Advances on melamine determination by micellar liquid chromatography: A review

One step construction of an electrochemical sensor for melamine detection in milk towards an integrated portable system

Excessive intake of melamine (MEL) can be harmful to human health, and it is important to establish a rapid and accurate MEL detection method. As the electrochemical activity of MEL is very low, ferrocenylglutathione (Fc-ECG) was used as an electron transfer mediator to assist with the detection of MEL using screen-printed carbon electrode (SPCE). This modified electrode (MEL/Fc-ECG/SPCE) was prepared by stepwise drop-casting and was fully characterized. Results showed that MEL significantly enhanced signal of Fc-ECG/SPCE sensor due to the three p-π conjugated double bonds that facilitated electron transfer. Under optimal conditions, the sensor exhibits two linearities in the range of 0.20-2.00 μM and 8.00-800 μM, with a sensitivity of 15.03 μA·μM^-1·cm^-2. The selectivity, stability, and reproducibility were investigated and successfully used to detect MEL in raw milk and confirms safety verification of foods. Moreover, a portable testing platform was designed for MEL detection based on a CH32 chip.

Sonodecoration of magnetic phosphonated-functionalized sporopollenin as a novel green nanocomposite for stir bar sorptive dispersive microextraction of melamine in milk and milk-based food products

The novel green magnetic phosphonated-functionalized sporopollenin nanocomposite (MPSP-nanocomposite) was synthetized and used for stir bar sorptive dispersive microextraction (SBSDME) of melamine in milk and milk-based food products. TEM, SEM-EDX, FT-IR, VSM techniques were applied for characterization of MPSP-nanocomposite. The influential parameters including pH, extraction time, stirring rate, elution solvent type and volume, sample volume, desorption time, and ionic strength were studied and at optimum conditions, the linear range of 1-500 (µg L^-1), the LOD (S/N = 3) of 0.30 (µg L^-1), and the LOQ (S/N = 10) of 0.95 (µg L^-1) were achieved. The intra-day precision values (RSD (%), n = 7) of 3.5% for the melamine concentration of 25 (µg L^-1). The relative recoveries of 95.8% to 99.6% were acquired for the real samples which confirmed that the proposed method could be successfully utilized in complex matrixes with high matrix effects.

Cyclodextrin-Modified Micellar UPLC for Direct, Sensitive and Selective Determination of Water Soluble Vitamins in Milk

Cyclodextrin-modified micellar ultra pressure liquid chromatography (CD-MUPLC) was firstly developed and directly applied to the simultaneous determination of water-soluble vitamins thiamine hydrochloride (VB1), pyridoxine hydrochloride (VB6) and ascorbic acid (VC) in milk samples. A hybrid isocratic mobile phase consisting of β-cyclodextrin (β-CD, 5.0 mmol L-1) and cetyltrimethylammonium bromide (CTAB, 0.1 mol L-1) in the presence of acetic acid (0.1 mol L-1) at pH 2.9 on a RP-C18 column at 25.0°C was successfully used. The separation of vitamins was achieved in less than 10 min at a 0.2 mL min-1 flow rate showing adequate linearity at 245 nm in the ranges of 5.0-500.0 μg L-1 for VB1, 5.0-1000.0 μg L-1 for VB6 and 5.0-10000.0 μg L-1 for VC with coefficients of variation (r2) of 0.9999, 0.9987 and 0.9971, respectively. In addition, limits of detection obtained were 0.885, 1.352 and 1.358 μg L-1 and limits of quantification were 2.681, 4.096 and 4.115 μg L-1 for VB1, VB6 and VC, respectively. The high sensitivity of the proposed CD-MUPLC-UV method permitted its applications to the determination of water-soluble vitamins VB1 (32-488 μg L-1), VB6 (82-95 μg L-1) and VC (790-45000 μg L-1) in breast and bovine milk samples. The relative standard deviations and recoveries ranged between 0.07 and 2.14% and between 85.27 and 114.8%, respectively, indicating the accurate and precise measurements without any negative impact of matrix. The current analytical method illustrated several advantages including direct, sensitive, selective and non-consuming organic solvents over the hitherto published methods. These features could be attributed to the four-point competitive interactions among analytes, pseudostationary phases and modified C18 stationary phases.

Use of Micellar Liquid Chromatography to Determine Mebendazole in Dairy Products and Breeding Waste from Bovine Animals

Mebendazole is an anthelmintic drug used in cattle production. However, residues may occur in produced food and in excretions, jeopardizing population health. A method based on micellar liquid chromatography (MLC) was developed to determine mebendazole in dairy products (milk, cheese, butter, and curd) and nitrogenous waste (urine and dung) from bovine animals. Sample treatment was expedited to simple dilution or solid-to-liquid extraction, followed by filtration and direct injection of the obtained solution. The analyte was resolved from matrix compounds in less than 8 min, using a C18 column and a mobile phase made up of 0.15 M sodium dodecyl sulfate (SDS)–6% 1-pentanol phosphate buffered at pH 7, and running at 1 mL/min under isocratic mode. Detection was performed by absorbance at 292 nm. The procedure was validated according to the guidelines of the EU Commission Decision 2002/657/EC in terms of: specificity, method calibration range (from the limit of quantification to 25–50 ppm), sensitivity (limit of detection 0.1–0.2 ppm; limit of quantification, 0.3–0.6 ppm), trueness (92.5–102.3%), precision (<7.5%, expressed at RSD), robustness, and stability. The method is reliable, sensitive, easy-to-handle, eco-friendly, safe, inexpensive, and provides a high sample-throughput. Therefore, it is useful for routine analysis as a screening or quantification method in a laboratory for drug-residue control.

Rational design of MnO nanoparticles assemblies for sensitive magnetic relaxation detection of melamine

A versatile protocol has been developed for highly sensitive magnetic relaxation detection of the analyte based on the fabrication of MnO nanoparticles (NPs) assemblies. Based on the strategy that positively charged analyte could induce the assembly of negatively charged MnO NPs through electrostatic interaction, which will generate the change of magnetic relaxation rate of MnO NPs, we achieved highly sensitive and convenient detection of the analytes. By applying the detection of melamine as an example, we found that the detection limit can be as low as 0.733 ppb. Furthermore, this strategy has been applied for the initially detection of commercially available milk spiked with melamine as proof of its potential applicability of detection in complicated food samples.

Designing a sustainable mobile phase composition for melamine monitoring in milk samples based on micellar liquid chromatography and natural deep eutectic solvent

Modified micellar liquid chromatography (MLC) with a natural deep eutectic solvent (NADES), produced from choline chloride (ChCl) and ethylene glycol (EG), was employed for melamine (MEL) monitoring in milk matrix. This sustainable mobile phase was attained through chemometrical optimization of crucial variables including concentration of sodium dodecyl sulphate ([SDS]) along with volume percentages of both NADES and glacial acetic acid (GAC). The desirability function and central composite design were utilized as chemometrical tools. Retention time (t_R-MEL), and chromatographic peak width of MEL at 50% of its height (W_50%-MEL) were considered for finding the best possible arrangement of the influential factors in the configuration of the mobile phase. Under the optimal experimental conditions of 0.10 mol L^-1 SDS, 4% (v/v) NADES, and 4% (v/v) GAC, the results showed that both t_R-MEL and W_50%-MEL drastically decreased when NADES was a part of the mobile phase composition. This indicated that ChCl-EG-based NADES had a significant impact on improving the chromatographic behaviour of an ionizable polar compound, MEL. At the optimal point, MEL was eluted in approximately 10 min without being interfered by coexisting proteins and endogenous species in milk. The practical performance of the mobile phase was established through direct injection of milk samples into the MLC system. The eligibility criteria of the United State-Food and Drug Administration (US-FDA) were considered for validation of the introduced methodology.

Micellar liquid chromatography determination of rivaroxaban in plasma and urine. Validation and theoretical aspects

A Micellar Chromatographic method to determine rivaroxaban in plasma and urine has been developed. The samples were dissolved in the mobile phase (SDS 0.05 M - 1-propanol 12.5%, phosphate buffered at pH 7) and 20 μL directly injected, avoiding the extraction and purification steps. Using a C18 column and running under isocratic mode at 1 mL/min, analyte was eluted without interference from the matrix in <6.0 min. The detection absorbance wavelength was set to 250 nm. The procedure was validated by Food and Drug Administration guidelines in terms of: system suitability, calibration range (0.05-5 mg/L), linearity, sensitivity, robustness, carry-over effect, specificity, accuracy (-11.1 to 4.2%), precision (<19.9%), stability and analysis of incurred samples. The method was found reliable, practical, easy-to-conduct, rapid, relatively eco-friendly, safe, inexpensive, widely available and with a high sample throughput. The method was applied to the analysis of incurred samples, including incurred sample reanalysis, to verify that the instrumentation works correctly. In addition, the constants of the different partition equilibria occurring in the column were elucidated in order to have a better comprehension of the theoretical aspects of the retention mechanism. A moderately strong association between rivaroxaban and the stationary phase and the micelles was found, weakened by short chain alcohol.

Optimization and Validation of a Chromatographic Method for the Quantification of Isoniazid in Urine of Tuberculosis Patients According to the European Medicines Agency Guideline

Isoniazid is a drug that is widely used against tuberculosis. However, it shows high interpatient variability in metabolism kinetics and clinical effect, which complicates the prescription of the medication and jeopardizes the success of the therapy. Therefore, in a specific patient, the pharmacokinetics of the drug must be elucidated to decide the proper dosage and intake frequency to make the drug suitable for therapeutic drug monitoring. This can be performed by the quantification of the drug in urine as this process is non-invasive and allows the effects of long-time exposure to be inferred. The paper describes the development of a micellar liquid chromatographic method to quantify isoniazid in urine samples. Extraction steps were avoided, making the procedure easy to handle and reducing the waste of toxic organic solvents. Isoniazid was eluted in less than 5 min without interference from other compounds of the urine using a mobile phase containing 0.15 SDS⁻12.5% 1-propanol (v/v)⁻Na₂HPO₄ 0.01 M buffered at pH 7, running at 1 mL/min under isocratic mode through a C18 column with the detection wavelength at 265 nm. The method was validated by following the requirements of the Guidelines on Bioanalytical Method Validation issued by the European Medicines Agency (EMA) in terms of selectivity, calibration curve (r² = 0.9998 in the calibration range (0.03⁻10.0 μg/mL), limit of detection and quantification (10 and 30 ng/mL respectively), precision (<16.0%), accuracy (-0.9 to +8.5%), carry-over, matrix effect, and robustness. The developed method was applied to quantify isoniazid in urine samples of patients of an Indian hospital with good results. The method was found to be useful for routine analysis to check the amount of isoniazid in these patients and could be used in its therapeutic monitoring.

Development and validation of a micellar liquid chromatographic method to determine three antitumorals in plasma

Aim: A micellar liquid chromatographic method to determine several anticancer drugs (pazopanib, dabrafenib and regorafenib) in plasma was developed and validated by the guidelines of the EMA. Experimental: Plasma samples were directly injected, after a 1/5-dilution in a micellar solution. The drugs were resolved in <18 min using a C18 column. The mobile phase was an aqueous solution of 0.12 M SDS – 2% 1-pentanol, buffered at pH 7. The detection was performed by absorbance at 260 nm. Results: The values of the main validation parameters were: LOD (0.1–1 mg/l), calibration range (0.2–2 to 80 mg/l), accuracy (-12.5 to +11.7%) and precision (<11.9%). Conclusion: The procedure was conducted by minimum cost, effort, manipulation, time and quantity of hazardous chemicals. The method was useful to determine the drugs at their respective target concentrations, and was found useful for clinical analysis.

Determination of oxolinic acid, danofloxacin, ciprofloxacin, and enrofloxacin in porcine and bovine meat by micellar liquid chromatography with fluorescence detection

A method was developed for the determination of oxolinic acid, danofloxacin, ciprofloxacin and enrofloxacin by micellar liquid chromatography - fluorescence detection in commercial porcine and bovine meat. The samples were ultrasonicated in a micellar solution, free of organic solvent, to extract the analytes, and the supernatant was directly injected. The quinolones were resolved in <22min using a mobile phase of 0.05M SDS - 7.5% 1-propanol - 0.5% triethylamine buffered at pH 3, running through a C18 column at 1mL/min using isocratic mode. The method was validated by the in terms of: selectivity, calibration range (0.01-0.05 to 0.5mg/kg), linearity (r²>0.9998), trueness (89.3-105.1%), precision (<8.3%), decision limit (<12% over the maximum residue limit), detection capability (<21% over the maximum residue limit), ruggedness (<5.6%) and stability. The procedure was rapid, eco-friendly, safe and easy-to-handle.

Rapid Quantification of Melamine in Different Brands/Types of Milk Powders Using Standard Addition Net Analyte Signal and Near-Infrared Spectroscopy

Multivariate calibration (MVC) and near-infrared (NIR) spectroscopy have demonstrated potential for rapid analysis of melamine in various dairy products. However, the practical application of ordinary MVC can be largely restricted because the prediction of a new sample from an uncalibrated batch would be subject to a significant bias due to matrix effect. In this study, the feasibility of using NIR spectroscopy and the standard addition (SA) net analyte signal (NAS) method (SANAS) for rapid quantification of melamine in different brands/types of milk powders was investigated. In SANAS, the NAS vector of melamine in an unknown sample as well as in a series of samples added with melamine standards was calculated and then the Euclidean norms of series standards were used to build a straightforward univariate regression model. The analysis results of 10 different brands/types of milk powders with melamine levels 0~0.12% (w/w) indicate that SANAS obtained accurate results with the root mean squared error of prediction (RMSEP) values ranging from 0.0012 to 0.0029. An additional advantage of NAS is to visualize and control the possible unwanted variations during standard addition. The proposed method will provide a practically useful tool for rapid and nondestructive quantification of melamine in different brands/types of milk powders.