Photochemical micro-digestion in a multi-pumping flow system for phosphorus fractionation in cereals

Simple multi-signal calibrations exploiting flow analysis systems

Multi-signal calibrations have been recently exploited in molecular spectrochemical analysis alternatively to traditional calibration methods, improving analytical frequency and accuracy. The application of these strategies is simple and minimizes efficiently matrix effects by analyzing two calibration solutions comprising sample plus standard (S1), and sample plus blank (S2). The plot of the signals obtained with S1 and S2 at multiple settings (e.g. different wavelengths) yield a slope that can be related to the analyte concentration in the sample. Similarly, transient signals could also be related to the analyte concentration exploiting a similar strategy. Thus, in this work, two multi-signal approaches developed in flow-based systems are proposed, based on the responses at multiple wavelengths (online multi-energy calibration, OMEC), and on the dispersion profile of the samples, herein denominated multi-dispersion calibration (MDC). The calibrations were carried out with sample solutions after 2-fold dilution with a standard solution and with water. The feasibility of OMEC and MDC were demonstrated using KMnO4 solutions (without chemical reactions) under continuous and pulsed flow regimes. The applicability of this strategy was also demonstrated by the spectrophotometric determination of urea in milk and pet potty spray in a multi-pumping flow system, based on the color change of bromothymol blue after catalyzed hydrolysis by urease from jack beans (Canavalia ensiformis). MDC and OMEC were compared with external calibrations (EC) and classical standard addition. The limits of detection for urea were estimated at 13 mg L-1, 16 mg L-1, and 10 mg L-1 using MDC, MEC and EC, respectively. Recoveries from 93 to 101%, and the agreement of sample analyzes with the reference procedure demonstrated the good accuracy achieved by the proposed methods. Therefore, it was demonstrated the feasibility of MDC and OMEC for analytical purposes in a simple and efficient way with the advantages of flow-based manifolds.

Exploitation of flow-based procedures for reagentless hydrochlorothiazide determination and accelerated degradation studies of pharmaceutical preparations

Drug quality assessment and stress testing are important to ensure both treatment efficacy and patient safety. High performance liquid chromatography may be considered a standard technique for pharmaceutical analysis, showing good precision and accuracy, but it also involves relatively high cost and low analytical frequency. Flow injection analysis presents high sample throughput, lower cost and might be used for selective drug analysis with an appropriate assay and/or detector. In this paper, for the first time, photoreactions promoted by UV radiation were employed for reagentless spectrophotometric determination of hydrochlorothiazide. Optimized parameters led to a linear range of 50 to 500 mg L^-1, estimated limit of detection of 3.0 mg L^-1 and 24 determinations per hour. The use of diluted NaOH solution as a carrier allowed solubilization of hydrochlorothiazide and analysis without organic solvents. The presence of the most common excipients was evaluated and no significant interferences were observed. The results from the analysis of samples by the proposed and by the reference procedures demonstrated accuracy and matching results. The proposed in-line photolysis of the pharmaceutical, performed in 5 min, is a promising alternative to the conventional hydrolytic forced degradation, which requires elevated temperature and prolonged time period. To evaluate the degree of photoconversion, a capillary zone electrophoresis method was developed, which performed well for separations manifesting good analytical frequency and reduced amount of waste. The combination of in-line photodegradation followed by separation by capillary electrophoresis is a promising approach for the stress test of hydrochlorothiazide in pharmaceutical formulations.

Preparation of a New Iron-Carbon-Loaded Constructed Wetland Substrate and Enhanced Phosphorus Removal Performance

Iron-carbon substrates have attracted extensive attention in water treatment due to their excellent processing ability. The traditional iron-carbon substrate suffers from poor removal effects, separation of the cathode and anode, hardening, secondary pollution, etc. In this study, a new type of iron-carbon-loaded substrate (NICLS) was developed to solve the problems of traditional micro-electrolytic substrates. Through experimental research, a preparation method for the NICLS with Fe and C as the core, zeolite as the skeleton, and water-based polyurethane as the binder was proposed. The performance of the NICLS in phosphorus-containing wastewater was analyzed. The results are as follows: The optimal synthesis conditions of the NICLS are 1 g hydroxycellulose, wood activated carbon as the cathode, an activated carbon particle size of 200-60 mesh, and an Fe/C ratio of 1:1. Acidic conditions can promote the degradation of phosphorus by the NICLS. Through the characterization of the NICLS (scanning electron microscope (SEM), X-ray diffractometer (XRD), and energy-dispersive spectrometer (EDS), etc.), it is concluded that the mechanism of the NICLS phosphorus removal is a chemical reaction produced by micro-electrolysis. Using the NICLS to treat phosphorus-containing wastewater has the advantages of high efficiency and durability. Therefore, it can be considered that the NICLS is a promising material to remove phosphorus.

Simultaneous determination of total dissolved nitrogen and total dissolved phosphorus in natural waters with an on-line UV and thermal digestion

A flow injection method combined with an on-line UV and thermal digestion for simultaneous determination of total dissolved nitrogen (TDN) and total dissolved phosphorus (TDP) in natural waters was established in this study. A novel flow manifold made the proposed system compact and automatic. The conversion rates of various nitrogen and phosphorus compounds to their nitrate and phosphate forms with different digestion models and different concentrations were well investigated using the flow injection technique. The reagent concentrations for colorimetric analysis were optimized based on a univariate experimental design. The detection limits were 0.8 μmol L^-1 and 0.2 μmol L^-1, and linear analytical ranges were up to 300 μmol L^-1 and 25 μmol L^-1 for TDN and TDP, respectively. The sample throughput was ~ 5 h^-1. The recovery of spiked natural water samples varied from 86.8% to 102.6% for TDN and 88.0% to 102.0% for TDP. The present approach was successfully applied for the determination of TDN and TDP in natural water samples and was found to have good agreement with reference methods. The outcomes of present study indicated that the proposed method is suitable for routine analysis as well as for potential on-line monitoring.

Flow analysis in Brazil: contributions over the last four decades

Timeline with the main contributions of Brazilian researchers to flow analysis.

Distinguishing between organic and inorganic phosphorus in hydroxyapatite by elemental analysis

A method is developed to determine the amount of organic and inorganic phosphorus in an inorganic polymer (hydroxyapatite (HAP)) modified with an organic phosphorus - containing complexant. The simplicity and precision of the vanadate method has made it useful for measuring the total phosphorus content in phosphorus - containing organic polymers that are first digested in concentrated sulfuric acid. However, it can be important to quantify the organic and inorganic phosphorus capacities in modified (hybrid) polymers and this method does not distinguish between the two. In the current report, HAP was modified with 1-hydroxyethane-1,1-diphosphonic acid (HEDP) and a method developed to give the respective phosphorus capacities. HAP was contacted with HEDP for 17 h, 28 h, 56 h, 84 h, 112 h, and 140 h. By combining results from the sulfuric acid digestion of the modified polymer with those from a separate digestion in HCl, it was determined that there was a monotonic increase in the organic phosphorus capacity from 0.04 to 2.44 mmol / g, and a decrease in the inorganic phosphorus capacity from 4.68 to 2.54 mmol / g.