M. Granados

Speciation of the Ionizable Antibiotic Sulfamethazine on Black Carbon (Biochar)

Adsorption of ionizable compounds by black carbon is poorly characterized. Adsorption of the veterinary antibiotic sulfamethazine (SMT; a.k.a., sulfadimidine; pK(a1) = 2.28, pK(a2) = 7.42) on a charcoal was determined as a function of concentration, pH, inorganic ions, and organic ions and molecules. SMT displayed unconventional adsorption behavior. Despite its hydrophilic nature (log K(ow) = 0.27), the distribution ratio K(d) at pH 5, where SMT(0) prevails, was as high as 10(6) L kg(-1), up to 10(4) times greater than literature reported K(oc). The K(d) decreases at high and low pH but not commensurate with the decline in K(ow) of the ionized forms. At pH 1, where SMT(+) is predominant and the surface is positive, a major driving force is π-π electron donor-acceptor interaction of the protonated aniline ring with the π-electron rich graphene surface, referred to as π(+)-π EDA, rather than ordinary electrostatic cation exchange. In the alkaline region, where SMT(-) prevails and the surface is negative, adsorption is accompanied by near-stoichiometric proton exchange with water, leading to the release of OH(-) and formation of an exceptionally strong H-bond between SMT(0) and a surface carboxylate or phenolate, classified as a negative charge-assisted H-bond, (-)CAHB. At pH 5, SMT(0) adsorption is accompanied by partial proton release and is competitive with trimethylphenylammonium ion, signifying contributions from SMT(+) and/or the zwitterion, SMT(±), which take advantage of π(+)-π EDA interaction and Coulombic attraction to deprotonated surface groups. In essence, both pK(a1) and pK(a2) increase, and SMT(±) is stabilized, in the adsorbed relative to the dissolved state.

Analytical procedures for the determination of organotin compounds in sediment and biota: a critical review.

Analytical procedures reported over the last 10 years for the determination of organotin compounds in sediment and biota have been critically reviewed in terms of sample handling, sensitivity, analytical cost, environmental acceptance, accuracy and precision. Critical steps in the analytical procedures are identified. Finally, research needs in extraction and determination are suggested.

High-throughput multiclass method for antibiotic residue analysis by liquid chromatography–tandem mass spectrometry☆

A simple and rapid method has been developed for the residue analysis of 39 antibiotics (tetracyclines, quinolones, penicillins, sulfonamides and macrolides) in foodstuffs of animal origin. The method combines an effective extraction technique, which uses water-methanol as extracting solvent, with ultra-high-pressure liquid chromatography-tandem mass spectrometry, allowing both confirmation and quantification in a single chromatographic run. The multiresidue method has been validated in chicken muscle matrix according to European Union Decision 2002/657/EC. It has been implemented as a routine method in a Public Health Laboratory, instead of the five plates test and LC methods previously used.

Determination of macrolide antibiotics by liquid chromatography

The liquid chromatographic separation of seven macrolides used in food producing animals in the European Union has been studied. Separation was performed by using an end-capped high-purity silica-based C18 column and mobile phases consisting of phosphate buffer (pH 2.5)-acetonitrile mixtures. The effect of pH and acetonitrile percentage on the separation was examined. Two UV-based detection systems, wavelength programming and diode array, were assayed. Detection limits were in the range 6-33 microg l(-1) for spiramycin, tilmicosin, tylosin, kitasamicin and josamicin and about 400 microg l(-1) for erythromycin and oleandomycin. The suitability of the method for multiresidue determination of the five macrolides is demonstrated by the analysis of spiked samples of chicken muscle.

Estimation of figures of merit using univariate statistics for quantitative second-order multivariate curve resolution

Abstract In this study, a straightforward approach is proposed for determining the figures of merit in multivariate curve resolution. The method is based on the recovery of the pure response profiles of the analytes after a curve resolution procedure. Figures of merit such as limit of detection, sensitivity, precision and accuracy are estimated from these pure analyte responses using univariate statistics directly from a calibration graph, as usual in univariate calibration. Examples of the calculation of the figures of merit in the determination of triphenyltin in synthetic and natural sea water samples by using excitation–emission matrix fluorescence are given.

Residue analysis of macrolides in poultry muscle by liquid chromatography-electrospray mass spectrometry.

A liquid chromatography-mass spectrometry method is proposed for the determination of seven macrolides authorised in the EU as veterinary drugs for food-producing animals. Sample treatment involves extraction of the analytes with a water-methanol mixture containing metaphosphoric acid and clean-up by SPE with a cation-exchange cartridge. Separation was carried out in an end-capped silica-based C18 column and mobile phases consisting of water/acetonitrile mixtures containing trifluoroacetic acid. A gradient elution, from 28 to 40% acetonitrile was used. Detection was performed by mass spectrometry with electrospray ionisation in the positive mode. Several parameters affecting the mass spectra were studied. The protonated molecular ion was selected for quantitation purposes under selected ion monitoring mode. Detection limits were in the range 1-20 microg l(-1). Recoveries ranged between 56 and 93% with RSD lower than 12%. The method has been successfully applied for multiresidue determination of seven macrolides below the MRLs established by the European Union.

Restricted access materials for sample clean-up in the analysis of trace levels of tetracyclines by liquid chromatography. Application to food and environmental analysis.

Restricted access materials (RAM) based on alkyl diol silica (ADS) porous particles were evaluated for the sample clean-up in tetracyclines analysis in milk and water samples by liquid chromatography. RAM with C(4), C(8) and C(18) bonded to the inner pore surfaces were tested, with C(8) providing the best performance. A switching column LC system which combines an ADS C(8) RAM column and an analytical C(18) column connected to a fluorimetric detector was used for tetracyclines analysis. The RAM clean-up removed large peaks that otherwise appeared in the initial time window of the chromatograms, attributed to proteins in milk samples and humic substances in water samples. Thus, quantification of analytes in real samples, especially of the most polar compounds such as oxytetracycline and tetracycline, was clearly improved.

Detection techniques in speciation analysis of organotin compounds by liquid chromatography

Analysis of organotin (OT) species in the environment demands very selective, sensitive methods. Liquid chromatography (LC) with a suitable detection system is one of the techniques of choice. The constraints imposed by the required sensitivity mean that, among the instrumental techniques used for detection with LC, only inductively-coupled plasma-mass spectrometry (ICP-MS), mass spectrometry (MS) and fluorimetry are well suited to environmental OT analysis. This article reviews the applications and compares the performances of these detection systems coupled with LC for OT analysis.

Targeted analysis with benchtop quadrupole-orbitrap hybrid mass spectrometer: application to determination of synthetic hormones in animal urine.

Sensitive and unequivocal determination of analytes/contaminants in complex matrices is a challenge in the field of food safety control. In this study, various acquisition modes (Full MS/AIF, Full MS+tMS/MS, Full MS/dd MS/MS and tSIM/ddMS/MS) and parameters of a quadrupole-orbitrap hybrid mass spectrometer (Q Exactive) were studied in detail. One of the main conclusions has been that, reducing the scan range for Full MS (using the quadrupole) and targeted modes give higher signal-to-noise (S/N) ratios and thereby better detection limits for analytes in matrix. The use of Q Exactive in a complex case, for the confirmatory analysis of hormones in animal urine is presented. A targeted SIM data dependent MS/MS (tSIM/ddMS/MS) acquisition method for determination of eight synthetic hormones (trenbolone, 17α ethinylestradiol, zeranol, stanozolol, dienestrol, diethylstilbestrol, hexestrol, taleranol) and a naturally occurring hormone (zearalenone) in animal urine were optimized to have sensitive precursors from targeted SIM mode and trigger MS/MS scans over the entire chromatograph peak. The method was validated according to EC/657/2002. CCα (decision limit) for the analytes ranged between 0.11 μg L(-1) and 0.69 μg L(-1) and CCβ (detection capability) ranged between 0.29 μg L(-1) and 0.90 μg L(-1).

Antibiotics in food: Legislation and validation of analytical methodologies

In this paper, European food safety legislation is presented, and special attention is devoted to monitoring residues of veterinary drugs in foodstuffs of animal origin. After a short review of the state of the art of analytical methodology for antibiotic residue analysis, the paper focuses on validation of analytical methods, with Decision 657/2002/EC as reference document. Finally, the main issues of the quality control of the analytical data, i.e. analysis of reference materials and participation in proficiency tests, are briefly addressed.