ICP Spectroscopy Research Articles

Analysis of Toxic Element with Icp-Oes and Libs Methods in Marine Sediments Around the Sea of Marmara in Kapidağ Peninsula

In this work, the LIBS (Laser Induced Breakdown Spectroscopy) and ICP-OES technique has been applied to the determination of total contents of heavy metals (Fe, Zn, Al, Mn, Co, Cr, Cu, Ni, Na, Mg, K, Ca) in soil samples of Marmara Sea. In order to validate the technique, LIBS data were compared with data obtained on the same soil samples by application of conventional Inductively Coupled Plasma ICP spectroscopy. The partial agreement obtained between the two sets of data suggested the potential applicability of the LIBS technique to the measurement of heavy metals in soils. According to the results, it was seen that the elements determined by ICP-OES analysis were also determined by LIBS method. The LIBS method is an important and practical technique for determining the elements that are enriched with anthropogenic factors as well as the elements resulting from natural processes.

Facile preparation of palladium catalyst supported on silica nanoparticles through CS2 plasma pretreatment: Application to the Heck reaction for vinyl monomers and π-conjugated polymer synthesis

The preparation of a recyclable palladium complex supported on coated silica nanoparticles (SiNP) and its effectiveness as a catalyst in the Heck reaction is described. Functionalized silica-based NP were synthesized in three steps. First, commercial SiNP were subjected to a CS2 cold plasma. Thus, a thin coating film was formed, along with the creation of a thiol functional surface. Subsequently, a thiol-ene reaction with 2-vinylpyridine induced by AIBN produced (Py)-CH2-CH2S covalently bonded to the SiNP, which after PdCl2(CH3CN)2, ligand exchange afforded the corresponding palladium complex catalyst (Pd-SiNP). Functionalized Pd-SiNP were characterized by SEM, ICP, and XPS spectroscopy. The SiNP were straightforwardly converted to an effective palladium catalyst applicable in a number of Heck cross-coupling reactions with iodobenzene (IBz) and a variety of vinyls. Indeed, such heterogeneous catalyst probed to be recyclable (up to 9 times). Nevertheless, leaching of metal was evidenced by TEM, HRTEM, XRD, and XPS. Furthermore, due to the outstanding results, we extended the use of the new heterogeneous catalyst to achieve the synthesis of a soluble phenylenevinylene type (PPV) copolymer from 1,4-bis(dodecyloxy)-2,5-diiodobenzene and p-divinylbenzene (DVB).

Evaluation and efficacy of metal oxides in terms of antibacterial activity and toxic chemical degradation

Inorganic metal oxides Ag2O, CuO and ZnO were examined using SEM, XRD, TGA and ICP spectroscopy to analyze their structures and physical properties in terms of resistance to germs and toxic chemicals. Zone of inhibition testing and the plate-counting method were used in this study to examine the antibacterial activities of the metal oxides against Gram-negative Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa), and Gram-positive Staphylococcus aureus (S. aureus) and Bacillus subtilis (B. subtilis). Furthermore, 2‑chloro‑ethyl ethyl sulfide (2‑CEES) was used to study the degradation efficacy of the metal oxides by the NMR method. The objective of the study was to develop and evaluate metal oxides that are able to protect against chemical and biological warfare agents. Excellent antibacterial and catalytic toxic chemical degradation properties were obtained.

Synthesis of M (M=Co2+, Co2+/Ni2+)-doped FeS2 Nanospheres with Enhanced Visible-light-induced Photocatalytic Activity

Nano-spherical Co2+-doped FeS2 was synthesized through a simple solvothermal method. The products were investigated using XRD, FE-SEM, BET, ICP, EDS, TEM, HRTEM, XPS, and UV-vis spectroscopy. The results indicated that Co2+ ion could change the particle nucleation process and inhibited the particle growth of FeS2. In addition, when the content of doped Co2+ was 15%, the degradation efficiency of methylene blue (MB) achieved 60.72% after 210 min irradiation, which increased by 52.01% than that of the undoped FeS2. Moreover, comparison experiments also demonstrated that the M (M=Co2+, Co2+/Ni2+)-doped FeS2 photocatalytic activity efficiency sequence was Co2+ > Ni2+>Co2+/Ni2+. This is ascribed to the fact that the Co2+ doping could induce the absorption edge shifting into the visible-light region and increased the surface area of the samples. The effect mechanisms of M-doping on the band gap and the photocatalytic activity of FeS2 were also discussed.

A novel tetrazole functionalized polymer-supported palladium nano-catalyst for the synthesis of various N-benzylated arylcyanamides

4-(Benzyloxy)benzyl chloride polymer-bound (BBC-Polym) was functionalized with 1-phenyl-1H-tetrazole-5-thiol (PTT), and the corresponding novel nano-particle Pd catalyst prepared by the subsequent addition of PdCl2 (BBC-Polym@PTT@Pd). The Pd catalyst was characterized using powder XRD, SEM, EDX, ICP, TGA-DTA, and FT-IR spectroscopy. Then, the Pd catalyst was used as an efficient heterogeneous catalyst for the synthesis of various N-benzylated arylcyanamides at 60 °C in acetonitrile.

Nitrate-intercalated Mg 1−x Al x -Layered Double Hydroxides with different layer charges ( x ): Preparation, characterization, and study by impedance spectroscopy

Three phases of nitrate-intercalated Layered Double Hydroxides (LDH), based on magnesium and aluminum with different layer charges (x) (x = 0.2, 0.25 and 0.33), were synthesized by coprecipitation method, characterized by XRD, TGA, FTIR and analyzed by ICP and Impedance Spectroscopy. In this work, layer charge was found to have a strong influence on the lattice parameters, nitrate disposition, vibration bonds, thermal stability and particularly, electrical and dielectric properties that were investigated at room temperature under dry and wet air trough impedance spectroscopy. In fact, under dry air, electrical modeling showed three contributions attributed to the polarization of grains, grain boundary and electrode-sample interface, respectively, which were brought out by the frequency dependence of the imaginary part of complex modulus and complex impedance, the parameters of electrical equivalent circuit were determined and their dependence on the layer charge was also discussed. Ionic conductivity was found to depend on the layer charge and polarizing power, to follow double power law, and to show an increase of values about three orders of magnitude under wet air. Moreover, the dependence of dielectric constant and that of dielectric loss tangent on the layer charge and frequency were also presented and discussed.

Pure, lithium- or magnesium-doped ferroelectric single crystals of Ca9Y(VO4)7: cation arrangements and phase transitions

Abstract Single crystals of Ca9Y(VO4)7 (1), Ca9Y(VO4)7:Li+ (2) and Ca9Y(VO4)7:Mg2+ (3) were grown by the Czochralski method. Their chemical composition was analyzed by ICP spectroscopy and their crystal structure was examined by single crystal X-ray analysis. The crystals are characterized by trigonal symmetry, space group R3c. Hexagonal unit-cell parameters are as follows: a=10.8552(1) Å, c=38.0373(2) Å, V=3881.65(1) Å3 for 1; a=10.8570(1) Å, c=38.0161(3) Å, V=3880.77(4) Å3 for 2; a=10.8465(1) Å, c=38.0366(2) Å, V=3875.36(3) Å3 for 3. All crystals are characterized by β-Ca3(PO4)2-type structure with statistical distribution of Ca2+ and Y3+ over M1, M2 and M5 sites in different ratios and with completely empty M4-cationsite. The impurity of Mg2+cations in structure 2 has been detected in octahedral M5 site. Ferroelectric phase transitions are evidenced by DSC and SHG. At about 1220 and 1300 K, they demonstrate phase transitions. Upon heating the symmetry of the crystal structure changes according to the scheme R3c→R3̅c→R3̅m and is restored during consequent cooling. The first of them is of ferroelectric and the second of non-ferroelectric nature. Even a small amount of impurities in Ca9Y(VO4)7 structure is accompanied by a noticeable decrease in the temperature of the ferroelectric-paraelectric phase transition.

Recovery of Macro and Micro-Nutrients by Hydrothermal Carbonization of Septage.

In this study, septic tank waste (i.e., septage) was hydrothermally carbonized (HTC) in order to recover macro and micronutrients, while tracking the fate of residual heavy metals. Three different HTC temperatures (i.e., 180, 220, and 260 °C) at autogenous pressures and two reaction times (i.e., 30 and 120 min) were applied on both solid and liquid septages. Hydrochar and HTC process liquids were characterized using ICP, CHNS, and UV-vis spectroscopy. Treatment at 260 °C for 120 min maximized ammonia recovery, producing a liquid with 1400 mg/L of ammonia. Overall, about 70% of available nitrogen ended up in the liquid phase as nitrate or ammonia. Solid hydrochars show potential for fertilizer use, with high phosphorus content of 100-130 kg/tonne. It was found that heavy metals mainly remained in the solid phase, although the concentrations of heavy metals are mostly lower than U.S. EPA regulation for biosolids with the exception of selenium.

Synthesis and study of the structure, magnetic, optical and methane gas sensing properties of cobalt doped zinc oxide microstructures

Undoped and Cobalt (Co) doped zinc oxide (ZnO & CZx) nanoparticles were synthesized by Solvothermal method. The samples were studied by X-Ray Diffraction (XRD), Energy Dispersive X-ray Spectroscopy (EDS), Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), UV–Vis spectroscopy and Scanning and Transmission Electron Microscopy (SEM & TEM). Moreover the gas sensing properties of the nanoparticles for methane gas took place. Purity of the samples and Co concentration was investigated by EDS and ICP spectroscopy respectively. XRD results described the hexagonal wurtzite structure for all the samples in which crystallinity and the crystallites size decreased with increase of Co doping level. Using UV–Vis spectroscopy the band gap energy was evaluated and redshift of band gap energy was observed by increasing of Co concentration. SEM images demonstrated that nanoparticles were agglomerated with increase of Co doping level. TEM images revealed the nanoparticles size in the range 11–44 nm. Methane sensing properties was enhanced after Co doping of the ZnO nanoparticles for Co concentration up to 4%.

Electrochromic WO3 Films with Controlled High-Rate Deposition By Hollow Cathode Gas Flow Sputtering

An amorphous WO3 is one of the most important materials for electrochromic (EC) devices because of its blue coloration caused by electron injection. For the industrial applications including EC smart windows, there are strong demands for EC devices to be produced with a high deposition rate, with a higher stability and at lower costs. Gas flow sputtering (GFS) has the possibility for very high deposition rate because of using high density hollow cathode discharge and a large amount of sputtering gas (Ar) flow and the stability of the reactive sputtering process in the wide range of the reactive gas (O2) flow, so there is no “transition region” which should appear in the conventional reactive sputtering processes. In this study, reactive GFS was adopted to deposit amorphous WO3 films with the high EC properties with the high deposition rate. WO3 films were deposited on unheated ITO-coated glass substrate by GFS using two W metal targets which were mounted parallel with each other. Sputtering power was fixed at 1000 W. Ar and O2 flows were 5.0 slm and 10-125 sccm, respectively. Total gas pressures during the depositions were 70 Pa and 90 Pa. X-ray diffraction measurements showed that the all films were amorphous. The density of WO3 films were estimated from data measured by X-ray fluorescence and ICP spectroscopy. The films were electrochemically intercalated with protons and lithium ions. The deposition rates were almost constant with O2 flow during depositions. Figure shows the coloration efficiency of proton intercalated WO3 films as a function of O2 flow during depositions. The coloration efficiency had a tendency to decrease with increasing O2 flow during depositions. [1] N. Oka, Y. Shigesato, et al., Thin Solid Films 532, 1-6 (2013). Figure 1

Study on the oxidation transformation of diethylamine in a confined region of ZSM-22

ZSM-22 zeolite has been synthesized using diethylamine (DEA) as structure directing agent. The crystal obtained was characterized by XRD, IR, TG/DTA, elemental analysis, ICP and 13C MAS NMR spectroscopy. It is found that DEA is incorporated intact in its protonated form in TON. Furthermore, the oxidation of DEA restricted in the TON by H2O2 and HIO4 has been studied. Based on the IR, TG/DTA, EA and 13C NMR spectra data, it has been found that the oxidation products were saturated hydrocarbons and some other amines by H2O2, whereas saturated hydrocarbons, other amines and ethyleneimine produced by HIO4. These oxidation products are different from the bulk reaction. This work opens new opportunities for further research of molecular reactions on the inorganic hybrids.

Dehydration of fructose and glucose to 5-hydroxymethylfurfural over Al-KCC-1 silica

In this research, the influence of several factors such as reaction time, catalyst weight, temperature and different solvents on dehydration reaction of fructose and glucose to 5-hydroxymethylfurfural (HMF) was surveyed. Nanosphere Al-KCC-1 silica with fibrous morphology was manufactured and used as proficient and recyclable catalyst for this reaction. SEM, TEM, BET, XRD, EDX, elemental mapping, ICP and FT-IR spectroscopy methods were applied for characterization of the Al-KCC-1 (molar ratio Si/Al= 5, 40) catalysts. 162°C and 1h are the best conditions for the fructose dehydration. Under this situation HMF yield and selectivity are 92.9% and 94.5% respectively and fructose conversion is 98.4%. Also 170°C and 2h are the best conditions for the glucose dehydration. In this situation HMF yield and selectivity are 39.0% and 39.9% respectively and glucose conversion is 97.8%.

Enhancement of hydrogen storage on multi-walled carbon nanotube through KOH activation and nickel nanoparticle deposition

Hydrogen uptake of multi-walled carbon nanotube (MWCNT) was enhanced via a two-step activation/deposition process. At the rst step, MWCNT was chemically activated by KOH. The hydrogen uptake of the activated MWCNT was considerably higher than the pristine one. The BET analysis of the activated MWCNT demonstrateda great improvement in its textural properties compared to the pristine MWCNT. This was attributed to the defects generated on its external surface during activation process as evidenced by Raman and SEM analyses. At the second step, electroless deposition technique without any surface pretreatment was employed for preparation of Ni-MWCNT composite. The successful deposition of nickel into the activated MWCNT was approved by the EDS analysis and its amount was determined by ICP spectroscopy which was 2.8 wt.%with respect to Ni available in the electroless deposition bath. The maximum H2 storage capacity achieved by Ni doped MWCNT sample was  1 wt.% at 288 K and 45 bar.

Controlling calcium and phosphate ion release of 3D printed bioactive ceramic scaffolds: An in vitro study

This paper characterizes in an in vitro setting the release of calcium (Ca) and phosphate (PO4) of 3D printed bioactive ceramic scaffold prepared from extrudable paste containing hydroxyapatite and β-tricalcium phosphate (β-TCP). Hydroxyapatite and β-TCP were calcined at 800 °C for 11 h, fabricated into four experimental groups (100% HA, 100% β-TCP, 15%/85% HA/β-TCP, and 15%/85% HA/β-TCP (design)), sintered to 1100 °C for 4 h. Calcium and phosphorus concentrations were evaluated using ICP spectroscopy, and the release of Ca and PO4 ions during dissolution of the CaP-based scaffolds was measured by submerging in 0.05 mol/L Tris(hydroxymethyl)aminomethane-HCl and maintaining a temperature of 37 °C. The Ca and PO4 concentrations of the solutions were measured with the utilization of a calcium assay kit and a phosphate assay kit and read in a UV–visible spectrophotometer. The 100% HA scaffold group showed the greatest concentration of Ca ions (~1.9 mg/dL), but ultimately released at a lower amount as time increased; the 100% HA scaffold also showed the lowest total amount of calcium ions released over the course of evaluation. The results for the 100% β-TCP were on the opposite of the HA with the highest amount of calcium ion release over the study. While the PO4 ion release showed a similar trend as those observed with Ca ions with an apparent difference in the 100% HA scaffold group. There was nearly 0 mg/dL of the phosphate ions released in the first 24 h, in comparison to the amount of Ca ions released during the same time frame. Since various formulations can lead to different properties of these bioactive ceramic scaffolds, it is important to understand how the tailoring of this important biphasic material can impact the long-term outcome of an ever-important in vivo clinical trial in the future.

Evaluation of new biodegradable fluid on the basis of accelerated durability test, FTIR and ICP spectroscopy

The paper deals with the properties of newly developed synthetic biodegradable fluid in terms of its operational and physico-chemical properties. The evaluated fluid is a new biodegradable fluid MOL Farm UTTO Synt, which belongs to the group of universal gear-hydraulic fluids. At the beginning, the fluid was subjected to accelerated durability test under laboratory conditions, with monitoring its impact on technical conditions of the used hydraulic pump UD 25. After that, the FTIR spectroscopy analysis was performed, with monitoring thermal oxidation, oxidation by acid products, water content and additives depletion. Depletion of additives was also monitored by the ICP spectroscopy. Based on these results, it can be stated that the newly developed fluid has good operational and physico-chemical properties after the durability test and is suitable for further testing under operational conditions without a risk of damaging agricultural machines.

Nanostructured polysaccharidic microcapsules for intracellular release of cisplatin

Carbohydrate polimeric microcapsules were assembled using a LbL approach onto a CaCO3 core. The microcapsules were used to delivery the anticancer drug cisplatin into HeLa and MCF-7 cancer cell lines. Drug encapsulation, measured by ICP spectroscopy, was around 50% of the charging solution. Fluorimetric measurements showed an efficient cellular uptake of polysacchardic microcapsules in both cell lines. The drug-loaded capsules demonstrated a better efficiency against cell viability than the free drug. Specifically, the amount of platinum reaching genomic DNA was measured, showing that encapsulation improves the nuclear delivery of the drug for both cell lines.

469 - Implications of Altered Trace Minerals and Iron Trafficking Proteins on Oxidant Stress in Thalassemia

Thalassemia (THAL) patients have a genetic anemia causing incomplete erythropoiesis and iron overload, possibly leading to cardiomyopathy and diabetes. Plasma zinc (Zn) and Copper (Cu) deficiency are also observed in some patients with THAL, however, these effects are not as well characterized. It has been suggested that oxidative stress can be caused by increased labile plasma iron (LPI), and decreased serum Zn and Cu levels, however this is unproven. LPI can initiate peroxidation releasing malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE). Thus, we hypothesized that that a functional Zn or Cu deficiency can increase oxidative stress and that changes in the levels of key iron trafficking proteins, such as soluble transferrin receptor (sTfR) or hemopexin (HPX) would also affect oxidative stress. 39 subjects with informed consent were enrolled (29 patients with THAL and 10 healthy controls). LPI was measured using dihydrorhodamine 123. Both MDA and 4-HNE were measured using N-methyl-2-phenylindole. Iron trafficking proteins were measured by MRM mass spectrometry. Trace mineral levels were assessed by ICP spectroscopy. Plasma levels of the iron trafficking proteins, transferrin, HPX and haptoglobin (HAP) were all decreased in THAL patients (P

Germanium separation and purification by leaching and precipitation

In this research work, extraction and purification of germanium from zinc leach residues (ZLR) were investigated. The results of ICP, XRF, and atomic adsorption spectroscopy (AAS) tests show that contents of germanium, iron, lead, and zinc within the leaching residue were 105×10−6, 3.53%, 10.35%, and 8.8%, respectively. XRD results indicate that the main minerals were in different forms of sulfates (CaSO4·2H2O, PbSO4 and ZnSO4·6H2O), silicate (SiO2), and oxide (Fe2O3). Dissolution of leaching filter cake was carried out using 5 parameters and each in 4 levels (acid concentration, temperature, time, liquid-to-solid ratio, and stirring speed) by Taguchi method (L16), and then optimization of the effective parameters by response surface method. Under optimum conditions, zinc and germanium dissolution efficiencies were 88.71% and 8%, respectively. Leaching tests with sulfuric acid (added di-ammonium oxalate monohydrate) and hydrochloric acid (HCl) on the residues obtained from previous-stage sulfuric acid dissolution, yielded germanium and iron recoveries of 83%, 88%, 40%, and 90%, respectively. Thus, leaching experiment with sulfuric acid (added di-ammonium oxalate monohydrate) was superior to that with hydrochloric acid due to high and low extraction amounts of germanium and iron, respectively. Precipitation experiments revealed that germanium purification with tannic acid presented a better result compared to sodium hydroxide and ammonia. Under optimum conditions, contents of germanium and iron in the solution after precipitation were 0.1505% and 14.7% with precipitation yields of 91% and 52%, respectively.

Bulk Composition of Mt. Mica Pegmatite, Maine, USA: Implications For the Origin of An Lct Type Pegmatite By Anatexis

Abstract The Mt. Mica pegmatite is famous for producing gem tourmaline for nearly 200 years. The dike, ranging in thickness from 1 to 8 m and dipping 20° SE, has a simple zonal structure consisting of a wall zone and core zone. The wall zone is essentially devoid of K-feldspar. The outer portion of the pegmatite consists of quartz, muscovite, albite (An 1.8), and schorl. Muscovite is the dominant K-bearing species in the outer portion of the pegmatite. Potassium feldspar only appears in the core zone adjacent to pockets. The pegmatite is subparallel to the foliation of the enclosing migmatite, and leucosomes show a gradational contact with the pegmatite where juxtaposed. Texturally, the pegmatite and leucosomes appear to be in equilibrium with no change in grain size or composition where the two are in contact. Garnet-biotite thermometry of the migmatite at the contact yields an average temperature of 630 °C, which is consistent with the pressure-temperature conditions inferred for a Sebago Migmatite Domain (SMD) assemblage of sillimanite, quartz, muscovite, biotite, and alkali feldspar formed at 650 °C and 3 kb. Gradational contact between the leucosomes and pegmatite suggests that the pegmatitic melt was at the same temperature. Coromoto Minerals LLC began mining in 2003 and the mine now extends down-dip for over 100 m to a depth of 33 m. A very detailed and accurately surveyed geologic map produced by owner/operator Gary Freeman during mining shows the total area of pegmatite removed, the spatial distribution and aerial extent of pockets, massive lepidolite (compositions near trilithionite) pods, microcline, and xenoliths. The map was analyzed using image analysis and thickness values of the units to calculate the total volumes of pegmatite mined, lepidolite pods, and all pockets found. Forty-five drill cores were taken across the pegmatite from the hanging wall to foot wall contacts, along a transect intentionally avoiding lepidolite pods and miaroles. Cores were pulverized, thoroughly mixed and homogenized, and the percent Li content calculated from the mapped volume was added to produce a sample that was representative of the bulk composition of Mt. Mica. The sample was then analyzed by fusion ICP spectroscopy for major and trace elements and DCP spectroscopy for B and Li. Structural water was determined by LOI. Water content was calculated using the calculated volume of open space (pocket volumes), assuming that the pockets were filled with water-rich fluid. This fluid content was added to LOI water (above 500 °C) to estimate a maximum H 2 O content of 1.16 wt.% of the pegmatite melt. REE plots of bulk pegmatite versus leucosomes from the migmatite are strikingly similar. Chondrite-normalized REE patterns of leucosomes and pegmatite are very flat with no Eu anomaly, whereas the Sebago granite is more strongly LREE-enriched and displays a pronounced negative Eu anomaly. Spider diagrams of leucosomes and pegmatite versus average crust show very similar patterns. These results suggest that the Mt. Mica pegmatitic melt did not form by fractional crystallization of the older Sebago pluton, but instead was derived directly from partial melting of the metapelitic rocks of the SMD. Batches of anatectic melt accumulated and coalesced into a larger volume that subsequently formed the pegmatite. This is the first chemical evidence presented for the formation of an LCT type pegmatite by direct anatexis.

Preparation and characterization of single phase, biphasic and triphasic calcium phosphate whisker-like fibers by homogenous precipitation using urea

Whisker-like calcium phosphate fibers were prepared by a homogenous precipitation method under refluxing conditions in solutions with a Ca/P molar ratio of 1.67 at 90°C and pH 3.0 using urea as additive. The precipitates were characterized by XRD, FTIR, SEM, and FE-SEM. The ICP spectroscopy and elemental analyzer were used to determine Ca/P ratio and carbonate content of products, respectively. The results indicate that the morphology and structural characteristics of the precipitates depend on the urea concentration and reaction time. Whisker-like biphasic monetite/hydroxyapatite (HA) fibers with a mean length of 60µm and a mean width of 1.0µm were obtained with the use of a low concentration of urea. Calcination of the biphasic calcium phosphate at 800°C led to the formation of a triphasic mixture of HA/whitlockite (β-TCP)/calcium pyrophosphate (CPP) with a whisker-like morphology. The use of a higher concentration of urea was caused to form a mixed morphology of spherulites/whisker-like fibers consisting of octacalcium phosphate (OCP) and HA phases. When the reaction time was increased to 10 days, both the above biphasic calcium phosphates transformed to a single phase HA which its morphology and growth pattern were similar to those of a whisker, according to FE-SEM images. The HA whiskers produced by a lower amount of urea had a lower carbonate content compared to those obtained using a higher urea concentration.