Ionisatsiooni efektiivsus elektropihustusionisatsiooni allikas, seosed analüüdi füüsiko-keemiliste omadustega

Väitekirja elektrooniline versioon ei sisalda publikatsiooneVedelikkromatograafi-massispektromeetria (LC-MS) võimaldab tuvastada erinevates proovides väga erinevaid ühendeid ja on tõusnud praegusel ajal domineerivaks analüüsimeetodiks orgaaniliste ühendite madalate sisalduste määramisel. Selle süsteemi üks võtmekomponente on ioonallikas, mida kasutatakse LC-MS aparatuuri juures nende kahe liidesena. Elektropihustusionisatsiooni (ESI) ioonallikas on tänu sellele, et võimaldab ioniseerida ja analüüsida väga laia omaduste spektri ja massivahemikuga ühendeid üks enimkasutatavaid ioonallikaid massispektromeetrias. Vaatamata ESI populaarsusele, ei ole siiani päris selge, millised ühendite füsiko-keemilised omadused määravad aine ioniseerumise effektiivsuse ESI allikas. Nimelt, erinevad ühendid võivad anda sama kontsentratsiooni juures massispektris väga erineva intensiivsusega signaale. Käesoleva töö peamiseks eesmärgiks oli jõuda seosteni, mis määravad ühendi ionisatsiooni efektiivsuse ESI allikas lähtudes ühendi füsiko-keemilistest parameetritest. Selleks töötati välja metoodika analüüsimaks erinevaid ühendeid samadel tingimustel ESI massispektromeetriga. Selle tulemusena on loodud suhteliste ionisatsioonieffektiivsuste skaala (solvendisüsteemis 80% - atsetonitriili, 20% - 0.1% sipelghappe vesilahust), mis hetkel sisaldab 344 väga erinevate füsiko-keemiste omadustega ühendit. Kaasates kõiki analüüsitud ühendeid ja nende 11 parameetrit (aluselisus vees, atsetonitriilis ja gaasifaasis, osakese pindala, ruumala, molekulmass, dipoolmoment, polaarse pinna suurus, lipofiilsus/hüdrofoobsus, protoneerumistsenter ja laengu jaotumist iseloomustav parameeter) viidi läbi multilineaarne regressioonanalüüs (MLR) leidmaks peamised seosed mainitud parameetrite ning ühendi ionisatsioonieffektiivsuse vahel ESI allikas kasutatud tingimustel. Kuna kõigi analüüsitud ühendite jaoks ei ole eksperimentaalseid parameetrite väärtuseid, siis käesoleva töö raames arvutati puuduvad väärtused kõigile ühenditele ja kasutati neid MLR analüüsis. MLR analüüsi tulemusena joonistuvad selgelt välja seosed ühendi ionisatsioonieffektiivsuse (ESI allikas antud tingimustel) ning kolme füsiko-keemilise omaduse vahel: aluselisus (vesilahuses), molekuli/iooni suurus ja iooni lipofiilsus/hüdrofoobsus. Mida tugevamini väljendunud on ainel need kolm omadust, seda intensiivsemalt see ESI allikas ioone annab. Käesolev töö on suure olulisusega kõigile, kes töötavad LC-ESI-MS meetodiga.Liquid chromatography mass spectrometry (LC-MS) enables to identify various compounds from different samples and it is currently the dominant method for detecting organic compounds in low concentrations. Ion source is the interface between the LC and MS and is a key component of an LC-MS apparatus. One of the most widely applied ionization source in mass spectrometry is electrospray ionization source (ESI) due to its capability to ionize and analyse different compounds with wide span of parameters’ values. Despite of the commonness of ESI-MS the relationships between the ionization efficiency and compounds’ physico-chemical parameters have still not been fully elucidated. The signals in mass-spectrum of different compounds having the same concentration in the sample can vary strongly. The main purpose of this study was to analyse the relationships between ionisation efficiencies and physico-chemical properties of analytes and find out which physico-chemical parameters influence ionization efficiency the most. The ESI-MS method for analysing the ionization efficiencies of various compounds under the same experimental conditions and the scale of relative ionization efficiencies of 344 compounds with widely differing physico-chemical parameter values (in solvent system 80% - acetonitrile, 20% - 0.1%formic acid aqueous solution) was developed. Multilinear regression analysis involving all the analysed compounds and the 11 physico chemical parameters (basicity in acetonitrile, in water and gas phase basicity, the area and the volume of the particle, molecular mass, dipole moment, polar surface area, lipophilicity/hydrophobicity, protonation centre and the (de)localization of the charge on the surface of the particle) was used to determine the most relevant relations between ionization efficiencies and those parameters. Since the experimental data on some of those parameters is not available, the computational values were calculated for all the compounds and used in multilinear regression analysis when experimental values were not available. The results of MLR analysis enable concluding that three main descriptors of compound determine its ionization efficiency in ESI source under the used conditions: the basicity on aqueous solution, the size of the ion/molecule and the lipophilicity/hydrophobicity of the ion. The more strongly these mentioned parameters of compounds are expressed, the more intensive is ionization in ESI source. This study is expected to be significant to all chemists and researchers working with the LC-ESI-MS method.https://www.ester.ee/record=b544943

Reconnection in Marginally Collisionless Accretion Disk Coronae

We point out that a conventional construction placed upon observations of accreting black holes, in which their nonthermal X-ray spectra are produced by inverse comptonization in a coronal plasma, suggests that the plasma is marginally collisionless. Recent developments in plasma physics indicate that fast reconnection takes place only in collisionless plasmas. As has recently been suggested for the Sun's corona, such marginal states may result from a combination of energy balance and the requirements of fast magnetic reconnection.Comment: Revised in response to referee. Accepted ApJ. 11 pp., no figures. Uses aastex 5.0

The Emergence Of Specialty Medical Homes In The U.S. Health Care System: Initial Financial Performance Data & The Financial Implications For Provider Organizations

The U.S. health care system is in the midst of significant change in both service delivery model and financing.     Rising costs are driving payers – public and private alike – to rethink the current financing and care management strategies.  One significant shift in policy is around the structure of care coordination for insured individuals – particularly individuals with complex health service and social support needs.  These individuals, while small in number, are responsible for a large proportion of health care spending.   Traditionally, the care of individuals with complex conditions has been left to a wide range of medical specialists – and rarely been coordinated across all specialties.  But in the past four years, health payers have moved toward ‘integrating’ care coordination with a health care team responsible for all services regardless of specialty. This integrated care coordination model  – referred to as a medical home – has been rapidly adopted by many payers.  And, a specialized version of the medical home model – referred to as a heatlh home or specialty medical home – has been developed for consumers with complex needs.  The model has changed both the relationship of the insured individual to the payer and to their medical specialists. It is early in the adoption of specialty medical homes and two key financial questions are yet unanswered.  The first, do specialty medical homes reduce health care spending for complex consumers.  The second, what are the financial implications of a specialty medical home model for heatlh care provider organizations.  This research examines the available research literature and other published data for preliminary answers to these questions of financial impact of this emerging heatlh care system model.