Improved separation of IA and IIA metal cations in matrices with high sodium concentration by capillary electrophoresis with contactless conductometric detection

Abstract

Um dos usos mais comuns da eletroforese capilar com detecção condutométrica é a análise de vários tipos de amostras contendo metais alcalinos e alcalinos terrosos. No entanto, a alta concentração de sódio, a qual é uma ocorrência bastante comum, pode causar perda de resolução de alguns picos. Neste trabalho, as condições e o eletrólito de corrida conveniente para análises de soro e fluído para hemodiálise são apresentados. A idéia básica é deslocar os picos de Ca 2+ e Mg 2+ pela redução de suas mobilidades pela adição de lactato e metanol ao eletrólito de corrida. Limites de detecção da ordem de 0,5 a 1,0 µmol L -1 e razão molar Na + /Ca 2+ da ordem de 1000 foram obtidos. Estas condições excedem as necessidades da aplicação pretendida.One of the most common uses of capillary electrophoresis with conductometric detection is the analysis of different samples containing alkaline and alkaline earth metals. However, the high sodium content, which is a very common occurrence, may cause loss of resolution of some peaks. In this work, the conditions and a running buffer suitable for serum and hemodialysis fluid analyses are presented. The approach basically consists in the reduction of mobilities of Ca 2+ and Mg 2+ by addition of methanol and lactate in the running buffer. Limits of detection in the range from 0.5 to 1.0 µmol L -1 with molar Na + /Ca 2+ ratios as high as 1000 were obtained, which are conditions that exceed the requirements of the proposed determination.Keywords: capillary electrophoresis, contactless conductivity detection, human serum, hemodialysis fluid IntroductionMetal cations from groups IA and IIA play an important role in numerous processes in the human body, such as volume and osmotic regulation, myocardial rhythm, blood coagulation, neuromuscular excitability, as cofactors in enzyme activation, in the regulation of ATPase ion pumps, and so on. The reference ranges for potassium, sodium, calcium, and magnesium in serum of normal individuals are 3.4-5.0, 135-145, 0.65-1.0, and 2.15-2.65 mmol L -1 , respectively. Abnormal concentration values for these ions can help in the diagnosis of many metabolism disorders, such as diabetes, advanced renal disease, polydipsia, aldosterone deficiency or excess, cardiac disorders, alcoholism etc. 1 Capillary electrophoresis (CE) is a separation technique based on differences of mobility of charged species and has been applied for determination of several kinds of analytes, from small ionic species to macromolecules. 2,3 Metal cations from groups IA and IIA have been mainly analyzed by free solution capillary electrophoresis (FSCE) with indirect UV-visible absorption detection. [4][5][6][7] Although these cations can be readily separated at low concentrations (typically 10 -6 mol L -1 ), separations of concentrated samples require the use of complexating agents to selectively modify the ion mobility and improve resolution. Examples of ligands widely used in FSCE separations include carboxylic acids 4-6 -such as oxalic, tartaric, lactic, α-hydroxyisobutyric (HIBA...

Contactless Conductivity Detection in Capillary Electrophoresis: A Review

“…The determination of alkali and alkaline earth metals concurrently with transition metals has been possible by the inclusion of a-hydroxyisobutyric acid (HIBA) in the buffers as a weak complexing agent to modify the mobilities of transition metals [34,50], and an application of this method to the analysis of rinse water samples from the galvanics industry has been reported [51]. Another possibility to alter the separation selectivity of inorganic cations was demonstrated by Fracassi da Silva and co-workers [52] who added 10% methanol to the electrolyte solution in order to achieve complete separation of Na þ , Ca 2þ and Mg 2þ in blood serum samples in the presence of a high concentration of Na þ . The presence of an electroosmotic flow (EOF) in capillary electrophoresis, which is towards the cathode, means that anions migrate in the direction opposite to the EOF.…”

Conductivity detection for conventional and miniaturised capillary electrophoresis systems

“…The detector was modified [66] and miniaturised [67] for increased flexibility of positioning of the detector on the capillary, leading to successful simultaneous detection of cations and anions. Do Lago and co-workers [68] used their detector for the determination of aliphatic alcohols in micellar electrokinetic chromatography, for the CE separation of mono and disaccharides [69], fatty acids [70], and class IA and IIA metal ions [71]. The detector was also used in combination with CE separations in a project for environmental monitoring [72,73].…”

Determinação simultânea de cátions empregando eletroforese capilar com detecção condutométrica sem contato em equipamento construído em laboratório

“…5,7,[9][10][11][12] Na grande maioria destes trabalhos, soluções tampão contendo uma mistura de ácido 2-N-morfolinoetanossulfônico (MES) e histidina (His) em meio ácido são empregados como eletrólitos de trabalho, que mantêm a condutividade de fundo em níveis relativamente baixos. Geralmente, são adicionados ao eletrólito de trabalho agentes complexantes como éter coroa, ácido α-hidroxi-isobutírico (HIBA), ácido lático (Hlac), ácido málico e ácido tartárico para alterar as mobilidades eletroforéticas dos íons metálicos, 1,4,6,[12][13][14][15][16][17][18] além de solventes orgânicos como metanol para melhorar a resolução dos sinais no eletroferograma. 1,4,5,9,14 Este trabalho descreve a construção de um sistema CE-C …”

“…Geralmente, são adicionados ao eletrólito de trabalho agentes complexantes como éter coroa, ácido α-hidroxi-isobutírico (HIBA), ácido lático (Hlac), ácido málico e ácido tartárico para alterar as mobilidades eletroforéticas dos íons metálicos, 1,4,6,[12][13][14][15][16][17][18] além de solventes orgânicos como metanol para melhorar a resolução dos sinais no eletroferograma. 1,4,5,9,14 Este trabalho descreve a construção de um sistema CE-C …”