Detection of homogentisic acid by electrospray ionization mass spectrometry

OBJECTIVE

Homogentisic acid (HGA) is excreted in excessive amounts in the urine of patients with alkaptonuria, which is a hereditary metabolic disorder of phenylalanine and tyrosine. Therefore, the detection of HGA in urine is useful for the diagnosis of alkaptonuria. To evaluate the detection of HGA, we confirmed the color shift of HGA solutions and analyzed them by electrospray ionization mass spectrometry (ESI-MS).

METHODS

We observed the color change of the HGA solutions under different pH conditions (pH 6.0, 7.0, and 8.0) and examined the influences of adding potassium hydroxide (KOH) and ascorbic acid (AA) to the HGA solutions. Then, we analyzed the chemical reaction in HGA solutions using ESI-MS.

RESULTS

The HGA solution at pH 8.0 became brown after incubation at room temperature for 24 h and became darker brown with the addition of KOH; however, HGA solutions at pH 6.0 and 7.0 showed no color changes. The brown color change of the HGA solution at pH 8.0 was also inhibited by AA. Moreover, all HGA sample solutions showed the deprotonated molecular ion peak at m/z 167.035 in the negative ion mode after incubation at room temperature for 24 h and with the addition of KOH and AA.

CONCLUSION

We identified the molecular ion of HGA in all sample solutions by ESI-MS, regardless of different pH conditions, color changes, or the presence of AA. These results suggest that spectral analysis by ESI-MS is suitable for the detection of HGA and the diagnosis of alkaptonuria.

Performance evaluation of Hipee S2 point-of-care testing urine dipstick analyser: a cross-sectional study

OBJECTIVE

With advances in mobile technology, smartphone-based point-of-care testing (POCT) urinalysis hold great potential for disease screening and health management for clinicians and individual users. The purpose of this study is to evaluate the analytical performance of Hipee S2 POCT urine dipstick analyser.

DESIGN

A multicentre, hospital-based, cross-sectional study.

SETTING

Analytical performance of the POCT analyser was conducted at a clinical laboratory, and method comparison was performed at three clinical laboratories in China.

PARTICIPANTS

Urine samples were collected from 1603 outpatients and inpatients at three hospitals, and 5 health check-up population at one of the hospitals.

OUTCOME MEASURES

All tests were performed by clinical laboratory technicians. Precision, drift, carry-over, interference and method comparison of Hipee S2 were evaluated. Diagnostic accuracy of semiquantitative albumin-to-creatinine ratio (ACR) for albuminuria was carried out using quantitative ACR as the standard.

RESULTS

The precision for each parameter, assessed by control materials, was acceptable. No sample carry-over or drift was observed. Ascorbate solution with 1 g/L had an inhibitory effect for the haemoglobin test. Agreement for specific gravity (SG) varied between moderate to substantial (κ values 0.496-0.687), for pH was moderate (κ values 0.423-0.569) and for other parameters varied between substantial to excellent (κ values 0.669-0.991), on comparing the Hipee S2 with laboratory analysers. The semiquantitative microalbumin and creatinine were highly correlated with the quantitative results. The sensitivity of semiquantitative ACR to detect albuminuria was 87.2%-90.7%, specificity was 70.7%-78.4%, negative predictive value was 85.3%-87.9% and positive predictive value was 73.9%-83%.

CONCLUSIONS

Hipee S2 POCT urine analyser showed acceptable analytical performance as a semiquantitative method. It serves as a convenient alternate device for clinicians and individual users for urinalysis and health management. In addition, the POCT semiquantitative ACR would be useful in screening for albuminuria.

Simultaneous quantification of peroxidase/ascorbate in vegetables with slope and intercept of kinetic curves in a flow-injection recirculating-catalysis system

In using a flow-injection recirculating-catalysis system developed by us to research the simultaneous quantification for peroxidase and ascorbate, it was discovered that the concentrations of peroxidase activity and ascorbate are correlative with the slope and the negative intercept of the linear response curve during a peroxidase-catalyzed kinetic course. Therefore, based on this finding, a new analytical method and a simplified equation for quantifying the peroxidase activity concentration were proposed, Then, test conditions were optimized, finally the use of the method has realized the simultaneous determination for peroxidase of 2-40 U/L and ascorbate of 0.4-12 mg/L in various vegetables (60 μL). The assayed results were consistent with the comparison method, in which the repeatability (RSD < 1.43%, n = 11) was satisfactory. Another important conclusion obtained in this study is that the determination of the peroxidase activity in biosamples must use the kinetic curve method for fear of the influence from the ascorbate's lag phase.

Enzyme-free fluorescence determination of uric acid and trace Hg(II) in serum using Si/N doped carbon dots

A new fluorescence probe method for the detection of Hg(II) in serum was established, which has the detection limit of 3.57 nM and quantification limit of 5 nM, based on the electrostatic induced agglomeration quenching and complexation between Hg(II) and silicon-nitrogen-doped carbon nanodots (Si/N-CDs). Furthermore, the fluorescence probe also showed the satisfactory results in the determination of Hg(II) in human serum. Subsequently, take advantage of the uric acid (UA) to recover the fluorescence of the Si/N-CDs-Hg(II) complex probe, another enzyme-free ways to determine UA was developed. The complex probe can selectively detect the UA content in the 0.5-30 μM range, and its detection limit can reach 0.14 μM, which has successfully detected the UA in total serum, and the results were no significant difference comparing with the controls.

Direct microfluidic antibiotic resistance testing in urine with smartphone capture: significant variation in sample matrix interference between individual human urine samples

Direct antibiotic susceptibility tests for urinary tract infections should be assessed using a wide range of individual urine samples to identify matrix interference.

Exploration and quantification of ascorbate affecting peroxidase-catalyzed chromogenic reactions with a recirculating-flow catalysis detection system

This research used a recirculating-flow catalysis detection system to explore the ascorbate interference with peroxidase-catalyzed reactions and simultaneously determined peroxidase and ascorbate with a kinetic curve.