Determination of inorganic cations and anions by ion-exchange chromatography with evaporative light-scattering detection

New Analytical Approach for The Determination of Calcium Phosphate Dibasic and Tribasic in Processed Food by Comparison of Ion Chromatography With High-Performance Liquid Chromatography

An analytical method to measure solubilized orthophosphate ions (HPO42- and PO43- ) from the water-insoluble food additives calcium phosphate dibasic (DCP) and calcium phosphate tribasic (TCP) in processed foods was optimized by comparing ion chromatography (IC) coupled with DS6 conductivity detector (Cond.) and high-performance liquid chromatography (HPLC) with Evaporative light scattering detector (ELSD) methods. The ion-pairing HPLC method could analyze calcium and phosphate ions successively. However, this method exhibited low reproducibility after approximately 48 hours of measurements. The IC method was established as an effective method of measuring orthophosphate ions with high reproducibility using distilled water and KOH solution as the mobile phase with a Dionex column. Matrix-based limit of detections (LOD) and limit of quantifications (LOQ) for snacks and cereals were estimated in the range of 0.01-0.91 µg/mL and 0.21-2.74 µg/mL, respectively. In inter-day and intra-day tests, the calculated precision (%RSD) and accuracy (recovery %) ranged from 0.5% to 6.6% and 82% to 117%, respectively, in both food samples. The levels of DCP or TCP could be analyzed in various positive food samples, and the developed IC method demonstrated good applicability in the analysis of DCP and TCP in collected processed foods.

Identification of selenosugars and other low-molecular weight selenium metabolites in high-selenium cereal crops

Several novel selenium containing compounds were characterized in staple crops (wheat, rice and maize) grown on soils naturally rich in selenium. A dedicated method based on the coupling of liquid chromatography with multiplexed detection (ICP-MS, ESI-Orbitrap MS(/MS)) was developed for the speciation of low-molecular weight (<5 kDa) selenium metabolites. Nine species present in different proportions as a function of the crop type were identified by cation-exchange HPLC-ESI-Orbitrap MS on the basis of the accurate molecular mass and MS/MS spectra. The natural origin of these species was then validated by varying extraction conditions and by using hydrophilic interaction LC (HILIC)-ESI-Orbitrap MS(/MS). Among the identified compounds, Se-containing monosaccharides (hexose moiety, m/z 317 and m/z 358) or Se-containing disaccharides (hexose-pentose moiety, m/z 407 and m/z 408) were the first selenosugars reported in edible plants. It is also the first report of the presence of 2,3-dihydroxypropionyl-selenolanthionine (m/z 345) in rice. Because these crops can be an important source of selenium in animal and human nutrition, the understanding of the origin and the fate of these species during metabolic processes will be of great interest.

Quantitative analysis of tris(2-carboxyethyl)phosphine by anion-exchange chromatography and evaporative light-scattering detection

Tris(2-carboxyethyl)phosphine (TCEP) belongs to the trialkylphosphine class of reducing agents that are widely used in research and industry. In this paper, we discuss a sensitive high-performance liquid chromatography (HPLC) method equipped with an evaporative light scattering detector (ELSD) for the determination of TCEP in pharmaceutical samples containing therapeutic protein and stabilizing additives. TCEP was first completely oxidized with hydrogen peroxide to form TCEP oxide (TCEPO). Proteins and salts were removed from the sample by solid phase extraction. TCEPO concentrations were determined by anion exchange chromatography coupled with ELSD. Because of the 1:1 oxidation stoichiometry for the reaction, the concentration of TCEP in the sample is directly proportional to the measured concentration of TCEPO. A good linearity fit of ELSD response versus TCEPO concentration was observed over the range of 20-2000 μM. The specificity, precision, accuracy, and robustness of the method were evaluated and suitable for the quantitation of TCEP in biological samples. Moreover, selective treatment with peroxide prior to solid-phase extraction may be used to determine the mass balance of TCEP species or track the oxidation rate in pharmaceutical samples.

Determination of inorganic pharmaceutical counterions using hydrophilic interaction chromatography coupled with a Corona CAD detector

A simple generic approach was investigated for the determination of inorganic pharmaceutical counterions in drug substances using conventional high performance liquid chromatographic (HPLC) instruments. An intuitive approach combined Corona charged aerosol detection (CAD) with a polymer-based zwitterionic stationary phase in the hydrophilic interaction chromatography (HILIC) mode. Two generic methods based on this HILIC/CAD technique were developed to quantitate counterions such as Cl-, Br-, SO(4)(2-), K+, Ca2+ and Mg2+ in different pharmaceutical compounds. The development and capability of this HILIC/CAD technique analysis were examined. HILIC/CAD was compared to ion chromatography (IC), the most commonly used methodology for pharmaceutical counterion analysis. HILIC/CAD was found to have significant advantages in terms of: (1) being able to quantitate both anions and cations simultaneously without a need to change column/eluent or detection mode; (2) imposing much less restriction on the allowable organic percentage of the eluents than IC, and therefore being more appropriate for analysis of counterions of poorly water-soluble drugs; (3) requiring minimal training of the operating analysts. The precision and accuracy of counterion analysis using HILIC/CAD was not compromised. A typical precision of <2.0% was observed for all tested inorganic counterions; the determinations were within 2.0% relative to the theoretical counterion amount in the drug substance. Additionally, better accuracy was shown for Cl- in several drug substances as compared to IC. The main drawback of HILIC/CAD is its unsuitability for many of the current silica-based HILIC columns, because slight dissolution of silica leads to high baseline noise in the CAD detector. As a result of the universal detection characteristics of Corona CAD and the unique separation capabilities of a zwitterionic stationary phase, an intuitive and robust HPLC method was developed for the generic determination of various counterions in different drug substances. HILIC/CAD technique is a useful alternative methodology, particularly for determination of counterions in low-solubility drugs.

Comparison of liquid chromatography and capillary electrophoresis methods for quantification of sodium residuals

Liquid chromatography (LC) and capillary electrophoresis (CE) methods were developed to perform the determination of residual sodium in mother liquors and successive washes of an active pharmaceutical ingredient (API). The addition of sodium chloride to the product solution results in rapid and complete crystallization of the API. The LC method was coupled to evaporative light scattering detection (ELSD) while the CE approach was based on indirect UV detection. Both methods were fully validated. Selectivity, response function, trueness, precision, accuracy, linearity and limits of detection (LOD) and quantification (LOQ) were the criteria investigated. The LC-ELSD method was found to be more sensitive than the CE/indirect UV approach. The methods were found to be valid over concentration ranges of 62-500 and 235-1500 ppm for the LC and the CE methods, respectively. Both methods were compared and used for the determination of actual samples coming from different batches of the same API chemical synthesis.

Simultaneous liquid chromatographic determination of metals and organic compounds in pharmaceutical and food-supplement formulations using evaporative light scattering detection

A novel method for the non-derivatization liquid chromatographic determination of metals (potassium, aluminium, calcium and magnesium) and organic compounds (ascorbate and aspartate) was developed and validated based on evaporative light scattering detection (ELSD). Separation of calcium, magnesium and aluminium was achieved by the cation exchange column Dionex CS-14 and an aqueous TFA mobile phase according to the following time program: 0-6 min TFA 0.96 mL L(-1), 6-7 min linear gradient from TFA 0.96-6.4 mL L(-1). Separation of potassium, magnesium and aspartate was achieved by the lipophilic C18 Waters Spherisorb column and isocratic aqueous 0.2 mL L(-1) TFA mobile phase. Separation of sodium, magnesium, ascorbate and citrate was also achieved by the C18 analytical column, according to the following elution program: 0-2.5 min aqueous nonafluoropentanoic acid (NFPA) 0.5 mL L(-1); 2.5-3.5 min linear gradient from 0.5 mL L(-1) NFPA to 1.0 mL L(-1) TFA. In all cases, evaporation temperature was 70 degrees C, pressure of the nebulizing gas (nitrogen) 3.5 bar, gain 11 and the flow rate 1.0 mL min(-1). Resolution among calcium and magnesium was 1.8, while for all other separations was > or = 3.2. Double logarithmic calibration curves were obtained within various ranges from 3-24 to 34-132 microg mL(-1), and with good correlation (r>0.996). Asymmetry factor ranged from 0.9 to 1.9 and limit of detection from 1.3 (magnesium) to 17 microg mL(-1) (ascorbate). The developed method was applied for the assay of potassium, magnesium, calcium, aluminium, aspartate and ascorbate in pharmaceuticals and food-supplements. The accuracy of the method was evaluated using spiked samples (%recovery 95-105%, %R.S.D. < 2) and the absence of constant or proportional errors was confirmed by dilution experiments.

Determination of piperazine in pharmaceutical drug substances using capillary electrophoresis with indirect UV detection

A fast, selective capillary electrophoresis (CE) method was developed for piperazine counter-ion analysis and applied to the analysis of an active pharmaceutical ingredient (API) that exists as a hemipiperazine salt. Due to the poor chromophore, the detection method chosen was indirect UV detection using benzylamine as the UV absorbing probe. Piperazine quantitation was performed using diethylamine as an internal standard and the method was validated for specificity, linearity, precision, and accuracy. The results indicate the method is suitable for piperazine counter-ion analysis in support of salt form characterization.