Chloride determination by ion chromatography in petroleum coke after digestion by microwave-induced combustion

Ion chromatography: A comprehensive review of sample preparation methods for analysis of halogens and allied nonmetals in critically challenging inorganic matrices

The inorganic matrices such as metal concentrates, steel, cement, glass, clay, coal, graphite, rocks and sediments, ores etc. play a pivotal role in infrastructure development, transportation, and energy. The presence of non-metallic elements particularly halogens influence their quality, processing cost, and environment dynamics. The analysis of non-metals in such matrices is critically challenging due to their hardness, rigidity, and non-digestibility. This comprehensive review provides a critical comparison of various sample preparation methods in conjunction with pros and cons of advanced techniques for the detection of non-metals in complex matrices, particularly focusing on ion chromatography. Moreover, the review also addresses the challenges related to the enrichment and automation of non-metals analysis. In addition, the previous literature on non-metals determination in diverse range of inorganic matrices has been tabulated for the first time. These insights are intended to guide researchers, quality control analysts, environmental scientists, and policymakers in enhancing pollution monitoring and control strategies.

Polypyrrole deposited on the core-shell structured nitrogen-doped porous carbon@Ag-MOF for signal amplification detection of chloride ions

An electrochemical platform for signal amplification probing chloride ions (Cl-) is constructed by the composite integrating core-shell structured nitrogen-doped porous carbon@Ag-based metal-organic frameworks (NC@Ag-MOF) with polypyrrole (PPy). It is based on the signal of solid-state AgCl derived from Ag-MOF, since both NC and PPy have good electrical conductivity and promote the electron transport capacity of solid-state AgCl. NC@Ag-MOF was firstly synthesized with NC as the scaffold and then, PPy was anchored on NC@Ag-MOF by chemical polymerization. The composite NC@Ag-MOF-PPy was utilized to modify the electrode, which exhibited a higher peak current and lower peak potential during Ag oxidation compared with those of Ag-MOF and NC@Ag-MOF-modified electrodes. More importantly, in the coexistence of chloride (Cl-) ions in solution, the NC@Ag-MOF-PPy-modified electrode displayed a fairly stable and sharp peak of solid-state AgCl with the peak potentials gradually approaching zero, which might effectively overcome the background interference caused by electroactive substances. The oxidation peak currents of solid-state AgCl increased linearly with the concentration of  Cl- ions in a broad range of 0.15 µM-40 mM and 40-250 mM, with detection limits of 0.10 µM and 40 mM, respectively. The practical applicability for Cl- ions determination was demonstrated using human serum and urine samples. The results suggest that NC@Ag-MOF-PPy composite could be a promising candidate for the construction of the electrochemical sensor.

A highly sensitive, long-time stable Ag/AgCl ultra-micro sensor for in situ monitoring chloride ions inside the crevice using SECM

Tracking the variation of Cl- timely within the crevice is of great significance for comprehending the dynamic mechanism of crevice corrosion. The reported chloride ion selective electrodes are difficult to realize the long-time Cl- detection inside the confined crevice, due to their millimeter size or a relative limited lifespan. For this purpose, an Ag/AgCl ultra-micro sensor (UMS) with a radius of 12.5 μm was fabricated and optimized using laser drawing and electrodeposition techniques. Results show the AgCl film's structure is significantly impacted by the deposited current density, and further affects the linear response, life span and stability of Ag/AgCl UMS. The UMS prepared at current density of 0.1 mA/cm2 for 2 h shows a rapid response (several seconds), excellent stability and reproducibility, strong acid/alkali tolerance, sufficient linearity (R2 > 0.99), and long lifespan (86 days). Moreover, combined with the potentiometric mode of scanning electrochemical microscope (SECM), the Ag/AgCl UMS was successfully applied to monitor the in-situ radial Cl- concentration in micro-regions inside a 100 μm gap of stainless steel. The findings demonstrated that there was obvious radial difference in Cl- concentration inside the crevice, where the fastest rise in Cl- concentration was at the opening. The proposed method which combines the UMS with SECM has attractive practical applications for microzone Cl- monitoring in real time inside crevice. It may further promote the study of other localized corrosion mechanism and the development of microzone ions detection method.

Electrochemical Sensing of Urinary Chloride Ion Concentration for Near Real-Time Monitoring

Urinary chloride concentration is a valuable health metric that can aid in the early detection of serious conditions, such as acid base disorders, acute heart failure, and incidences of acute renal failure in the intensive care unit. Physiologically, urinary chloride levels frequently change and are difficult to measure, involving time-consuming and inconvenient lab testing. Thus, near real-time simple sensors are needed to quickly provide actionable data to inform diagnostic and treatment decisions that affect health outcomes. Here, we introduce a chronopotentiometric sensor that utilizes commercially available screen-printed electrodes to accurately quantify clinically relevant chloride concentrations (5-250 mM) in seconds, with no added reagents or electrode surface modification. Initially, the sensor's performance was optimized through the proper selection of current density at a specific chloride concentration, using electrical response data in conjunction with scanning electron microscopy. We developed a unique swept current density algorithm to resolve the entire clinically relevant chloride concentration range, and the chloride sensors can be reliably reused for chloride concentrations less than 50 mM. Lastly, we explored the impact of pH, temperature, conductivity, and additional ions (i.e., artificial urine) on the sensor signal, in order to determine sensor feasibility in complex biological samples. This study provides a path for further development of a portable, near real-time sensor for the quantification of urinary chloride.

Microbial community and functional prediction during the processing of salt production in a 1000-year-old marine solar saltern of South China

In Hainan Island, South China, a 1000-year-old marine saltern has been identified as an intangible cultural heritage due to its historical complicated salt-making techniques, whereas the knowledge about this saltern is extremely limited. Herein, DNA sequencing and biochemical technologies were applied to determine bacterial and fungal communities of this saltern and their possible functions during four stages of salt-making, i.e. seawater storage, mud solarization, brine concentrating, and solar crystallization. The results showed that both of bacterial and fungal communities were suffered from significant changes during processing of salt-making in Danzhou Ancient Saltern, whereas the richness and diversity of bacterial community dominated by Proteobacteria, Bacteroidota and Cyanobacteria was considerably greater than that of fungal community dominated by Ascomycota, Basidiomycota and Mortierellomycota. Additionally, the succession of bacterial community was closely associated with both of salt physicochemical properties (Na⁺, Cl^-, total phosphorus, total nitrogen, Ca²⁺ and Mg²⁺) and bacteria themselves, whereas fungal community was more closely associated with physicochemical properties than fungi themselves. Importantly, Cyanobium_PCC-6307, Synechococcus_CC9902, Marinobacter, Prevotella and Halomonas as dominant bacterial genera respectively related to the metabolisms of amino acid, carbohydrate, terpenoids/polyketides, lipid and nucleotide were correlated with salt flavors. Saprophytic and saprotroph-symbiotroph fungi dominated by Aspergillus, Mortierella, Amanita, Neocucurbitaria and Tausonia also played core roles in the formation of salt flavors including umami and sweet smells. These findings revealed the highly specified microbiome community in this 1000-year-old saltern that mainly selected by brine solarization on basalt platforms, which is helpful to explore the underlying mechanisms of traditional salt-making techniques and to explore the useful microbes for nowadays food, medicine and chemical industries.

Microwave-induced combustion for petroleum coke digestion: a promising sample preparation strategy for subsequent elemental determination

The increasing demand for the elemental determination of petrochemical samples by inductively coupled plasma techniques requires the development of suitable sample preparation methods that permit high sample throughput and are in accordance with green chemistry recommendations. For this aim, the development of microwave-induced combustion (MIC) method has been attempted to completely digest petroleum coke samples and address quantitative determination of elements, such as Ag, Al, Ba, Ca, Cd, Co, Cu, Fe, Mg, Mn, Mo, Na, Ni, Pb, Sr, V and Zn, by inductively coupled plasma optical emission spectrometry (ICP OES). A sequential procedure to evaluate the sample mass and the solution to retain the analytes quantitatively was first conducted. Satisfactory results were obtained (residual carbon content in final solutions was lower than 0.5%) by digesting 400 mg of samples using 20 bar of oxygen and analytes were quantitatively retained in a dilute acid solution such as 4.2 mol L^-1 HNO₃. An agreement better than 87% was achieved using certified reference materials and the performance of the proposed method was also compared to that of the standard procedure recommended by the American Society of Testing and Materials ASTM D 5600. Despite both methods producing similar results, the proposed method by MIC was much simpler, offered a higher sample throughput and the digests were compatible with ICP OES measurements avoiding interferences in the determination step compared the ASTM D 5600 method. These results clearly demonstrated that the proposed MIC method in combination with ICP OES could be a promising alternative to obtain quantitative information about the elemental composition of petroleum coke.

Comparison of analytical methods for measuring chloride content in crude oil

Although chloride compounds are the main cause of corrosion damage in distillation unit, standard methods to determine them do not guarantee good results. In this study, the chloride concentration of different crude oils was measured using different techniques and the results were compared. ASTM D3230, D4929 as standard methods, XRF as alternative technique and Neutron Activation Analysis as reference method, were applied. It is concluded that XRF method is an effective technique for measuring the chloride concentration of oils.

A solid sampling approach for direct determination of Cl and S in flour by an elemental analyzer

Direct analysis of flour was proposed for the determination of Cl and S by an elemental analyzer for the first time. The main operational conditions of the direct solid sampling elemental analysis (DSS-EA) were optimized and calibrated by standard solutions, rather than by certified reference material (CRM). Accuracy was evaluated by the analysis of CRM of rice flour and by comparison with analyte determination by independent techniques, i.e., ion chromatography and inductively coupled plasma optical emission spectrometry; both were carried out after microwave-induced combustion. Sample mass from 0.5 to 260 mg was used and limits of quantification of 1.2 µg g^-1 for Cl and 0.2 µg g^-1 for S were achieved. Wheat, whole wheat, potato and corn flour were analyzed by DSS-EA. Concentrations of Cl and S ranged from 4.8 to 685 µg g^-1 and from 13 to 1328 µg g^-1, respectively.

Improved Chloride Ion Sensing Performance of Flexible Ag-NPs/AgCl Electrode Sensor Using Cu-BTC as an Effective Adsorption Layer

We designed the flexible chloride ion selective sensor that directly monitors electrochemical reactions of chloride ions without using a reference electrode. A flexible polytetrafluoroethylene (PTFE) substrate was utilized to provide bendability to the fabricated sensor. As an ion selective material, Ag nanoparticles were employed on the MWCNTs loaded on the PTFE substrate. Enhanced adsorption property of the fabricated sensor toward the chloride ions was given by incorporation of hydrophilic copper benzene-1,3,5-tricarboxylate (Cu-BTC) with great flexibility and stability. Accordingly, compared to the bare sensor the sensing performance of the Cu-BTC treated Ag NPs/AgCl electrode sensor was improved by indicating the decrease in response and recovery time about 4 times. It elucidated that the Cu-BTC layer could work as an effective medium between the Ag-NPs surface and electrolyte containing chloride ions. As a result of contact angle measurement, the hydrophilicity much increased in the Cu-BTC treated sensor because the exposed surface of the sensor not treated by the Cu-BTC largely consisted of hydrophobic MWCNTs. Furthermore, the Cu-BTC layer could hold the electrolyte for effective adsorption of analytes with large specific surface area.

Development of a selective chloride sensing platform using a screen-printed platinum electrode

A new and selective voltammetric method for chloride determination is proposed, based on platinum and chloride interactions. A screen-printed platinum electrode (SPPtE) functions as a sensing platform, which promotes the formation of chloro-adsorbed species on the electrode surface, acting as an effective means of anion-determination in several matrices. The pretreatment of the SPPtE and careful control of the cathodic stripping voltammetric parameters yielded a well-defined electrochemical signal. This cathodic peak was due to the adsorption of chlorine, which had previously been oxidized from chloride anions in the initial anodic deposition step. It offers a simple, low-cost, fast, reproducible (RSD < 6%) and precise method for selective chloride determination, with limit of detection of 0.76 mM, and a sensitivity of - 24.147 µA mM ^-1 for a broad determination range of up to 150 mM. Chloride determination was correctly performed with single drops of environmental, pharmaceutical and food samples. In addition, the sensor was successfully adapted as a flexible screen-printed platinum electrode sensor using Gore-Tex^® as support for printing.

Microwave-induced combustion: towards a robust and predictable sample preparation method

Ideal gas equation was used as a tool for calculating the stoichiometric amount of O₂ for efficient sample digestion using MIC method.

Analytical methods for the determination of halogens in bioanalytical sciences: a review

Fluorine, chlorine, bromine, and iodine have been studied in biological samples and other related matrices owing to the need to understand the biochemical effects in living organisms. In this review, the works published in last 20 years are covered, and the main topics related to sample preparation methods and analytical techniques commonly used for fluorine, chlorine, bromine, and iodine determination in biological samples, food, drugs, and plants used as food or with medical applications are discussed. The commonest sample preparation methods, as extraction and decomposition using combustion and pyrohydrolysis, are reviewed, as well as spectrometric and electroanalytical techniques, spectrophotometry, total reflection X-ray fluorescence, neutron activation analysis, and separation systems using chromatography and electrophoresis. On this aspect, the main analytical challenges and drawbacks are highlighted. A discussion related to the availability of certified reference materials for evaluation of accuracy is also included, as well as a discussion of the official methods used as references for the determination of halogens in the samples covered in this review.

Total sulfur determination in residues of crude oil distillation using FT-IR/ATR and variable selection methods

Total sulfur concentration was determined in atmospheric residue (AR) and vacuum residue (VR) samples obtained from petroleum distillation process by Fourier transform infrared spectroscopy with attenuated total reflectance (FT-IR/ATR) in association with chemometric methods. Calibration and prediction set consisted of 40 and 20 samples, respectively. Calibration models were developed using two variable selection models: interval partial least squares (iPLS) and synergy interval partial least squares (siPLS). Different treatments and pre-processing steps were also evaluated for the development of models. The pre-treatment based on multiplicative scatter correction (MSC) and the mean centered data were selected for models construction. The use of siPLS as variable selection method provided a model with root mean square error of prediction (RMSEP) values significantly better than those obtained by PLS model using all variables. The best model was obtained using siPLS algorithm with spectra divided in 20 intervals and combinations of 3 intervals (911-824, 823-736 and 737-650 cm(-1)). This model produced a RMSECV of 400 mg kg(-1) S and RMSEP of 420 mg kg(-1) S, showing a correlation coefficient of 0.990.

Determination of total organic halogen (TOX) in humic acids after microwave-induced combustion

Chemically chlorinated organic matter as well as natural background humic acids contain significant amounts of organically bound halogens that must be determined for assessment of environmental pollution. In this work the use of ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) is proposed for the determination of total organic Cl, Br and I concentration in humic acids extracted from various forest soil horizons after a single digestion by microwave-induced combustion (MIC). Samples were pressed as pellets and combusted using 20 bar of oxygen and ammonium nitrate solution as igniter. Analytes were absorbed in diluted alkaline solution (50mM (NH(4))(2)CO(3)) and a reflux step was applied after combustion to improve analyte recoveries (5 min, microwave power of 1400W). The accuracy was evaluated using certified reference materials (CRM) and spiked samples. Using MIC the agreement with CRM values and spike recoveries was higher than 97% for all analytes. As an advantage over conventional procedures, using MIC it was possible to digest up to eight samples in only 25 min, obtaining a single solution suitable for all halogens determination in humic acids samples by different techniques (IC and ICP-MS). The limit of detection (3σ) for Cl, Br and I obtained by IC was 1.2, 2.5 and 4.3μgg(-1) and by ICP-MS it was 1.4, 0.03 and 0.002μgg(-1), respectively.

Heavy crude oil sample preparation by pyrohydrolysis for further determination

In this work, a method for chlorine determination in heavy crude oil using pyrohydrolysis for sample decomposition was developed. Chlorine was determined using ion chromatography (IC), inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry. In this case an ICP-MS spectrometer equipped with a dynamic reaction cell (DRC-ICP-MS) was used. Heavy crude oil samples were homogenized and placed on a quartz holder, which was then introduced into the pyrohydrolysis apparatus. Nitric acid (0.2 mL) was used to assist the decomposition of the sample. Solutions with different concentrations of ammonium hydroxide were evaluated to collect the volatile chloride produced using pyrohydrolysis. A 0.75 mol L-1 ammonium hydroxide solution was chosen in view of the better accuracy achieved. Best precision and accuracy were obtained by heating the sample for 10 min up to 1000 °C. The limits of quantification (LOQs, 10σ) of chlorine measured by IC, ICP OES and DRC-ICP-MS were 4.5, 48 and 3.6 µg g-1, respectively. A sample amount of 300 mg and final volume of 20 mL were taken into account to calculate the LOQs. The relative standard deviation (RSD) was lower than 5% (4 replicates). Accuracy was evaluated by analysis of certified reference material (NIST 1634c) and comparison with the results obtained using the ASTM D6470 method. In both cases the results obtained using pyrohydrolysis were in agreement. The proposed method was suitable for heavy crude oil decomposition and chlorine determination by IC, ICP OES and DRC-ICP-MS. Three samples per hour can be processed using a simple and low-cost pyrohydrolysis apparatus. The pyrohydrolysis procedure is easy to perform, which is very attractive for routine analysis of crude oil, a very complex matrix. According to the authors' knowledge this is the first application of pyrohydrolysis for heavy crude oil sample preparation.

Fast digestion procedure for determination of catalyst residues in La- and Ni-based carbon nanotubes

A procedure based on microwave-induced combustion (MIC) was applied for carbon nanotube (CNT) digestion and further determination of La and Ni by inductively coupled plasma optical emission spectrometry (ICP OES). Samples (up to 400 mg) were completely combusted at 20 bar of oxygen, and a reflux step was applied to improve the analyte absorption. Combustion was finished in less than 50 s, and analytes were absorbed in diluted acid solution. Absorbing solutions ranging from 1 to 12 mol L(-1) for HCl and from 1 to 14 mol L(-1) HNO(3) were tested. Accuracy for both analytes was evaluated using certified reference materials and analyte spikes. Neutron activation analysis was also used to check accuracy for La. Agreement was better than 96% for La and Ni using a 4 mol L(-1) absorbing solution of HNO(3) or HCl and 15 min of reflux. The residual carbon content was lower than 0.5%. Up to eight samples could be digested simultaneously in 36 min, that makes the throughput using MIC more suitable when it is compared to the digestion by dry ashing as recommended by other procedures. The obtained limits of detection using MIC were lower than those using dry ashing, and a single absorbing solution, e.g., diluted HNO(3), can be used for simultaneous determination of La and Ni by ICP OES.