Novel sample double dilution calibration method for determination of lithium in biological samples using automatic flow system with in-syringe reaction.

A novel sample double dilution calibration method (SDDCM) and an automatic flow system with in-syringe reaction and spectrophotometric detection were developed for determining lithium in biological samples. The method is based on the reaction of lithium with Thorin in an alkaline medium and the signal was measured at 480 nm. The reaction was performed simultaneously for both standards and samples in three syringes of the automatic flow system. The method was validated and successfully applied to the determination of lithium in synthetic and pharmaceutical samples, with results consistent with the ICP OES method. The novel calibration method, developed for the determination of lithium in biological samples, uses a sample with two dilution degrees. Using the method, the concentration of the analyte is determined by relating the signal for a less diluted sample to the calibration plot for a more diluted sample and vice versa. The implementation of the calibration method was facilitated by preparing solutions directly in the flow system. The use of two sample dilutions makes it possible to determine the analyte in the sample without preliminary preparation. Moreover, obtaining two results based on signals for a sample diluted to different degrees allows them to be verified for accuracy. The proposed approach was successfully verified by the determination of lithium in certified reference materials of blood serum and urine. Using the developed method lithium was determined within the concentration range of 0.06-1.5 mg L-1, with precision (CV, %) less than 6.7, and accuracy (RE, %) better than 6.9. The detection limit was 0.03 mg L-1.

Novel Approach to Automated Flow Titration for the Determination of Fe(III).

A novel approach to automated flow titration with spectrophotometric detection for the determination of Fe(III) is presented. The approach is based on the possibility of strict and simultaneous control of the flow rates of sample and titrant streams over time. It consists of creating different but precisely defined concentration gradients of titrant and analyte in each successively formed monosegments, and is based on using the calculated titrant dilution factor. The procedure was verified by complexometric titration of Fe(III) in the form of a complex with sulfosalicylic acid, using EDTA as a titrant. Fe(III) and Fe(II) (after oxidation to Fe(III) with the use of H2O2) were determined with good precision (CV lower than 1.7%, n = 6) and accuracy ( | RE | lower than 3.3%). The approach was applied to determine Fe(III) and Fe(II) in artesian water samples. Results of determinations were consistent with values obtained using the ICP-OES reference method. Using the procedure, it was possible to perform titration in 6 min for a wide range of analyte concentrations, using 2.4 mL of both sample and titrant.