Interferencia por ácido 2, 4 diamino-N10-metilpteroico en la determinación de metotrexato tras la administración de glucarpidasa / Interference due to 2, 4 diamino-N10-methylpteroic acid in the determination of methotrexate after the administration of glucarpidase

El tratamiento con metotrexato (MTX) a dosis elevadas implica una monitorización estrecha de los niveles del fármaco para confirmar su correcta eliminación. Uno de los posibles efectos secundarios es el fracaso renal, lo que ocasiona una acumulación de fármaco y un mayor efecto tóxico. La glucarpidasa (carboxipeptidasa-G2 o CPDG2) es una enzima recombinante que se utiliza para disminuir los niveles de MTX en pacientes que desarrollan fallo renal durante el tratamiento con altas dosis de MTX. La enzima reduce la concentración de MTX en un 95-99% de 15 a 30min después de la dosis. La glucarpidasa escinde el MTX en glutamato y ácido 2,4-diamino-N10-metilpteroico un metabolito menor e inactivo. Es conocida la reactividad cruzada del ácido 2,4-diamino-N10-metilpteroico en la medición de MTX mediante ensayos inmunológicos, que da lugar a una enorme sobreestimación de MTX. Sin embargo, los ensayos inmunológicos son la técnica mayoritariamente empleada en los laboratorios clínicos para la medición de MTX. Se presenta un caso de interferencia explicando la detección de MTX en las muestras de suero mediante cromatografía líquida acoplada a espectrometría de masas (LC-UHR-QTOF)

High-dose methotrexate (MTX) treatment involves close monitoring of drug level in order to confirm its proper elimination. One of the possible side effects of this therapy is renal failure, causing accumulation of the drug, and therefore is a mayor toxic effect. Glucarpidase (carboxypeptidase-G2 or CPDG2) is a recombinant enzyme used to reduce MTX serum levels in patients who develop acute renal failure during high-dose MTX treatment. The enzyme reduces MTX concentration by 95-99% within 15-30minutes after the dose. Glucarpidase cleaves MTX into glutamate and 2,4-diamino-N10-methylpteroic acid, a minor and non-active metabolite. Cross-reactivity of 2,4-diamino-N10-methylpteroic acid in immunological assays of MTX has been previously reported, and is said to cause an enormous overestimation in serum MTX analysis. However immunoassay is a widely used technique for MTX analysis, being the main method for its determination in most clinical laboratories. An interference case report is presented and MTX analysis in serum samples by liquid chromatography coupled with Ultra-High Resolution Q-Time of Flight Mass Spectrometry (LC-UHR-QTOF) is described

Flow-through optosensing device implemented with photochemically-induced fluorescence for the rapid and simple screening of metsulfuron methyl in environmental waters.

This paper describes the implementation of a flow-injection solid phase spectroscopy (FI-SPS) system with photochemically induced fluorescence (PIF) in micellar medium for the determination of metsulfuron-methyl (MET). The micelles containing a strongly fluorescent photoproduct generated after UV irradiation of the herbicide are strongly retained on C(18) silica gel filling the flow-cell placed in the detection area and the photoproduct is monitored at 323 and 378 nm for excitation and emission wavelengths, respectively. The solid support is easily regenerated for subsequent sample injections (at least up to 500 cycles tested). The system was calibrated for two injection volumes, 300 and 1000 microl. The detection limits and relative standard deviations were 0.71 and 0.14 ng ml(-1), and 4.5 and 3.3% for each injection volume, respectively. The system shows a very high throughput, 34 (300 microl) and 36 (1000 microl) analysis per hour. The optosensor was successfully applied to the herbicide determination in river, well and irrigation waters (recovery ranges from 96.0 to 106.0%).

Simultaneous flow-injection solid-phase fluorometric determination of thiabendazole and metsulfuron methyl using photochemical derivatization.

A flow-through optosensor implemented with photochemically induced fluorescence (PIF) is reported for the simultaneous determination of thiabendazole (TBZ) and metsulfuron methyl (MET). TBZ is determined by measuring its native fluorescence once retained on the solid support filling the flow-cell of a FI-system. On the other hand, a strongly fluorescent photoproduct from MET is generated on-line in micellar medium by UV irradiation and monitored in a similar way to TBZ. MET photoproduct and TBZ are separated by placing in the flow-system a minicolumn, filled with C(18) silica gel, which allows their sequential arrival to the detection area. The sorption of the species on the solid support in the detection area provides a noticeable improvement in sensitivity and selectivity when comparing with their determination in homogeneous solution. The detection limits and RSDs for TBZ and MET are 2.5 and 3.3 ng ml(-1) and 1.1 and 2.4%, respectively. The method is successfully applied to environmental water samples.

Determination of sub-ppb reserpine by an optosensing device based on photochemically induced fluorescence.

A flow injection-solid-phase spectroscopy (FI-SPS) system implemented with photochemically induced fluorescence (PIF) is described for the rapid and very sensitive determination of reserpine in biological fluids and pharmaceutical formulations. An intensively fluorescent photoproduct is in-line generated, retained on C18 silica gel in the detection area and monitored at 394/489 nm (lambdaex/lambdaem). After the establishment of the appropriate working variables, the system is calibrated at two different injection volumes, 100 and 800 microL, achieving detection limits of 0.33 and 0.05 ng mL(-1), respectively. The RSD for reserpine at 2 ng mL(-1) (800 microL) was 1.5% (n=10). The sampling rates were 46 and 43 h(-1) for each injection volume, respectively. The potential interference of some common species coexisting with reserpine in the analysed samples was also studied. The procedure was successfully applied to commercial formulations, urine and serum without any previous treatment of samples. Recoveries ranged from 94.9 to 100.2%.

Multicommutated flow-through optosensors implemented with photochemically induced fluorescence: determination of flufenamic acid.

This article describes a multicommutated flow injection-solid phase spectroscopy system implemented with photochemically induced fluorescence for the determination of flufenamic acid (FFA). A strongly fluorescent photoproduct is generated when FFA is irradiated online under UV light in a strong sulfuric medium. The photoproduct generated is retained on C(18) silica gel (which fills the detection area of the flow cell) and directly monitored on the active solid support at 258/442 nm (lambda(ex)/lambda(em)). After maximum signal recording, the sensing zone is regenerated by eluting the retained photoproduct with an appropriate H(2)SO(4)/MeOH solution. The sensor, completely automated, is based on the use of three-way solenoid valves conveniently operated by a homemade multicommutation software written in Java language. The system is calibrated at 10 and 60s for sampling time, showing detection limits of 1.28 x 10(-9) and 5.33 x 10(-10) molL(-1) and sampling rates of 38 and 28 h(-1), respectively, with relative standard deviations of 0.9 and 1.2%. The applicability of the method is demonstrated for the determination of FFA in human serum, human urine, and a pharmaceutical preparation without any pre-treatment. Good recovery levels were achieved between 90.5 and 103.7%.