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A multianalyte flow‐through sensor is proposed for the simultaneous determination of aspartame (AS) and acesulfame‐K (AK) in tabletop sweeteners. The procedure is based on the transient retention of AK in the ion exchanger Sephadex DEAE A‐25 placed in the flow‐through cell of a monochannel flow injection analysis (FIA) set‐up using pH 2.70 ortophosphoric acid/sodium dihydrogen phosphate buffer 0.06 M as carrier. In these conditions AS is very weakly retained, which makes it possible to measure the intrinsic ultraviolet (UV) absorbance of first AS and then AK after desorption by the carrier itself. The applicable concentration range, the detection limit, and the relative standard deviation were the following: for AS, from 10 to 100 µg mL−1; 5.65 µg mL−1; 3.4% (at 50 µg mL−1); and for AK, between 40 and 100 µg mL−1; 11.9 µg mL−1 and 1.61% (at 50 µg mL−1). The method was applied and validated satisfactorily for the determination of AS and AK blends in tabletop sweeteners. The results were compared a...

A preconcentration membrane for the retention and phosphorimetric determination of pharmaceuticals nalidixic and piromidic acids is proposed. The membrane has a circular zone of plasticized PVC adhered to the surface of a polyester strip, which constitutes the preconcentration area where the analytes are retained by absorption from a solution that contains it. Measurement of intrinsic phosphorescence in the synchronous phosphorescence spectra performed at 281/371 nm for nalidixic acid and 331/471 nm for piromidic acid make the resolution of the mixture possible. The applicable concentration range, detection limit, and precision (as relative standard deviation) are from 0.3 to 3.0 mg · l−1, 0.08 mg · l−1, and 5.1% for nalidixic acid and from 0.03 to 0.15 mg · l−1, 0.002 mg · l−1, and 5.2% for piromidic acid. The method was applied to the determination of residues of both pharmaceuticals in cow milk and human urine.

A flow-through optosensor with solid phase UV spectroscopic detection is proposed for the direct determination of the antioxidant Butilated Hydroxytoluene (BHT) without previous derivatization. The method is based on the transient retention of this compound in a flow-through cell packed with C18 silica using ethanol : water mixture as a carrier, and its intrinsic absorbance monitored at 274 nm. Afterwards, the recording of the analytical signal BHT was easily and quickly desorbed from the solid support by the same carrier. The calibration graphs were linear over the range 2.0–300.0 mg L−1 using area as the analytical parameter. The relative standard deviation (RSD) was between 0.5 and 1.6%. The method was applied to the determination of this antioxidant in several cosmetics samples and was validated using the standard addition methodology and an HPLC reference method.

A new procedure to determine copper has been proposed using an irreversible and disposable multilayer optical test strip. Two layers form the sensing zone: a copper sensitive and a dialysis layer. The test strip is characterised to be a disposable polyester sheet contained in a circular film 6 mm in diameter and 25 µm in thickness, with all reagents necessary to produce a selective response. The sensing zone was formed by Nafion as polymer, bathocuproine as a chromogenic reagent and p-anisidine as reducer. When it is applied to determination of copper in plasma samples, another layer of hydrogel D-6 is put on this membrane to eliminate the interference of proteins. When the test strip was introduced for 60 min into a plasma sample an orange colour developed. The absorbance at 475 nm was used as the analytical signal. The test strip responded linearly in the range 0.05–1.00 mg L−1. The reproducibility in the measurement of copper at 3.0 mg L−1, was 7.8%. The procedure was applied to the determinat...

Acetylsalicylic acid (ASA) and Codeine (CO) are two active ingredients usually found together in pharmaceutical preparations. A lot of procedures for determination of ASA are based on its previous hydrolysis to salicylic acid (SA). In this paper a procedure for both direct determination of CO and indirect determination of ASA in pharmaceuticals is proposed based on the measurements of the native fluorescence of CO and SA (obtained from hydrolysis of ASA). SA was determined in the range 0.1 -1.5 mg/L in the presence up to 10 mg/L of CO at λem 405 nm (λexc = 297nm). CO could not be determined at the low ratio usually found in pharmaceuticals with respect to ASA due to the spectral overlap, so a previous separation of SA was carried out by retention of this on an anion exchange resin. Thus CO was determined in the range 0.1-3 mg/L (λexc=215 nm, λem=350 nm.) in the presence of at least 520 mg/ L of ASA. The procedures were applied to the determination of CO and ASA in commercial pharmaceuticals with goods res...

A method for the determination of the pesticide morestan by means of transmitted room temperature solid phase spectrophosphorimetry has been developed. The method is based on the native phosphorescence showed by the morestan when it is fixed in a Whatman No 4 paper as a solid support. The excitation and emission wavelengths were 362 and 527 nm, respectively. The optimum phosphorescent emission was obtained when the delay time was 0.15 ms and the gate time 12.0 ms without need of a heavy atom. The linear dynamic range was between 0.1 and 1.0 μg.ml−1, and the detection and quantification limits were 0.03 and 0.09 μg.ml−1, respectively. The precision of the method, expressed as the relative standard deviation of ten samples at the 0.6 μg.ml−1 concentration level, was 3.0%. The method was applied to the determination of the pesticide in different type of waters, potatoes and vegetables.

Benzo(a)pyrene (BaP) which presents native fluorescence in solution has been determined in waters by synchronous solid-phase spectrofluorimetry. The relative fluorescence intensity of BaP fixed in Sephadex G-25 gel is measured after being packed in an 1-mm silica cell. Spectral characteristics of BaP-gel system are described. The applicable concentration range was 0.52–3.45 μg.L−1 with a relative standard deviation of 1.2% and detection limit of 0.07 μg.L−1. The method was applied to the analysis of waters with different provenances.

A method for the microdetermination of tin at the μg 1−1 level has been developed, based on Solid-Phase Spectrophotometry (SPS). Tin reacts with Pyrocatechol Violet at pH 3 to form a 2:1 (PCV:Sn) complex which is fixed on a dextran type anion-exchange gel. The gel phase absorbance is measured directly, and allows for the determination of tin in the range of 0.8–15.0 μg 1−1, with an RSD of 4.3 %. The method has been applied to the determination of Sn(IV) in natural and sea waters and pineapple juice.

A very sensitive method for the determination of trace amounts of cobalt has been developed, based on Solid-Phase Spectrophotometry (SPS). The method is based on the fixation of cobalt (II) as the 4- (2-pyridilazo) resorcinol complex on an anion-exchange resin. Resin phase absorbance is measured directly, and it allows the determination of cobalt (with a RSD of 2.4 %) in the range of 0.4–3.8 μg 1−1. The method was applied to the determination of cobalt (II) in different samples, namely beers, drugs and waters.

A microdetermination method at μg 1−1 levels for vanadium by solid-phase spectrophotometry has been developed. 5-Bromosalicylhydroxamic acid was used as chromogenic reagent to form a 1:2 violet complex which is easily sorbed and concentrated on a dextran-type anion-exchange resin. The resin-phase absorbances at 560 and 850 nm were measured directly. Vanadium can be determined in the 5 - 60 μg 1−1 range with a RSD of 4.3%. The method is applied to the determination of vanadium in pet roleiim crudes and natural water, samples.

A method for the determination of microgram per litre level of copper has been developed, based on Solid-Phase Spectrophotometry (SPS). Copper reacts with bichinconinic acid to form a 1:2 anionic reddish purple of Cu(I), which is fixed on a dextran-type anion-exchange resin. Resin phase absorbance is measured directly and allows for the determination of copper within the range of 1–20 μg. 1−1, using a 2,000 ml sample with an RSD of 1.7%. The method has been used in the determination of copper in natural waters.

A method based on Solid Phase Spectrophotometry was developed for the determination of methyl benzoate. Hydroxamic acid formed by the reaction between the above and hydroxylamine, reacts with V(V) and oxalate yielding a violet compound, which is sorbed on an anion-exchange resin. The absorbance of the resin phase at 546 and 750 nm is measured directly. The calibration graph is linear for the 4.8–23 μM concentration range. RSD is shown as 3.7%, with a detection limit of 0.09 mg. 1−1. This method has been applied to the determination of aromatic esters in brandies.