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Seven β2-agonist (clenproperol, clenbuterol, salbutamol, bronbuterol, ractopamine, clenpenterol and clencyclohexerol) were determined simultaneously in human and bovine urine by isotope dilution LC-ESI-MS/MS in a triple quadrupole instrument. The method is based on the application of multiple linear regression in combination with compound-specific minimally 13C-labelled analogues. Additionally, the increase of the bandpass of the first quadrupole during the selected reaction monitoring (SRM) measurement procedure allowed the simultaneous quantification of the seven compounds at sub ngg-1 levels in a single chromatogram without resorting to a methodological calibration graph. Recovery values at concentration levels between 5.0 and 0.05ngg-1 ranged from 95 to 110% in fortified bovine urine and from 91 to 108% in human urine, with relative standard deviations lower than 5% except for salbutamol and ractopamine. The proposed methodology was validated by analyzing the certified reference material BCR-503 (lyophilized bovine urine) certified for clenbuterol and salbutamol. The limits of detection (LOD) for a sample volume of 10mL of both human and bovine urine was found to be lower than 0.012ngg-1 for all compounds, except to salbutamol in bovine urine which was of 0.029ngg-1. The use of compound-specific isotopically labelled analogues minimally labelled in 13C minimized the occurrence of isotope effects and corrected for matrix effects during ESI ionization and can be efficiently applied for the quantification of ultra-trace concentrations of β2-agonists in human and bovine urine.

In this work, the implementation of isotope dilution mass spectrometry (IDMS) using minimal labeling and isotope pattern deconvolution (IPD) is evaluated as a strategy for the minimization of matrix effects during trace determination of β 2 -agonists in complex matrices by liquid chromatography electrospray ionization mass spectrometry (LC–ESI-MS). First, the parameters affecting the measurement of isotopic composition of organic compounds by liquid chromatography electrospray ionization high resolution mass spectrometry with a time-of-flight analyzer were evaluated using as a case of study three different β 2 -agonists: clenbuterol, clenproperol and brombuterol. Then, a calibration graph-free IDMS methodology was evaluated in order to overcome matrix effects in LC–ESI-MS in complex samples. In this procedure singly 13 C-labeled analogues of clenbuterol, clenproperol and brombuterol were employed in combination with IPD. Using this approach accurate and precise results were obtained in the simultaneous quantification of β 2 -agonists in human urine and bovine liver, even at the sub ng g −1 and particularly in spite of the previously reported matrix effects. Recovery rates in the range of 97–114% in fortified human urine and from 95% to 111% in fortified bovine liver were obtained with RSD (%) of independent recovery experiments always lower than 6%. These results demonstrate that the proposed methodology based on the use of 13 C 1 -labeled standards and IPD is a reliable approach for accurate LC–MS quantitation of small molecules and compatible with full-scan high-resolution mass spectrometry.

The development of a simple and rapid multielemental speciation method is described with the ultimate goal to simultaneously determine various organometallic compounds of mercury, lead and tin (inorganic mercury, methylmercury, trimethyllead, triethyllead, monobutyl-, dibutyl- and tributyltin) in natural water samples. The analytical method consists on the ethylation with NaBEt 4 , simultaneous headspace-solid phase microextraction (HS-SPME) of the derivatives and final gas chromatographic-mass spectrometric (GC–MS) analysis. After optimization of important process parameters, like SPME fiber coating, extraction time and extraction temperature, the analytical characteristics were evaluated. Detection limits in the low ng l −1 level, linearity over three orders of magnitude and repeatability in the range of 3–20% were achieved for all compounds under study. The accuracy of the method in terms of average percentage recovery of the compounds in spiked river water and seawater samples was better than 90%. Finally, application of the proposed method to real natural aqueous samples enabled the simultaneous determination of all the compounds under study in seawater samples obtained from the marina area of Gijon (Asturias, Spain).

The feasibility of developing a single-step clean-up, enrichment procedure for organochlorine pesticides (OCPs) in fish tissue samples based on solid-phase microextraction (SPME) was investigated. The general analytical methodology developed combines conventional solid-liquid extraction of the OCPs from the sample using an organic solvent with SPME over the organic extract followed by gas chromatography-electron-capture detection (GC-ECD) analysis. Experimental SPME conditions such as extraction time, temperature and matrix effects were optimised. Under optimised conditions, precision, linearity range, detection limits and accuracy were evaluated. Detection limits obtained for fish tissue samples were in the range of 0.1-0.7 ng g(-1). Good recoveries (over 70% in all cases) were achieved from samples spiked at a concentration level of 10 ng g(-1). The accuracy of the developed SPME-GC-ECD procedure in real samples has been verified by analysing, using the standard addition method, a certified reference material (CRM 430, OCPs in pork fat) with satisfactory results.