich gewürdigt. Der Autor versucht, Gemeinsamkeiten aufzuzeigen und Sensibilität zur Prävention zu erzeugen. (Autor)Compared to other school accidents, accidents in chemistry classes are so rare that they cannot be recorded in percentage. However, if something does happen, it usually makes headlines in the media. Additionally the incident usually has a judicial impact and results in staff regulation alterations. The author highlights similarities and generates awareness for prevention. (Author

Detection of lactose (and maltose) in the context of school: Woehlk test, Fearon\u27s test and the hexamethylenediamin method - amine based color reactions as detection reactions for carbohydrates

Kohlenhydrate sind eine sehr bekannte chemische Stoffgruppe, für die es zahlreiche Nachweisreaktionen gibt. Innerhalb der Stoffgruppe der Kohlenhydrate sind Lactose und Maltose zwei sehr wichtige Verbindungen. Da sie auf natürliche Weise in Milch und Milchprodukten bzw. beim Abbau von Stärke auftreten, sind sie in Lebensmitteln aller Art vertreten und besitzen somit eine hohe Alltagsrelevanz. Weiterhin sind viele Schülerinnen und Schüler von dem Phänomen der Lactoseintoleranz betroffen und wissen aus eigener Lebenserfahrung, wie wichtig die Kenntnis über den Milchzuckergehalt verschiedener Lebensmittel bei der Zubereitung der eigenen Nahrung ist. Diese Fakten werden von den Lernenden als sehr interessant empfunden und tragen durch ihre Aussagekraft und Anschaulichkeit zur Lebendigkeit des experimentellen Chemieunterrichts bei. Wie eine Auswertung aktueller, gängiger Schulbücher im Rahmen dieser Arbeit zeigt, mangelt es derzeit jedoch sowohl an schulisch geeigneten Experimenten als auch an Unterrichtskonzepten für den Nachweis und die Verwendung von Lactose und Maltose im Unterricht. Daher ist es ein Ziel dieser Arbeit, sowohl schulische geeignete Experimente als auch anwendbare Kontexte zu finden, um das von Lactose und Maltose ausgehende Potential für schülerorientierte Lernvorgänge zu nutzen. (DIPF/Orig.)Carbohydrates are a very well-known chemical group of substances for which numerous detection reactions are available. Within the carbohydrate group, lactose and maltose are two rather important compounds. Since they occur naturally in milk and dairy products and in the degradation of starch, they are present in various foods around the globe and thus have a high relevance for everyday life. In addition, the phenomenon of lactose intolerance, which also affects many students, demands a high level of attention in the preparation of daily food. These facts considered to be quite interesting by the learners and add to the liveliness of the experimental chemistry lessons due to their expressiveness and vividness. However, an analysis of current standard textbooks in the context of this thesis shows that there is currently a lack of teaching concepts and experiments suitable for the school contexts for the detection and the use of lactose and maltose in the classroom. Therefore, one of the aims of this thesis is to find both suitable experiments for schools and applicable contexts to use the potential of lactose and maltose for student-oriented learning processes. (DIPF/Orig.

A sequence motif responsible for ER export and surface expression of Kir2.0 inward rectifier K+ channels

AbstractIntegral membrane proteins are sorted via the secretory pathway. It was proposed that this pathway is non-selective provided that the cargo protein is properly assembled and lacks an endoplasmic reticulum (ER) retention signal. However, recent experimental evidence suggests that efficient export of proteins from the ER to the Golgi complex is not simply a default pathway. Here we demonstrate a novel sequence motif (FxYENEV) in the cytoplasmic C-terminus of mammalian inward rectifier potassium (Kir) channels which determines ER export. This motif is found to be both necessary and sufficient for efficient export from the ER that eventually leads to efficient surface expression of Kir2.1 channels

Experimental measurement, calculation and thermal visualization condenser temperature of cooling device with a heat pipe technology

This work deal with evaluation of condenser temperature by experimental measurement, calculation and thermal visualization of cooling device working with a heat pipe technology. The referred device in the article is cooling device capable transfer high heat fluxes from electric elements to the surrounding. One from many things influenced the heat flux amount transferred from electronic elements through the cooling device to the surrounding is condenser construction, its capacity and option of heat removal. The work contain description, working principle and construction of cooling device. Experimental part describe the measuring method and mathematical calculation to condenser temperature evaluation of cooling device depending on the loaded heat of electronic components in range from 250 to 750 W. The mathematical calculation is based on physical phenomena of boiling, condensation and natural convection heat transfer. The results of experimental measurement and mathematical calculation are verified by thermal imagining of device condenser by IR camera

Flow and heat transfer in a closed loop thermosyphon. Part I – theoretical simulation

A natural circulation, closed loop thermosyphon can transfer heat over relatively large distances without any moving parts such as pumps and active controls. Such loops are thus considered suitable for nuclear reactor cooling applications where safety and high reliability are of paramount importance. A theoretical basis from which to predict the flow and heat transfer performance of such a loop is present-ed. A literature survey of the background theory is undertaken and the theoretical equations describing the single and two-phase flow as well as heat trans-fer behaviour are given. The major assumptions made in deriving these equations are that the work-ing fluid flow is quasi-static and that its single, two-phase flow and heat transfer behaviour may be cap-tured by dividing the working fluid in the loop into a number of one dimensional control volumes and then applying the equations of change to each of these control volumes. Theoretical simulations are conducted for single phase, single and two-phase and heat pipe operating modes, and a sensitivity analysis of the various variables is undertaken. It is seen that the theoretical results capture the single and two-phase flow operating modes well for a loop that includes an expansion tank, but not for the heat pipe operating mode. It is concluded that the theo-retical model may be used to study transient and dynamic non-linear effects for single and two-phase modes of operation. To more accurately predict the heat transfer rate of the loop however, loop specific heat transfer coefficients need to be determined experimentally and incorporated into the theoretical model

Flow and heat transfer in a closed loop thermosyphon. Part I – theoretical simulation

A natural circulation, closed loop thermosyphon can transfer heat over relatively large distances without any moving parts such as pumps and active controls. Such loops are thus considered suitable for nuclear reactor cooling applications where safety and high reliability are of paramount importance. A theoretical basis from which to predict the flow and heat transfer performance of such a loop is present-ed. A literature survey of the background theory is undertaken and the theoretical equations describing the single and two-phase flow as well as heat trans-fer behaviour are given. The major assumptions made in deriving these equations are that the work-ing fluid flow is quasi-static and that its single, two-phase flow and heat transfer behaviour may be cap-tured by dividing the working fluid in the loop into a number of one dimensional control volumes and then applying the equations of change to each of these control volumes. Theoretical simulations are conducted for single phase, single and two-phase and heat pipe operating modes, and a sensitivity analysis of the various variables is undertaken. It is seen that the theoretical results capture the single and two-phase flow operating modes well for a loop that includes an expansion tank, but not for the heat pipe operating mode. It is concluded that the theo-retical model may be used to study transient and dynamic non-linear effects for single and two-phase modes of operation. To more accurately predict the heat transfer rate of the loop however, loop specific heat transfer coefficients need to be determined experimentally and incorporated into the theoretical model