Mirella Zancato

pH-stat techniques in titrimetric analysis: IV. pH-stat monitoring of chelatometric titrations

Abstract The theory of pH-stat chelatometric titrations recently developed [Anal. Chim. Acta 456 (2002) 313] is experimentally substantiated here. The titrations of four representative doubly charged cations having different behaviour (copper, zinc, calcium, magnesium) are taken as examples. Copper is titratable between pH 3 and 5, zinc between 3 and 6, calcium between 6 and 10, and magnesium between 7 and 10. The shapes of the titration plots agree well with the theory, accounting for simultaneous equilibria involving proton exchange. The technique yields accurate and precise results, which compare favourably with those of other instrumental techniques, in particular photometric titrations.

The protein profile of Theobroma cacao L. seeds as obtained by matrix‐assisted laser desorption/ionization mass spectrometry

The water-soluble protein profile of the seeds of green, red, and yellow Theobroma cacao L. fruits has been determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS). The seeds were powdered under liquid nitrogen and defatted. The residues were dialyzed and lyophilized. The obtained samples were suspended in the matrix solution of sinapinic acid. The obtained MALDI mass spectra showed the presence of a wide number of proteins with molecular weight ranging from 8000 to 13,000 Da and a cluster of peaks centered at 21,000 Da that were attributed to albumin. The abundance of this peak was found to depend on the different portion of the seed (husk, apical and cortical parts); however, the MALDI mass spectra obtained from the different varieties of cocoa were practically superimposable. Changes in the protein profiles were also observed after the cocoa seeds were treated by fermentation and roasting, which are processes usually employed for the commercial production of cocoa.

Simultaneous microdetermination of chlorine, bromine and phosphorus in organic compounds by ion chromatography

Abstract A procedure for the simultaneous microdetermination of chlorine, bromine and phosphorus in organic compounds is described. It consists of ion chromatographic analysis, after suitable dilution, of the solution resulting from the collection in water containing hydrogen peroxide of the combustion products obtained by decomposition of the sample in a Schoniger flask. Before analysis, this solution undergoes a post-combustion procedure involving further hydrolysis of the combustion products which allows a nearly quantitative recovery of phosphorus to be achieved even in the presence of other heteroatoms such as chlorine and bromine. This post-combustion step avoids negative errors in the microdetermination of phosphorus by ion chromatography owing to the minor but not insignificant amounts of both pyrophosphate and a cyclic metaphosphate which are formed together with the predominant orthophosphate in the conventional Schoniger combustion of organophosphorus compounds. The accuracy and precision of the overall procedure were evaluated.

Simultaneous potentiometric micro-scale determination of chlorine and bromine in organic compounds

The experimental conditions for the micro-scale argentimetric potentiometric titration of organic chlorides and bromides present in the same solution were investigated. Coprecipitation phenomena affect the titration but can be minimised by various means, thus making it possible to determine both halogens with an absolute error of less than 0.40%. For the mineralisation of organic compounds containing halogens a Schoniger flask, modified in order to allow an exact titration of small solution volumes, was used. The titrations were performed with an automatic apparatus.

Pharmacokinetic analysis of antibiotic adsorption (vancomycin and teicoplanin) by the Lixelle extracorporeal unit

Purpose The pharmacokinetic properties of vancomycin (VAN) and teicoplanin (TEC) may be affected by adsorption during hemofiltration as well as hemoperfusion therapies. The aim of this in vitro study was to investigate VAN and TEC removal adsorption kinetics with mass balance analysis by direct hemoperfusion (DHP) with the Lixelle S-35 cartridge (Lixelle, Kaneka Corporation, Tokyo). Methods Mock DHP was performed for 120 min using VAN and TEC solutions (46.08 ± 0.81 and 74.79 ± 1.24 mg/l per N = 6). Clinical plasma antibiotic concentrations were circulated in a closed circuit simulating DHP using an adsorption column (Lixelle S-35) at flow rate of 250 ml/min. Samples were collected at 10, 60, and 120 min through both arterial and venous ports; drug levels were measured with particle enhanced turbidimetric inhibition immunoassay and fluorescence polarization immunoassay. All tests were performed in triplicate. Results: Results subsequent to DHP at the primary assessment interval for VAN mass was 49.06 ± 1.47 mg, indicating a significant reduction of the starting mass (94.74 ± 1.63 mg). The observed reduction of TEC levels greatly exceeded that of VAN at the first interval (10 min). At 120 min of DHP, the estimated mass adsorption of VAN was 45.68 ± 2.26 mg, while the mesured total TEC mass adsorbed was 126.86 ± 0.91 mg. Conclusions A VAN adsorption plateau indicating the VAN loading dose may be required in patients receiving DHP with the Lixelle S-35. The total TEC mass was adsorbed subsequent to 60 min of circulation, so the loading dose should be closely considered. In addition, the Lixelle S-35 may represent an option as a rescue therapy in accidental overdose of TEC.

Sequential potentiometric microdetermination of chloride and phosphate and its application to the determination of phosphorus and chlorine in organic compounds.

Orthophosphate has been determined at the micro level in the presence of chloride by argentimetric potentiometric titration. Chloride is titrated first, at pH 3 in water-propan-2-ol (1:1 v/v), and phosphate in the same solution, buffered at pH 8.5-9.0. Under these conditions, the titration error from partial co-precipitation of silver oxide near the equivalence point is minimized. A procedure for performing the titration with an automatic apparatus is described. The method has been applied to the determination of phosphorus and chlorine in the same organic compound after mineralization by the Schöniger method.

Optimisation of the micro-scale determination of phosphates by direct potentiometric titration with silver ions and its application to the determination of phosphorus in organic compounds

The micro-scale determination of orthophosphate ions by argentimetric titration with potentiometric detection of the end-point using a combined massive silver electrode was investigated. The best results were obtained when this titration was carried out in water-isopropanol (50%V/V) buffered at pH 8.80. Under such conditions the titration error arising from the partial coprecipitation of silver oxide near the equivalence point is minimised and the results obtained have a satisfactory accuracy (errors within ±0.30%) and good reproducibility. The concentration range in which reasonable accuracy and precision are attained and the most suitable titration rate to be adopted when an automatic titrimetric device is used were also considered. This optimised titration method was successfully applied to the determination of phosphorus in organophosphorus compounds after mineralisation in a suitably modified Schoniger flask.

New option for the treatment of hyperbilirubinemia: in vitro direct hemoperfusion with the Lixelle S-35

Purpose Limited options are available to treat critically ill patients with acute liver failure (ALF) and acute-on-chronic liver failure (AoCLF), therefore we set up an in vitro study in order to test the bilirubin adsorption capacity of the Lixelle S-35 cartridge by direct hemoperfusion (DHP). Methods Mock DHP was performed for 120 min using hyperbilirubinic human plasma and blood obtained from a plasmapheresis and exchange transfusion, respectively. The total bilirubin (TBIL) and direct bilirubin (DBIL) baseline concentrations were 17.57 ± 0.53, 12.57 ± 0.23 mg/dl for plasma and 23.10 ± 0.47, 15.37 ± 0.24 mg/dl for blood. Plasma and blood were separately circulated in a closed circuit simulating DHP using an adsorption column (Lixelle S-35) at flow rate of 100 ml/min. TBIL and DBIL levels were measured at 10, 30, 60, and 120 min from arterial and venous ports and assessed with the Jendrassik-Grof method. All tests were performed in triplicate. Results The total removal subsequent to DHP (120 min) was seen as TBIL in plasma 55.60%, TBIL in blood 62.16%, DBIL plasma 58.87%, DBIL in blood 64.41%, respectively. The estimated mass adsorption of TBIL in plasma 958.20 ± 5.72 mg, TBIL in blood 1233.60 ± 10.22 mg, DBIL in plasma 680.70 ± 10.68, DBIL in blood 818.10 ± 4.68, respectively. Conclusions The bilirubin adsorption rates after DHP were very promising for both hyperbilirubinic plasma and blood. Although further in vitro investigations are required, including comparisons with other techniques, these findings have shown that the Lexille S-35 should represent an option for the management of hyperbilirubinemia in ALF or AoCLF.

Kinetics of Linezolid in Continuous Renal Replacement Therapy: An in Vitro Study

Background: Continuous veno-venous hemofiltration (CVVH) could affect the pharmacokinetic profile of linezolid (LZD). The aim of this study was to evaluate the LZD extracorporeal clearance using an in vitro CVVH model. Methods: A sham miniaturized CVVH circuit (CARPEDIEM; Bellco, Mirandola, Italy) was set up with a polysulfone hemofilter (0.25 m2; cutoff 50,000 Da) for 240 minutes using normal saline solution (0.9% wt/vol NaCl) and blood (n = 6) spiked with LZD. Drug solution samples were collected during CVVH at 10, 30, 60, 120, and 240 minutes. LZD levels were measured by high-performance liquid chromatography. Results: Results were used to estimate pharmacokinetic parameters. The LZD baseline level decreased from 17.24 ± 0.54 to 9.73 ± 4.85 mg/L and from 11.75 ± 0.08 to 5.01 ± 0.67 mg/L in the first 10 minutes, and then increased to 13.2 ± 3.10 and 7.4 ± 0.71 mg/L in normal saline solution and blood, respectively. Mass balance analysis reported a rapid adsorption of LZD onto a polysulfone membrane followed by its release: a rebound phenomenon occurred. Conclusions: Although further studies are necessary to clarify this phenomenon, LZD level variations observed in our study should be considered to avoid antimicrobial underexposure. Several strategies are available for adjusting the dosage regimen of LZD, but therapeutic drug monitoring is highly recommended when it is used.

Optimization of the micro-scale determination of arsenates by direct potentiometric titration with silver ions and its application to the determination of arsenic in organic compounds

Abstract A micro-scale argentimetric method for the determination of orthoarsenates by potentiometric detection of the end-point has been developed. The optimal results were obtained when this titration was carried out in water-methanol medium, buffered at pH 7.50. This method minimizes the error of old methods arising from the small coprecipitation of silver oxide near the equivalence point and the data obtained are characterized by good accuracy and reproducibility. The procedure to perform the titration with an automatic apparatus is described as well as the optimum concentration range and titration rate. The method was then applied to the determination of arsenic in organic compounds after mineralization in the Schoniger flask using a quartz spiral.