Development of purity certified reference materials to establish metrological traceability for the measurement of nitroimidazoles in agricultural products.

It is of significant importance to public health that reliable monitoring of nitroimidazoles be conducted, while certified reference materials (CRMs) are essential for accurate and reliable detection. A project has been initiated with the objective of developing nitroimidazole purity CRMs to ensure that results from nationwide monitoring laboratories for nitroimidazoles in antibiotic residues can be compared and traced. The candidates were successively characterized in terms of their structure by means of infrared (IR) spectroscopy and mass spectrometry (MS). The mass balance (MB) method and the quantitative nuclear magnetic resonance (qNMR) method were utilized to determine the purity of nitroimidazoles with remarkable accuracy. Furthermore, a methodical investigation was conducted on homogeneity, stability, and uncertainty. Six nitroimidazole purity CRMs, including tinidazole (GBW09252), secnidazole (GBW09286), ronidazole (GBW09288), metronidazole (GBW(E)090755), dimetridazole (GBW(E)090819), and ornidazole (GBW(E)090820), were finally manufactured following authorization from China's State Administration for Market Regulation (SAMR). By using these CRMs, it is possible to improve the traceability, accuracy, and comparability of nitroimidazole measurements in a range of agricultural products, protecting public health.

Solvothermal and Ultrasonic Preparation of Two Unique Cluster-Based Lu and Y Coordination Materials: Metal-Organic Framework-Based Ratiometric Fluorescent Biosensor for an Ornidazole and Ronidazole and Sensing Platform for a Biomarker of Amoeba Liver Abscess.

Through powerful solvothermal and facile ultrasonic synthetic strategies, two unique cluster-based lanthanide Lu and Y nanoporous metal organic frameworks (MOFs) have been successfully prepared, namely, {[Lu2(L)2]·2DMF·H2O}n (Lu-MOF) and [Y(L)(DMF)0.75]n (Y-MOF) (H3L = terphenyl-3,4'',5-tricarboxylic acid). In addition, both the morphologies and nanosizes of Lu-MOF and Y-MOF materials also have been deliberately tuned by adjustable ultrasonic conditions including irradiation time (40, 60, and 80 min) and power (70 w, 100 w). Currently, it is noted that the abuse of antibiotics such as ornidazole and ronidazole leads to great damage to human health, and therefore the development of highly effective and facile detection methods for ornidazole and ronidazole is quite important. Herein, to improve the fluorescent sensing sensitivity of antibiotics, Eu3+ and Tb3+ have been introduced into Lu-MOF (under a solvothermal preparation method) to fabricate a dual-emission hybrid material Eu3+/Tb3+@Lu-MOF through a postsynthesis strategy, which can be successfully applied as a self-calibrated ratiometric fluorescent sensor for ornidazole and ronidazole with high selectivity and sensitivity (the Ksv value for ornidazole is 1.0854 × 106 [M-1], and the Ksv value for ronidazole is 1.0595 × 107 [M-1]) and low detection limit values (2.85 nM for ornidazole and 26.7 nM for ronidazole). On the other hand, amoeba liver abscess (ALA) will easily lead to irregular fever, night sweats, and other tortured symptoms; C-reactive protein autoantibody (CRP Ab) is the important biomarker for the detection of ALA. Given this, Y-MOF (under the solvothermal preparation method) also has been successfully designed to combine FAM-labeled NH-ssDNA to construct the scarcely reported excellent hybrid FAM-labeled NH-ssDNA/Y-MOF sensing platform for the highly effective discrimination of CRP Ab with excellent sensitivity and selectivity in real samples such as human serum solution.

A voltammetric screening method to determine ronidazole in bovine meat.

An original voltammetric screening method, employing glassy carbon electrode (GCE) with the differential-pulse voltammetry technique (DPV), has been developed to determine residues of the anti-parasitic agent Ronidazole (RNZ) in bovine meat. By using cyclic voltammetry (CV), it has been demonstrated that an irreversible cathodic process occurs at approximately -0.740 V (vs. Ag|AgCl, KCl 3 mol L-1) in a 0.100 mol L-1 phosphate buffer at pH 6.5 as supporting electrolyte. Furthermore, the behavior of RNZ in CV indicates the occurrence of a diffusion mass transfer process to the working electrode surface. The RNZ reduction mechanism was proposed as a 6-electron transfer, similar to Metronidazole under the same pH range. Quantification of RNZ and method validation were then carried out by DPV. The relative standard deviation (RSD) were 3.21% for intraday precision of 10 consecutive repetitions and 6.78% for interday precision after five analysis. Limits of detection and quantification were also obtained, and the values were 0.107 and 0.358 mg kg-1, respectively. The recovery percentage for three different concentrations of RNZ in the bovine meat matrix ranged between 98.1% and 100.3%. The method proved to be efficient for screening RNZ in bovine meat.

A Water-Stable 3D Luminescent Metal-Organic Framework Based on Heterometallic [EuIII6ZnII] Clusters Showing Highly Sensitive, Selective, and Reversible Detection of Ronidazole.

A water-stable 3D luminescent metal-organic framework (MOF), [Eu6Zn(µ3-OH)8(NDC)6(H2O)6]n (1), constructed from heterometallic [EuIII6ZnII] clusters and electron-rich π-conjugated 1,4-naphthalenedicarboxylic acid (H2NDC) ligands exhibits highly sensitive, selective, and reversible detection of ronidazole, which represents the first example of luminescent MOFs based on Ln-TM heterometallic clusters for the detection of antibiotics in aqueous solution.

Quantification of nitroimidazoles residues in swine liver by liquid chromatography-mass spectrometry with atmospheric pressure chemical ionization.

A liquid chromatography-mass spectrometry method was developed for the simultaneous determination of ronidazole (RNZ), metronidazole (MNZ) and dimetridazole (DMZ) residues in swine liver. Following liquid-liquid extraction, the HLB solid-phase extraction was used for further purification. The targets were detected by atmospheric pressure chemical ionization (APCI) following the reverse phase liquid chromatography separation. Consequently, the detection limits for the method were 0.5 microg/kg for MNZ, 1.0 microg/kg for RNZ and 0.5 microg/kg for DMZ, respectively. The accuracies were determined using swine liver samples fortified at levels of 0.5, 1, 2, and 4 microg/kg and the mean recoveries of the analytes were between 66% and 81%.

Simultaneous determination of nitroimidazole residues in honey samples by high-performance liquid chromatography with ultraviolet detection.

A rapid and sensitive high-performance liquid chromatography (LC) method was developed for the simultaneous determination of metronidazole (MNZ), dimetridazole (DMZ), ronidazole (RNZ), tinidazole (TNZ), and 2-hydroxymethyl-1-methyl-5-nitroimidazole (HMMNI) in honey. After extraction with ethyl acetate and evaporation, the residue containing the nitroimidazoles was dissolved in ethyl acetate-hexane and subjected to solid-phase extraction cleanup by amine extraction columns. The effluent was evaporated to dryness, and residues were dissolved and determined by LC with an ultraviolet detector set at 315 nm. The limits of detection were 1.0-2.0 ng/g for MNZ, DMZ, RNZ, TNZ, and HMMNI in honey. Average recoveries ranged from 71.5-101.4% in honey fortified at 10, 20, 50, and 100 ng/g. The method was validated for the analysis of real honey samples.

A QuEChERS-Based Sample Preparation Method for the Analysis of 5-Nitroimidazoles in Bovine Milk by HPLC-DAD.

In this study, a simple, cost-effective, and sensitive HPLC diode-array detection method was developed for the simultaneous determination of six different 5-nitroimidazoles [metronidazole, 2-hydroxymethyl-1-methyl-5-nitro-1H-imidazole, dimetridazole (DMZ), ronidazole, ornidazole, and ipronidazole] in bovine milk samples. A QuEChERS-based sample preparation procedure was optimized by evaluating different cleanup sorbents, including zirconium-based sorbents (Z-Sep and Z-Sep+), C18, and primary-secondary amine (PSA), as well as EMR-Lipid cleanup solution. Acceptable analytical performance for all analytes was observed with recoveries in the range of 45-93% and RSDs of less than 15%. Negligible matrix interference was observed for most of the analytes due to application of PSA sorbent in a dispersive solid-phase extraction cleanup step. Method LOQs (mLOQs) for five of the six investigated analytes were set at a satisfactory low food product value of 2.5 ng/mL. For DMZ only, the mLOQ was set at 10 ng/mL. The procedure was evaluated through the analysis of 10 different natural samples.

Transfer of nitroimidazoles from contaminated beeswax to honey.

Nitroimidazoles are not authorised for the treatment of honey bees in the European Union. However, they can be found in honey largely because they are illegally used in apiculture for the treatment of Nosema. The aim of the study was to examine the possible transfer of nitroimidazoles (metronidazole, ronidazole, dimetridazole and ipronidazole) from contaminated beeswax to honey. The wax foundations fortified with a mixture of four nitroimidazoles at three concentration levels (1000, 10,000 and 100,000 µg kg-1) were placed in beehives to let the honeybees (Apis mellifera L.) draw out the contaminated wax foundations to honeycombs. At 1 month from the start, the frames filled with capped honey were removed from the hives for a first sampling of honey. Next, the honeycombs were further incubated for 5 months in the laboratory at 35°C and sampled monthly. In the sampled honey, the concentrations of nitroimidazoles and their main metabolites (hydroxymetronidazole, 2-hydroxymethyl-1-methyl-5-nitroimidazole, hydroxyipronidazole) were determined by LC-MS/MS and compared with those determined in the nitroimidazole-containing wax foundations. Each of the tested nitroimidazoles could migrate from beeswax to honey kept in the contaminated combs at each tested concentration level. Higher maximum concentrations of residues in honey sampled from contaminated combs at 1000, 10,000 and 100,000 µg kg-1 were observed for metronidazole (28.9, 368.5 and 2589.4 µg kg-1 respectively) and ronidazole (27.4, 232.9 and 2351.2 µg kg-1 respectively), while lower maximum concentrations were measured for dimetridazole (0.98, 8.4 and 67.7 µg kg-1) and ipronidazole (0.9, 7.9 and 35.7 µg kg-1 respectively). When we took into account that a frame completely filled with honey on both sides of the comb contained 110 g of beeswax and 2488 g of honey, and that this ratio was constant, then maximum amounts of initial metronidazole, ronidazole, dimetridazole and ipronidazole that migrated from contaminated wax foundations to honey could be calculated: 65-89%, 55-63%, 1.7-2.7% and 1.4-2.3%, respectively.

Analysis of four 5-nitroimidazoles and their corresponding hydroxylated metabolites in egg, processed egg, and chicken meat by isotope dilution liquid chromatography tandem mass spectrometry.

An isotope dilution liquid chromatography-electrospray ionization-tandem mass spectrometry method is presented for the simultaneous analysis of several 5-nitroimidazole-based veterinary drugs, which are dimetridazole (DMZ), ronidazole (RNZ), metronidazole (MNZ), ipronidazole (IPZ), and their hydroxylated metabolites (DMZOH, MNZOH, and IPZOH), in egg (fresh egg, whole egg powder, and egg yolk powder) and chicken meat. Data acquisition was achieved by applying multiple reaction monitoring, and quantitation was performed by means of five deuterated internal standards (ISs), namely, DMZ-d3, RNZ-d3, IPZ-d3, DMZOH-d3, and IPZOH-d3, whereas MNZ and MNZOH were quantitated using DMZOH-d3. At the lowest fortification levels (i.e., 0.5 microg/kg for fresh egg and chicken meat and 1.0 microg/kg for other egg-based matrices) and for compounds having their own corresponding deuterated analogue used as an IS, acceptable performance data were obtained (corrected recoveries, 88-111%; decision limits, 0.07-0.36 microg/kg; detection capabilities, 0.11-0.60 microg/kg; and within-lab precision, < or = 15%). The method failed to give acceptable quantitative results for MNZ and MNZOH due to the unavailability of the corresponding deuterated ISs. Nevertheless, a reliable identification of these two analytes at levels < or = 1 microg/kg was still feasible.

Determination of the persistence of dimetridazole, metronidazole and ronidazole residues in black tiger shrimp (Penaeus monodon) tissue and their stability during cooking.

The depletion of three banned nitroimidazole drugs - dimetridazole (DMZ), metronidazole (MNZ) and ronidazole (RNZ) - was investigated in black tiger shrimp (Penaeus monodon) following in-water medication. The highest concentrations of residues were measured immediately after the 24-h immersion (d0). At this time, MNZ and MNZ-OH residues were measured in shrimp tissue samples at concentrations ranging from 361 to 4189 and from 0.28 to 6.6 µg kg(-1), respectively. DMZ and its metabolites HMMNI ranged in concentration between 31,509 and 37,780 and between 15.0 and 31.9 µg kg(-1), respectively. RNZ and HMMNI concentrations ranged from 14,530 to 24,206 and from 25.0 to 55 µg kg(-1), respectively. MNZ, DMZ and RNZ were the more persistent marker residues and can be detected for at least 8 days post-treatment. MNZ-OH was only detectable on d0 following treatment with MNZ. HMMNI residues were only detectable up to d1 (0.97-3.2 µg kg(-1)) or d2 (1.2-4.5 µg kg(-1)) following DMZ and RNZ treatment, respectively. The parent drugs MNZ, DMZ and RNZ were still measureable on d8 at 0.12-1.0, 40.5-55 and 8.8-18.7 µg kg(-1), respectively. The study also investigated the stability of nitroimidazole residues under various cooking procedures (frying, grilling, boiling, and boiling followed by microwaving). The experiments were carried out in shrimp muscle tissue containing both high and low concentrations of these residues. Different cooking procedures showed the impact on nitroimidazole residue concentration in shrimp tissue. Residue concentration depleted significantly, but partially, by boiling and/or microwaving, but the compounds were largely resistant to conventional grilling or frying. Cooking cannot therefore be considered as a safeguard against harmful nitroimidazole residues in shrimp.

Determination of three nitroimidazole residues in poultry meat by gas chromatography with nitrogen-phosphorus detection.

A method was developed for the determination of the nitroimidazole compounds dimetridazole (DMZ), ronidazole (RNZ) and metronidazole (MNZ) by gas chromatography with nitrogen phosphorus detection. Nitroimidazole compounds were extracted with acetonitrile, followed by acidification using acetic acid and cleanup using strong cation-exchange (SCX) SPE column. Validation in chicken muscle fortified at a concentration of 5 microg/kg gave mean recoveries of 85% DMZ, 90% RNZ, 80% MNZ with RSDs of 13.0, 14.3, 11.2%, respectively (n=6). The method is suitable for statutory residue testing and is used as a quick screening method in the National Residue Surveillance Plan in China.

Chromatographic and spectroscopic characterization of sulphur-bound dimetridazole and ranidazole derivatives.

The 5-nitroimidazoles, dimetridazole and ronidazole, two important veterinary drugs, were reacted under reductive conditions with the sulfhydryl-containing substrates cysteine and glutathione to yield 5-amino-4-S-substituted imidazoles. After purification by reversed-phase liquid chromatography (RP-LC), the four adducts were characterized by RP-LC with photodiode array detection using conditions where their parent drugs were not eluted from the column. Structural identification was conducted by spectroscopic techniques, mainly 1-dimensional and 2-dimensional NMR. While the dimetridazole adducts were found to be monosubstituted at the C-4 position, the two ronidazole products contained two units of the sulfhydryl substrate, located at the C-4 and C-6 positions.

Determination of nitroimidazoles and their metabolites in swine tissues by liquid chromatography.

A liquid chromatographic method was developed for determination of metronidazole (MNZ), ronidazole (RNZ), dimetridazole (DMZ), and 2-hydroxymethyl-1-methyl-5-nitroimidazole (DMZOH) in swine tissue. After extraction with ethyl acetate and evaporation, the nitroimidazoles were redissolved in hydrochloric acid. Hexane was used in the liquid-liquid extraction to remove fat. An Oasis HLB solid-phase extraction was performed after neutralization of the acidic extract. The limits of detection were 1.0-2.0 microg/kg for DMZOH, MNZ, RNZ, and DMZ in muscle and liver. Average recoveries ranged from 80.1 to 83.9% in muscle fortified at 10, 20, and 50 microg/kg; average recoveries in liver ranged from 78.9 to 82.3%. The procedure provides a simple and sensitive method for monitoring DMZOH, MNZ, RNZ, and DMZ residues in swine tissues.

Microbiological method for determining macrolides in animal feeds in the presence of other drugs by thin-layer chromatography detection.

A method was developed to separate, detect, and quantitate erythromycin (ERY) and tylosin (TYL) in animal feeds in the presence of 11 other drugs: 3 nitrofurans, 2 tetracycline antibiotics, 3 sulfonamides, 2 coccidiostats, and 1 antibacterial growth promoter. ERY and TYL were separated from coexisting drugs, detected by thin-layer chromatography, and quantitated microbiologically by an agar diffusion method. Analysis of 125 experimental animal feed samples fortified at 5 levels (7.5-400 ppm) with ERY and TYL and at 1 level (50 ppm) with the rest of the drugs gave limits of quantitation of 2 and 5 ppm, recoveries of 90.3 and 92.4%, and relative standard deviations of 4.3-7.3% and 3.6-6.1%, respectively.

A false positive case due to matrix interference in the analysis of ronidazole residues in muscle tissue using LC-MS/MS.

In contrast with the information of the inspection body concerning the use of ronidazole, several non compliant muscle samples were detected using a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method in accordance with confirmation criteria of Decision 2002/657/EC. This led to the suspicion that non compliance could be due to false positive results. In this context, a liquid chromatography-high resolution mass spectrometry (LC-HRMS) method was developed and sample extracts were re-analyzed, resolving the co eluting isobaric interfering peak, which also has an interfering product ion with the transition product (m/z 201>140).

Detection of metronidazole and ronidazole from environmental samples by surface enhanced Raman spectroscopy.

In this study, the surface enhanced Raman spectra (SERS) of two prohibited veterinary drugs, metronidazole (MNZ) and ronidazole (RNZ), have been acquired, and compared to the theoretically calculated spectra using density function theory (DFT). The experimental Raman and SERS spectra of MNZ and RNZ exhibit high resemblance with the DFT calculations. SERS detection of MNZ and RNZ from standard solutions as well as real environmental samples (tap, lake, swamp waters and soil) was performed on highly sensitive and reproducible silver nanorod array substrates. The limits of detection for MNZ and RNZ are 10 and 1 µg/mL in methanol and ultra-pure water, respectively, and 10-50 µg/mL in the environmental samples. The SERS-based method demonstrates its potential as a rapid, simple, and inexpensive means for the onsite screening of banned antibiotics from the aquatic and sediment environments, with minimal requirement for sample pretreatment.

Development of a rapid method for the determination and confirmation of nitroimidazoles in six matrices by fast liquid chromatography-tandem mass spectrometry.

A rapid liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed to identify and to quantify nitroimidazoles, metronidazole (MNZ), ronidazole (RNZ) and dimetridazole (DMZ) and their corresponding hydroxy metabolites, MNZ-OH and 2-hydroxymethyl-1-methyl-5-nitroimidazole (HMNNI) in plasma, milk, muscle, egg, honey and feed samples. The same sample clean-up procedure including a novel solid-phase extraction (SPE) on polymeric Strata-SDB cartridges was used for each matrix. The analytes were separated on Kinetex XB C-18 core-shell type HPLC column using isocratic elution mode with a mobile phase containing 0.1% formic acid in water/methanol (88/12, v/v, pH 2.6) at a flow rate of 0.7 ml/min. The main advantage of the developed method is that the analysis time of only 3 min, which is about three to ten times shorter than in other reported HPLC methods. The developed method was validated using a matrix-comprehensive in-house validation strategy. The matrix effect of LC-MS/MS analysis was also investigated. Results are presented from the successful application of the developed method to an incurred pork meat certified reference material and to incur porcine plasmas in a proficiency test in year 2011.

[Determination of nitroimidazoles in oral hygiene by ultra-performance liquid chromatography-tandem mass spectrometry].

A method for the simultaneous determination of metronidazole, tinidazole, ornidazole, ronidazole and dimetridazole in oral hygiene by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) has been developed. The sample was diluted with 0.1% formic acid/acetonitrile (95:5, v/v), then centrifuged and filtered with a membrane. The separation was carried out on a Cloversil C18 column (100 mm x 2.1 mm, 3.5 microm) with the gradient elution of 0.1% formic acid and acetonitrile as the mobile phases. The analytes were determined by UPLC-MS/MS and quantified by external standard method. The calibration curves showed good linearity in the range of 1.0-60.0 microg/L with r > or = 0.9992. The recoveries were 91.5%-108% at the three spiked levels of 10.0, 20.0 and 100 mg/kg, and the relative standard deviations were 1.14%-5.22%. This method is easy, sensitive and suitable for the determination of nitroimidazoles in oral hygiene.

Determination of dimetridazole, metronidazole and ronidazole in salmon and honey by liquid chromatography coupled with tandem mass spectrometry.

A liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed to determine the residues of dimetridazole (DMZ), metronidazole (MNZ) and ronidazole (RNZ) in salmon and honey. These compounds were extracted with ethyl acetate from samples and cleaned up using a silica solid phase extraction (SPE) cartridge. These compounds were determined by reversed-phase LC using a C18 column with distilled water-methanol as the mobile phase, and MS detection in the positive mode by applying selected reaction monitoring (SRM). DMZ-d(3), MNZ-(13)C(2),(15)N(2) and RNZ-d(3) were used as internal standards. The method was validated in salmon and honey spiked with these compounds at 0.4-2 µg/kg, and average recoveries were in the range of 91.2-107.0%. Repeatability was 1.7-17.1% and intermediate precision was less than 20%. The detection limits of DMZ, MNZ and RNZ in salmon and honey were 0.05-0.2 µg/kg. The method was applied to 3 salmon and 20 honey samples. The concentrations of these compounds in all samples were lower than the detection limits established by the Ministry of Health, Labour and Welfare in Japan.