Automated continuous monitoring of drug dissolution process using a flow injection on-line dialysis sampling – solvent extraction separation spectrophotometric system

Inductively coupled plasma optical emission spectrometry (ICP-OES) was used for the element-specific determination of water-soluble organosilicon species separated by high-performance liquid chromatography (HPLC). Leachates from different waste deposit sites were investigated. The polydimethylsiloxane (PDMS) degradation product dimethylsilanediol (DMSD) could be detected in almost all samples in the low mg L^–1 range, and it was furthermore possible to determine trimethylsilanol (TMSOL) in some leachate samples in the μg L^–1 range. TMSOL was additionally analyzed by a method established before (LT-GC/ICP-OES). This study proved the occurrence of silanol compounds in leachates from locations were silicone material is deposited. Received: 10 July 1998 / Revised: 2 November 1998 / Accepted: 5 November 1998     

Automated solid phase dynamic extraction – Extraction of organics using a wall coated syringe needle

Extractions of liquid samples were carried out using wall coated needles prepared from stainless steel capillary columns instead of syringe needles. This micro extraction technique was applied to the analysis of pesticides in water. Important parameters influencing the extraction such as sample velocity, extraction time and also the desorption parameters were investigated and optimized. Automation of this technique was realized using a conventional automatic sampler. Limits of detection were improved using the multiple extraction / desorption technique. Chromatographic data and limits of detection were compared with those obtained by solid phase micro extraction (SPME). Using a needle with a 7 μm film yielded limits of detection varying from 0.001–0.1 μg/L and were in the same range as those resulting from the extraction using a 100 μm polydimethylsiloxane (PDMS) SPME fiber. The main advantages of the needle extraction technique were the significantly higher extraction speed and the practical aspects of a stable steel needle compared to those of a fragile fiber. The extraction speed using a needle with a ¶7 μm film was up to five times higher than the speed of SPME using a 100 μm PDMS fiber. The steel needle could be stressed mechanically in a higher extent than a SPME fiber. Sample volumes and aliquots of liquid media could be handled and moved from one bottle to another using the automatic sampler.     

Dynamic extraction coupled on-line to liquid chromatography with a parallel sampling interface—a proof of concept for monitoring extraction kinetics

On-line hyphenation of extraction with chromatography has been explored in several different types of combinations. However, monitoring the complete process of a dynamic, continuous-flow extraction is not possible with any hyphenated system reported so far. The current work demonstrates that this challenging task can be effectively fulfilled by using a parallel sampling interface, which mimics the concept of comprehensive two-dimensional chromatography. In this study, pressurised hot water extraction was coupled on-line with ultra-high-performance liquid chromatography. The set-up was utilised in a kinetic study of dynamic pressurised hot water extraction of curcuminoids from turmeric powder. Compound-specific extraction curves were obtained, which clearly indicated the rate-limiting factors of the extraction processes under different conditions. Additionally, thermal degradation of curcumin during the extraction could also be demonstrated in some of the extractions.

     

Automated determination of the pK a values of 4-hydroxybenzoic acid in cosolvent–water mixtures and related solvent effects using a modified HPLC system

An automated spectrophotometric method based on an HPLC system with a diode array detector was used to determine the pK _a values of compounds with low water solubility in a universal buffer containing acetonitrile as cosolvent. The column of the system was replaced with a capillary connecting the injection system and the diode array detector. Specific solvent effects were corrected for using the dielectric constants of the mixed solvent and pure water. The method was tested using 4-hydroxybenzoic acid and the results were compared with those obtained with a spectrophotometer. Linear regression lines with different slopes were obtained from spectrophotometric measurements of different cosolvent–water mixtures. These effects were shown to depend upon the polarity of the solventwater mixture, and they were explained by the solvatochromic behavior of the 4-hydroxybenzoic acid in the solvent–water mixture.     

Speciation,separation and enrichment of Cr(III) and Cr(VI) in environmental samples by ion-pair solvent extraction using a β-diketone ligand

A simple speciation, separation and enrichment method has been developed for the determination of Cr(III) and Cr(VI) ions in different samples by ion-pair solvent extraction with a β-diketone ligand, 2-(4-methoxybenzoyl)-N′-benzylidene-3-(4-methoxyphenyl)-3-oxo-N-phenyl-propono hydrazide (MBMP). Cr(III) was separated from Cr(VI) as Cr(III)-(MBMP)-perchlorate ternary ion-pair complex. The influences of various analytical parameters including pH, amount of reagent, shaking time, sample volume and ionic strength on the recovery of Cr(III) and/or Cr(VI) were investigated. Total chromium was obtained after reducing Cr(VI) to Cr(III) with NH₂OH?·?HCl. Recoveries were found to be higher than 95% and the relative standard deviation (RSD) was less than 2%. The method detection limit based on 3σ criterion for Cr(III) was found to be 0.32?µg?L^?1. The formed ternary ion-pair complex, Cr(III)?:?MBMP?:?2ClO₄, has a molar ratio of 1?:?1?:?2. The developed method has been applied successfully to the speciation of chromium in various natural water, soil, sediment and hair samples with satisfactory results.     

Designing a simple semi-automated system for preconcentration and determination of nickel in some food samples using dispersive liquid–liquid microextraction based upon orange peel oil as extraction solvent

A simple semi-automated dispersive liquid–liquid microextraction system was designed and used for off-line preconcentration and determination of nickel (II) ion in some food samples. The methodology submitted in the present work is based upon the microextraction of [Ni(C₃₈H₂₈O₂N)₂] complex employing an orange peel oil (OPO) as an extractant without a dispersing solvent and the estimation of nickel (II) ion in sediment by electrothermal atomic absorption spectrometry (ETAAS). 3 mL of sample solution, 0.5 mL of acetate buffer (pH 6), and 300 µL of the complexing agent (1-[4-[(2-hydroxynaphthalen-1-yl)methylideneamino] phenyl]ethanone) (HNE) dissolved in OPO were automatically transferred to separation tube and the cloudy solution was obtained by dispersing OPO as droplets throughout the aqueous phase using nitrogen gas. Under the optimized conditions, the analytical methodology used in this study provided a good efficiency in term of sensitivity and selectivity where the calibration plot was linear in the range of 5–150 ngL^–1, while, the enhancement factor (EF) and the detection limit were 300 and 0.87 ngL^–1, respectively for a sample volume of 3 mL. On the other hand, the method was completely free of most potential interferences. Certified reference wheat sample (NCS ZC11018) and some food samples were used to evaluate the developed method and results were compared using ICP–MS. Moreover, the new [Ni(C₃₈H₂₈O₂N)₂] complex was synthesized and characterized using diverse characterization techniques.