Urea In Serum Samples Research Articles

Use of Water Soluble and Phosphorescent MPA-capped CdTe Quantum Dots for the Detection of Urea.

To describe a method for the determination of urea in blood serum using urease enzyme and 3-MPA-capped CdTe quantum dots. The method is based on the increase in pH of the solution as a result of the reaction between urea and urease, which causes an increase in the phosphorescence signal of MPA-CdTe quantum dots in the pH range of 2.5-5.0. Under the optimum conditions, the linear range of urea was 0.016-0.16 mM (1-10 mg/L) and the limit of detection based on 3 s/b was calculated as 0.003 mM (0.17 mg/L). The relative standard deviation was calculated as 3.4% at 4 mg/L urea concentration (n=7). The method was applied to human serum samples. The same samples were analyzed by an independent laboratory and the results were not statistically different, at 95% confidence level (F test). The proposed method does not need sample pretreatment, is simple, selective, and cost-effective for the determination of urea in serum samples.

Determining urea levels in dialysis human serum by means of headspace solid phase microextraction coupled with ion mobility spectrometry and on the basis of nanostructured polypyrrole film

A simple and sensitive headspace (HS) solid phase microextraction (SPME) coupled with ion mobility spectrometry (IMS) method is presented for analysis of urea in dialysis human serum samples. A dodecylbenzenesulfonate-doped polypyrrole coating was used as a fiber for SPME. The HS-SPME-IMS method exhibits good repeatability (relative standard deviation of 3% or less), simplicity, and good sensitivity. The influence of various analytical parameters such as pH, ionic strength, extraction time and temperature was investigated and the parameters were optimized. The calibration graph was linear in the range from 5 to 50 μg mL(-1), and the detection limit was 2 μg mL(-1). The method was applied successfully for determination of urea in human serum and with acceptable recovery (more than 98%). Finally, a standard addition calibration method was applied to the HS-SPME-IMS method for the analysis of human serum samples before and at the end of dialysis. The proposed method appears to be suitable for the analysis of urea in serum samples as it is not time-consuming and requires only small quantities of the sample without any derivatization process.

Monitoring urea levels during haemodialysis with a pulsed-flow chemiluminescence analyser

We have developed a rapid and robust method for the determination of urea in spent haemodialysis fluid as a measure of the efficiency of haemodialysis treatments. A novel flow analysis instrument (which generates a pulsed solution flow) was coupled with a chemiluminescence detection system, based on the oxidation of urea with hypobromite. The ‘pulsed-flow chemiluminescence analyser’ exhibited high precision (1.6% relative standard deviation (R.S.D.) for a 1×10 −5 M urea standard, n=10) and good limit of detection (9×10 −7 M, S/N=3) as a result of the rapid and reproducible mixing of small volumes of reagent and sample at the point of detection. The proposed chemiluminescence technique and an established urease-based laboratory procedure were compared, and showed a very similar trend for the change in urea concentration during a typical haemodialysis treatment. The relative chemiluminescence response from the oxidation of species with similar structure has revealed the inherent selectivity of the light producing pathway, but a positive interference was obtained from protein when this technique was applied to the determination of urea in serum samples. Arginine was identified as the predominant source of this interference.

Preparation of Urea Sensors with a Series Piezoelectric Crystal Device

Abstract The use of a series piezoelectric crystal (SPC) device for the preparation of biosensors has been investigated. These biosensors are fabricated by mounting the immobilized urease layer or the jack bean tissue slices on the probe surfaces of the SPC ammonia sensor. The urease sensor exhibits favourable frequency response to 1 x 10−5-3x10−3 M urea with a response time of ca.3 min. Dynamic range, reproducibility, response time and selectivity of the sensors are discussed. Results show the SPC is an attractive alternative internal sensing element to develop biosensing devices. The urease sensor has been used successfully for the determination of urea in serum samples; the results are comparable to those from a spectrophotometric method.

Flow-injection analysis of serum urea using o-phthalaldehyde and naphthylethylenediamine

An analytical procedure is developed for the determination of urea using flow injection analysis. The methodology is based on the color that develops (λ max, 517 nm) when urea reacts with o-phthalaldehyde in the presence of naphthylethylenediamine under acidic conditions. Calibration curves are found to be linear up to 51 mg urea N/dl when the FIA manifold is operated at 42°, utilizing 90-μl samples and a flow-rate of 0.44 ml/min. By manual injection up to 40 samples can be analysed per hour. Recovery yields varied between 95–99%. The within day CV was 0.5–2.2% whereas the day to day CV was 2.1–3.9%. When applied to the analysis of urea in serum samples, excellent correlations (0.998) are obtained when the FIA results are compared with those obtained for the same serum samples analysed by the free urease/Berthelot's and the hospital method (employing the Abbot Bichromatic Analyser). Interferences are observed with sulphur compounds such as sulphanilamide (0.76 mg/dl) as well as with many amino acids but at relatively high concentrations (21 mg/dl).

Determination of urea in serum by a fiber-optic fluorescence biosensor

A new fiber-optic biosensor for urea has been developed, based on immobilized urease coupled to a fluorescence ammonia sensor. The enzymatically generated ammonia diffuses through the membrane into a solution of the fluorescent pH indicator trisodium 8-hydroxypyrene-1,3,6-trisulfonate. The sensor has been successfully used for the determination of urea in serum samples, with results in good agreement with those reported by a local hospital. The proposed sensor is reversible and selective to urea. The ease of construction of the sensor tip offers the possibility of designing disposable tips for use in clinical applications.

Urease coupled to poly(vinyl alcohol) activated by 2-fluoro-1-methylpyridinium salt: preparation of a urease potentiometric electrode and application to the determination of urea in serum

A urease electrode is described for the determination of urea in serum samples. The electrode was prepared by chemically immobilizing urease to 2-fluoro-1-methylpyridinium toluene-4-sulphonate-activated poly(vinyl alcohol) and physically adsorbing the resulting conjugate directly on to the hydrophobic membrane of an ammonia gas-sensing electrode. Linear calibration was obtained over the range 10 −4–10 −1 M urea. The recovery varied between 97 and 102%. The within-day relative standard deviation (R.S.D.) was 1.2–2.7% and the day-to-day R.S.D. was 2.9–4.5%. There was only a 14% decrease in electrode activity over a period of 28 days. Up to 30 serum samples can be analysed per hour.

Urea Determination in Human Sera With an Ammonium Ion Selective Electrode Made With Solid Inner Electric Contact and Immobilised Urease

Abstract A PVC matrix nonactin based membrane electrode assembled with a solid carbon-epoxy inner electric contact has been successfully used in ammonium and urea analysis. Different buffers have been tested and sodium and potassium interferences have been evaluated in order to obtain the best calibration curve for determination of ammonium and urea in serum samples. Three immobilization techniques for the enzyme urease have been compared. Nylon net immobilization procedure was found to have the best analytical features when coupled with this electrode and it has been selected for urea determination in sera. Results were in good agreement with those obtained with the clinical standard spectrophotometric method.

A flow-through detector for simultaneous determination of glucose and urea in serum samples

Glucose and urea electrodes are prepared by immobilizing glucose oxidase and urease on nylon net and fixing the nets on oxygen and ammonia gas sensors. Both enzyme electrodes are fixed in a single flow cell (40 μl volume). Serum is diluted tenfold with 0.1 M Tris buffer (pH 8.3) to fit the calibration graphs for both sensors. Samples are pumped for 1 min, with wash periods of 2 min for recovery to the baseline. Results on serum samples are in good agreement with the results obtained by conventional spectrophotometry.

Preparation and Response Properties of Selective Bio-Electrodes Utilizing Polymer Membrane Electrode-Based Ammonia Gas Sensors

Abstract A new type of potentiometric ammonia gas sensor is employed in the preparation of selective bio-electrodes for urea and glutamine. The bio-electrodes are constructed by immobilizing the enzyme urease and intact porcine kidney cells, respectively, at the surface of a disposable ammonium selective polymer membrane electrode-based ammonia gas sensor. The resulting electrodes have favorable response properties when compared to corresponding devices previously assembled with costly commercial gas sensors. Preliminary studies with the urea electrode demonstrate its usefulness for the rapid determination of urea in serum samples.