Method validation for the determination of lead in raw cow's milk by electrothermal atomic absorption spectrometry

In this study, lead in raw cow's milk has been determined by validated electrothermal atomic absorption spectrometry (ETAAS) with Zeeman-effect background correction. Maximum pyrolysis and optimum atomization temperatures of lead were determined in the presence of modifiers. Pd + Mg(NO3)2 has been found a powerful modifier mixture for the determination of lead. The analytical parameters of the method such as limit of detection, limit of quantification and the effect of interfering ions have been investigated. The detection limit (3sigma) achieved by the method was calculated to be 0.62 ng/mL for Pb. Repeatability of the method evaluated as the relative standard deviation of 16-17 replicates using 5 ng/mL, under optimum experimental conditions were about 1.5% for synthetic sample solution and about 3% for real sample (N = 5). The described method has been validated by analyzing certified reference material (BCR-CRM 150) and by comparing the results with those obtained by inductively coupled plasma mass spectrometry (ICP-MS). The validated method was applied to raw cow's milk samples produced in 7 different regions of Turkey in 2003-2004. Raw cow's milk contained a mean (range) of 31.4 (2.5 - 313) microg kg(-1) lead with a relative error below 2%.     

A liquid chromatography-mass spectrometric method for the determination of oak moss allergens atranol and chloroatranol in perfumes

This paper describes a validated liquid chromatographic-tandem mass spectrometric method for quantitative analysis of the potential oak moss allergens atranol and chloroatranol in perfumes and similar products. The method employs LC-MS-MS with electrospray ionization (ESI) in negative mode. The compounds are analysed by selective reaction monitoring (SRM) of 2 or 3 ions for each compound in order to obtain high selectivity and sensitivity. The method has been validated for the following parameters: linearity; repeatability; recovery; limit of detection; and limit of quantification. The limits of detection, 5.0 ng/mL and 2.4 ng/mL, respectively, for atranol and chloroatranol, achieved by this method allowed identification of these compounds at concentrations below those causing allergic skin reactions in oak-moss-sensitive patients. The recovery of chloratranol from spiked perfumes was 96+/-4%. Low recoveries (49+/-5%) were observed for atranol in spiked perfumes, indicating ion suppression caused by matrix components. The method has been applied to the analysis of 10 randomly selected perfumes and similar products.     

Determination of multi-class pharmaceuticals in wastewater by liquid chromatography–tandem mass spectrometry (LC–MS–MS)

An analytical method for multi-class pharmaceuticals determination in wastewater has been developed and validated. Target compounds were: sulfonamides (sulfadiazine, sulfaguanidine, sulfamethazine, sulfamethoxazole), fluoroquinolones (ciprofloxacin, enrofloxacin, norfloxacin), diaminopyrimidine (trimethoprim), anaesthetic (procaine), anthelmintic (praziquantel and febantel), and macrolide (roxithromycin). The method involves pre-concentration and clean-up by solid-phase extraction (SPE) using Strata-X extraction cartridges at pH 4.0. Target analytes were identified and quantitatively determined by liquid chromatography–tandem mass spectrometry using multiple reaction monitoring (MRM). Recoveries were higher than 50% with relative standard deviation (RSD) below 18.3% for three concentrations. Only for sulfaguanidine was low recovery obtained. Matrix effect was evaluated using matrix-matched standards. The method detection limit (MDL) was between 0.5 and 5 ng L⁻¹ in spiked water samples. The precision of the method, calculated as relative standard deviation, ranged from 0.5 to 2.0% and from 1.4 to 8.3 for intra-day and inter-day analysis, respectively. The described analytical method was used for determination of pharmaceuticals in effluent wastewaters from the pharmaceutical industry.     

Simultaneous screening of 21 potential adulterants in dietary supplements for the treatment of prostate diseases using ultra-performance liquid chromatography and liquid chromatography-electrospray ionization-tandem mass spectrometry

Reports of the number of adulteration cases using illegal therapeutic substances in dietary supplements have increased. In recent years, various dietary supplements are being distributed that exaggerate the efficacy of treatment for prostate-related diseases. To develop the preemptive monitoring method, we selected 21 prostate-related therapeutic substances and optimized the simultaneous ultra-performance liquid chromatography and liquid chromatography-electrospray ionization-tandem mass spectrometry and pretreatment procedures for various types of matrices including solid, liquid, and soft capsule samples. The methods were validated by determining the specificity, linearity, limit of detection, limit of quantification, method detection limit, method quantitation limit, precision, accuracy, recovery, stability, and matrix effect. The simultaneous methods were validated according to the international guidelines. In addition, using the validated methods, 81 real samples, which were searched and purchased by focusing on promotional phrases, such as prostate and prostatic hyperplasia, were successfully screened. As a result, sildenafil and tadalafil were detected in one seized capsule sample (5.15 and 14.6 mg/g, respectively). Synthetically, our approach could be useful for the determination of illegal therapeutic substances potentially adulterated in various types of dietary supplements.     

Development and validation of a solid-phase extraction and gas chromatography-tandem mass spectrometry method for the determination of isopropyl-9H-thioxanthen-9-one in carton packaged milk

A simple and efficient method for the determination of isopropyl-9H-thioxanten-9-one (ITX) in different fat content milk samples and baby milk samples stored in packaged cartons was developed and validated. Samples were extracted using solid-phase extraction (SPE) and analysed by gas chromatography-tandem mass spectrometry operated in selected reaction monitoring mode (SRM). Validation was carried out in terms of limit of detection (LOD), limit of quantitation (LOQ), linearity, precision and trueness. LOD and LOQ values in the low microg/L were achieved, whereas linearity was established within 0.5-500 microg/L range. Good precision was obtained both in terms of intra-day repeatability and inter-day precision on two concentration levels (RSD% lower than 2%). Good percentage recoveries were obtained (92.0-102.0%) even in the presence of high amount of fat. Finally, the developed method was successfully applied to analyse a number of commercial milk samples with different fat content and baby milk samples.     

Quantitative determination of dihydrostreptomycin in bovine tissues and milk by liquid chromatography-electrospray ionization-tandem mass spectrometry

Dihydrostreptomycin (DHS) is an aminoglycoside antibiotic used in veterinary medicine in combination with benzylpenicillin for the treatment of bacterial infections in cattle, pigs and sheep. A method to determine its residues in edible tissues of cattle, as well as in milk, was developed and validated. Extraction of DHS from the tissues was performed using a liquid extraction with a 10 mM phosphate buffer containing 2% (w/v) trichloroacetic acid, while milk samples were treated with a 50% (w/v) trichloroacetic acid solution, followed by a solid-phase clean-up procedure on a carboxypropyl (CBA) weak cation exchange column. Ion-pair chromatography, using a mixture of 20 mM pentafluoropropionic acid in water and acetonitrile as the mobile phase, was used to retain DHS and the internal standard streptomycin (STR) on a Nucleosil (5 microm) reversed-phase C18 column. The components were detected and quantified by electrospray ionization (ESI) tandem mass spectrometry. The method could be validated according to EC (European Community) requirements with respect to linearity, trueness and precision, the latter evaluated at the maximum residue limit (MRL) - 1000 ng g(-1) for kidney, 500 ng g(-1) for muscle, liver and fat, and 200 ng g(-1) for milk -, at one-half of the MRL and at one and a half times the MRL. A limit of quantification of 10 ng g(-1) and 1 ng ml(-1) was obtained for all tissues and for milk, respectively, which is far below one-half of the MRL as requested, while the limit of detection was in the low ppb range, varying between 1.9 and 4.2 ng g(-1) for the different tissues tested, and being 0.6 ng ml(-1) for milk. The method was used for the monitoring of DHS residues in incurred tissue and milk samples coming from cattle medicated with DHS in combination with benzylpenicillin by intramuscular injection, in order to evaluate withdrawal times.     

A sensitive liquid chromatography–tandem mass spectrometry method for quantitative bioanalysis of fingolimod in human blood: Application to pharmacokinetic study

A simple and sensitive liquid chromatography–tandem mass spectrometry (LC–MS/MS) method has been developed and validated for the determination of fingolimod in human blood. The analyte and internal standard fingolimod-d4 were extracted from 300 μl of human blood using protein precipitation coupled with solid-phase extraction method. The chromatographic separation was achieved with a Kinetex biphenyl column (100 × 4.6 mm, 2.6 μm) under isocratic conditions at the flow rate of 0.8 ml/min and column temperature was maintained at 45°C. The detection of analyte and internal standard was carried out by tandem mass spectrometry, operated in positive ion and multiple reaction monitoring acquisition mode. The method was fully validated for its selectivity, precision, accuracy, linearity, stability, detection and quantification limit. The extraction recovery of fingolimod in human blood ranged from 98.39 to 99.54%. The developed method was linear over the concentration range of 5–2500 pg/ml with a detection limit of 1 pg/ml. The developed method was validated and successfully applied for pharmacokinetic study after oral administration of fingolimod capsules.     

气相色谱-三重四极杆质谱测定中老年奶粉中甲基硒代半胱氨酸

采用气相色谱-三重四极杆质谱联用仪对中老年奶粉中的甲基硒代半胱氨酸进行定性确证和定量分析。样品经三氯乙酸和乙腈提取后,用氯甲酸乙酯在乙醇吡啶介质中衍生,衍生物经HP-5MS色谱柱分离并使用多反应监测模式进行定性和定量分析。甲基硒代半胱氨酸的线性范围为0.005～1.0 mg/L,方法检出限和定量下限分别为0.01、0.05 mg/kg。奶粉样品在0.05、0.2、0.4 mg/kg 3个加标水平下的平均回收率为79%～86%,相对标准偏差为2.8%～4.0%。该方法能满足中老年奶粉中甲基硒代半胱氨酸的质量控制需要。     

Quantification of anthelmintic drug residues in milk and muscle tissues by liquid chromatography coupled to Orbitrap and liquid chromatography coupled to tandem mass spectrometry

A simple method for the determination of some anthelmintic drugs and phenylbutazone residues in milk and muscle was developed. Following a fast and easy extraction and evaporation procedure, the extract was injected into an ultra performance liquid chromatography system coupled to a single stage Orbitrap detector. The high mass resolution of 50,000 full width at half maximum and corresponding narrow mass windows permitted a very selective and sensitive detection of analytes without requiring fragmentation of the observed [M+H]⁺ or [M+Na]⁺ ions. This eliminated some difficulties which have plagued the analysis of compounds belonging to the group of avermectins. The analytical method was validated according to the EU commission decision for Orbitrap based, but also for more traditional tandem mass spectrometry based detection and quantification. Equal repeatability but significantly higher sensitivity for critical compounds (avermectins) was obtained for the Orbitrap based detection. A result of this study was the conclusion that analytes with poor fragmentation properties (e.g. sodium-cationized molecules) can be more easily quantified by single stage high resolution mass spectrometry than by tandem mass spectrometry.     

超快速液相–质谱法同时测定液体奶和奶粉中磺胺和喹诺酮类药物残留

建立超快速液相–质谱联用法测定乳制品中磺胺和喹诺酮类药物残留的方法。试样加入乙腈沉淀蛋白,用0.22μm滤膜过滤,经EndeavorsilTMC18柱分离,选用乙腈–0.1%甲酸为流动相。在0.05~100.00μg/L范围内,17种兽药的质量浓度均与色谱峰面积均呈良好的线性,相关系数(r2)为0.990 6~0.999 8,方法检出限为0.05~0.10μg/kg,加标回收率为75.88%~116.00%,测定结果的相对标准偏差为1.5%~13%(n=5)。该方法快速、灵敏,可以满足对乳制品中多种兽药残留的快速检测要求。     

Determination of tetracycline antibiotics in cow's milk by liquid chromatography/tandem mass spectrometry

A liquid chromatographic/tandem mass spectrometric (LC/MS/MS) multiresidue method for the simultaneous quantitative determination of oxytetracycline, 4-epi-oxytetracycline, tetracycline, 4-epi-tetracycline, chlortetracycline, 4-epi-chlortetracycline and doxycycline in milk has been developed. An extraction procedure consisting of a liquid extraction of the milk samples with trichloroacetic acid was performed. The extract was centrifuged and the supernatant was filtered. Solid-phase extraction (SPE) with an OASIS HLB SPE column was used to clean up the sample extracts. The samples were analysed by LC/MS/MS. The LC separation was performed on a reversed-phase C18 column using gradient elution with a mobile phase consisting of water and a mixture of methanol/acetonitrile. The tetracycline analytes were detected with a quadrupole mass spectrometer using positive ion electrospray ionisation. The confirmatory method has acceptable detection limits and the different tetracyclines can be detected at a residue concentration between 5 and 20 microg/L. The method is validated according to the European requirements for veterinary drug residues and all determined parameters were found to conform to the criteria. The recovery values ranged from 90.4 to 101.2% with relative standard deviations (RSDs) no larger than 9.7%. The overall or between-day precision of the analytical assay determined as repeatability at several residue concentrations and expressed as RSD ranged from 3.3 to 10%. This analytical assay is a useful tool within the Belgian monitoring programme for confirmation of samples which have been positively screened for residues of tetracyclines in raw farm cow's milk.     

Food safety evaluation: Detection and confirmation of chloramphenicol in milk by high performance liquid chromatography-tandem mass spectrometry

A simple and rapid procedure for extraction of chloramphenicol (CAP) in milk and analysis by high-performance liquid chromatography coupled with quadrupole mass spectrometry in tandem was developed. The method consisted of one step of liquid-liquid extraction using ethyl acetate and acidified water (10 mmol L⁻¹ formic acid) and HPLC-MS/MS detection. CAP-D5 was used as internal standard. The method was validated according to Commission Decision 2002/657/EC. The calibration curves were linear, with typical r² values higher than 0.98. Absolute recovery of CAP from milk proved to be more than 95%, however CAP-D5 absolute recovery was 75%. The method was accurate and reproducible, being successfully applied to the monitoring of CAP in milk samples obtained from the Brazilian market. Decision limit (CCα) was 0.05 ng mL⁻¹ and detection capability (CCβ) was 0.09 ng mL⁻¹.     

Determination of enrofloxacin and its metabolite ciprofloxacin in goat milk by high-performance liquid chromatography with diode-array detection. Optimization and validation

A high-performance liquid chromatography-diode array detection method (HPLC-DAD) combined with liquid chromatography-mass spectrometry was developed for the determination of enrofloxacin and its metabolite ciprofloxacin in goat milk. The HPLC-DAD method validation was compliant with the "DG SANCO 1805/2000" European regulation. The residues were extracted from milk with phosphate buffer, purified on a C18 Speedisk cartridge SPE (Baker) and then analysed using HPLC-DAD set at 277 nm. The decision limit (CCa) calculated by spiking samples at 100 microg/kg with both analytes, taking into account the maximum residue limit (MRL) of 100 microg/kg established by the European Union for the sum of enrofloxacin and its metabolite ciprofloxacin in milk, was 105.3 microg/kg for enrofloxacin and 105.5 microg/kg for ciprofloxacin. The detection capability (CCbeta) was 110.7 and 110.9 microg/kg for enrofloxacin and ciprofloxacin, respectively. The mean recoveries of the method, calculated by spiking samples at 50, 100 and 150 microg/kg were 84% for enrofloxacin and 88% for ciprofloxacin. The limit of quantification was 20 microg/kg for both analytes. The HPLC-DAD validated method was successfully applied for the first time in goats milk, and proved to be suitable for the sensitive and accurate quantification and confirmation analysis of enrofloxacin and ciprofloxacin for regulatory purposes.     

Determination of chloramphenicol in royal jelly by liquid chromatography/tandem mass spectrometry

A liquid chromatographic/tandem mass spectrometric method was developed and validated for the determination of chloramphenicol (CAP) in royal jelly. Royal jelly samples were first denatured with lead acetate solution, and the CAP was extracted with solid-phase extraction before separation by liquid chromatography. A triple-quadrupole mass spectrometer operated in the negative electrospray ionization and selected-reaction monitoring mode was used for the detection of CAP. For method validation, royal jelly samples were fortified at CAP levels between 0.1 and 10.0 microg/kg; at these levels, recovery values (internal standard-corrected) ranged from 93.3 to 105.0%, and the within-laboratory reproducibility (relative standard deviation) was < or = 9.1%. The decision limit was 0.07 microg/kg, and the detection capability was 0.1 microg/kg.     

Determination of anthelmintic drug residues in milk using ultra high performance liquid chromatography–tandem mass spectrometry with rapid polarity switching

A new UHPLC–MS/MS (ultra high performance liquid chromatography coupled to tandem mass spectrometry) method was developed and validated to detect 38 anthelmintic drug residues, consisting of benzimidazoles, avermectins and flukicides. A modified QuEChERS-type extraction method was developed with an added concentration step to detect most of the analytes at <1 μg kg⁻¹ levels in milk. Anthelmintic residues were extracted into acetonitrile using magnesium sulphate and sodium chloride to induce liquid–liquid partitioning followed by dispersive solid phase extraction for cleanup. The extract was concentrated into dimethyl sulphoxide, which was used as a keeper to ensure analytes remain in solution. Using rapid polarity switching in electrospray ionisation, a single injection was capable of detecting both positively and negatively charged ions in a 13 min run time. The method was validated at two levels: the unapproved use level and at the maximum residue level (MRL) according to Commission Decision (CD) 2002/657/EC criteria. The decision limit (CCα) of the method was in the range of 0.14–1.9 and 11–123 μg kg⁻¹ for drugs validated at unapproved and MRL levels, respectively. The performance of the method was successfully verified for benzimidazoles and levamisole by participating in a proficiency study.     

Determination of Perfluorochemicals in Human Milk Using Isotope‐dilution Liquid Chromatography Tandem Mass Spectrometry

A highly precise and accurate analytical method utilizing an isotope‐dilution liquid chromatography tandem mass spectrometry was developed and validated to determine two perfluorochemicals (PFCs): perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS) in human milk samples. Identification of the analytes was confirmed under negative electrospray with multiple reaction monitoring (MRM) mode by the monitoring of one precursor ion and two product ions, and matching of relative ion intensities of the ions concerned in samples and calibration standards. Quantitation was based on the measurement of concentration ratios of the natural and labeled‐analogues in the samples and calibration mixtures. The isotope‐labeled internal standards were also used to correct the matrix effect and variations associated with the analysis. Intra‐ and inter‐day repeatabilities of replicate analyses of the PFOA and PFOS in milk samples were below 8%. The limit of quantitation was 2 pg/mL in a 5 mL milk sample. The PFOA and PFOS were detected in all 20 human milk samples at concentrations from 27.0 to 207 pg/mL. This is the first study to measure the occurrence of PFOA and PFOS in human milk from Taiwan.     

Online fully automated SPE‐HPLC‐MS/MS determination of ceftiofur in bovine milk samples employing a silica‐anchored ionic liquid as sorbent

Solid‐phase extraction coupled online with high performance liquid chromatography and tandem mass spectrometry was successfully applied to determine low concentrations of ceftiofur antibiotic in bovine milk samples. A silica‐anchored ionic liquid was applied as sorbent material to be used as extraction phase in the proposed online system. The material was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. In order to improve the system reproducibility, the following experimental parameters were optimized: organic solvent percentage, time and sample loading flow rate. Subsequently, the method was validated presenting satisfactory results as adequate selectivity, good linearity and correlation coefficient higher than 0.98. The limit of detection and quantification were 0.1 and 0.7 μg/L, respectively. The precision of the methodology was evaluated as repeatability and intermediate precision, with relative standard deviation values lower than 15%. The accuracy of the method ranged from 72.8 to 137% and the minimum and maximum recovery values were 73.4 and 111.3%, respectively. After the validation, seven milk samples were analyzed and although ceftiofur was not detected in any of them the method was demonstrated to be efficient when applied to the analysis of milk samples fortified with the pollutant of interest.     

Liquid chromatographic determination of diminazene diaceturate (Berenil) in raw bovine milk

A simple liquid chromatographic (LC) method is presented for the determination of diminazene (DZ) in raw bovine milk. DZ is extracted from raw milk by chilled aqueous centrifugation and is isolated from milk components on a cyano solid-phase extraction column. DZ is eluted by using a methanol-ion pairing reagent. A Phenomenex LUNA CN column and an acetonitrile-buffered mobile phase with a counter ion are used for gradient LC. The LC effluent is monitored at a detection wavelength of 372 nm by using a deuterium lamp. Under the parameters described, the retention time of DZ is 8-10 min with a peak area response of 6.5 mAU/ng. The method demonstrated excellent precision over all levels tested (25-400 ppb) with an overall average recovery of 90.4 +/- 14.5%. The method is applicable to the monitoring of milk for DZ residues at the 25 ppb level with a limit of quantitation of 10 ppb.     

Determination of Chloramphenicol in Milk Using a QuEChERS-Based on Liquid Chromatography Tandem Mass Spectrometry Method

A quantitative method for the determination of chloramphenicol in milk samples was developed based on the QuEChERS (quick, easy, cheap, effective, rugged, and safe) approach for liquid chromatography–tandem mass spectrometry (LC–MS/MS). Homogenized milk samples were extracted with acetonitrile. The partitioning step was performed after the addition of magnesium sulfate and sodium chloride. Chloramphenicol was determined using the electrospray negative ionization mode with tandem mass spectrometry. The procedure was validated according to the requirements of Commission Decision 2002/657/EC. The apparent recovery ranged from 90% to 110% and within-laboratory reproducibility was lower than 12%. The calculated limit of decision was 0.10 μg kg^?1 and the detection capability was 0.15 μg kg^?1. Validation results demonstrated that this method fulfills criteria for the determination of chloramphenicol in milk.     

Development of a method for the quantification of whey allergen traces in mixed-fruit juices based on liquid chromatography with mass spectrometric detection

The availability of accurate and sensitive detection methods for food allergens is crucial for the food industry to ensure the correct labelling of their products in order to protect allergic consumers. For this purpose a method using solid-phase extraction and liquid chromatography coupled to mass spectrometry was developed to detect traces of three allergenic cow milk proteins (lactalbumin, lactoglobulins A and B) in mixed-fruit juice samples. Different sample pre-treatments were compared and the best recoveries were obtained with a method employing a solid-phase extraction cartridge. Recoveries ranging from 68% to 79% were achieved for 5 and 20microg/ml tested and the limit of detection was set at 1microg/ml. Both full scan and multiple ion monitoring acquisition modes were investigated and compared. The method was utilized to analyse 15 mixed-fruit juices collected from the market and was found to be capable of positively identifying all three milk proteins. The developed method enables the unambiguous determination of allergenic whey proteins in mixed-fruit juices and can assist in the protection of milk allergic individuals.