Indirect UV Detection Research Articles

Single-isomer carboxymethyl-γ-cyclodextrin as chiral resolving agent for capillary electrophoresis

Herein we report on the synthesis, characterization and the novel capillary electrophoretic use of octakis-(2,3-di-O-methyl-6-O-carboxymethyl)-γ-cyclodextrin sodium salt (ODMCM). ODMCM is the first single-isomer carboxymethyl-γ-cyclodextrin that is fully methylated on its secondary side and carries ionizable carboxymethyl functions on its primary side. ODMCM was prepared with high isomeric purity through a four-step synthetic procedure. The purity of each intermediate was characterized by appropriate chromatographic methods, while the isomeric purity of the carboxymethylated product was determined by an HPLC method using a CD-Screen-IEC column and by a capillary electrophoretic method using indirect UV detection, as well. The structural identification of the ODMCM was carried out by 1D, 2D NMR spectroscopy and ESI-MS. The acid-base characterization of the chiral selector was carried out by 1H NMR-pH titration. The chiral separation ability of the synthesized selector was studied by chiral capillary electrophoresis. ODMCM was used as a background electrolyte additive to separate enantiomers of representative pharmacologically significant model molecules such as propranolol, citalopram, ketamine, tapentadol and dapoxetine. The effects of the selector concentration and the pH of the background electrolyte on the enantiorecognition properties were investigated. 1H NMR spectroscopy was further applied to get deeper insight of the host-guest inclusion complex formation. The pH-dependent enantioselectivity of this new single-isomer chiral selector was demonstrated by chiral capillary electrophoresis and 1H NMR spectroscopy.

Main Organic Acids in Rice Wine and Beer Determined by Capillary Electrophoresis with Indirect UV Detection Using 2, 4-Dihydroxybenzoic Acid as Chromophore

A rapid and sensitive analytical method for the determination of main organic acids in wines was developed by capillary electrophoresis (CE) with indirect UV detection. Separation parameters including the pH of electrolyte, chromophore, and its concentration were optimized. The results showed that the optimal electrolyte for the separation of organic acids consisted of 10 mmol L−1 2, 4-dihydroxybenzoic acid (DHBA) at pH 3.6 containing 0.4 mmol L−1 cetyltrimethlammonium bromide (CTAB). DHBA as chromphore was selected based on the close mobility to the analyte and relatively large molar extinction coefficient. The method showed good linearity with limits of detection (LOD), ranging from 0.5 to 7.5 mg L−1. The relative standard deviation (RSD) of interday precisions for the peak area and the migration time were less than 7.2 and 0.8 %, respectively. The recoveries of the analyte in Chinese rice wine sample were between 90.3 and 106.9 % with RSD ranging from 1.4 to 8.9 %. The method was successfully applied to the commercial rice wine and beer samples with dilution and filtration.

Capillary electrophoresis method for the simultaneous determination of carbohydrates and proline in honey samples

A capillary electrophoresis method with indirect UV detection for the simultaneous determination of three carbohydrates (fructose, glucose and sucrose) and the amino acid proline in honey samples was developed. This method included the use of a background electrolyte consisting of 10mM sodium benzoate and 1.5mM cetyltrimethylammonium bromide, pH12.4. Under optimal capillary electrophoresis conditions, the separation of the investigated substances was achieved in less than 5min and single dilution of each sample was employed. The detection limits for fructose, glucose and sucrose were 0.58gL−1, 0.67gL−1 and 0.12gL−1 respectively, and 0.72mgL−1 for proline. Precision measurements calculated in terms of %RSD in the range of 0.92 to 5.43%, were obtained. The proposed method was applied to honey samples from Argentina and Sweden and enables the determination of the three carbohydrates and the amino acid proline. The results show that the proposed method is simple, requires short analysis times, low consumption of reagents and sample, minimum waste and that there is no need to perform any sample pre-treatment. This method is a good alternative to carry out the quality control of honey samples. Finally, it is a promising methodology for achieving green chemistry goals.

Determination of chloroacetic acids in water by capillary zone electrophoresis with field-amplified sample injection

ABSTRACTA simple and sensitive method has been developed for the determination of chloroacetic acids and acetic acid in water using capillary zone electrophoresis under modified electroosmotic flow with indirect UV detection. Potassium hydrogen phthalate at pH 5.40 was used as background electrolyte (BGE), and hexadecyltrimethylammonium bromide was used as electroosmotic flow modifier. Field-amplified sample injection (FASI) method was used to enhance the sensitivity. Results showed that the limit of detection for these analytes was enhanced more than 15-fold and the repeatabilities were good with relative standard deviations (RSDs %) of migration time and corrected peak areas being below 0.33%, 4.45% (intra-day) and 0.87%, 9.67% (inter-day), respectively. An off-line liquid–liquid extraction (LLE) process with methyl tert-butyl ether was carried out to detect these compounds in water samples. The dissociation constants of acetic acid and monochloroacetic acid (MCA) were determined with two methods and the results obtained were consistent with the reference values.

Sample pretreatment for the capillary electrophoretic determination of organic acids in chromium(III) plating baths.

This work deals with the development and optimization of the sample pretreatment and consequent electrophoretic analysis of two modern plating baths containing chromium(III) and either citric acid or oxalic acid. Some model mixtures containing known amounts of components of industrial baths have been prepared to simulate simplified bath matrices. Prior to analysis, a sample pretreatment consisting of the addition of some agents that could release acid from the stable chromium complex was tested. Determination of organic anions was accomplished by indirect UV detection. The best results were achieved by precipitation of chromium(III) hydroxide. The content of oxalate and citrate in real samples was calculated as 96.5% (SD 2.3%) and 97.3% (SD 0.8%), respectively, of the declared amount. Very good robustness of the method and satisfactory repeatability of migration time and peak area were obtained. This simple inexpensive method is suitable for routine determination of citric and oxalic acid in chromium(III)-based plating baths.

Determination of γ-hydroxybutyric acid in saliva by capillary electrophoresis coupled with contactless conductivity and indirect UV absorbance detectors.

The aim of the current study was to optimise and validate the methodology for determination of γ-hydroxybutyric acid (GHB) in saliva by CE combined with a contactless conductivity detector (C(4)D) and indirect UV absorbance detection (λ(ABS) = 210 nm). The optimized BGE, consisting of 8.5 mM maleic acid, 17 mM arginine, 255 μM cetyltrimethylammonium bromide (CTAB), and 15% acetonitrile, was evaluated for the separation of GHB in saliva within 6 min. The performance characteristics of the CE-C(4)D-indirect UV methodology was validated. The instrument detection and quantification limits were 0.49 and 1.6 mg/L for C(4)D, and 5.1 mg/L and 17.0 mg/L for indirect UV, respectively. The linearity was obtained over the range from 2.5 to 400 mg/L for C(4)D and from 12.5 to 400 mg/L for indirect UV. The interday precisions were within 2.3-5.7% and intraday precisions were within 1.6-9.0% for C(4)D as well as 2.1-9.3%, 5.6-10.1% for indirect UV in spiked saliva, respectively. The recoveries were within 87.2-104.4%. The matrix effects were +53.2% for small concentrations up to 25 mg/L for C(4)D and +23.6% for concentrations up to 75 for mg/L for indirect UV detection. No matrix effects were observed for higher concentration levels. In conclusion, CE-C4D-indirect UV can offer a rapid, accurate, sensitive, and definitive method for the determination of GHB abuse in saliva samples as a forensic screening tool.

Analysis of γ-hydroxy butyrate by combining capillary electrophoresis-indirect detection and wall dynamic coating: application to dried matrices.

γ-Hydroxybutyric acid (GHB) is a powerful central nervous system depressant, currently used in medicine for the treatment of narcolepsy and alcohol dependence. In recent years, it has gained popularity among illegal club drugs, mainly because of its euphoric effects as well as doping agent and date rape drug. The purpose of the present work was the development of a rapid analytical method for the analysis of GHB in innovative biological matrices, namely dried blood spots (DBSs) and dried urine spots (DUSs). The analytical method is based on capillary zone electrophoresis with indirect UV absorption detection at 210nm and capillary wall dynamic coating. The background electrolyte is composed of a phosphate buffer containing nicotinic acid (probe for detection) and cetyltrimethylammonium bromide (CTAB, reversal of electroosmosis in wall dynamic coating). The influence of probe and CTAB concentration, together with buffer pH, on migration time and signal response was investigated. Under the optimized conditions, analytical linearity and precision were satisfactory; absolute recovery values were also high (>90%); the use of dried matrices (DBSs and DUSs) was advantageous as an alternative matrix to classical ones. No interferences were found either from the most common exogenous or from endogenous compounds. This analytical approach can offer a rapid, precise and accurate method for GHB determination in innovative biological samples, which could be important for screening purposes in clinical and forensic toxicology. Graphical Abstract CE method, by combined indirect UV detection and dynamic coating, for GHB determination in DBSs and DUSs.

Enantiomeric separation of 1,3-dimethylamylamine by capillary electrophoresis with indirect UV detection using a dual-selector system.

The CE method employing an indirect UV detection for the enantioseparation of 1,3-dimethylamylamine (DMAA), widely used in various preworkout and dietary supplements labeled as a constituent of geranium extract has been developed. The dual-selector system consisting of negatively charged sulfated α-CD (1.1% w/v) and sulfated β-CD (0.2% w/v) in 5 mM phosphate/Tris buffer (pH 3.0) containing the addition of 10 mM benzyltriethylammonium chloride (BTEAC) as the chromophoric additive was used for the enantiomeric separation of DMAA stereoisomers with the LODs in the range of 7.82-9.24 μg/mL. The method was partly validated and applied for the determination of the stereoisomeric composition of DMAA in commercial dietary supplements to verify the potential natural origin of DMAA.

Determination of Sulfate Anions in Heparin by Capillary Electrophoresis with Improved Indirect UV Detection

A simple, sensitive and environmentally friendly capillary electrophoresis method for the determination of free sulfate anions in heparin and low-molecular-weight heparin with indirect UV detection is reported. The background electrolyte consists of 20 mM nitrate (pH 5.5) containing 0.2 mM CTAB. The use of nitrate as the probe anion is based on the consideration that nitrate has a very close electrophoretic mobility to that of sulfate, leading to a very narrow peak shape. Moreover, the apparent molar absorptivity of nitrate at 202 nm (8413 L mol−1 cm−1) is much higher than that of the commonly used probe anion chromate at 254 nm (2400 L mol−1 cm−1). The combination of the narrow peak shape with the high apparent molar absorptivity of the probe ion improved the limit of detection by 2.4 times and the limit of quantitation by 3.2 times. The effect of various CE parameters on the separation of sulfate from chloride was investigated and optimized. The method displays linearity in the range from 0.05 to 20 mM. The RSD % for intraday (n = 6), and interday (n = 3) repeatability in terms of migration times and peak areas were all less than 3 %. The limit of detection (S/N = 3) and limit of quantitation (S/N = 10) for sulfate were determined as 18 and 53 µM, respectively. The method was successfully applied for the quantification of sulfate anions in heparin and low-molecular-weight heparins.

Determination of polyphosphates in fish and shrimp muscles by capillary electrophoresis with indirect UV detection after phosphatase inhibition using high pressure pretreatment

A method was proposed for the determination of polyphosphates (P2O74−, P3O105− and (PO3)33−) in fish and shrimp muscles by capillary electrophoresis with indirect UV detection after phosphatase inhibition using high pressure pretreatment (HPP). Separation parameters were optimized and the effects of HPP on deactivation of enzyme were investigated. Well resolution was obtained with 10mM adenosine 5′-phosphate (ATP) in 16mM disodium hydrogen phosphate combining with 32mM citric acid buffer (pH=6.4) containing 0.1mM cetyltrimethyl ammonium bromide, and phosphatase was effectively inhibited by HPP at 400MPa for 10min. Method was validated with LOD (0.23–0.33mgg−1) and LOQ (0.77–1.0mgg−1). Recovery of P2O74−, P3O105− and (PO3)33− in the fortified samples were in the range of 91.6–100.1%, 97.6–104.6% and 79.1–88.1%, respectively, and the corresponding RSD ranged from 1.1% to 6.8%. Finally, the method was applied in the determination of polyphosphates in food samples collected from local markets.

Pembuatan Kolom Monolitik Berbasis Polimer Organik untuk Pemisahan Anion menggunakan Kromatografi Cair Kinerja Tinggi

Methacrylate-based monolithic columns have been prepared in silanized silicosteel column (100 ´ 0.5 mm id) by in situ polymerization reaction, using glycidyl methacrylate (GMA) as monomer, ethylene dimethacrylate (EDMA) as crosslinker, porogen (1-propanol, 1,4 butandiol, water) and initiator AIBN. Monolith poly-(GMA-co-EDMA) was then modified with diethylamine and benzyl chloride to obtain ammonium quartener as strong anion exchanger. From the characterization of 4 monolith in this study, monolithic columns poly-(GMA-co-EDMA) with %T 40, %C 25 and polymerization time 24 h has good mechanical stability and permeability, adequate molecular recognition sites (indicated by binding capacity value of 10,119 mg/mL), and has good proportion of flow throughpore and mesopores (45,04% and 41,32% respectively). It can successfully separate the mixture sample of anion consisting of fluoride, bromide, sulfate and nitrate ions by indirect UV detection .

Separation and Determination of Carbohydrates in Food Samples by Capillary Electrophoresis Using Dynamically Coating the Capillary with Indirect UV Detection

In this study, the separation and determination of carbohydrates in food samples were developed by capillary electrophoresis using dynamically coating the capillary with indirect UV detection. The polycationic polymers of hexadimethrine bromide (HDB) were used as electroosmotic flow (EOF) modifier to reverse the EOF. A highly alkaline pH condition was used in order to charge every carbohydrate negatively. Several important parameters influencing buffer concentration, pH, and HDB concentration were optimized. The optimal background electrolyte composed of 20 mmol L−1 sorbic acid, 0.005 % (w/v) HDB, and 40 mmol L−1 NaOH at pH 12.2. Under optimal conditions, 32 carbohydrates including mono-, di-, oligosaccharides, and sugar alcohols were separated in less than 12 min. The proposed method provided a good linearity, low limits of detection, and good repeatability of the carbohydrates. This method was then utilized to analyze carbohydrates in food samples. The results indicated that the developed method is an excellent alternative for the carbohydrate routine analysis in the food field.

Preparation of a hybrid monolithic stationary phase with allylsulfonate for the rapid and simultaneous separation of cations in capillary ion chromatography.

A hybrid monolithic column with sulfonate functionality was successfully prepared for the simultaneous separation of common inorganic cations in ion-exchange chromatographic mode through a simple and easy single-step preparation method. The strong cation-exchange moieties were provided directly from allylsulfonate, which worked as an organic monomer in the single-step reaction. Inorganic cations (Li(+), Na(+), K(+), NH4(+), Cs(+), Rb(+), Mg(2+), Ca(2+), and Sr(2+)) were separated satisfactorily by using CuSO4 as the eluent with indirect UV detection. The allysulfonate hybrid monolith showed a better performance in terms of speed and pressure drop than the capillary packed column. The number of theoretical plates achieved was 19,017 plates/m (in the case of NH4(+) as the analyte). The relative standard deviations (n = 6) of both retention time and peak height were less than 1.96% for all the analyte cations. The allysulfonate hybrid monolithic column was successfully applied for the rapid and simultaneous separation of inorganic cations in groundwater and the effluent of onsite domestic wastewater treatment system.

Determination of pyrrolidinium ionic liquid cations by ion chromatography-indirect ultraviolet detection with imidazolium ionic liquids as both an ultraviolet absorption reagent and an eluting agent

Using imidazolium ionic liquids as ultraviolet absorption reagents and eluting agents for the indirect UV detection of pyrrolidinium cations.

Dynamic pH junction-sweeping technique for on-line concentration of acidic amino acids in human serum by capillary electrophoresis with indirect UV detection.

Glutamic acid (Glu) and aspartic acid (Asp), as two important neurotransmitters, have been the focus of increasingly intense research over the past several years. Glu and Asp are present in biological fluids such as serum at trace levels, but complex components in biological matrices make it difficult to determine them in biological samples. In this paper, a sensitive and simple method coupled with indirect UV detection, using benzoic acid (BA) as the UV-absorbing probe, was developed and validated for the quantitative determination of Glu and Asp in human serum and Compound Amino Acid Injection-18 AA. The method combines a dynamic pH junction with a sweeping technique using β-cyclodextrin (β-CD) as the complexing agent for sweeping. Employing this proposed method, low detection limits of 0.061μg/mL for Glu and 0.032μg/mL for Asp were obtained. The sensitivity was improved 30- and 55-fold for Glu and Asp compared to conventional CE method. Standard curves were linear (r>0.999) over the concentration range of 0.1-8.0μg/mL. To further improve the resolution of Asp from interfering substances in human serum, 6% (v/v) methanol was added to the sample matrix, and resulted in the detection limits of 0.125μg/mL for Glu and 0.057μg/mL for Asp. With a simple precipitation of protein, the method has been successfully applied to the analysis of human serum, and the recoveries (82% for Glu and 87% for Asp) were achieved with relative standard deviations of 1.9% and 2.0%, respectively.

A novel covalently modified aminated silica-based anion exchanger for ion chromatography

A novel method for the synthesis of anion exchangers for ion chromatography that provides the covalent attachment and spatial movement of the ion-exchange layer away from the silica surface is proposed. The new approach includes the following steps: alkylation of aminated silica with 1,4-butanediol diglycidyl ether and then amination using polyethyleneimine. The obtained anion exchanger allows the simultaneous separation of 11 anions (C2H5COO−, CH3COO−, HCOO−, BrO3−, Cl−,NO2− Br−, NO3− I−, SCN−, ClO4−) in 18 minutes and demonstrates good efficiency (up to 62,000 TP/m for I-) in the single column ion chromatography mode with indirect UV-detection using potassium hydrogen phthalate as an eluent.

Generalized polymer effective charge measurement by capillary isotachophoresis

In this work, we have generalized the use of capillary isotachophoresis as a universal method for determination of effective charge of anionic and cationic (co)polymers on ordinary capillary electrophoresis instruments. This method is applicable to a broad range of strong or weak polyelectrolytes with good repeatability. Experimental parameters (components and concentrations of leading and terminating electrolytes, capillary diameters, constant electric current intensity) were optimized for implementation in 100μm i.d. capillaries for both polyanions and polycations. Determined values of polymer effective charge were in a very good agreement with those obtained by capillary electrophoresis with indirect UV detection. Uncertainty of the effective charge measurement using isotachophoresis was addressed and estimated to be ∼5–10% for solutes with mobilities in the 20–50×10−9m2V−1s−1 range.

A small structural change resulting in improved properties for product development

AZD9343 is a water-soluble gamma amino butyric acid (GABAB) agonist intended for symptomatic relief in gastroesophageal reflux disease (GERD) patients. The compound has good chemical stability in aqueous solutions, as well as in the solid state. Only one crystal modification has been observed to date. This polymorph is slightly hygroscopic (1.5% water uptake at 80% relative humidity (RH)), which is an improvement compared to the structurally similar agonist lesogaberan (AZD3355) which liquefies at 65% RH. Since the substance is very polar and lacks a UV chromophore, conventional separation and detection techniques cannot be used to characterize the substance and its impurities. The analytical techniques are described, focusing on the capillary electrophoresis method with indirect UV detection for assay and purity, the liquid chromatographic method for enantiomeric separation with derivatization with UV chromophore and three complementary nuclear magnetic resonance (NMR) approaches (31P-NMR, 13C-NMR and 1H-NMR) for impurities. For oral solutions, it was important to select the right concentration of phosphate buffer for the specific drug concentration and routinely use small additions of EDTA. I.V. solutions containing physiological saline as tonicity modifier could not be stored frozen at −20 °C. Properties of AZD9343 will be discussed in light of experiences from the structurally similar lesogaberan and (2R)-(3-amino-2-fluoropropyl)sulphinic acid (AFPSiA).

THE ANALYSIS OF SMALL IONS WITH PHYSIOLOGICAL IMPLICATIONS USING CAPILLARY ELECTROPHORESIS WITH CONTACTLESS CONDUCTIVITY DETECTION

Simultaneous electrophoretic separation of inorganic anions and cations from ground waters by dual opposite end injection and their capacitively coupled contactless conductometric detection is described. The chemometry assisted method development revealed that using this type of detection, apart from many advantages, implies a careful fine tuning of experimental variables. Proper choice of buffer components is the most critical aspect of the recorded signal's quality and the obtained resolution, where minor changes could lead to major changes in the recorded electropherograms. From a big variety of acidic and basic electrolytes, a pyromellitic acid/citric acid based buffer (pH = 3.70) was chosen for the baseline separation of 11 cations and anions in a single, less than 3 min run, using a PVA coated fused silica capillary. The estimated limits of detection (0.07–2 ppm) and defined limits of quantification (0.3–7 ppm) were comparable or better than those described for indirect UV detection, allowing much broader linear ranges (up to 120 ppm) for most of the studied ions. Following method validation the method was successfully applied for the assessment of inorganic ion content of 51 geotagged drinking water (domestic well) samples collected from the rural area of Cluj County, Romania, and correlations between sample composition and their geographical origin were identified by multivariate data analysis.

Study on dicarboxylic acids in aerosol samples with capillary electrophoresis.

The research was performed to study the simultaneous detection of a homologous series of α, ω-dicarboxylic acids (C2–C10), oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, and sebacic acids, with capillary electrophoresis using indirect UV detection. Good separation efficiency in 2,6-pyridinedicarboxylic acid as background electrolyte modified with myristyl trimethyl ammonium bromide was obtained. The dicarboxylic acids were ionised and separated within five minutes. For the study, authentic samples were collected onto dry cellulose membrane filters of a cascade impactor (12 stages) from outdoor spring aerosols in an urban area. Hot water and ultrasonication extraction methods were used to isolate the acids from membrane filters. Due to the low concentrations of acids in the aerosols, the extracts were concentrated with solid-phase extraction (SPE) before determination. The enrichment of the carboxylic acids was between 86 and 134% with sample pretreatment followed by 100-time increase by preparation of the sample to 50 μL. Inaccuracy was optimised for all the sample processing steps. The aerosols contained dicarboxylic acids C2–C10. Then, mostly they contained C2, C5, and C10. Only one sample contained succinic acid. In the study, the concentrations of the acids in aerosols were lower than 10 ng/m3.