A dye encapsulated zinc-based metal-organic framework as a dual-emission sensor for highly sensitive detection of antibiotics.

Self-assembly of two Zn-MOFs, [Zn2L(DMF)3]·H2O·5DMF (1) and [Zn2L(H2O)2]·4H2O·3DMF (2), was achieved with an amide-functionalized tetracarboxylate ligand under similar conditions. Incorporated amide groups make the tetratopic linkers exhibit different configurations, tetrahedron and square, and subsequently combine tetrahedral [Zn2(CO2)4] clusters or square paddle-well [Zn2(CO2)4] clusters to afford a lon net for 1 and a nbo net for 2. Remarkably, 2 demonstrated high porosity and amide group decorated cages, and thereby proved to be a good capturing agent for a fluorescent dye molecule (DMASM). Consequently, a dual-emitting DMASM@2 sensor was successfully fabricated based on effective energy transfer from the host framework to DMASM with the variable luminescent color being visible to the naked eye. DMASM@2 could be used for the detection of metronidazole (MDZ) and dimetridazole (DTZ) with high sensitivity and remarkable recyclability.

A highly sensitive poly-arginine based MIP as an electrochemical sensor for selective detection of dimetridazole.

In this experiment, a highly effective electrochemical sensor based on a molecularly imprinted polymer has been developed for ultrasensitive detection of dimetridazole. The sensor was made by incorporating of dimetridazole as a template molecule during the electropolymerization of poly-arginine on a glassy carbon electrode. The modified electrode GCE/P-Arg@MIP was characterized by voltammetric and microscopic techniques. Differential pulse voltammetry method was used to detect target analyte under the optimum condition. The DPV response to dimetridazole was linear at 0.1 × 10-9 to 10 × 10-6 mol L-1 (R2 = 0.996), with a method detection limit (S/N = 3) of 0.1 × 10-9 mol L-1. Moreover, the proposed sensor shows satisfactory recovery ranges for the determination dimetridazole in commercially available egg, milk and 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.

Multi-class method for the determination of nitroimidazoles, nitrofurans, and chloramphenicol in chicken muscle and egg by dispersive-solid phase extraction and ultra-high performance liquid chromatography-tandem mass spectrometry.

This study describes the development of a multiresidue method for the efficient identification and quantification of nitroimidazoles, nitrofurans, and chloramphenicol in chicken and egg. After derivatization of nitrofuran metabolites, dispersive-solid phase extraction was used for the extraction of target analytes. An optimization strategy involved the selection of sorbents and extraction solutions for dispersive-solid phase extraction in order to achieve acceptably high recoveries and reduce co-extractives in the final extracts. Analytes were determined by ultra-high performance liquid chromatography-tandem mass spectrometry, in one single injection with a chromatographic run time of 7.5min. Mean recoveries ranged from 86.4% to 116.7% and interday precision was lower than 18%. The limits of quantification were between 0.1 and 0.5µg/kg, which were satisfactory to support surveillance monitoring. Finally, the method was applied to real samples, and metabolite of furazolidone, metronidazole and its metabolite, dimetridazole and its metabolite were detected in both chicken and egg samples.

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.

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 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.

Gamma irradiation of pharmaceutical compounds, nitroimidazoles, as a new alternative for water treatment.

The main objectives of this study were: (1) to investigate the decomposition and mineralization of nitroimidazoles (Metronidazole [MNZ], Dimetridazole [DMZ], and Tinidazole [TNZ]) in waste and drinking water using gamma irradiation; (2) to study the decomposition kinetics of these nitroimidazoles; and (3) to evaluate the efficacy of nitroimidazole removal using radical promoters and scavengers. The results obtained showed that nitroimidazole concentrations decreased with increasing absorbed dose. No differences in irradiation kinetic constant were detected for any nitroimidazole studied (0.0014-0.0017 Gy(-1)). The decomposition yield was higher under acidic conditions than in neutral and alkaline media. Results obtained showed that, at appropriate concentrations, H(2)O(2) accelerates MNZ degradation by generating additional HO(); however, when the dosage of H(2)O(2) exceeds the optimal concentration, the efficacy of MNZ degradation is reduced. The presence of t-BuOH (HO() radical scavenger) and thiourea (HO(), H() and e(aq)(-) scavenger) reduced the MNZ irradiation rate, indicating that degradation of this pollutant can take place via two pathways: oxidation by HO() radicals and reduction by e(aq)(-) and H(). MNZ removal rate was slightly lower in subterranean and surface waters than in ultrapure water and was markedly lower in wastewater. Regardless of the water chemical composition, MNZ gamma irradiation can achieve i) a decrease in the concentration of dissolved organic carbon, and ii) a reduction in the toxicity of the system with higher gamma absorbed dose.

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%.

The development of a multi-nitroimidazole residue analysis assay by optical biosensor via a proof of concept project to develop and assess a prototype test kit.

An assay based on optical biosensor technology has been developed to detect a broad range of nitroimidazole drug residues and their metabolites (dimetridazole (DMZ), metronidazole (MNZ), ronidazole (RNZ), hydroxymetronidazole (HO-MNZ) and hydroxydimetridazole (HO-DMZ)) in chicken muscle. The detection limit for the procedure was determined as 0.5 ppb for DMZ and detection capabilities (CCbetas) ranged from <1 ppb for DMZ, MNZ and RNZ to <2 ppb for HO-MNZ and HO-DMZ. Intra-assay variation (n=6) was calculated as 11.6% at a concentration of 1 ppb DMZ and 4.7% at a concentration of 2 ppb DMZ. Inter-assay variation (n=3) was determined to be 14.2% at a concentration of 1 ppb DMZ and 3.5% at a concentration of 2 ppb DMZ. A prototype kit based on this assay was produced and a multinational study was undertaken to independently evaluate its performance. The resulting data showed that the kit can be implemented with little difficulty in laboratories of varying expertise and is sensitive enough to meet the standards required by international law. Feedback from this study led to the incorporation of some minor improvements to the kit. The commercial partner in the project, XenoSense Ltd., was consulted with regards to producing a commercial test kit based on the prototype assay. As feedback from the collaborative study had been positive with respect to speed, ease of use and performance of the kit, the decision to commercialise the kit was taken. In conclusion, the prototype nitroimidazole kit was shown to offer numerous advantages over existing analytical techniques.

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.

Validation of a method for the detection and confirmation of nitroimidazoles and the corresponding hydroxy metabolites in pig plasma by high performance liquid chromatography-tandem mass spectrometry.

Nitroimidazoles (Ronidazole, Dimetridazole, Metronidazole, Ipronidazole) and their hydroxy metabolites are banned substances with antibiotic and anticoccidial activity. They are suspected to be carcinogenic and mutagenic. Since nitroimidazoles showed an inhomogeneous distribution and a rapid degradation in incurred muscle samples, plasma is the preferred target matrix for residue analysis. The analytical method of Polzer et al. [J. Polzer, C. Stachel, P. Gowik, Anal. Chim. Acta 521 (2004) 189] was adapted for liquid chromatography-tandem mass spectrometry detection and was validated in house according to the Commission Decision 2002/657/EC. The method is specific for all nitroimidazole except for Ipronidazole and its metabolite, due to interferences at their retention times in chromatograms of blank plasma and reagents samples. The absence of a matrix effect enables the use of a (linear) calibration curve in solution for quantitation. The apparent recovery (obtained after correction with a deuterated internal standard) is between 93% and 123%, except for the metabolite of Metronidazole (58-63%). The repeatability (CVr=2.49-13.39%) and intralaboratory reproducibility (CVRW=2.49-16.38%) satisfy the Horwitz equation. The obtained values for the detection capacity (CCbeta) range from 0.25 to 1 microg L(-1), while values obtained for the decision limit (CCalpha) are below CCbeta.

Confirmation of four nitroimidazoles in porcine liver by liquid chromatography-tandem mass spectrometry.

A sensitive and reliable multiresidue method is described for analysis of ronidazole, metronidazole, dimetridazole and the common metabolite of ronidazole and dimetridazole, 2-hydroxymethyl-1-methyl-5-nitroimidazole in swine liver. The sample preparation procedure was based on liquid-liquid extraction and mixed mode cation exchange/reverse phase solid-phase extraction. The compounds of interest were determined by reverse phase gradient liquid chromatography separation and tandem mass spectrometry (MS/MS) in the multiple reaction monitoring (MRM) mode. The limits of confirmation were 0.1-0.5 microg kg(-1) for the analytes.

[Determination of three nitroimidazole residues in royal jelly by high performance liquid chromatography-tandem mass spectrometry].

A method for analysis of trace metronidazole (MTZ), dimetridazole (DMZ) and ronidazole (RNZ) residues in royal jelly was developed by high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). After samples were dissolved in sodium hydroxide solution to disassociate target analytes from matrix, liquid-liquid extraction methods by ethyl acetate solvent were used. Matrix effects were minimized and good quantitation results were obtained by using highly-selective reaction monitoring (H-SRM) technology when deuterated dimetridazole (dimetridazole-D3) was selected as internal standard. Limits of detection (LODs) were 1.0 microg/kg for DMZ, 0.5 microg/kg for MTZ and RNZ (S/N > 5). Limits of quantitation (LOQs) were 2.0 microg/kg for DMZ, 1.0 microg/kg for MTZ and RNZ (S/N > 10). The linear ranges were 2.0 - 200 microg/L for all target analytes. Recoveries and relative standard deviations (RSDs) were in the ranges of 96.6% - 110.6% and 2.1% -7.4%, respectively. This method is suitable for statutory residue testing in the National Residue Surveillance Plan in China and meets the requirement for export.

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 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.

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.

Determination of dimetridazole, ronidazole and their common metabolite in poultry muscle and eggs by high performance liquid chromatography with UV detection and confirmatory analysis by atmospheric pressure chemical ionisation mass spectrometry.

A method was developed for the determination of the nitroimidazole compounds dimetridazole (DMZ) and ronidazole (RNZ) and their common metabolite, 2-hydroxymethyl-1-methyl-5-nitroimidazole (2-OH-M). Extracts obtained from a clean-up process using strong cation exchange (SCX) solid phase extraction (SPE) can be analysed either by high performance liquid chromatography with UV detection (HPLC-UV) or by high performance liquid chromatography with atmospheric pressure chemical ionisation mass spectrometry (HPLC-APCI-MS) as a confirmatory method. Up to 20 samples can be extracted in approximately 4 h. The HPLC-UV analysis had a limit of detection of 0.5 microgram kg-1. Validation in chicken muscle fortified at a concentration of 5 micrograms kg-1 gave recoveries of 75% DMZ, 77% RNZ and 81% 2-OH-M with RSDs of 16.4, 11.3 and 14.0%, respectively (n = 17). Validation in egg fortified at the same concentration gave recoveries of 77% DMZ, 80% RNZ and 80% 2-OH-M, with RSDs of 14.9, 22.0 and 18.2%, respectively (n = 18). The limit of detection of the HPLC-APCI-MS method was 0.1 microgram kg-1 for DMZ and RNZ and 0.5 microgram kg-1 for 2-OH-M. This method gave mean recoveries in fortified egg samples of 65% DMZ, 87% RNZ and 75% 2-OH-M with RSDs of 22, 11 and 14%, respectively (n = 10). The ratios of the peak areas of the molecular ion and a fragment ion were monitored as added confirmation of the presence of the analyte. Both the HPLC-UV screening procedure and the HPLC-APCI-MS confirmatory method have subsequently been used for the analysis of several hundred samples as part of UK surveillance programmes.

Determination of dimetridazole in poultry tissues and eggs using liquid chromatography-thermospray mass spectrometry.

A method is presented for the determination of the nitroimidazole drug dimetridazole (DMZ) in poultry tissues and eggs by liquid chromatography (LC)-thermospray mass spectrometry (MS). Deuteriated DMZ was employed as an internal standard. Samples were extracted with dichloromethane (muscle) or toluene (liver, egg) and applied to silica gel cartridges. Dimetridazole was eluted with acetone and the eluate evaporated to dryness at 40 degrees C under nitrogen. The residue was redissolved in methanol-water (1 + 1, v/v) and washed with hexane before LC-MS analysis. Quantification was by the ratios of the positive [M + H]+ ions at m/z 142 and 145 for DMZ and the internal standard, respectively. Internal standard corrected recoveries were between 93 and 102% with RSDs between 1.2 and 7.7% for liver spiked at 5, 10 and 20 ng g-1 and muscle and eggs spiked at 5 ng g-1. Absolute recoveries were approximately 80%. The method is suitable for statutory residue testing and was used to measure DMZ residues in eggs from chickens fed a diet containing DMZ at 10 mg kg-1.