Analysis of inorganic cations in biological samples by the combination of micro‐electrodialysis and capillary electrophoresis with capacitively coupled contactless conductivity detection

Abstract

Micro-electrodialysis (μED) and CE were combined for rapid pretreatment and subsequent determination of inorganic cations in biological samples. Combination of μED with CE greatly improved the analytical performance of the latter as the adsorption of high molecular weight compounds present in real samples on the inner capillary wall was eliminated. Fifty microliter of 80-fold diluted human body fluids such as plasma, serum and whole blood was used in the donor compartment of the μED system requiring less than 1 μL of the original body fluid per analysis. Inorganic cations that migrated through a cellulose acetate dialysis membrane with molecular weight cut-off value of 500 Da were collected in the acceptor solution and were then analyzed using CE-C⁴D. Baseline separation of inorganic cations was achieved in a BGE solution consisting of 12.5 mM maleic acid, 15 mM L-arginine and 3 mM 18-crown-6 at pH 5.5. Repeatability of the CE-C⁴D method was better than 0.5% and 2.5% for migration times and peak areas, respectively; limits of detection of all inorganic cations in the presence of 2 mM excess of Na(+) were around 1 μM and calibration curves were linear with correlation coefficients better than 0.998. Repeatability of the sample pretreatment procedure was calculated for six independent electrodialysis runs of artificial and real samples and was better than 11.8%. Recovery values between 96.3 and 110% were achieved for optimized electrodialysis conditions of standard solutions and real samples; lifetime of the dialysis membranes for pretreatment of real samples was estimated to 100 runs.

Single‐breath analysis using a novel simple sampler and capillary electrophoresis with contactless conductometric detection

“…C 4 D is also one of the best detection modes to be used in portable and point‐of‐care instrumentation due to its compact size and low power demand. So far, CE‐C 4 D was used to analyze saliva , blood plasma and urine samples, and recently also for the analysis of ionic content of EBC . Unfortunately, the irreproducibility of EBC sampling (often attributed to uncontrolled dilution of respiratory droplets in the collected EBC and poor standardization of both sampling equipment and sampling procedure) still remains the bottleneck of the method, regardless of the analytical technique used for final analysis.…”

Use of disposable open tubular ion exchange pre-columns for in-line clean-up of serum and plasma samples prior to capillary electrophoretic analysis of inorganic cations

“…In Fig. 3, the constant increase in migration times can be clearly observed for 15 consecutive injections of blood serum (full symbols) because the proteins from serum gradually adsorbed to the inner walls of the analytical capillary [10]. A 4-layer PBMA sample clean-up precolumn (6 cm) was then in-line coupled to the analytical capillary for clean-up of these samples.…”

“…30 nL, see Section 2.1. The column breakthrough capacity (expressed as number of injections) was estimated based on the stability of migration times of inorganic cations [10]. As expected, the capacity was lowest for all three lengths of 2-layer PBMA precolumns.…”

“…Usually, they cannot be combined on-line with CE. Alternative approaches for clean-up of biological samples include ultrafiltration [7,8], electrodialysis [9,10], liquid phase microextraction [11][12][13] and electric field driven sample pretreatment [14][15][16]. Note however, that even though these techniques offer higher selectivity, lower the consumption of organic solvents and reduce the pretreatment time, they are mostly performed off-line and additional sample handling is therefore required.…”

Inorganic analysis using CE: Advanced methodologies to face old challenges

“…A good deal of effort on developing advanced sample preparation methods was recently invested by Boček and his coworkers. This group has pursued a variety of approaches, such as electrokinetic injection (EKI) or electromembrane extraction , both across a supported liquid membrane, microdialysis , or a membraneless configuration using disposable open tubular ion‐exchange microcolumns , most of which proved to be feasible to handle various proteinaceous samples. Noteworthy is the fact that very small sample volumes (several microliters) could be accommodated; this asset offers an advantage in analysis of such samples, some of which are not available in large quantities.…”