Academic Journal List

Nanoflow liquid chromatography-electrospray ionization-tandem mass spectrometry (nanoLC-ESI-MS-MS) was used for the first time in a comprehensive analysis of human urinary phospholipids (PL). PL mixtures from human urine were separated with a reversed phase LC capillary column coupled to ESI-MS-MS. This study used the dual scan method in which two consecutive LC-ESI-MS-MS runs were done in both positive ion mode to detect phosphatidylcholine (PC) and phosphatidylethanolamine (PE), and in negative ion mode to detect phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidic acid (PA), and phosphatidylglycerol (PG). We focused on identifying the maximum number of PLs from a healthy human urine sample by varying the extracted volume of urine along with the evaluation of extraction efficiency for urinary PLs. We found that 22 PCs, 14 PEs, 15 PIs, 13 PSs, 7 PAs, and 4 PGs were identified during nLC-ESI-MS-MS when phospholipids in urine were extracted by ultracentrifugation. The efficiency of lipid extraction by ultracentrifugation versus lyophilization was evaluated by reducing the initial urine volume. We found that lyophilization was more efficient than ultracentrifugation for extracting lipids from small volumes (1 mL) of urine.

In a study of calibration with HPLC data for acetaldehyde-DNPH, we have collected replicate data (5–11 points each) for 33 samples spanning the range 0.0004–3 µg of detected analyte. Over most of this range, the data uncertainty is proportional to the signal, implying that weighted least squares is required to obtain the calibration function, since minimum-variance estimation requires weights inversely proportional to the data variance. When a variance function derived from an analysis of the replicate statistics is used to assign weights, wi = 1/σi2, the resulting values of χ2 for the calibration fit are too large by a factor of 400. This implies that the method error is dominated by sample preparation rather than measurement uncertainty, and it means that in the calibration fit, the peak area should be taken as the independent variable and the amount as the dependent. In this reversed regression, the generalized LS method (GLS) is used to estimate the total method variance function from the residuals. The resulting method variance function resembles the instrumental variance, in containing constant and proportional error terms. The calibration data demand at least a cubic polynomial for adequate representation, but other response functions are statistically equivalent, with the result that this model uncertainty is comparable to the directly computed statistical uncertainty of the calibration function. In these computations, emphasis is placed on the virtues of χ2 as a statistical figure of merit over the widely used R.

This work herein reports the approach for the simultaneous determination of heavy metal ions including cadmium (Cd(II)), lead (Pb(II)), and chromium (Cr(VI)) using a bismuth film electrode (BFE) by anodic stripping voltammertry (ASV). The BFE used was plated in situ. Due to the reduction of Cr(VI) with H2O2 in the acid medium, on one hand, the Cr(III) was produced and Cr(VI) was indirectly detected by monitoring the content of Cr(III) using square-wave ASV. On the other hand, Pb(II) was also released from the complex between Pb(II) and Cr(VI). Furthermore, the coexistence of the Cd(II) was also simultaneously detected with Pb(II) and Cr(VI) in this system as a result of the formation of an alloy with Bi. The detection limits of this method were 1.39 ppb for Cd(II), 2.47 ppb for Pb(II) and 5.27 ppb for Cr(VI) with a preconcentration time of 120 s under optimal conditions (S/N = 3), respectively. Furthermore, the sensitivity of this method can be improved by controlling the deposition time or by using a cation-exchange polymer (such as Nafion) modified electrode.

The potential of liposome electrokinetic chromatography (LEKC), which is applied to estimate compound penetration through the skin, was evaluated in this report. Quantitative retention-activity relationships (QRARs) were successfully constructed between the compound skin permeability coefficient (log Kp) and the retention values (log k), as well as some calculated molecular descriptors by the stepwise regression method (R2 = 0.902). Furthermore, the developed vector method was applied to compare the similarity between the reported lipophilicity measuring scales and compounds through the skin. Both results indicated that the transport of a compound into the liposomal membrane was more similar to its penetration through the skin than that into other systems including the octanol–water system. In a word, LEKC is a promising simple method to predict drug penetration through the skin.

The small injection volumes and narrow dimensions characteristic of microseparation techniques place constraints on concentration sensitivity that is required for trace chemical analyses. On-line sample preconcentration techniques using dynamic pH junction and its variants have emerged as simple yet effective strategies for enhancing concentration sensitivity of weakly ionic species by capillary electrophoresis (CE). Dynamic pH junction offers a convenient format for electrokinetic focusing of dilute sample plugs directly in-capillary for improved detection without off-line sample pretreatment. In this report, we highlight new advances in dynamic pH junction which have been reported to enhance method performance while discussing challenges for future research.

The first page of this article is displayed as the abstract.

The first page of this article is displayed as the abstract.

The first page of this article is displayed as the abstract.

The first page of this article is displayed as the abstract.

A simple poly(dimethylsiloxane) (PDMS) microchip was employed to establish a relationship between red blood cell (RBC) antioxidant status and the ability of RBCs to interact with metal-activated C-peptide, a bio-active peptide reported to reduce some complications often associated with diabetes. It is known that the reduced form of glutathione (GSH) levels in the RBCs obtained from people with type 2 diabetes are lower in comparison to those RBCs obtained from healthy controls and accordingly, this correlation has the potential to implicate type 2 diabetes in high-risk individuals. A parallel channel microfluidic device for the quantification of GSH in age-based fractions, along with control and diabetic RBCs is described. Important to the fluorescence-based measurement is the simultaneous determination of the antioxidant without prior separation in either a six- or twelve-channel microchip. Here, we separated the RBCs using a density-based Percoll solution and quantitatively determined the concentration of GSH in younger, less dense RBCs to be increased more than 2-fold (336.7 ± 29.6 amol/RBC) than older, more dense RBCs (137.0 ± 25.3 amol/RBC). The ability of C-peptide to interact with the RBC membrane of the separated fractions was determined by immunoassay and it was found that the recovery of the C-peptide added to the younger RBCs increased by more than 40.6 ± 12.7% above basal levels while with the older cells C-peptide increased by only 9.18 ± 4.60%. These results suggest that GSH concentrations in the RBC may be useful in screening for resistance to C-peptidein vivo.