Greening microwave-assisted digestion method using hydrogen peroxide for determination of elemental impurities by ICP-OES in antihypertensive active pharmaceutical ingredients

Microwave-assisted wet digestion (MAWD) using only H2O2 was proposed for oxidizing active pharmaceutical ingredients (APIs) for hypertension treatment and subsequent determination by inductively coupled plasma optical emission spectrometry (ICP-OES). Diltiazem hydrochloride (DIL) presented the most refractory characteristic for oxidation using MAWD-H2O2. This proposed MAWD-H2O2 method was validated for specificity, accuracy, and precision according to United States Pharmacopeia (USP) Chapter 233 guidelines. Regarding specificity, the most sensitive emission lines were utilized to analyze all elemental impurities in the digests, and no significant spectral interferences were observed. Sample masses of 500 mg for all APIs and a digestion temperature of 250 °C provided digests with residual carbon (RC) below 2400 mg L-1 of C. Additionally, the residual acidity of the MAWD-H2O2 digests was lower than the acidity presented by the HNO3 digests. The highest and lowest residual carbon content (RCC) for digests were observed for DIL and captopril (CAP), respectively, using MAWD-H2O2. When comparing the RCC for MAWD-H2O2 and MAWD-HNO3 digests for APIs containing aromatic rings, it was evident that H2O2 offered equivalent conditions for digesting these compounds. Accuracy tests showed recovery values of 91-110% for all elemental impurities, as recommended by USP chapter 233. Validation experiments for precision presented relative standard deviation (RSD) values below 6.4% and 10% under repeatability and intermediate precision conditions, respectively. The limits of quantification (LOQs) provided by MAWD-H2O2 are at most half of those recommended by of USP and International Council for Harmonisation of Technical Requirements (ICH). In conclusion, MAWD-H2O2 can be considered an alternative method for API digestion, aligning with green analytical chemistry principles, as it does not employ toxic reagents, minimizes waste, and the main products of H2O2 oxidation are water and oxygen. Considering the analytical Eco-Scale, the MAWD-H2O2 method scored 81, classifying it as an excellent green analysis.

Development of an eco-friendly sample preparation protocol for metal determination in food samples: an oxygen pressurized single reaction chamber using diluted nitric acid

Many efforts have been recently made to improve the digestion efficiency by using powerful equipment or by using an auxiliary reagent. In this work, an alternative method is reported, which explores a digestion system based on a single reaction chamber (SRC) technology pressurized with O₂ for reducing the amount of acid, without impairing the digestion efficiency. Before digestion, the system was pressurized with compressed air (20 bar, 20% O₂) while the temperature was evaluated from 180 up to 270 °C. The procedure was also carried out under O₂ pressure (20 bar). For each temperature several acid concentrations were evaluated (0.1 to 3 mol L^-1 HNO₃), being possible to correlate the effectiveness of each acid concentration with temperature. The proposed method was applied to the simultaneous digestion of several organic matrices with variable content of fat, protein, and carbohydrate (whole milk powder, bovine liver, parsley, and linseed). The residual carbon content was lower than 4% (C lower than 200 mg L^-1 in digests), showing the high digestion efficiency of the proposed approach. Up to 250 mg of all food matrices were digested using a sub-stoichiometric amount of HNO₃ (1 mol L^-1 solution), which was only achieved due to the use of O₂ as an auxiliary reagent. Barium, Ca, Cu, Fe, K, Mg, Mn, Na, Sr, and Zn were determined by ICP-OES, and the accuracy was better than 95% for standard reference materials of corn bran, whole milk powder, and bovine liver. It is an important feature, being in agreement with green chemistry recommendations because very low amounts of reagents are required for sample digestion, as well as low amounts of residues are generated.

An ultrasound-assisted sample preparation method of carbonatite rock for determination of rare earth elements by inductively coupled plasma mass spectrometry

RATIONALE

A method for the determination of rare earth elements in carbonatite rocks by inductively coupled plasma mass spectrometry (ICP-MS) was developed.

METHODS

An alkaline rock, carbonatite, was submitted to ultrasound-assisted extraction (USAE) using an ultrasound bath, a cup horn system or an ultrasound probe. The main USAE parameters were evaluated, such as extraction time (1 to 30 min), extraction temperature (20 to 100°C) and ultrasound amplitude (10 to 100%). For ICP-MS, a desolvation system (APEX-Q) was used to reduce interference in lanthanide determination. To evaluate if the effect of ultrasound improved extraction, experiments were carried out using magnetic stirring (500 rpm) for comparison.

RESULTS

The temperature and ultrasound amplitude optimized for the method were 70°C and 40%, respectively, using dilute nitric acid (3% v/v). Quantitative analyte recoveries were obtained using an ultrasound bath (25 kHz/100 W) which allowed for the simultaneous extraction of twelve replicates.

CONCLUSIONS

All the results obtained with the use of ultrasound systems were better than those obtained with mechanical stirring. The extracts were suitable for ICP-MS analysis and the results were in agreement with those obtained by the reference method (using wet acid digestion). Based on the results, the use of USAE can be considered an alternative method for sample preparation of carbonatite rocks, under milder conditions, for further ICP-MS analysis.

La2O3 Nanoparticles: Study of Uptake and Distribution in Pfaffia glomerata (Spreng.) Pedersen by LA-ICP-MS and μ-XRF

The production and use of nanoparticles (NPs) in different fields increased in the last years. However, some NPs have toxicological properties, making these materials potential emerging pollutants. Therefore, it is important to investigate the uptake, transformation, translocation, and deposition of NPs in plants. In this work, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and micro X-ray fluorescence (μ-XRF) were used to investigate the uptake and translocation of La₂O₃ NPs to stem and leaves of Pfaffia glomerata (Spreng.) Pedersen after in vitro cultivation of plants in the presence of 400 mg L^-1 of La₂O₃ NPs. By using LA-ICP-MS and μ-XRF, image of the spatial distribution of La in the leaves was obtained, where higher concentration of La was observed in the main veins. Differences in the signal profile of La in leaves of plants cultivated in the presence of bulk La₂O₃ (b-La₂O₃) and La₂O₃ NPs were observed. Sharp peaks of La indicated that NPs were transported to the stems and leaves of plants treated with La₂O₃ NPs. Both LA-ICP-MS and μ-XRF techniques have shown to be useful for detecting NPs in plants, but LA-ICP-MS is more sensitive than μ-XRF and allowed better detection and visualization of La distribution in the whole leaf.

TiO2 nanoparticles coated with deep eutectic solvents: characterization and effect on photodegradation of organic dyes

Deep eutectic solvents (DES) have been used to modulate the catalytic activity of TiO₂ nanoparticles.

Rare earth elements profile in a cultivated and non-cultivated soil determined by laser ablation-inductively coupled plasma mass spectrometry

Rare earth elements (REEs) have several applications but the effects on environment are not well known. Therefore, the aim of this work is to establish a method for direct solid sample analysis by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) to evaluate the concentration and distribution of REEs in cultivated and non-cultivated soil. Samples were collected in two areas to 40 cm of depth. The LA-ICP-MS method is easy to be implemented and the sample treatment is very fast comprising only its drying, grounding and pressing as a pellet. The accuracy of the method was evaluated by using a certified reference material (BCR 667 - Estuarine Sediment, Institute for Reference Materials and Measurements (IRMM)) where good agreement with the certified values was obtained. Analyte recovery at two levels of concentration (2.5 and 15.0 μg g^-1) was also performed and recoveries in the range of 85%-120% were achieved, values that are acceptable for LA-ICP-MS analysis. In general, the concentration of the REEs is higher in the cultivated soil and increased from the surface to deeper layers, which can be a consequence of fertilizer application.

Ultrasound-assisted extraction of rare-earth elements from carbonatite rocks

In view of the increasing demand for rare-earth elements (REE) in many areas of high technology, alternative methods for the extraction of these elements have been developed. In this work, a process based on the use of ultrasound for the extraction of REE from carbonatite (an igneous rock) is proposed to avoid the use of concentrated reagents, high temperature and excessive extraction time. In this pioneer work for REE extraction from carbonatite rocks in a preliminary investigation, ultrasonic baths, cup horn systems or ultrasound probes operating at different frequencies and power were evaluated. In addition, the power released to the extraction medium and the ultrasound amplitude were also investigated and the temperature and carbonatite mass/volume of extraction solution ratio were optimized to 70°C and 20mg/mL, respectively. Better extraction efficiencies (82%) were obtained employing an ultrasound probe operating at 20kHz for 15min, ultrasound amplitude of 40% (692Wdm^-3) and using a diluted extraction solution (3% v/v HNO₃+2% v/v HCl). It is important to mention that high extraction efficiency was obtained even using a diluted acid mixture and relatively low temperature in comparison to conventional extraction methods for REE. A comparison of results with those obtained by mechanical stirring (500rpm) using the same conditions (time, temperature and extraction solution) was carried out, showing that the use of ultrasound increased the extraction efficiency up to 35%. Therefore, the proposed ultrasound-assisted procedure can be considered as a suitable alternative for high efficiency extraction of REE from carbonatite rocks.

Microwave-assisted wet digestion with H2O2 at high temperature and pressure using single reaction chamber for elemental determination in milk powder by ICP-OES and ICP-MS

In this work a green digestion method which only used H2O2 as an oxidant and high temperature and pressure in the single reaction chamber system (SRC-UltraWave™) was applied for subsequent elemental determination by inductively coupled plasma-based techniques. Milk powder was chosen to demonstrate the feasibility and advantages of the proposed method. Samples masses up to 500mg were efficiently digested, and the determination of Ca, Fe, K, Mg and Na was performed by inductively coupled plasma optical emission spectrometry (ICP-OES), while trace elements (B, Ba, Cd, Cu, Mn, Mo, Pb, Sr and Zn) were determined by inductively coupled plasma mass spectrometry (ICP-MS). Residual carbon (RC) lower than 918mgL(-1) of C was obtained for digests which contributed to minimizing interferences in determination by ICP-OES and ICP-MS. Accuracy was evaluated using certified reference materials NIST 1549 (non-fat milk powder certified reference material) and NIST 8435 (whole milk powder reference material). The results obtained by the proposed method were in agreement with the certified reference values (t-test, 95% confidence level). In addition, no significant difference was observed between results obtained by the proposed method and conventional wet digestion using concentrated HNO3. As digestion was performed without using any kind of acid, the characteristics of final digests were in agreement with green chemistry principles when compared to digests obtained using conventional wet digestion method with concentrated HNO3. Additionally, H2O2 digests were more suitable for subsequent analysis by ICP-based techniques due to of water being the main product of organic matrix oxidation. The proposed method was suitable for quality control of major components and trace elements present in milk powder in consonance with green sample preparation.