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Article

Centrifuge-Less Mixed Micelle-Mediated Cloud Point Extraction-Spectrophotometric Determination of Vanadium Using 4-Nitrocatechol and Cetylpyridinium Chloride

by
Andrea Gajdošová
1,
Petya Racheva
2,
Denitsa Kiradzhiyska
2,
Vidka Divarova
2,
Antoaneta Saravanska
2,
Jana Šandrejová
1 and
Kiril Gavazov
2,*
1
Department of Analytical Chemistry, Institute of Chemistry, Pavol Jozef Šafárik University in Košice, SK-04154 Košice, Slovakia
2
Department of Chemical Sciences, Faculty of Pharmacy, Medical University of Plovdiv, 120 Buxton Bros Str., 4004 Plovdiv, Bulgaria
*
Author to whom correspondence should be addressed.
Int. J. Mol. Sci. 2025, 26(12), 5808; https://doi.org/10.3390/ijms26125808
Submission received: 31 May 2025 / Revised: 13 June 2025 / Accepted: 16 June 2025 / Published: 17 June 2025
(This article belongs to the Special Issue Molecular Mechanisms and Applications of Spectrophotometric Determination)
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Versions Notes

Abstract

A novel, environmentally friendly cloud point extraction (CPE) method based on 4-nitrocatechol (H2L) was developed in this study to spectrophotometrically determine trace vanadium. This method utilizes a mixed micelle-mediated system comprising a cationic surfactant (cetylpyridinium chloride, CPC) and a nonionic surfactant (Triton X-114). In contrast to conventional CPE, the present approach does not employ centrifugation to separate the two phases. The distinguishing characteristic of the extracted species, (CP+)[VVOL2], is its ability to absorb light across the entire visible spectrum. The measurement at 670 nm, where the complex displays a local maximum, is advantageous for two primary reasons. Firstly, the blank exhibits virtually no absorption, a property that engenders stable and reproducible results. Secondly, selectivity is high because almost all other metal complexes have absorption bands at shorter wavelengths. The proposed method has the following characteristics: a linear range of 2–305 ng mL−1, a limit of detection of 0.6 ng mL−1, a molar absorptivity coefficient of 1.22 × 105 M−1 cm−1, a Sandell sensitivity of 0.42 ng cm−2, and a blue applicability grade index (BAGI) of 67.5. Its efficacy was demonstrated in the analysis of mineral water, a spent vanadium-containing catalyst, and a dietary supplement.

1. Introduction

Vanadium is a dispersed trace element identified in 283 minerals [1], with an average content of 97 μg g−1 in the upper continental crust [2]. It is essential for various terrestrial and aquatic organisms and is considered the second most abundant transition metal in seawater [3]. Vanadium’s entry into the biosphere occurs through natural processes and anthropogenic (human-related) activities such as the combustion of fossil fuels, oil refinement, mining, ore processing, sulfuric acid production, agricultural chemicalization, and the manufacturing and utilization of various materials (steel, rubber, plastics, textiles, and paper). A notable increase in its Anthropogenic Enrichment Factor (AEF), a metric used in environmental and pollution studies, has been observed in recent years [4,5,6]. Given the toxic properties of its most common oxidation state (+V), the element is appropriately characterized as a “re-emerging environmental hazard” that we must address [6].
From another perspective, it has been demonstrated that vanadium exerts beneficial effects on human health. Vanadium-containing compounds are commercially available as dietary supplements for bodybuilders and athletes [7,8]. A substantial body of research has proven its efficacy in enhancing glucose metabolism in patients diagnosed with type 2 diabetes [9,10]. Vanadium has demonstrated anticancer properties, which may be attributable to its capacity to induce apoptosis (programmed cell death) in cancerous cells [11,12,13]. However, the balance between benefits and potential adverse effects remains to be fully elucidated. This underscores the necessity for the rigorous monitoring of patients’ conditions [7] and the development of suitable methodologies for vanadium determination in diverse samples.
A multitude of techniques have been utilized to ascertain the vanadium content. These include, but are not limited to, flame atomic absorption spectrometry [14,15,16], graphite furnace atomic absorption spectrometry [17,18,19,20,21,22,23], and inductively coupled plasma optical emission spectrometry [24]. Other techniques are inductively coupled plasma mass spectrometry [25], voltammetry [26], neutron activation analysis [27,28], and UV-vis spectrophotometry [29,30]. Spectrophotometry merits particular attention due to its operational simplicity, broad accessibility of instrumentation, cost-effectiveness, and energy efficiency. When utilized in conjunction with extraction methodologies, its performance is further enhanced, yielding improved sensitivity and selectivity across a wide range of applications.
In recent years, a significant number of chromogenic chelating reagents have been proposed for the spectrophotometric determination of vanadium following different types of extraction preconcentration. Examples include azo dyes [31,32,33,34,35,36], N-benzoyl-N-phenylhydroxylamine [37], 4-(2′,3′,4′-trihydroxyphenyl)-3-nitro-5-sulfoazobenzene [38], tannic acid [39], and thiophenols [40,41]. In the category of simple reagents with OH groups located in the ortho position, the following compounds warrant particular attention: 2,3-dihydroxynaphthalene [42], pyrogallol [43], and 4-nitrocatechol (4NC) [44,45]. Given the prominence of green technologies in contemporary analytical chemistry, cloud point extraction (CPE) is often regarded as a superior alternative to classical liquid–liquid extraction (LLE) [46,47,48,49,50]. In contrast to solid-phase extraction (SPE), which relies on costly solid sorbents or cartridges, CPE utilizes inexpensive surfactants. This technique requires only rudimentary equipment, such as a refrigerator and a hot plate, and in some variants (centrifuge-less CPE, CL-CPE), it does not even necessitate a centrifuge.
In this paper, we investigate a CL-CPE system containing 4-nitrocatechol (1,2-dihydroxy-4-nitrobenzene, 4NC) as a chelating chromophore reagent and cetylpyridinium chloride as an ion association reagent and, concomitantly, a cationic surfactant. The system also contains the nonionic surfactant Triton TX-114 (TX), which serves to enhance hydrophobic interactions. The employment of such mixed micelle (MM) systems is on the rise, as they are regarded as being particularly promising, especially when the objective is to extract charged, less hydrophobic substances [49,50].
4NC is a low-cost, widely available compound that has been identified as one of the most advantageous organic analytical reagents [51,52]. According to the CLP Regulation, the substance is classified as a non-hazardous material [53], indicating that it poses minimal risk to human health and the environment.

2. Results and Discussion

2.1. Optimization of Working Conditions

The spectra of the extracted species at two different 4NC concentrations (7.5 × 10−5 M and 7.5 × 10−4 M) are displayed in Figure 1. The primary absorption maximum of the vanadium complex is observed at 410 nm (Spectrum 1). Nevertheless, a wavelength of 670 nm was selected for the subsequent studies (see Spectrum 2). The utilization of this wavelength results in two notable advantages:
  • The blank sample demonstrates virtually zero absorption, a property that facilitates the experimental process (measurements are made against water) and promotes the high repeatability of the results.
  • The majority of the other 4NC complexes exhibit yellow or yellow-orange coloration (λ of 380–480 nm). The molar absorption coefficients of these complexes at 670 nm are negligible, a prerequisite for the development of a highly selective spectrophotometric method for determining vanadium.
The effects of pH on the absorbance are demonstrated in Figure 2. A series of buffer solutions, prepared from 2 M acetic acid and ammonia, was used to support the pH level. The analytical signal exhibited its maximum intensity at a pH of 5.5, a value that is regarded as optimal.
The impact of the buffer volume is shown in Figure 3. The subsequent studies were conducted in the presence of 2.0 mL buffer. The employment of reduced buffer volumes is not recommended, as it is difficult to separate a surfactant-rich phase (SRP). In such cases, the application of centrifugal force is imperative.
The effects of reagent concentrations are shown in Figure 4. The optimal 4NC concentration is 7.5 × 10−4 M (curve 1), and the optimal CPC concentration is 5.0 × 10−4 M (curve 2). The utilization of more concentrated 4NC solutions is not recommended, as this renders the procedure more costly and may result in the partial reduction of VV to VIV [44].
The effects of the TX mass fraction (wTX) are displayed in Figure 5. Achieving a stable SRP necessitates a minimum wTX of 0.3%. The subsequent studies were conducted at wTX = 0.4%. This corresponds to a mass ratio of the two surfactants of approximately 1:22 (CPC:TX).
The influence of incubation temperature and incubation time (tinc) is illustrated in Figure 6 and Figure 7, respectively. The subsequent studies were conducted in a water bath set to 60 °C. The recommended incubation time, as deduced from Figure 7, is 70 min. The temporal measurement was initiated from the moment when the samples were submerged in the preheated (60 °C) bath.
The complete set of optimized parameters is enumerated in Table 1. The cooling time and SRP treatment are analogous to those described in our previous paper dealing with the MoVI complex [52].

2.2. Stoichiometry, Complex Formation Equation, and Extraction Constant

The molar ratios between the components of the extracted complex were determined using the straight-line Asmus method [54] (Figure 8) and the mobile equilibrium method [55] (Figure 9). The findings from both methods (n4NC:nV = 2:1 and nCPC:nV = 1:1) suggest that the CL-CPE of the ternary complex can be represented by the following equation: 2H2L(aq) + H2VO4−(aq) + CP+(aq) ≡ (CP+)[VVOL2](SRP) + 3H2O. This equation is consistent with the forms of the existence of VV [2,56] and 4NC (H2L) [57,58,59] under the optimal conditions.
The conditional extraction constant (Kex) was calculated using the Holme–Langmyhr method [60] and the mobile equilibrium method [55]. The obtained logarithmic values demonstrate a high degree of agreement: LogKex = 4.67 ± 0.15 (± SD; n = 7, Holme–Langmyhr method) and LogKex = 4.57 ± 0.10 (± SD; n = 4, mobile equilibrium method).

2.3. Analytical Characteristics

A calibration graph was constructed under optimal conditions (see Table 1) using vanadium standards with concentrations ranging from 10 to 815 ng mL−1. The linear interval extends up to 305 ng mL−1 VV (n = 9), and positive deviations from Beer’s law are observed at higher concentrations. The linear regression equation was found to be A = 2.40γ − 0.004, where A is the absorbance, and γ is the VV concentration (µg mL−1). The standard deviations of the slope and intercept were 0.02 and 0.004, respectively. The apparent molar absorption coefficient, which corresponds to the slope, was determined to be 1.22 × 105 M−1 cm−1. The Sandell sensitivity was 0.42 ng cm−2. The limits of detection and quantitation were 0.6 ng mL−1 and 2 ng mL−1, respectively. These values were calculated as three and ten times the standard deviation (SD) of the blank (4.8 × 10−4, n = 10) divided by the slope. A preconcentration factor of 16.4 was found by dividing the maximum sample volume (50 mL) by the volume of the diluted SRP (VSPR = 3.05 mL). VSPR was determined using the mass of the final solution (3.00 g) and its density (measured with a pycnometer).
The absorbance of the complex demonstrates high stability over time. A 20 h experiment was conducted to evaluate this stability. The results, expressed in terms of calibration curve parameters, are presented in Table 2. As can be seen, the changes are negligible during the first 2–3 h. It is only after 20 h that the slope of the calibration plot increases slightly, by approximately 6%. This increase can be attributed to the evaporation of the solvent or the reduction of VV to VIV. It is noteworthy that throughout the experiment, the linearity of the calibration plot remained perfect, and the intercept was statistically indistinguishable from zero.

2.4. Effect of Diverse Ions

The effect that diverse ions have on the determination of VV is demonstrated in Table 3. Substantial quantities of common ions, such as alkali and alkaline earth ions, Cl−, Br−, NO3−, and SO42−, do not elicit interference. Many transition metal ions, including CdII, CoII, HgII, MnII, NiII, and ZnII, also do not interfere. However, a 250-fold excess of PbII, a 100-fold excess of UVI, and a 5-fold excess of CrVI cause the sample to become turbid, thereby obstructing the analysis. MoVI, WVI, and CuII form extractable complexes [52,61], but their absorption bands are situated at shorter wavelengths. A 20-fold excess of MoVI and 50-fold excesses of WVI and CuII are considered tolerable. The most significant interferences are induced by AlIII, FeIII, and Cr. The incorporation of NaF effectively mitigated the adverse effect caused by AlIII. The same masking agent possesses the capacity to extinguish interference from minor excesses of FeIII. In such instances, the measurement of light absorption should be conducted at a longer wavelength (e.g., 720 nm). The elimination of CrIII interference can be achieved by masking with sodium citrate and recording the absorbance at 700 or 720 nm. The measurement at these wavelengths results in sensitivity reductions of 5% and 11%, respectively.

2.5. Analytical Application

The novel method was tested in the analysis of mineral water samples, a spent Monsanto LP-110 catalyst, and a vanadium-containing dietary supplement (Chromium & Vanadium, Natural Factors®, Canada).
The mineral water analysis results are outlined in Table 4.
The analysis of the spent catalyst yielded a vanadium content of (2.72 ± 0.03)% and an RSD of 1.1% (n = 4). This content was corroborated by an alternative LLE method [62] (2.76 ± 0.07)%.
The dietary supplement was analyzed in the presence of sodium citrate, as it contains chromium. The analytical result obtained was 24.8 µg of vanadium per capsule, with an RSD of 1% (n = 4). This value was statistically indistinguishable from the manufacturer’s declared value of 25 µg.

2.6. Comparison with Other Methods and Practicality Assessment

Table 5 provides a comparative analysis of the present method’s key characteristics with those of other spectrophotometric extraction methods. This method is characterized by its simplicity, convenience, robustness, repeatability, selectivity, budget-effectiveness, and ecological friendliness. Unlike conventional CPE methods [19,24,31,43,63], a centrifuge is not necessary because of spontaneous phase separation. Adding a salting-out agent to increase extraction efficiency, as outlined in the method in [43], is also unnecessary. In contrast to the methods [24,33,39] that use a micro-syringe or spatula for the final phase isolation, the present method offers a simpler and faster approach: decantation. The reagents, 4NC and CPC, are inexpensive and widely available. No synthesis of reagents is required, as is the case with the methods in [24,35,64]. The calibration plot demonstrates excellent linearity, and the absorption remains stable over time. Furthermore, the blank’s absorbance is negligible and can be disregarded for most applications. This streamlines processing and boosts the method’s productivity.
Table 5. Comparison with other extractive spectrophotometric methods for vanadium determination.
Table 5. Comparison with other extractive spectrophotometric methods for vanadium determination.
Reagent(s)Extraction TechniqueExtractantLinear Range,
ng mL−1		λmax, nmε·10−4,
L mol−1 cm−1		LOD,
ng mL−1		SampleRef.
Br-PADAP CPETX-1147–300603NR2.2Tap water and river water[31]
DCDHNAQSPECarbon-1810–45057324.53.2Water, alloy, soil, and urine [64]
DPs + HAsLLEChloroform400–16,000614–6302.95–3.859Soil, water, and food samples[40]
EDTA +
Safranin T		UA-CPETX-1142–180 (VV)
1–40 (VIV)		530NR0.53 (VV)
0.26 (VIV)		Vegetal oils and vinegar[63]
HTAR + H2O2CPETX-100Up to 51058216.60.8Lake water and spent catalysts[36]
HTAR + TTCLLEChloroform15–20005495.24.6Spent catalysts and pharmaceuticals[62]
HTAR + NTCLLEChloroform23–11005565.26.8–[62]
N-BPHALLEChloroform0–15005300.545NRNatural waters[37]
NTA8HQ + BIABP + H2O2CPETX-1141–70 (VV)
10–100 (VIV)		634
625		160 (VV)
206 (VIV)		0.72 (VV)
1.78 (VIV)		Water, soil, rice, and vegetables[35]
PARMCPETX-11450–6005681.855.51Tap water[33]
PAR + BDTASPEClinoptilolite10–3000550NR0.07Synthetic samples and alloys[65]
PG + Safranin T UA-CPETX1142–500533NR0.58Beverages[43]
TA + CTABDLLME-SFOD1-Undecanol6–1000600NR1.8Fruit juice samples[39]
TAN + H2O2 CL-CPETX-100Up to 7606078.841.4Natural water, aluminum alloy, catalyst, and solution for infusion[32]
TAR + H2O2CL-CPETX-100Up to 5105697.41.7Dietary supplement and catalysts[34]
4NC + MTTLLEChloroform120–12004003.1335Steel and catalysts[45]
4NC + CPCMM-CL-CPETX1142–30567012.20.6Mineral water, dietary supplement, and spent catalystThis work
Abbreviations: 4NC, 4-nitrocatechol; BDTA, benzyldimethyltetradecyleammonium chloride; BIABP, 2-[(benzoimidazolyl)azo]-4-benzyl phenol; Br-PADAP, 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol; CL-CPE, centrifuge-less CPE; CPC, cetylpyridinium chloride; DCDHNAQ, 2,3-dichloro-6-(2,7-dihydroxy-1-naphthylazo)quinoxaline; DLLME-SFOD, dispersive liquid–liquid microextraction based on solidified floated organic drop; DPs, dithiolphenoles; HAs, hydrophobic amines; HTAR, 6-hexyl-4-(2-thiazolylazo)-resorcinol; LLE, liquid–liquid extraction; MCPE, micro-CPE; MM-CL-CPE, mixed micelle centrifuge-less CPE; MTT, 3-(4,5-dimethyl-2-thiazol)2,5- diphenyltetrazolium bromide; N-BPHA, N-benzoyl-N-phenylhydroxylamine; NR, not reported; NTA8HQ, 2-[2-(5-nitrothiazolyl)azo]-8-hydroxyquinoline; PAR, 4-(2-pyridylazo)resorcinol; PG, pyrogallol; SPE, solid-phase extraction; TAN, 1-(2-thiazolylazo)naphthol; TAR, 4-(2-thiazolylazo)resorcinol; TX-100, Triton X-100; TX-114, Triton X-114; UA-CPE, ultrasonic-assisted CPE.
A potential drawback of the current CL-CPE approach is the relatively long heating and cooling times. However, if necessary, the cooling time can be reduced by following the standard CPE procedures of centrifugation and ice bath application [19,24,31,43,63] without compromising sensitivity and selectivity. The heating process can likely be expedited through the use of a microwave oven, as evidenced in [66]. However, further research and optimization would be required to implement this approach. It is evident that a reduction in these times would result in other concomitant drawbacks, such as heightened labor requirements and the necessity for additional equipment.
Despite the aforementioned slow processes, this novel method can be considered “practical”. The validity of this conclusion is reinforced by the findings presented in Figure 10, which indicate a score of 67.5 on the blue applicability grade index (BAGI) [67].

3. Materials and Methods

3.1. Reagents and Chemicals

The chemicals were procured from Merck (Schnelldorf, Germany) and utilized without further purification as aqueous solutions. The VV standard solution was prepared from ammonium metavanadate (puriss. p.a.) at a concentration of 2.0 × 10−4 M. Solutions of 4NC (≥96.0%) and CPC (cetylpyridinium chloride monohydrate, ≥96.0%) were prepared at concentrations of 1.875 × 10−2 M and 2.50 × 10−2 M, respectively. The mass fraction of the laboratory-grade TX solution was 10%. Buffer solutions with a pH range of 4.5–9.1 were prepared by blending 2.0 M solutions of ammonia and acetic acid. Water was purified by either deionization (18.2 MΩ cm) or distillation.

3.2. Instrumentation

The UV-Vis spectrophotometer used was the Ultrospec 3300 pro (Garforth, UK). The instrument was outfitted with 10 mm macro-cuvettes, with a capacity of 2.5 mL. The CPE experiment utilized an Ohaus Pioneer PA214C top-loading analytical balance (Parsippany, NJ, USA) and a GFL 1023 (Berlin, Germany) water bath. The pH measurements were conducted using a WTW InoLab 7110 pH meter (Weilheim, Germany).

3.3. Samples and Sample Preparation

Bottled mineral water (Gorna Banya®, Sofia, Bulgaria) was procured from a local supermarket. Another source of mineral water was extracted directly from the spring in the town of Bratsigovo, Bulgaria. The analysis was conducted on the following day. Aliquots of 30 mL were used for each of these analyses.
The spent catalyst (Monsanto LP-110), employed in the production of H2SO4, was obtained from Holding KCM 2000, Plovdiv, Bulgaria. The preparation for analysis was carried out in accordance with the established procedure [62]. Aliquots of 0.5 mL were utilized in the CPE step.
The dietary supplement, Chromium & Vanadium (Natural Factors®, Coquitlam, BC, Canada), was obtained from a local pharmacy. According to the product’s specifications, each capsule should contain 25 μg of vanadium (citrate) and 100 μg of chromium (GTF chelate). The formulation also contains microcrystalline cellulose, gelatin, and vegetable-grade magnesium stearate. The following procedure was implemented to dissolve the capsules. First, the gelatin shells were removed, and the contents were transferred to a beaker. Then, 15–20 mL of 0.1 M hydrochloric acid was added and gently heated to approximately 40 °C for 30 min. The mixture was then filtered through an FN 2 paper filter, and the filtrate was collected in a 25 mL volumetric flask. The oxidation of VIV to VV was achieved by the addition of several drops of 0.02 M KMnO4. The pink color should be visible for 1–2 min. Finally, 2 mL of ethanol was added to reduce any CrVI, and the flask was filled to the mark with 0.1 M HCl.

3.4. Optimization Procedure

Solutions of TX, buffer, 4NC, VV, and CPC were transferred to pre-weighed, 50 mL conical-bottom centrifuge tubes. The mixtures were diluted with water to 50 mL and then incubated in a water bath at 40–60 °C for 10–80 min. The tubes were then cooled briefly under running water and stored in a freezer set to –20 °C for 40–60 min. This finalized the precipitation process and facilitated the removal of the upper layer through decantation. Subsequently, 0.5 mL of ethanol and a few drops of water were added to the viscous SRP, yielding a total mass of 3.00 g for each sample. Finally, the mixtures were homogenized and loaded into cuvettes to measure the corresponding absorbances.

3.5. Recommended Procedure for Determining Vanadium

Place an aliquot of the analyzed solution containing no more than 305 ng mL−1 VV in a 50 mL conical-bottom tube. Then add 2.0 mL of 10% TX solution, 2.0 mL of pH 5.5 buffer solution, 2.0 mL of a 1.875 × 10−2 M 4NC solution, and 1.0 mL of a 2.5 × 10−2 M CPC solution. If necessary, add a masking agent solution (sodium citrate or sodium fluoride). Dilute the sample to 50 mL with water, then place it in a water bath at 60 °C. After 70 min of incubation, cool the sample under running water, then put it in a freezer set at −20 °C for 55 min. Decant the top layer after that. Add 0.5 mL of ethanol to the SRP, then add enough water to bring the total mass to 3.00 g. Homogenize the mixture, then load the cuvette. Measure the absorbance against water at a wavelength of 670 nm. When masking CrIII with citrate, measurements at 700 or 720 nm are recommended. Finally, calculate the unknown VV concentration from a calibration curve.

4. Conclusions

A novel spectrophotometric method using CPE was proposed in this study for determining vanadium. It can be classified as a mixed micelle-mediated, centrifuge-less method, for which the acronym MM-CL-CPE is appropriate. The method’s merits were demonstrated through real-sample analyses and the implementation of the BAGI metric tool. The method was proven to be simple, convenient, robust, repeatable, sensitive, selective, cost-effective, and eco-friendly—in short, “practical”. This novel method has the potential to compete effectively with other methods for the analysis of total vanadium. One of its primary benefits is the negligible blank absorption, which leads to significant analytical advantages.

Author Contributions

Conceptualization, K.G. and J.Š.; methodology, K.G., A.G. and V.D.; validation, A.G., P.R., D.K. and V.D.; formal analysis, A.G. and K.G.; investigation, A.G., P.R., D.K. and A.S.; resources, K.G., V.D., P.R., D.K. and A.S.; data curation, K.G.; writing—original draft preparation, K.G.; writing—review and editing, A.G., J.Š., D.K. and K.G.; visualization, A.G. and K.G.; supervision, K.G. and J.Š.; project administration, K.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are contained within the article.

Acknowledgments

A.G. would like to express her gratitude to the Erasmus+ program for implementing PhD student mobility for traineeships in a partner country.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. IMA Database of Mineral Properties. Available online: https://rruff.info/ima/ (accessed on 27 May 2025).
  2. Huang, J.-H.; Huang, F.; Evans, L.; Glasauer, S. Vanadium: Global (bio)geochemistry. Chem. Geol. 2015, 417, 68–89. [Google Scholar] [CrossRef]
  3. Rehder, D. Vanadium in health issues. ChemTexts 2018, 4, 20. [Google Scholar] [CrossRef]
  4. Schlesinger, W.H.; Klein, E.M.; Vengosh, A. Global biogeochemical cycle of vanadium. Proc. Natl. Acad. Sci. USA 2017, 114, E11092–E11100. [Google Scholar] [CrossRef]
  5. Viers, J.; Dupré, B.; Gaillardet, J. Chemical composition of suspended sediments in World Rivers: New insights from a new database. Sci. Total Environ. 2009, 407, 853–868. [Google Scholar] [CrossRef] [PubMed]
  6. Watt, J.A.; Burke, I.T.; Edwards, R.A.; Malcolm, H.M.; Mayes, W.M.; Olszewska, J.P.; Pan, G.; Graham, M.C.; Heal, K.V.; Rose, N.L.; et al. Vanadium: A re-emerging environmental hazard. Environ. Sci. Technol. 2018, 52, 11973–11974. [Google Scholar] [CrossRef]
  7. Gruzewska, K.; Michno, A.; Pawelczyk, T.; Bielarczyk, H. Essentiality and toxicity of vanadium supplements in health and pathology. J. Physiol. Pharmacol. 2014, 65, 603–611. [Google Scholar]
  8. Fawcett, J.P.; Farquhar, S.J.; Thou, T.; Shand, B.I. Oral vanadyl sulphate does not affect blood cells, viscosity or biochemistry in humans. Pharmacol. Toxicol. 1997, 80, 202. [Google Scholar] [CrossRef]
  9. Scior, T.; Antonio Guevara-Garcia, J.; Do, Q.-T.; Bernard, P.; Laufer, S. Why antidiabetic vanadium complexes are not in the pipeline of “big pharm” drug research? A critical review. Curr. Med. Chem. 2016, 23, 2874–2891. [Google Scholar] [CrossRef]
  10. Amaral, L.; Moniz, T.; Silva, A.M.N.; Rangel, M. Vanadium compounds with antidiabetic potential. Int. J. Mol. Sci. 2023, 24, 15675. [Google Scholar] [CrossRef]
  11. Kostova, I. Anticancer metallocenes and metal complexes of transition elements from groups 4 to 7. Molecules 2024, 29, 824. [Google Scholar] [CrossRef]
  12. Kowalski, S.; Wyrzykowski, D.; Inkielewicz-Stępniak, I. Molecular and cellular mechanisms of cytotoxic activity of vanadium compounds against cancer cells. Molecules 2020, 25, 1757. [Google Scholar] [CrossRef] [PubMed]
  13. Crans, D.C.; Yang, L.; Haase, A.; Yang, X. Health benefits of vanadium and its potential as an anticancer agent. In Metallo-Drugs: Development and Action of Anticancer Agents; Astrid, S., Helmut, S., Eva, F., Roland, K.O.S., Eds.; De Gruyter: Berlin, Germany, 2018; pp. 251–280. [Google Scholar] [CrossRef]
  14. de Jesus, A.M.; Oliveira, L.F.; Canevari, N.T.; Pereira-Filho, E.R. Sequential preconcentration using cloud point extraction: Determination of vanadium and molybdenum in water and pharmaceutical samples using Flame Atomic Absorption Spectrometry. Braz. J. Anal. Chem. 2013, 10, 476–480. [Google Scholar]
  15. Gürkan, R.; Korkmaz, S.; Altunay, N. Preconcentration and determination of vanadium and molybdenum in milk, vegetables and foodstuffs by ultrasonic-thermostatic-assisted cloud point extraction coupled to flame atomic absorption spectrometry. Talanta 2016, 155, 38–46. [Google Scholar] [CrossRef] [PubMed]
  16. Filik, H.; Yanaz, Z.; Apak, R. Selective determination of total vanadium in water samples by cloud point extraction of its ternary complex. Anal. Chim. Acta 2008, 620, 27–33. [Google Scholar] [CrossRef]
  17. López-García, I.; Marín-Hernández, J.J.; Hernández-Córdoba, M. Graphite furnace atomic absorption spectrometric determination of vanadium after cloud point extraction in the presence of graphene oxide. Spectroc. Acta Part B Atom. Spectr. 2018, 143, 42–47. [Google Scholar] [CrossRef]
  18. Souza, V.S.; Teixeira, L.S.; Bezerra, M.A. Application of multivariate designs in the development of a method for vanadium determination in natural waters by HR-CS GF AAS after cloud-point extraction. Microchem. J. 2016, 129, 318–324. [Google Scholar] [CrossRef]
  19. Khan, S.; Kazi, T.G.; Baig, J.A.; Kolachi, N.F.; Afridi, H.I.; Wadhwa, S.K.; Shah, A.Q.; Kandhro, G.A.; Shah, F. Cloud point extraction of vanadium in pharmaceutical formulations, dialysate and parenteral solutions using 8-hydroxyquinoline and nonionic surfactant. J. Hazard. Mater. 2010, 182, 371–376. [Google Scholar] [CrossRef]
  20. Zhu, X.; Zhu, Z.; Wu, S. Determination of trace vanadium in soil by cloud point extraction and graphite furnace atomic absorption spectroscopy. Microchim. Acta 2008, 161, 143–148. [Google Scholar] [CrossRef]
  21. Liu, Y.; Xu, J.; Xue, Y.; Wang, J.; Chang, Y.; Xue, C. Determination of trace vanadium in sea cucumbers by ultrasound-assisted cloud point extraction and graphite furnace atomic absorption spectrometry. Int. J. Environ. Anal. Chem. 2015, 95, 258–270. [Google Scholar] [CrossRef]
  22. Filik, H.; Aksu, D. Determination of vanadium in food samples by cloud point extraction and graphite furnace atomic absorption spectroscopy. Food Anal. Meth. 2012, 5, 359–365. [Google Scholar] [CrossRef]
  23. Ullah, N.; Hazer, B.; Tuzen, M.; Saleh, T.A. Syringe-based microextraction for the removal of vanadium from different water and food samples using newly synthesized imino diacetate functionalized polystyrene as a new adsorbent: A multivariate approach. J. Mol. Liq. 2024, 394, 123703. [Google Scholar] [CrossRef]
  24. Mortada, W.I.; El-Defrawy, M.M.; Erfan, E.; El-Asmy, H.A. Cloud point extraction coupled with back-extraction for speciation of inorganic vanadium in water and determination of total vanadium in food samples by ICP-OES. J. Food Compos. Anal. 2022, 108, 104445. [Google Scholar] [CrossRef]
  25. D’Ilio, S.; Violante, N.; Majorani, C.; Petrucci, F. Dynamic reaction cell ICP-MS for determination of total As, Cr, Se and V in complex matrices: Still a challenge? A review. Anal. Chim. Acta 2011, 698, 6–13. [Google Scholar] [CrossRef] [PubMed]
  26. Wlazłowska, E.; Grabarczyk, M. Adsorptive stripping voltammetry for determination of vanadium: A review. Materials 2023, 16, 3646. [Google Scholar] [CrossRef]
  27. Kassem, A.; Sarheel, A.; Al-Somel, N. Determination of trace elements in soil and plants in the Orontes basin of Syria by using instrumental neutron activation analysis. J. Radioanal. Nucl. Chem. 2005, 262, 555–561. [Google Scholar] [CrossRef]
  28. Serfor-Armah, Y.; Carboo, D.; Akuamoah, R.; Chatt, A. Micelle-mediated extraction and neutron activation determination of nanogram levels of vanadium in seaweeds. J. Radioanal. Nucl. Chem. 2018, 318, 2039–2047. [Google Scholar] [CrossRef]
  29. He, W.-y.; Wang, K.-p.; Yang, J.-y. Spectrophotometric methods for determination of vanadium: A review. Toxicol. Environ. Chem. 2018, 100, 20–31. [Google Scholar] [CrossRef]
  30. Goswami, A.K. Spectrophotometric Determination of Vanadium, Chromium and Manganese: Reagents and Methods; De Gruyter: Berlin, Germany, 2024; pp. 21–42. [Google Scholar] [CrossRef]
  31. Deng, J.; Huang, K.; An, L.; Hu, C.; Ju, S.; Xiao, N. Cloud point extraction and simultaneous spectrophotometric determination of V(V), Co(II) and Cu(II) ions in water samples by 5-Br-PADAP using partial least squares regression. J. Radioanal. Nucl. Chem. 2014, 300, 835–842. [Google Scholar] [CrossRef]
  32. Stefanova-Bahchevanska, T.; Milcheva, N.; Zaruba, S.; Andruch, V.; Delchev, V.; Simitchiev, K.; Gavazov, K. A green cloud-point extraction-chromogenic system for vanadium determination. J. Mol. Liq. 2017, 248, 135–142. [Google Scholar] [CrossRef]
  33. Ghasemi, E.; Kaykhaii, M. Developing a new micro cloud point extraction method for simultaneous preconcentration and spectrophotometric determination of uranium and vanadium in brine. Anal. Sci. 2015, 31, 407–411. [Google Scholar] [CrossRef]
  34. Genç, F.; Milcheva, N.P.; Hristov, D.G.; Gavazov, K.B. A simple cloud point extraction-spectrophotometric method for total vanadium determination using 4-(2-thiazolylazo)resorcinol and H2O2. Chem. Pap. 2020, 74, 1891–1901. [Google Scholar] [CrossRef]
  35. Khammas, Z.A.; Ibrahim, Z.T.; Al-adilee, K.J. Two-steps cloud point extraction-spectrophotomtric method for separation, pre-concentration and determination of V (IV) and V (V) ions in real samples using laboratory-made organic reagents. Int. Res. J. Pure Appl. Chem. 2015, 8, 33–48. [Google Scholar] [CrossRef]
  36. Milcheva, N.P.; Genç, F.; Racheva, P.V.; Delchev, V.B.; Andruch, V.; Gavazov, K.B. An environmentally friendly cloud point extraction-spectrophotometric determination of trace vanadium using a novel reagent. J. Mol. Liq. 2021, 334, 116086. [Google Scholar] [CrossRef]
  37. Bychkova, O.A.; Zavodova, M.N.; Nikitina, T.G.; Nikonorov, V.V. Extraction–photometric determination of vanadium in natural waters. J. Anal. Chem. 2015, 70, 962–966. [Google Scholar] [CrossRef]
  38. Mardanova, V.I.; Nagiev, K.D.; Chyragov, F.M. Interaction of Vanadium(V) with 4-(2′,3′,4′-Trihydroxyphenyl)-3-Nitro-5-Sulfoazobenzene in the Presence of Cationic Surfactants. J. Anal. Chem. 2024, 79, 1426–1430. [Google Scholar] [CrossRef]
  39. Mortada, W.I.; Zedan, H.E.; Khalifa, M.E. Spectrophotometric determination of trace vanadium in fresh fruit juice samples by ion pair-based surfactant-assisted microextraction procedure with solidification of floating organic drop. Spectroc. Acta Part A Molec. Biomolec. Spectr. 2023, 302, 123107. [Google Scholar] [CrossRef]
  40. Kuliev, K.; Ibrahimov, H.; Ismailova, S.Y.; Aliyev, S.; Mamedova, S.A. Spectrophotometric determination of vanadium(IV, V) using dithiolphenols and aminophenols. Indo Am. J. Pharm. Sci. 2019, 6, 3267–3278. [Google Scholar] [CrossRef]
  41. Verdizade, N.; Magerramov, A.; Kuliev, K. Extraction-spectrophtometric determination of vanadium using 2, 6-dithiol-4-tert-butylphenol and aminophenols. J. Anal. Chem. 2011, 66, 1159–1164. [Google Scholar] [CrossRef]
  42. Mondal, R.K.; Rathore, D.P.S.; Tarafder, P.K. Determination of vanadium in steel and geological samples by its extraction and spectrophotometry determination using 2,3-dihydroxynaphthalene. Explor. Res. At. Miner. 2013, 23, 113–116. [Google Scholar]
  43. Temel, N.K.; Gürkan, R. Preconcentration and determination of trace vanadium(V) in beverages by combination of ultrasound assisted-cloud point extraction with spectrophotometry. Acta Chim. Slov. 2018, 65, 138–149. [Google Scholar] [CrossRef]
  44. Saravanska, A.D.; Racheva, P.V.; Divarova, V.V.; Toncheva, G.K.; Milcheva, N.P.; Delchev, V.B.; Gavazov, K.B. Extraction-spectrophotometric and theoretical studies on a ternary complex obtained from vanadium(V) and 4-nitrocatechol. Russ. J. Inorg. Chem. 2021, 66, 1880–1886. [Google Scholar] [CrossRef]
  45. Racheva, P.V.; Gavazov, K.B.; Lekova, V.D.; Dimitrov, A.N. Extraction equilibria and spectrophotometric determination of vanadium(V) with 4-nitrocatechol and the ion-pair reagent thiazolyl blue tetrazolium. J. Anal. Chem. 2010, 65, 21–25. [Google Scholar] [CrossRef]
  46. Arya, S.S.; Kaimal, A.M.; Chib, M.; Sonawane, S.K.; Show, P.L. Novel, energy efficient and green cloud point extraction: Technology and applications in food processing. J. Food Sci. Technol. 2019, 56, 524–534. [Google Scholar] [CrossRef] [PubMed]
  47. Mortada, W.I. Recent developments and applications of cloud point extraction: A critical review. Microchem. J. 2020, 157, 105055. [Google Scholar] [CrossRef]
  48. Halko, R.; Hagarová, I.; Andruch, V. Innovative Approaches in Cloud-Point Extraction. J. Chromatogr. A 2023, 1701, 464053. [Google Scholar] [CrossRef]
  49. Snigur, D.; Azooz, E.A.; Zhukovetska, O.; Guzenko, O.; Mortada, W. Recent innovations in cloud point extraction towards a more efficient and environmentally friendly procedure. Trac-Trends Anal. Chem. 2023, 164, 117113. [Google Scholar] [CrossRef]
  50. Semysim, F.A.; Shabaa, G.J.; Azooz, E.A.; Snigur, D. Alternative green solvents in cloud point extraction methods: Recent developments, challenges, and greenness evaluation. Trends Environ. Anal. Chem. 2025, 45, e00250. [Google Scholar] [CrossRef]
  51. Sommer, L.; Ackermann, G.; Burns, D.T.; Savvin, S.B. Present and future status of organic analytical reagents-Part I: General remarks. Pure Appl. Chem. 1990, 62, 2147–2166. [Google Scholar] [CrossRef]
  52. Divarova, V.; Gajdošová, A.; Racheva, P.; Gavazov, K. An Ionic liquid-assisted mixed micelle-mediated centrifuge-less cloud point extraction spectrophotometric method for the determination of molybdenum(VI). Int. J. Mol. Sci. 2025, 26, 4597. [Google Scholar] [CrossRef]
  53. Sigma-Aldrich Safety Data Sheet: 4-Nitrocatechol. Available online: https://www.sigmaaldrich.com/BG/en/sds/aldrich/n15553?userType=anonymous (accessed on 27 May 2025).
  54. Asmus, E. Eine neue Methode zur Ermittlung der Zusammensetzung schwacher Komplexe. Fresenius’ J. Anal. Chem. 1960, 178, 104–116. [Google Scholar] [CrossRef]
  55. Zhiming, Z.; Dongsten, M.; Cunxiao, Y. Mobile equilibrium method for determining composition and stability constant of coordination compounds of the form MmRn. J. Rare Earths 1997, 15, 216–219. [Google Scholar]
  56. Kurbatova, L.D.; Koryakova, O.V.; Valova, M.A.; Yanchenko, M.Y. Examination of extraction of vanadium(V) by trioctylamine from sulfuric solutions. Z. Anorg. Allg. Chem. 2015, 641, 617–621. [Google Scholar] [CrossRef]
  57. Gavazov, K.B. Nitroderivatives of catechol: From synthesis to application. Acta Chim. Slov. 2012, 59, 1–17. [Google Scholar] [PubMed]
  58. Nurchi, V.M.; Pivetta, T.; Lachowicz, J.I.; Crisponi, G. Effect of substituents on complex stability aimed at designing new iron(III) and aluminum(III) chelators. J. Inorg. Biochem. 2009, 103, 227–236. [Google Scholar] [CrossRef]
  59. Giroux, S.; Aury, S.; Rubini, P.; Parant, S.; Desmurs, J.-R.; Dury, M. A spectroscopic investigation of the complexing ability of catecholate or salicylate derivatives towards aluminium(III). Polyhedron 2004, 23, 2393–2404. [Google Scholar] [CrossRef]
  60. Holme, A.; Langmyhr, F.J. A modified and a new straight-line method for determining the composition of weak complexes of the form AmBn. Anal. Chim. Acta 1966, 36, 383–391. [Google Scholar] [CrossRef]
  61. Divarova, V.V.; Stojnova, K.T.; Radkovska, I.D.; Saravanska, A.D.; Toncheva, G.K.; Delchev, V.B.; Gavazov, K.B. Extraction system for the spectrophotometric determination of tungsten(VI) with 4-nitrocatechol and benzalkonium chloride. Acta Chim. Slov. 2024, 71, 519–527. [Google Scholar] [CrossRef]
  62. Gavazov, K.B.; Racheva, P.V.; Saravanska, A.D.; Toncheva, G.K.; Delchev, V.B. Extractive spectrophotometric determination and theoretical investigations of two new vanadium(V) complexes. Molecules 2023, 28, 6723. [Google Scholar] [CrossRef]
  63. Temel, N.K.; Kuş, B.; Gürkan, R. A new ion-pair ultrasound assisted-cloud point extraction approach for determination of trace V(V) and V(IV) in edible vegetal oils and vinegar by spectrophotometry. Microchem. J. 2019, 150, 104139. [Google Scholar] [CrossRef]
  64. Amin, A.S.; Saber, A.L.; Mohammed, T.Y. Study on solid phase extraction and spectrophotometric determination of vanadium with 2,3-dichloro-6-(2,7-dihydroxy-1-naphthylazo)quinoxaline. Spectroc. Acta Part A Molec. Biomolec. Spectr. 2009, 73, 195–200. [Google Scholar] [CrossRef]
  65. Rostampour, L.; Taher, M.A. Determination of trace amounts of vanadium by UV–vis spectrophotometric after separation and preconcentration with modified natural clinoptilolite as a new sorbent. Talanta 2008, 75, 1279–1283. [Google Scholar] [CrossRef] [PubMed]
  66. Stefanova, T.S.; Simitchiev, K.K.; Gavazov, K.B. Liquid–liquid extraction and cloud point extraction for spectrophotometric determination of vanadium using 4-(2-pyridylazo) resorcinol. Chem. Pap. 2015, 69, 495–503. [Google Scholar] [CrossRef]
  67. Manousi, N.; Wojnowski, W.; Płotka-Wasylka, J.; Samanidou, V. Blue applicability grade index (BAGI) and software: A new tool for the evaluation of method practicality. Green Chem. 2023, 25, 7598–7604. [Google Scholar] [CrossRef]
Ijms 26 05808 g001
Figure 1. Absorption spectra of ternary complex against blank (1 and 2) and corresponding blank against water (1′ and 2′) at two different 4NC concentrations. c4NC = 7.5 × 10−5 M (1 and 1′) and 7.5 × 10−4 M (2 and 2′); cV = 3 × 10−6 M; cCPC = 5 × 10−4 M; pH = 5.5; Vbuffer = 2.0 mL; wTX = 0.4%; tinc = 70 min at 60 °C.
Figure 1. Absorption spectra of ternary complex against blank (1 and 2) and corresponding blank against water (1′ and 2′) at two different 4NC concentrations. c4NC = 7.5 × 10−5 M (1 and 1′) and 7.5 × 10−4 M (2 and 2′); cV = 3 × 10−6 M; cCPC = 5 × 10−4 M; pH = 5.5; Vbuffer = 2.0 mL; wTX = 0.4%; tinc = 70 min at 60 °C.
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Figure 2. Effects of pH. cV = 4.0 × 10−6 M; c4NC = 7.5 × 10−4 M; cCPC = 5 × 10−4 M; wTX = 0.4%; Vbuffer = 2.0 mL; tinc = 70 min at 60 °C; λ = 670 nm.
Figure 2. Effects of pH. cV = 4.0 × 10−6 M; c4NC = 7.5 × 10−4 M; cCPC = 5 × 10−4 M; wTX = 0.4%; Vbuffer = 2.0 mL; tinc = 70 min at 60 °C; λ = 670 nm.
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Figure 3. Effects of buffer volume. pH 5.5; cV = 4.0 × 10−6 M; c4NC = 7.5 × 10−4 M; cCPC = 5 × 10−4 M; wTX = 0.4%; tinc = 70 min at 60 °C; λ = 670 nm.
Figure 3. Effects of buffer volume. pH 5.5; cV = 4.0 × 10−6 M; c4NC = 7.5 × 10−4 M; cCPC = 5 × 10−4 M; wTX = 0.4%; tinc = 70 min at 60 °C; λ = 670 nm.
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Figure 4. Effects of reagent concentrations. cV = 4 × 10−6 M; wTX = 0.4%; pH = 5.5; tinc = 70 min at 60 °C; λ = 670 nm. cCPC = 5 × 10−4 M (curve 1); c4NC = 7.5 × 10−4 M (curve 2).
Figure 4. Effects of reagent concentrations. cV = 4 × 10−6 M; wTX = 0.4%; pH = 5.5; tinc = 70 min at 60 °C; λ = 670 nm. cCPC = 5 × 10−4 M (curve 1); c4NC = 7.5 × 10−4 M (curve 2).
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Figure 5. Effects of TX mass fraction. cV = 4 × 10−6 M; c4NC = 7.5 × 10−4 M; cCPC = 5 × 10−4 M; pH = 5.5; tinc = 70 min at 60 °C; λ = 670 nm.
Figure 5. Effects of TX mass fraction. cV = 4 × 10−6 M; c4NC = 7.5 × 10−4 M; cCPC = 5 × 10−4 M; pH = 5.5; tinc = 70 min at 60 °C; λ = 670 nm.
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Figure 6. Effects of incubation temperature. cV = 4 × 10−6 M; c4NC = 7.5 × 10−4 M; cCPC = 5 × 10−4 M; wTX = 0.4%; pH = 5.5; tinc = 70 min; λ = 670 nm.
Figure 6. Effects of incubation temperature. cV = 4 × 10−6 M; c4NC = 7.5 × 10−4 M; cCPC = 5 × 10−4 M; wTX = 0.4%; pH = 5.5; tinc = 70 min; λ = 670 nm.
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Figure 7. Effects of incubation time at 60 °C. cV(V) = 4 × 10−6 M; c4NC = 7.5 × 10−4 M; cCPC = 5 × 10−4 M; wTX = 0.4%; pH = 5.5; λ = 670 nm.
Figure 7. Effects of incubation time at 60 °C. cV(V) = 4 × 10−6 M; c4NC = 7.5 × 10−4 M; cCPC = 5 × 10−4 M; wTX = 0.4%; pH = 5.5; λ = 670 nm.
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Figure 8. Determination of 4NC:VV (a) and CPC:VV (b) molar ratios by method of Asmus.
Figure 8. Determination of 4NC:VV (a) and CPC:VV (b) molar ratios by method of Asmus.
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Figure 9. Determination of 4NC:VV (straight-line 1) and CPC:VV (straight-line 2) molar ratios by mobile equilibrium method.
Figure 9. Determination of 4NC:VV (straight-line 1) and CPC:VV (straight-line 2) molar ratios by mobile equilibrium method.
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Figure 10. BAGI pictogram for proposed method.
Figure 10. BAGI pictogram for proposed method.
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Table 1. Optimal operating conditions.
Table 1. Optimal operating conditions.
ParameterOptimal Value
Wavelength, nm670
pH5.5
Volume of buffer, mL2.0
Concentration of 4NC, M7.5 × 10−4
Concentration of CPC, M5.0 × 10−4
Mass fraction of TX, %0.4
Incubation time, min70
Incubation temperature, °C60
Cooling time (at −20 °C), min55
Test tube capacity, mL50
Mass * of diluted SRP, g3.00
* In the presence of water and 0.5 mL C2H5OH.
Table 2. Changes in calibration plot * parameters over time.
Table 2. Changes in calibration plot * parameters over time.
TimeCalibration Plot Parameters
Slope ± SDIntercept ± SDR2
0 min = 30 min2.402 ± 0.026–0.0045 ± 0.00490.9998
60 min2.401 ± 0.025–0.0044 ± 0.00480.9998
120 min2.400 ± 0.024–0.0043 ± 0.00470.9998
200 min2.417 ± 0.023–0.0040 ± 0.00440.9998
20 h2.549 ± 0.015–0.0013 ± 0.00280.9999
* Calibration plots, including the zero-point, were constructed for VV concentrations of 0.10, 0.20, and 0.30 μg mL−1 (two replicates).
Table 3. The effect of foreign ions on the determination of 10.2 μg VV.
Table 3. The effect of foreign ions on the determination of 10.2 μg VV.
IonAdded Salt FormulaIon–V(V) Mass RatioV(V) Found, μgR, %
AlIIIAl2(SO4)3·18H2O 59.391.6
100 a10.098.4
BaIIBa(NO3)22000 b10.3101
Br− NaBr2000 b 9.997.6
CaIICa(NO3)22000 b10.6104
CdIICd(NO3)2·4H2O2000 b9.694.4
Citrate3−Na3C6H5O750010.098.3
20009.492.2
Cl− NaCl2000 b10.4102
CoIICoSO4·7H2O50010.098.1
CrIIICr2(SO4)3211.3110
5 c,d10.199.2
CrVIK2CrO4110.7105
211.1109
CuIICu(SO4)2·5H2O5010.4102
F−NaF5009.896.2
FeIIIFe2(SO4)3112.3121
2 a,d10.2100
HgIIHg(NO3)25009.896.1
HPO42− Na2HPO4·12H2O100010.098.5
I−KI10010.4102
MgIIMgSO4·7H2O2000 b9.795.6
MnIIMnSO4·5H2O100010.098.4
MoVINa2MoO42010.4102
NiIINiSO4·7H2O2000 b10.098.5
PbIIPb(NO3)210010.2100
ReVIINH4ReO47510.199.5
SrIISr(NO3)22000 b10.199.4
Tartrate2−KNaC4H4O6·4H2O100010.199.0
UVIUO2(CH3CO2)2·H2O509.492.4
WVINa2WO4·2H2O5010.7105
ZnIIZnSO4·7H2O75010.098.3
a In the presence of F− (5.1 mg). b Higher mass ratios were not studied. c In the presence of citrate3− (5.1 mg). d Measured at λ = 720 nm.
Table 4. Determination of VV in unspiked and spiked mineral water samples.
Table 4. Determination of VV in unspiked and spiked mineral water samples.
Mineral WaterVV Concentration, ng mL−1RSD, %R, %
AddedFound c
Sample 1 a0Not detected––
20.421.0 ± 0.31.4103.3
40.839.7 ± 0.82.097.4
61.161.6 ± 0.30.5100.8
Sample 2 b02.1 ± 0.28.0–
20.420.9 ± 0.61.992.4
40.843.7 ± 1.51.9102.0
61.163.2 ± 3.36.5100.0
a Commercial bottled mineral water. b Mineral water extracted directly from spring. c ±SD, n = 3.
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Gajdošová, A.; Racheva, P.; Kiradzhiyska, D.; Divarova, V.; Saravanska, A.; Šandrejová, J.; Gavazov, K. Centrifuge-Less Mixed Micelle-Mediated Cloud Point Extraction-Spectrophotometric Determination of Vanadium Using 4-Nitrocatechol and Cetylpyridinium Chloride. Int. J. Mol. Sci. 2025, 26, 5808. https://doi.org/10.3390/ijms26125808

AMA Style

Gajdošová A, Racheva P, Kiradzhiyska D, Divarova V, Saravanska A, Šandrejová J, Gavazov K. Centrifuge-Less Mixed Micelle-Mediated Cloud Point Extraction-Spectrophotometric Determination of Vanadium Using 4-Nitrocatechol and Cetylpyridinium Chloride. International Journal of Molecular Sciences. 2025; 26(12):5808. https://doi.org/10.3390/ijms26125808

Chicago/Turabian Style

Gajdošová, Andrea, Petya Racheva, Denitsa Kiradzhiyska, Vidka Divarova, Antoaneta Saravanska, Jana Šandrejová, and Kiril Gavazov. 2025. "Centrifuge-Less Mixed Micelle-Mediated Cloud Point Extraction-Spectrophotometric Determination of Vanadium Using 4-Nitrocatechol and Cetylpyridinium Chloride" International Journal of Molecular Sciences 26, no. 12: 5808. https://doi.org/10.3390/ijms26125808

APA Style

Gajdošová, A., Racheva, P., Kiradzhiyska, D., Divarova, V., Saravanska, A., Šandrejová, J., & Gavazov, K. (2025). Centrifuge-Less Mixed Micelle-Mediated Cloud Point Extraction-Spectrophotometric Determination of Vanadium Using 4-Nitrocatechol and Cetylpyridinium Chloride. International Journal of Molecular Sciences, 26(12), 5808. https://doi.org/10.3390/ijms26125808

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