A three-factor Doehlert matrix design in optimising the determination of octadecyltrimethylammonium bromide by cation-exchange chromatography with suppressed conductivity detection.

A simple and effective chromatographic method with suppressed conductivity detection was developed and validated to determine dissolved samples of octadecyltrimethylammonium bromide (C18H37N+ Me3Br-, ODTAB) for purity testing. A response surface methodology generated with a Doehlert matrix design was applied to optimize the chromatographic and detection conditions in ion-exchange chromatography (IEC) with conductivity detection in the chemical suppression mode. A three-factor Doehlert design was performed to fit a second-order model and jointly optimize the peak intensity and shorten analysis time through a global desirability function. Regenerant flow rate, volume fraction of acetonitrile in the acidic eluent and its flow rate were studied at seven, five and three levels, respectively. The optimized separation and detection conditions were accomplished by using a cation-exchange column eluted at 0.5 mL min(-1) with an isocratic mobile phase composed of CH3CN and 25 mN H2SO4, 82/18 (v/v). Chemical suppression of ionic conductivity was performed by 100 mN tetrabutylammonium hydroxide (TBAOH) as a regenerant at a flow-rate of 4.0 mL min(-1). Remarkably good agreement was found between predicted and experimental values of signal intensity and chromatographic retention. With the developed method, a linear calibration curve of ODTA+ as bromide salt from 5 to 1000 ppm was obtained using hexadecyltrimethylammonium bromide as internal standard. The estimated limit of detection was 0.3 ppm (S/N=3). The effectiveness of electrochemically suppressed conductivity detection of ODTA+ was also demonstrated, thus making easier the whole detection operation and instrumental needs as well.

Naturally occurring glucosinolates in plant extracts of rocket salad (Eruca sativa L.) identified by liquid chromatography coupled with negative ion electrospray ionization and quadrupole ion-trap mass spectrometry.

A method for the comprehensive profiling of intact glucosinolates (GLSs), major and minor, occurring in leaves and seeds of rocket salad (Eruca sativa L.) is presented using optimized reversed-phase liquid chromatography (RP-LC) with electrospray ionization (ESI) ion trap mass spectrometry (ITMS). ESI-ITMS in the negative mode was confirmed to be very suitable to analyze these compounds in crude extracts. After extraction from the plant material with methanol/water (70:30 v/v) at 70 degrees C, the analytes of interest were separated on a C18 column using an eluent acidified with formic acid (0.1%) and modified with acetonitrile. All the GLSs found in leaves of rocket salad gave good signals corresponding to the deprotonated precursor ion, [M-H]-. Although the mass spectra also exhibited an analytically important non-covalent adduct ion at [2M-H]-, the structures of glucosinolates were confirmed by extensive sequential MS analysis, thereby substantially improving the identification of unknown compounds. The results obtained not only revealed in leaves of E. sativa at least twelve species of GLSs including seven aliphatic compounds (glucoraphanin with [M-H]- at m/z ratio of 436, glucoerucin at m/z 420, 4-mercaptobutyl-GLS at m/z 406, progoitrin/epiprogoitrin at m/z 388, sinigrin at m/z 358, 4-methylpentyl- and n-hexyl-GLS at m/z 402) and three indole glucosinolates (i.e., three N-heterocyclic compounds: 4-hydroxyglucobrassicin and 5-hydroxyglucobrassicin at m/z 463, and 4-methoxy-glucobrassicin at m/z 477), but also two structurally related compounds containing one intermolecular disulfide linkage (4-(beta-D-glucopyranosyldisulfanyl)butyl-GLS at m/z 600 and a dimeric 4-mercaptobutyl-GLS at m/z 811). This latter symmetric disulfide was previously considered as an artefact formed during extraction of GLSs from vegetative tissues. Glucosinolates were detected in the leaves with a wide range of contents (10-200 micromol/g) and a great variation in the composition. Only three GLSs were identified in seeds of rocket salad, namely glucoraphanin, glucoerucin and 4-methoxyglucobrassicin. As expected, the most abundant GLS in seeds is glucoerucin. The feasibility of the strategy was also demonstrated using a rapeseed extract of certified reference material (BCR367R). The results indicated the usefulness of this method for a rapid, sensitive and comprehensive profiling of the GLS family naturally occurring in extracts of crude plant matter.

Comparison of silver, gold and modified platinum electrodes for the electrochemical detection of iodide in urine samples following ion chromatography.

The electrochemical (EC) detection of iodide at gold, silver and platinum electrodes under similar experimental conditions was evaluated. To achieve optimal amperometric detection, the electrode sensitivity, selectivity, and stability was compared. Isocratic separation of iodide was attained by ion chromatography (IC) using an anion-exchange column with nitrate as an eluent ion (25 mM HNO(3) + 50 mM NaNO(3)). Although the Ag electrode showed the highest selectivity due to the relatively low applied potential (+0.10 V versus Ag|AgCl), it requires continuous surface polishing upon injection of standard solutions or real samples; in addition, the chromatographic peak of iodide exhibited a pronounced dip-tailing. The limit of detection (LoD) of iodide was estimated to be 3.5 microg/L (S/N=3) with an injection volume of 50 microL. Likewise, pulsed electrochemical detection at the silver electrode did not demonstrate the expected results in terms of peak shape and low detection limit. Using the same chromatographic conditions, iodide detection at the Au electrode (E(app)= +0.80 V versus Ag|AgCl) exhibited a regular peak shape accompanied by a sensitivity comparable to the silver one. Yet, upon continuous injections the signal intensity displayed a progressive lowering up to ca. 40% in 6h. Best results in terms of signal stability, peak shape and analytical response were obtained with a modified platinum electrode which allowed to achieve a LoD of 0.5 microg/L (S/N=3). The present IC-EC detection method using a modified Pt electrode (E(app)= +0.85 V versus Ag|AgCl) was successfully applied to determine low contents of iodide in human urine with solid phase extraction as pretreatment. Such a developed method correlated very well with the reference colorimetric method in urine (r=0.95273), and it is specifically suggested when the iodide content is relatively low, i.e., <20 microg/L.

Sensitive quantification of iodide by ion-exchange chromatography with electrochemical detection at a modified platinum electrode.

A rapid and very sensitive method for the accurate determination of free iodide in real samples is described. The method is based on anion-exchange chromatographic separation coupled with amperometric detection at a modified platinum electrode under constant applied potential (+0.85 V vs. Ag AgCl). An experimental setup with an in-line and very effective method of electrode modification is proposed using an amperometric thin-layer cross-flow detector and a flowing solution 300 mg/L of iodide; the working electrode is polarised to the limiting current for oxidation of iodide to iodine in acidic solutions with the consequent formation of an iodine-based film. The results indicated that the modified electrode exhibits high analytical response for iodide electrooxidation with good stability and long-life. The signal intensity of daily experimental sessions (8 h), during which standards and real samples were repeatedly injected, exhibits a moderate lowering (i.e. < 6%). Using a mixture of 25 mM HNO3 and 50 mM NaNO3 as an eluent phase in ion-exchange chromatography, the detection limit of iodide was estimated to be 0.5 microg/L (S/N = 3) with an injection volume of 50 microL. This method was applied successfully to quantify the iodide content of milk samples and in wastewaters as well as trace amounts in common vegetables and solutions containing high chloride levels.

[Magnetic resonance diagnosis of traumatic penile fracture].

PURPOSE: To report our experience with MRI in the preoperative evaluation of patients with traumatic penile fractures. MATERIALS AND METHODS: Between January 1998 and December 2001, we performed MRI examinations on five patients (aged 29-48 years; mean age 40 years) with suspected traumatic fracture of the penis occurred during sexual intercourse. In all cases, T1-weighted SE, T2-weighted FSE and GRE sequences in the axial, coronal and sagittal planes were acquired. The study was performed without IV administration of paramagnetic contrast agents and in conditions of detumescence. A small-sized surface coil was used in four cases and a body coil was used in one case. All patients had suspected penile fracture with indications for surgical repair. The MR examination was performed within 12 to 48 hours of the trauma and was requested to aid surgical planning. RESULTS: The MR image quality was adequate in all cases. The examination documented unilateral rupture of the corpus cavernosum in all patients. This finding was associated with haematoma located both subcutaneously and inside the corpus cavernosum itself. In no case was there rupture of both corpora cavernosa. In only one patient was there a suspicion of injuries to the urethral corpus spongiosum, which was confirmed by surgery along with the other MR findings. DISCUSSION AND CONCLUSIONS: Many imaging methods are available to evaluate traumatic penile lesions: ultrasound, colour-Doppler ultrasound, urethrography, cavernosography, angiography and MRI. In agreement with the literature, our experience shows that MRI is useful in evaluating penile injuries owing to its multiplanar capabilities, its good spatial resolution and its excellent tissue contrast resolution. These characteristics enabled a more adequate surgical approach. In our view, MRI can be regarded as an emerging method to obtain helpful diagnostic information, with no risks for the patient.