Üldistatud happelisuse skaala katseline teostus ja rakendused

Väitekirja elektrooniline versioon ei sisalda publikatsiooneHappelisus on keskkonna, toodete ja toidu puhul tähtis näitaja. Kõik teavad, et sidrun on hapum kui maasikas, kuid kõiki asju ei saa maitsta. Kuidas sellisel juhul happelisust hinnata? Happelisuse hindamiseks on kasutusel pH ning mida väiksem on mingi olluse pH näit, seda happelisem see on. Vees on pH skaala ulatus 0 kuni 14 ning skaala keskel, pH 7 juures on vesi neutraalne. Vees on pH mõõtmine lihtne, olles üks levinumaid mõõtmisi keemia laborites. Hoopis keerulisem on asi mittevesikeskkondades – bensiinis, taimeõlis, lihas jne. Sisuliselt võib öelda, et igal keskkonnal on oma pH skaala, kuid need ei ole omavahel võrreldavad. Temperatuuri mõõtmiseks kasutatakse näiteks Celsiuse ja Kelvini skaalat, kuid temperatuuri osatakse ühest skaalast teise teisendada. Sama ei saa öelda pH puhul, kuna skaalade nullpunktid eri keskkondades on teadmata. Seega kehtis kuni viimase ajani kahetsusväärne olukord, kus mõiste pH tähendab igas keskkonnas ise asja ja need pH väärtused ei ole omavahel võrreldavad. 2010. aastal töötati välja üldistatud happelisuse (pHabs) skaala kontseptsioon – üks skaala kõigi keskkondade jaoks. Selles skaalas esitatuna on võimalik kõikide keskkondade happelisusi omavahel võrrelda. Teoorias asendas üks skaala kõiki neid sadu ja tuhendeid pH skaalasid, kuid see kontseptsioon oli algselt olemas vaid teooria tasemel – mõõta pHabs väärtusi veel ei osatud. Doktoritöö eesmärk oli viia see teooria ellu ehk arendada välja meetod pHabs mõõtmiseks ning esimest korda ajaloos mõõta üldistatud happelisusi. Töö eesmärk täideti edukalt ning nüüd on olemas võimalus mõõta üldistatud happelisusi. Loodud meetodi esmaseks rakenduseks oli vesi-metanooli ja vesi-atsetonitriili segude üldistatud happelisuste mõõtmine. Neid segusid kasutatakse mobiilfaasidena vedelikkromatograafia-massispektromeetria meetodis, mis on praegusel ajal üks levinumaid ja võimekamaid analüüsimeetodeid. Valdavalt käib mobiilfaasi pH valimine katse-eksitusmeetodil. Tegeliku happelisuse teadmine võimaldab valida sobivaima mobiilfaasi, säästes keskkonda, aega ja raha. Selle töö suurim saavutus on mõõtevõimekuse tekitamine. Nüüdsest saab mõõta järgmiste huvipakkuvate objektide üldistatud happelisusi ning järjest avardada inimkonna arusaama happelisusest väljaspool teada-tuntud vesikeskkonda.Acidity is an important property of environment, products and food. Everybody knows that a lemon is more sour than a strawberry, but one cannot taste everything. In such a case, how can you evaluate the acidity? The typical measure of acidity is pH. The lower the pH value of a substance, the more acidic it is. The acidity scale in water ranges from 0 to 14 and in the middle, near pH 7, the water is neutral. It is easy to measure pH in water, being one of the most common measurements in chemical laboratories. It is a different story in nonaqueous medium – in gasoline, vegetable oil, meat etc. Basically one can say that every medium has its own pH scale but these scales are unfortunately incomparable. Temperature also has several scales, for example Celsius and Kelvin scale, but one can convert temperature value from one scale to another. The same is not true for pH, where the shifts of the zero points are unknown. So until now there was an unfortunate situation, where the term pH value had a different meaning in every medium and it was not possible to compare these values to each other. In 2010 the concept of unified acidity (pHabs) was put forward – one pH scale for all media! In this scale one can compare the acidities of every medium to one another. In theory this one scale substitutes all of those hundreds and thousands of pH scales, but only in theory – no one knew how to measure it. The aim of my work was to put the theory into practice, in other words develop a method to measure pHabs and for the first time in history measure unified acidities. This aim has been reached and now there is a possibility to measure unified acidities. The first experiments with the developed method were unified acidity measurements of water-methanol and water-acetonitrile mixtures. These mixtures are used as mobile phases in liquid chromatography mass spectrometry, currently one of the most used and capable method of analysis. Usually, choosing the pH of a mobile phase is done by trial and error. Knowing the pHabs helps to choose the most appropriate mobile phase, thus saving environment, time and money. The biggest achievement in this work is the measurement capability. From now on one can measure unified acidities of substances of interest and broaden the mankind’s knowledge about acidities beyond the well-known water

Evaluation and validation of detailed and simplified models of the uncertainty of unified pHabsH2O measurements in aqueous solutions

Highlights • First detailed evaluation of the uncertainty of pHabsH2O measurements. • Bottom-up uncertainty evaluations proven valid for 95% confidence. • Monte Carlo Simulation of pHabsH2O measurement ladder with least-squares minimisation. • Described simplified and detailed bottom-up uncertainty evaluations are equivalent. • Measurements from 2 to 10 pHabsH2O with a 95% expanded uncertainty of 0.26–0.51.The use of the unified pH concept, pHabsH2O, applicable to aqueous and non-aqueous solutions, which allows interpreting and comparison of the acidity of different types of solutions, requires reliable and objective determination. The pHabsH2O can be determined by a single differential potentiometry measurement referenced to an aqueous reference buffer or by a ladder of differential potentiometric measurements that allows minimisation of inconsistencies of various determinations. This work describes and assesses bottom-up evaluations of the uncertainty of these measurements, where uncertainty components are combined by the Monte Carlo Method (MCM) or Taylor Series Approximation (TSM). The MCM allows a detailed simulation of the measurements, including an iterative process involving in minimising ladder deviations. On the other hand, the TSM requires the approximate determination of minimisation uncertainty. The uncertainty evaluation was successfully applied to measuring aqueous buffers with pH of 2.00, 4.00, 7.00, and 10.00, with a standard uncertainty of 0.01. The reference and estimated values from both approaches are metrologically compatible for a 95% confidence level even when a negligible contribution of liquid junction potential uncertainty is assumed. The MCM estimated pH values with an expanded uncertainty, for the 95% confidence level, between 0.26 and 0.51, depending on the pH value and ladder inconsistencies. The minimisation uncertainty is negligible or responsible for up to 87% of the measurement uncertainty. The TSM quantified measurement uncertainties on average only 0.05 units larger than the MCM estimated ones. Additional experimental tests should be performed to test these uncertainty models for analysis performed in other laboratories and on non-aqueous solutions

Toward Unified pH of Saline Solutions

Fluctuations of pH in coastal systems are generally surveyed through potentiometric pH measurements. A new concept of a unified pH scale was introduced with the great advantage of enabling comparability of absolute values, pHabs, pertaining to any medium. Using water as an anchor solvent, yielding pHabsH2O, enables referencing the pHabs values to the conventional aqueous pH scale. The current work aims at contributing to implement pHabsH2O to saline solutions. To this purpose, differential potentiometric measurements, with a salt bridge of ionic liquid [N2225][NTf2], were carried out aiming at overcoming problems related to residual liquid junction potentials that affect the quality of such measurements. The ability to measure pHabsH2O with acceptable uncertainty was evaluated using Tris-Tris·HCl standard buffer solutions prepared in a background matrix close to the characteristics of estuarine systems (salinity of 20) as well as with NaCl solutions with ionic strength between 0.005 and 0.8 mol kg−1. The present study shows that for high ionic strength solutions, such as seawater, challenges remain when addressing the assessment and quantification of ocean acidification in relation to climate change. Improvements are envisaged from the eventual selection of a more adequate ionic liquid

The Evolution of Electrospray Generated Droplets is Not Affected by Ionization Mode

International audienceIonization efficiency and mechanism in ESI is strongly affected by the properties of mobile phase. The use of mobile phase properties to accurately describe droplets in ESI source is convenient but may be inadequate as the composition of the droplets is changing in the plume due to electrochemical reactions occurring in the needle tip as well as continuous drying and fission of droplets. Presently, there is paucity of research on the effect of the polarity of the ESI mode on mobile phase composition in the droplets. In this paper the change in the organic solvent content, pH and droplet size are studied in the ESI plume in both ESI+ and ESI-ionization mode. We 2 introduce a rigorous way-the absolute pH (pH abs H 2 O)-to describe pH change in the plume that takes into account organic solvent content in the mobile phase. pH abs H 2 O enables comparing acidities of ESI droplets with different organic solvent contents. The results are surprisingly similar for both ionization modes indicating that the dynamics of the change of mobile phase properties is independent from the ESI mode used. This allows us to conclude, that the evolution of ESI droplets first of all proceeds via the evaporation of the organic modifier and to a lesser extent via fission of smaller droplets from parent droplets. Secondly, our study shows that qualitative findings related to the ESI process obtained on the ESI+ mode can almost directly be applied also in the ESI-mode

Symmetric Potentiometric Cells for the Measurement of Unified pH Values

A unified pH scale of absolute values (pHabs scale) enables the comparison of acidities in different solvents. To date, very few different experimental setups have been used for the measurement of values on this scale. The article describes the design and performance of the different symmetric cells used for unified pH measurement by several institutions. Well-established and reliable standard aqueous buffer solutions are the first step of method validation necessary to achieve a robust metrological level for more complex media. The pH of aqueous standard buffers was measured by differential potentiometry, where the potential between two glass electrodes is measured directly. All the tested electrochemical cells prove to be suitable for unified pH measurements. This validation highlights that the method is, to a large extent, independent of the used equipment, including the cell geometry. The inherent symmetry of the cell design helps to reduce the experimental workload and improve the accuracy of obtained results