Indirect CE‐UV detection for the characterization of organic and inorganic ions of a broad mobility and pK_a range in engine coolants

Abstract

An alternative CE-(indirect ultraviolet) method for the analysis of inorganic and organic anions in ethylene glycol-based engine coolants is presented using a BGE with 4 mM pyromellitic acid and 3.4 mM 1,6-hexamethylene diamine, pH 3. Baseline separation of six inorganic (e.g. nitrite, nitrate, and sulfate) and five organic anions (e.g. acetic and glycolic acid) was achieved. Quantification of 8 out of 11 specified anions was possible in stressed engine coolant samples after simple aqueous dilution. LODs between 0.8 and 15.1 mg/L with RSD values of peak areas between 2.6 and 11.9% were obtained. Some limitations due to matrix effects can be overcome with slight adaptations of the BGE. The flexibility of the method is vital regarding the increasing demands for the composition of engine coolants for pollution reduction.

A rapid and simple method for the determination of organic acids in proteolytic enzymes by capillary electrophoresis with indirect ultraviolet detection

“…Determination of organic acids by CE with indirect UV detection can be achieved adding a UV absorbing compound in the BGE, but separation conditions must be carefully selected to avoid comigration of the target compounds and sample matrix components [26][27][28][29][30][31][32][33][34]. From the variety of additives described for indirect UV dectection, 2,6-PDC was selected because it has been widely applied before with excellent performance [26][27][28][29][30].…”

“…LC, besides needing in general organic solvents, is time-consuming and limited by the narrow linear dynamic range and the susceptibility to matrix interferences. Capillary electrophoresis (CE) with direct [22][23][24][25] or indirect [26][27][28][29][30][31][32][33][34] ultraviolet (UV) detection has also been demonstrated, but to a lesser extent, despite the well-known benefits of this high-performance microscale electroseparation technique [35]. CE provides complementary and, very often, better separations than hydrophobicity-driven reversed-phase LC.…”

“…CE has proven to be a good choice for the determination of organic acids in several beverages [22][23][24][25][28][29][30][31], microbial fermentation process samples [32], engine coolants [33] and ionic liquids from biomass hydrolysates [34], where no more than a simple dilution is needed. In addition, CE and capillary isotachophoresis have also been reported for determination of anions of organic acids as counterions of basic drugs [36][37][38].…”

“…In this work, we have developed a CE method with indirect UV detection for the determination of acetic acid and gluconic acid in proteases. Since most organic acids lack of a strong UV chromophore, the use of indirect UV detection offers an excellent alternative [26][27][28][29][30][31][32][33][34], without the need for any derivatization step or the use of a contactless conductivity detector [39][40][41]. After validating the method with standards, we optimized an appropriate sample pretreatment method for the extraction of organic acids from a commercial protease sample before CE-UV.…”

Development of a background electrolyte for the determination of inorganic cations in high ionic strength samples by capillary electrophoresis with indirect UV-absorption detection

“…Although both techniques are widely used, they fundamentally differ in selectivity mechanisms and driving force. IC shows simpler selectivity manipulation whereas CE offers several advantages such as instrumental simplicity, high peak capacity, possibility of miniaturization, and low reagent and solvent consumption [1][2][3][4][5].…”