Current Analytical Chemistry - Volume 5, Issue 1, 2009

The heat labile carotenoids cannot be analyzed by gas chromatography (GC) and GC-mass spectrometry (GC- MS). The only useful method appears to be high-performance liquid chromatography (HPLC) with UV/visible (UV/Vis) or mass spectrometric detection (LC-MS). Reversed-phase HPLC (RP-HPLC) is a preferred method, which is frequently used with C18 stationary phase, usually with gradient elution. In contrast to other ionization techniques, xanthophylls and carotenes form both molecular ions and protonated molecules during positive ion APCI (atmospheric pressure chemical ionization). APCI is an ideal method of ionization for low- to medium-polar compounds, which include also carotenoids and related compounds. Since their molecular mass does not exceed 2000 amu even in the case of glycosides or esters with fatty acids, this method is exceedingly suitable for their analysis. The review summarizes the data on its use for this group of compounds.

The detection of losses from nuclear material inventories is an important problem to be solved. The present paper considers the detection of such losses by using the fractal dimension of the material balance time series to detect the outliers that are the loss points. We find the proposed method to be successful.

A simple, rapid, selective and sensitive differential pulse anodic stripping voltammetric (DPASV) technique for the direct quantitative determination of inorganic total arsenic in natural hotwater was developed. The electrochemical determination of total arsenic has been carried out at the novel rotating lateral gold electrode in hydrochloric acid solution (37 % w/w). The analysis was performed with a special gold electrode whose active surface was located on the side. Reproductivity of measurement was achieved by the conditioning of the gold electrode. This was done every day before the measurements as well as when the background current varied strongly from measurement to measurement. The determination limit of 0.5 μg L-1 was achieved with 10 mL sample solution. The total arsenic concentration was made by appropriate selection of the deposition potential. During the deposition step, the total arsenic content was reduced at -1200 mV by nascent hydogen to As°. During the subsequent voltammetric determination, the preconcentration As° was again oxidized to determine the level. The method was applied successfully to the direct quantitative determination of total inorganic arsenic in hotwater. In order to show the accuracy of the results developed from voltammetric technique, the values obtained were compared with those obtained from inductively coupled plasma mass spectrometry (ICP-MS).

The aim of this study involves the determination of mercury ions at nanomolar level with the employment of the dipyridyl functionalized nanoporous silica gel - chemically modified carbon paste electrode (DPSG-CPE) by anodic stripping voltammetry. The experiments were conducted with a certain electrode composition of 25% paraffin oil, 60% high purity graphite powder and 15% DPSG as well as the usage of 0.20 M KNO3 as supporting medium. The reduction potential and time were set at, -200 mV and 450 s, respectively, and the scan rate at 100 mV s-1 in the scan range of -200 to 500 mV. The analytical performance of the modified electrode was evaluated with respect to the carbon paste composition, the solution pH at the accumulation step, the preconcentration time, the mercury concentration, the possible interferences and other variables. On this modified electrode, the anodic stripping voltammetric mercury determination at nanomolar level concentrations was successfully attempted. The resulting electrode demonstrated linear response across a wide mercury(II) concentration range (20-100 nM) with a detection limit value of 8 nM, on the basis of a signal to noise ratio of 3. The precision for six determinations (n=6) of 40 and 75 nM mercury(II) was 5.0% and 2.8% (relative standard deviation), respectively. After studying the influence of the potential interfering ions, it was found that the proposed procedure was free from most interference. To testify the accuracy of this method, comparative determination of mercury(II) in wastewater samples by the proposed method and cold vapor AAS method were done and a sufficient sensitivity for the practical analysis of the environmental samples was attained.

The voltammetric behavior of cinnamic acid (CA) and 3, 4-dihydroxy benzoic acid (BA) at an glassy carbon disc electrode has been investigated. The obtained cyclic voltammograms showed that their oxidation peaks were overlapped and it was difficult to determine them individually from a mixture without separation. To overcome this limitation, partial least squares (PLS) modeling, as a powerful multivariate statistical tool, was proposed for the resolution of the overlapped voltammetric signals from mixtures of CA and BA. With the help of the orthogonal signal correction (OSC), the unrelated information was removed and the results were confirmed. In this procedure, the genetic algorithm (GA) was used for the potentials selection for PLS. In addition, OSC-GA-PLS for the first time was used and the results of this method were better than those of the other methods. The proposed method was suitable for the determination of CA and BA in mixtures.

A fluorescent chemosensor based on modified β-cyclodextrin was used for the detection of pesticides and herbicides in water. Binding constants, thermodynamic parameters and sensitivity factors were calculated and supported by AM1 semi-empirical method calculation. The results show clearly that a fluorescent chemical sensor based on modified β- cyclodextrin detects quantitatively the presence of pesticides or herbicides and allow a direct analysis of these pollutants as a new method of detection with limits of the order of ppm for the whole of the analytes.

A new potassium ion-selective membrane electrode has been developed based on crown ether. The membrane consisted of benzo-15-5 crown ether as a neutral carrier, orto-nitrophenylphenyl ether as plasticizer and PVC as membrane matrix. An analytically useful potential change occurs in the 1x10-6-1x10-2 mol L-1 concentration range. The slope of the linear portion (1x10-2 - 1x10-4 mol L-1) was 56 ± 3 mV/10-fold concentration changes in potassium concentration. In the presence of 1x10-3 mol L-1 potassium, no interference was observed for Li+, Na+, NH4 +, Mg2+, Ca2+, Sr2+, Ba2+, Cr3+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, F-, Br-, I-, NO2 -, SO4 2-, CO3 2-, S2- ions. The measurements were made at constant ionic strength (0.1 mol L-1 NaNO3, medium) and at room temperature. The lifetime of the electrode was approximately 2 months, and the response time was about 20-30 seconds. This electrode has been used for the determination of potassium ion with standard addition method in orange juice, vitamin, and edible salt. The amount of K+ found was 1.97 ± 0.06 mg/mL in orange juice, 0.420 ± 0.008 % (m/m) in vitamin tablet and 0.52 ± 0.08 % (m/m) in edible salt.

Glucose assay was conducted on untreated diabetic patient's urine and blood using a combination electrode (CE) whose sensor was interfaced with a newly constructed handheld voltammetry. The CE was prepared using the common graphite pencil as a working electrode, handmade reference electrode, and platinum counter electrode, which were combined into one electrode system. The CE was optimized through cyclic and stripping voltammetry. Analytical working range was attained at 30.0-300.0 ugL-1 and at 100-800 ugL-1, under different conditions. The relative standard deviation of 0.5 mg/L that was observed at the optimum condition was 0.31% (n=15). The detection limit (S/N) was attained at 13.7 ugL-1 (7.6x10-8 M). The system that was developed in this study is compact and can be useful in ubiquitous, selfdiagnosis, and fast assays.

Laminar and pulsed flows typical of multi-commuted and multi-pumping flow systems, were evaluated in relation to analytical procedures carried out at high temperatures. As application, the spectrophotometric determination of total reducing sugars (TRS, hydrolyzed sucrose plus reducing sugars) in sugar-cane juice and molasses was selected. The method involves in-line hydrolysis of sucrose and alkaline degradation of the reducing sugars at about 98 °C. Better results were obtained with pulsed flows, due to the efficient radial mass transport inherent to the multi-pumping flow system. The proposed system presents favorable characteristics of ruggedness, analytical precision (r.s.d. < 0.013 for typical samples), stability (no measurable baseline drift during 4-h working periods), linearity of the analytical curve (r > 0.992, n = 5, 0.05 - 0.50% w/v TRS) and sampling rate (65 h-1). Results are in agreement with ion chromatography.

A high-resolution NMR spectrum, containing fine structures such as chemical shifts and scalar-coupling multiplet patterns, is helpful for analyzing molecular composition and structure. However, there are many cases where the magnetic environments are inhomogeneous, which may lead to severe signal overlapping and blur useful spectral information in liquid samples. Recently, many NMR techniques have been proposed to regain high-resolution spectral information in inhomogeneous magnetic fields. They can be mainly classified into three types that based on intermolecular multiple- quantum coherences, nutation echoes, and spatial encoding respectively. These methods can be applied to a wide range of samples, thereby opening a way to high-resolution in vivo and ex situ NMR spectroscopy. In this review, recent developments of these methods are presented and their applicability and efficiency are analyzed.