PubMed Health⌕ Search

Biomedical subjects

J Saurina

Publications and source records attributed to J Saurina.

At least 19 recordsLinked to original sources
PubMed2003

Quantitation in multianalyte overlapping peaks from capillary electrophoresis runs using artificial neural networks.

The potentiality of artificial neural networks for multicomponent analysis in unresolved peaks from capillary electrophoresis (CE) is evaluated. The system chosen consists of mixtures of three ebrotidine metabolites, which cannot be successfully separated by CE. Data selected for analysis consist of UV spectra taken at the maximum of the CE peak. The most dissimilar analyte, in terms of spectral differences, is accurately quantitated in any type of mixture with an overall prediction error of 5%. Because of the strong interference of the two most overlapped compounds, a preliminary procedure for spectral data filtering based on principal component analysis is performed to improve their quantitation.

Electrophoresis, Capillary↗
PubMed2001

Strategies for in-capillary derivatization of amino acids in capillary electrophoresis using 1,2-naphthoquinone-4-sulfonate as a labeling reagent.

This paper examines the potentiality of in-capillary derivatization for improving the sensitivity of the spectrophotometric detection of amino acids in capillary zone electrophoresis. 1,2-Naphthoquinone-4-sulfonate was selected as the labeling agent of amino acids. The underivatized sample and the reagent solution segments are injected by pressure into the capillary prior to applying the running voltage. The corresponding derivatization reaction occurs inside the capillary once the potential is applied, as it induces mixing of the sample with the reagent. Several introduction modes consisting of tandem or sandwich configuration have been evaluated. These techniques result in a straightforward and automated way of carrying out a derivatization. Furthermore, in-capillary procedures may become much more attractive than conventional pre-capillary derivatization in terms of sensitivity and reproducibility. The optimum operation mode found consists of a sandwich system where the sample is injected in between two reagent segments. The method was applied to the determination of amino acids in feed samples. Results show a good concordance with those given by a standard amino acid analyzer.

Amino Acids↗
PubMed2001

Multivariate calibration methods for quantification in strongly overlapping capillary electrophoretic peaks.

Capillary zone electrophoresis with diode-array detection was applied to the separation of ebrotidine and its metabolites. However, three of these, which are neutral in the conditions studied, co-migrated with the electroosmotic flow signal. Therefore, strongly overlapping peaks were observed. The main aim of this study was to show the potentiality of capillary electrophoresis in combination with chemometrics. Multivariate calibration methods were applied to quantify these analytes in synthetic mixtures. The results obtained using partial least squares (PLS) were in agreement with actual values, with an overall prediction error of 9.7%.

Calibration↗
PubMed2001

Determination of ebrotidine metabolites in overlapping peaks from capillary zone electrophoresis using chemometric methods.

This paper illustrates the possibilities of chemometric methods in the resolution and quantification of various compounds in overlapping peaks from capillary electrophoresis. Ebrotidine and most of its metabolites were efficiently separated by capillary zone electrophoresis (CZE) in a fused-silica capillary. However, the procedure was not suitable for the physical separation of the three less ionizable metabolites, which comigrated and overlapped with the electroosmotic flow signal. Multivariate curve resolution based on an alternating least squares procedure was used for their mathematical resolution. For such a purpose, data obtained in the CZE system with a diode array detector, which consisted of UV spectra registered over time, were analyzed. The ebrotidine metabolites were successfully resolved and quantified in synthetic mixtures and urine samples.

Benzenesulfonates↗
PubMed2001

Sensitivity enhancement by on-line preconcentration and in-capillary derivatization for the electrophoretic determination of amino acids.

This study describes an application of on-line preconcentration by large-volume stacking in combination with in-capillary derivatization for enhancing spectrophotometric detection sensitivity in capillary electrophoresis. The method is illustrated by an example dealing with the determination of amino acids with 1,2-naphthoquinone-4-sulfonate as a labelling agent. Samples are dissolved in water in order to create a stacking process based on differences in the conductivity between this medium and a concentrated running buffer. The in-capillary derivatization is accomplished following a sandwich procedure in which the sample is inserted between two segments of reagent. Amino acid derivatives are obtained and separated in a fused-silica capillary with a sodium borate electrolyte buffer using 2-propanol as an organic modifier. The method is applied to the analysis of amino acids in pharmaceutical and feed samples. A good concordance between the predicted values and those obtained with the standard method is observed, with overall quantification error below 5%. The proposed procedure allows the detection limits sensitivity to be enhanced in 1000-fold with respect to conventional precapillary derivatization.

Amino Acids↗
PubMed2001

Potentiometric sensor array for the determination of lysine in feed samples using multivariate calibration methods.

A potentiometric sensor array has been developed for the determination of lysine in feed samples. The sensor array consists of a lysine biosensor and seven ion-selective electrodes for NH4+, K+, Na+, Ca2+, Mg2+, Li+, and H+, all based on all-solid-state technology. The potentiometric lysine biosensor comprises a lysine oxidase membrane assembled on an NH4+ electrode. Because the selectivity of the lysine biosensor towards other cation species is not sufficient, there is severe interference with the potentiometric response. This poor selectivity can be circumvented mathematically by analysis of the richer information contained in the multi-sensor data. The sensor array takes advantage of the cross-selectivity of lysine for each electrode, which differs from the other species and quantification of lysine in complex feed sample extracts is accomplished with multivariate calibration methods, such as partial least-squares regression. The results obtained are in a reasonable agreement with those given by the standard method for amino acid analysis.

Animal Feed↗
PubMed2000

Determination of amino acids in overlapped capillary electrophoresis peaks by means of partial least-squares regression.

Amino acid derivatives of 1,2-naphthoquinone-4-sulfonate (NQS) can be separated by capillary electrophoresis at 30 kV in a fused-silica capillary by using a 40 mM sodium tetraborate-isopropanol (3:1, v/v) solution as background electrolyte. This procedure was suitable for the most common amino acids. However, the peaks of three amino acids (phenylalanine, isoleucine and tyrosine) were only partially resolved and peaks of histidine and leucine derivatives overlapped completely. Partial least-squares regression (PLS) may overcome the lack of selectivity for these amino acids. Spectroelectropherograms of the corresponding amino acid derivative peaks were monitored with a diode-array spectrophotometer in the range 225 to 540 nm. Both spectra and electropherograms can be used as multivariate data for further analysis. In general, the best predictions were obtained using the time domain.

Amino Acids↗
PubMed2000

Resolution of overlapped peaks of amino acid derivatives in capillary electrophoresis using multivariate curve resolution based on alternating least squares.

The application of chemometric techniques to the resolution of overlapped peaks in capillary electrophoresis (CE) is described. When a physical separation can not be completely accomplished, chemometrics might still resolve the determination of the analytes mathematically. CE with diode array detection can provide a large amount of data consisting of spectra registered over time. In this study, the capillary electrophoretic separation of 1,2-naphthoquinone-4-sulfonate derivatives of amino acids is studied. Most of the common amino acid derivatives can be separated at 30 kV in a fused-silica capillary by using a 40 mM sodium tetraborate + isopropanol (3:1 v/v) solution as background electrolyte. However, peaks of certain derivatives (Phe, His, Leu and Ile) still overlap. A multivariate curve resolution method based on an alternating least squares optimization procedure is used for the resolution of the overlapped electrophoretic peaks. The method takes advantage of spectral and electrophoretic differences of analytes to recover their pure electrophoretic and spectral profiles. In addition, each analyte in the mixture can be quantified using the corresponding standards.

2-Propanol↗
PubMed2000

Potentiality of proton nuclear magnetic resonance and multivariate calibration methods for the determination of dermatan sulfate contamination in heparin samples.

A 1H NMR method for the quantification of dermatan sulfate impurities in heparin industrial samples is proposed. The method is based on the analysis of 1H NMR spectral data by multivariate calibration. The 1H NMR spectra of heparin and dermatan sulfate standards showed characteristic profiles. Thus, differences in the methyl peaks of acetamido groups of heparin and dermatan sulfate were greatly advantageous for the analysis. Other hydrogens of the sugar ring were also relevant in this study. Thus, the determination of dermatan sulfate by multivariate calibration depended on all these differences. Partial least squares regression (PLS) was chosen as the calibration method. In addition, a data standardization procedure was developed in order that 1H NMR spectra registered with different instruments operating under different measurement conditions were comparable. The quantification of dermatan sulfate in the samples was satisfactory, with an overall prediction error of 6%.

Calibration↗
PubMed2000

Principal component analysis and cluster analysis for the characterization of dental composites.

Various experimental dental materials were characterized using chemometric methods. The main aim of the study was to ascertain which composite materials present the best properties for use in restorative dentistry. Bisphenol-alpha-glycidyl methacrylate-based composites containing hydroxyapatite as a filler and a coupling agent were prepared using a photocuring polymerization procedure. Several chemical and mechanical properties of experimental composites were measured and the corresponding data were further studied using principal component analysis and cluster analysis. Results from the characterization allowed the most appropriate materials to be selected. Various composites presented acceptable general properties suggesting their suitability as substitutes for commercial materials in dentistry.

Cluster Analysis↗
PubMed1999

Liquid chromatographic determination of aniline in table-top sweeteners based on pre-column derivatization with 1,2-naphthoquinone-4-sulfonate.

A liquid chromatographic method for the determination of aniline in cyclamate sweeteners based on a pre-column derivatization with 1,2-naphthoquinone-4-sulfonate (NQS) is proposed. Aniline traces were extracted from the cyclamate samples using dichloromethane. After solvent evaporation, the dry residue was derivatized with NQS at pH 9.5 and 85 degrees C for 1 min. The aniline derivative, which was extracted from the reacting mixture, was redissolved in the eluent solution and injected into the chromatographic system. The separation of aniline derivative from other amine impurities was carried out in a C18 column using a 2% acetic acid-methanol (40:60, v/v) mobile phase. Results from the analysis of aniline in the sweetener samples with the proposed method were compared with those from the standard method. A good concordance between the two methods was observed.

Aniline Compounds↗
PubMed1999

Determination of lysine in pharmaceutical samples containing endogenous ammonium ions by using a lysine oxidase biosensor based on an all-solid-state potentiometric ammonium electrode.

A new potentiometric method is proposed to determine lysine in pharmaceutical samples. This method is based on a lysine biosensor consisting of a chemically immobilized lysine oxidase membrane attached to an all-solid-state ammonium electrode. Lysine is degraded in the sensor to release ammonium, which is detected by means of the ammonium electrode. The presence of endogenous ammonium in the samples interferes with these determinations, since the response measured corresponds to the sum of the ammonium generated enzymatically and that present in the sample. This is a general drawback for all biosensors based on the detection of ammonium. Study of samples containing both lysine and ammonium showed that concentration ranges exist in which a near-logarithmic relationship between potentials measured and lysine concentrations is found. Therefore, within these ranges, lysine can be determined by using the standard addition method, with the subsequent data treatment involving an iterative linearization procedure. Results obtained with the proposed potentiometric method are consistent with those given by the standard method for amino acid analysis.

Amino Acid Oxidoreductases↗
PubMed1999

Amperometric determination of lysine using a lysine oxidase biosensor based on rigid-conducting composites.

In this study, amperometric biosensors based on rigid conducting composites are developed for the determination of lysine. These lysine biosensors consist of chemically immobilized lysine oxidase membranes attached to either graphite-methacrylate or peroxidase-modified graphite-methacrylate electrodes. The enzymatic degradation of lysine releases hydrogen peroxide, which is the basis of the amperometric detection. The direct oxidation of hydrogen peroxide is monitored at +1000 mV with a graphite-methacrylate electrode, while with the peroxidase-modified electrode reductive detection is performed. In addition, for the peroxidase-modified biocomposite electrode, both direct electron transfer and hydroquinone-mediated detection are studied. For the lysine biosensor based on the hydroquinone-mediated peroxidase biocomposite, the linear range is up to 1.6 x 10(-4) M, the sensitivity 11300 microA/M, the repeatability 1.8%, the detection limit 8.2 x 10(-7) M and the response time t95% is 42 s. The proposed biosensors are used to determine lysine in pharmaceutical samples. Results are consistent with those obtained with the standard method.

Biosensing Techniques↗
PubMed1998

Shell-vial culture and pp65 antigenemia assay in the detection of cytomegalovirus in the first blood sample of renal transplant recipients.

The aim of the study was to compare the efficacy of pp65 antigenemia assay and the shell-vial culture (SVC; viremia) for the diagnosis of cytomegalovirus (CMV) infection in renal transplant recipients, comparing the results obtained in the first blood sample and the total number of blood samples analyzed in this group of patients. During the study period, 70 renal transplant recipients were studied: 44 (62.8%) with CMV infection. The method of sedimentation in a dextran solution for leukocyte extraction was used in the pp65 antigenemia assay. The MRC-5 shell-vial assay was used for CMV isolation from leukocytes (viremia). Eighty blood samples were examined from 70 renal transplant recipients: Of the 44 positive samples studied, in 77.5% of cases, both the antigenemia assay and the SVC were positive. In 16.2%, only the antigenemia assay was positive, and, in 6.2%, only the SVC was positive. In all blood samples studied, the antigenemia was present in 93.7% of cases, and the SVC was present in 83.7% (P = 0.04). If the results obtained in only the first blood sample taken for the diagnosis are studied, then we observe that the antigenemia assay was positive in 39 patients (88.6%), whereas the SVC was positive in 41 patients (93.1%), although the difference was not statistically significant (P = 0.39). It is concluded that the inoculation of all of the leukocytes extracted from blood samples in the SVC seems to produce a slight increase in the sensitivity of the cell culture and that the SVC becomes positive before the antigenemia for the detection of CMV in peripheral blood, especially in the first blood sample.

Antibodies, Monoclonal↗
PubMed1998

An increase in the number of polymorphonuclear leukocytes inoculated on shell-vial culture increases the sensitivity of this assay in the detection of cytomegalovirus in the blood of immunocompromised patients.

A prospective study was conducted comparing the sensitivity of the pp65 antigenemia assay (AGA) to that of the shell-vial culture (SVC) inoculated with increasing quantities of polymorphonuclear leukocytes (PMNLs) in the detection of cytomegalovirus (CMV) in peripheral blood. From the cellular suspension, three SVCs were inoculated with 200,000, 400,000, and 800,000 PMNLs, respectively. Of the 201 patients studied, 67 (31.9%) had positive results in one of the two analytic tests (AGA or SVC). In this group, 13 (19.4%) presented a negative AGA assay; 13 (19.4%) an AGA of 1; 13 (19.4%) an AGA of between 2 and 5; and 28 (41.8%) an AGA with a value > 6 PMNL-positive x 100,000 PMNLs. The SVC inoculated with 200,000 PMNLs detected the presence of CMV in 42 cases (62.6%); 55 (82%) with 400,000; and 64 (95.5%) with 800,000. Statistically significant differences were observed between the isolation capacities of the SVC inoculated with 200,000 and 400,000, and the SVC inoculated with 800,000 PMNLs (p = 0.0001). In the comparison of the overall sensitivity of the AGA with that of the SVC with 200,000, the AGA was found to be significantly more sensitive (p = 0.0052). When comparing with the SVC with 400,000 PMNLs, the two techniques were found to be equally sensitive; and in the comparison with the SVC with 800,000, the culture displayed a greater detection sensitivity (p = 0.0023). According to these results, it seems evident that the increase in the absolute number of PMNLs inoculated in the SVC leads to a significant increase in the sensitivity of the SVC in the detection of low-level viremia by CMV.

Cytomegalovirus↗
PubMed1997

Evaluation of a direct immunofluorescence cytospin assay for the detection of herpes simplex virus in clinical samples.

A comparison between a direct immunofluorescence assay (DFA) and the shell-vial culture (SVC) was conducted to evaluate their efficacies according to the quality and origin of the sample and the type of herpes simplex (HSV) responsible for the infection. The SVC detected all 58 HSV-infected samples, while the DFA detected only 49 (84.5%) positive samples. The DFA detected HSV type 1 in 22 of 89 samples (24.7%) and HSV type 2 in 27 of 96 samples (28.1%). Compared with the SVC, the DFA had a sensitivity of 75.8% for HSV type 1 and 93.1% for HSV type 2. The sensitivity of the DFA depends on the quality of the sample. Thus, while DFA is recommendable as a screening method, the SVC remains the method of choice for obtaining the maximum diagnostic yield from the sample.

Female↗