Accuracy of analytical standard solutions and the uncertainty in their nominal concentrations

In the last step of the analysis, the accuracy of analytical standard solutions has a decisive influence on the measurement results of pesticide residues, as well as all other chemical contaminants, and, in the case of actual concentrations differing from nominal ones, can result in a systematic error during the determination of sample components. Therefore, most of the laboratories who feel responsible for their results pay special attention to the preparation and storage of standard solutions, and to replenishing solvent losses due to possible evaporation, based on the mass measurements of vessels storing standard solutions before and after use. However, in our experience, much less attention than necessary is paid in practical work to monitoring the possible decomposition of individual active ingredients, and not appropriate statistical methods are used for the evaluation of the monitoring results. In our article, we present the standard preparation methods of two laboratories employing “good analytical practices”, analyze the uncertainties of the different steps, and make a recommendation for the preparation of the most accurate standard solutions

Optimal embedded and enclosing isosceles triangles

Given a triangle Δ, we study the problem of determining the smallest enclosing and largest embedded isosceles triangles of Δ with respect to area and perimeter. This problem was initially posed by Nandakumar and was first studied by Kiss, Pach, and Somlai, who showed that if Δ′ is the smallest area isosceles triangle containing Δ, then Δ′ and Δ share a side and an angle. In the present paper, we prove that for any triangle Δ, every maximum area isosceles triangle embedded in Δ and every maximum perimeter isosceles triangle embedded in Δ shares a side and an angle with Δ. Somewhat surprisingly, the case of minimum perimeter enclosing triangles is different: there are infinite families of triangles Δ whose minimum perimeter isosceles containers do not share a side and an angle with Δ

Az analitikai standard oldatok pontossága és a névleges koncentrációjuk bizonytalansága

Az analitikai standard oldatok pontossága a növényvédő szermaradék, de minden más kémiai szennyező mérési eredményét a vizsgálat utolsó lépésében döntően befolyásolja, és a minta komponenseinek meghatározása során a névlegestől eltérő aktuális koncentráció tekintetében folyamatosan szisztematikus hibát eredményez. A legtöbb, eredményeiért felelősséget érző laboratórium ezért különös figyelmet fordít a standard oldatok elkészítésére és tárolására, illetve az oldószer esetleges elpárolgásából adódó veszteség pótlására a standard oldatokat tároló eszközök tömegének használat utáni és használat előtti mérése alapján. Tapasztalataink szerint azonban a gyakorlati munkában a szükségesnél sokkal kisebb figyelmet fordítanak az egyes hatóanyagok esetleges bomlásának ellenőrzésére, illetve nem a megfelelő statisztikai módszert alkalmazzák az ellenőrzési eredmények értékelésére. Cikkünkben bemutatjuk két, „jó analitikai gyakorlatot” alkalmazó laboratórium standard készítési módszereit, elemezzük az egyes lépések bizonytalanságát és javaslatot teszünk a legpontosabb standard oldatok elkészítési módjára

Beírt és körülírt egyenlő szárú háromszögek tulajdonságai

A szakdolgozat R. Nandakumar indiai matematikus tetszőleges háromszögek köré, illetve azokba írt háromszögek területére, illetve kerületére vonatkozó sejtésére ad megoldást

Optimal embedded and enclosing isosceles triangles

Given a triangle Δ, we study the problem of determining the smallest enclosing and largest embedded isosceles triangles of Δ with respect to area and perimeter. This problem was initially posed by Nandakumar [17, 22] and was first studied by Kiss, Pach, and Somlai [13], who showed that if Δ′ is the smallest area isosceles triangle containing Δ, then Δ′ and Δ share a side and an angle. In the present paper, we prove that for any triangle Δ, every maximum area isosceles triangle embedded in Δ and every maximum perimeter isosceles triangle embedded in Δ shares a side and an angle with Δ. Somewhat surprisingly, the case of minimum perimeter enclosing triangles is different: there are infinite families of triangles Δ whose minimum perimeter isosceles containers do not share a side and an angle with Δ

Kádártól Orbánig

Az 1980-as évekig Magyarországon mindenki egyetlen emberre figyelt, Kádár Jánosra. Közös tudás volt, hogy tőle függ, merrefelé mennek a dolgok az országban. A rendszerváltás ígérete az volt, hogy ilyen többet nem lesz. Aztán 2010-től ismét mindenki egyetlen emberre figyel, Orbán Viktorra. Ismét közös tudás, hogy végső soron minden úgy fog eldőlni, ahogy ő jónak gondolja. Ez a könyv arról szól, hogyan jutottunk csöbörből vödörbe

Testing the Accuracy of Analytical Standard Solutions Used for Quantitative Determination of Pesticide Residues

Pure analytical standards of pesticide residues may decompose or change their concentrations, especially in diluted standard solutions. The SANTE/11945/2015 guidance document on analytical quality control permits a ±10% difference between the concentrations in the new (100%) and the old standard solutions, which should be tested by comparing the average responses of the corresponding components obtained with a minimum of five replicate injections. To verify that the difference is within the permitted ±10%, the application of the two one-sided t-test (TOST) is recommended. It is shown here, with practical examples, that the two-sample t-test is not suitable for this purpose, because it is designed to prove that the old and new standard solutions have different means, not that the means of two sets are equal or within a specified limit. Furthermore, it is recommended that the standard solutions be prepared based on weighing with 0.01 mg accuracy and in duplicate, and that their average concentrations, determined with an appropriate instrumental technique, should be compared with the TOST to identify potential errors in their preparation. An automated Excel template, provided as supplemental material, simplifies the calculation

The effect of the antioxidant on the properties of thiolated poly(aspartic acid) polymers in aqueous ocular formulations

Thiolated polymers are a promising new group of excipients, but their stability against atmospheric oxidation has not been investigated in detail, and only a few efforts have been made to improve their stability. The oxidation of the thiol groups in solutions of thiolated polymers may result in a decrease of mucoadhesion and unpredictable in situ gelation. The aims of our work were to study the stability of aqueous solutions of thiolated polymers and the effects of stabilizing agents. We investigated thiolated poly(aspartic acid) polymers stabilized with dithiothreitol, glutathione or acetylcysteine. The effects of these antioxidants on the gel structure, mucoadhesion and drug release were determined by means of scanning electron microscopy, swelling, rheology, adhesion and drug release tests. It was concluded that the stability of polymer solutions containing antioxidants is sufficient for one day. Polymers stabilized with dithiotreitol demonstrated fast swelling and drug release, but weaker mucoadhesion as compared with the other samples. Polymers stabilized with glutathione displayed the weakest cohesive properties, resulting in fast and uncontrolled drug release and moderate mucoadhesion. Acetylcysteine-stabilized polymers exhibited an optimum cross-linked structure, with free thiol groups ensuring polymer-mucin interactions, resulting in the best mucoadhesive properties