Abdulmumin A. Nuhu

Liquid-phase and dispersive liquid-liquid microextraction techniques with derivatization: Recent applications in bioanalysis

Liquid phase microextraction (LPME), especially hollow fiber liquid-phase microextraction (HF-LPME), and dispersive liquid-liquid microextraction (DLLME) offer high enrichments of target analytes in a single step. The analytical usefulness of these techniques is significantly enhanced by coupling them with suitable derivatization methods. Due to their simplicity, diverse bioanalytical applications have recently been reported. This review focuses on the recent developments of the combined LPME (mainly HF-LPME and single drop microextraction (SDME)) and DLLME techniques with derivatization for the analysis of biological samples. A broad range of sample matrices such as urine, blood, plasma and human hair samples with various derivatization methods for polar or ionizable organic compounds will be considered. These techniques can also be extended to the determination of trace metal ions, such as the heavy metal ions (Hg, Pb, and Co) and Se. Future trends of the techniques will also be discussed.

Bio-catalytic desulfurization of fossil fuels: a mini review

For a long time now, the combustion of fossil fuels to give usable energy has led to the release of many types of pollutants into the atmosphere. Of particular interest is sulfur dioxide derived from combustion of diesel and related organic-sulfur containing media. Its presence in the air has resulted in the deterioration of health and depletion in aesthetic quality of materials. As a result, environmental regulations are now put in place to regulate the level of sulfur in different fuel types. To achieve this goal, many techniques have been tested, and bio-catalytic desulfurization is now being considered due to some limitations with conventional hydrodesulfurization approach. This essay discusses various kinds of microbial isolates that are harnessed for this purpose, and the influence of genetic engineering techniques and various factors on the activities of these biocatalysts. With increasing knowledge of microbial ecology, better understanding of biochemical systems, exploration of new conversion pathways and optimization of bioreactor design, enhancement in this approach is expected to bring an increase in its acceptability and improve the prospects of its full commercialization as viable alternative to the conventional hydrodesulfurization of fossil fuels.

Determination of polycyclic aromatic hydrocarbons in water using nanoporous material prepared from waste avian egg shell

For the first time a biocompatible calcium carbonate vateritic polymorph was recrystallized from eggshell waste and its application for the extraction of polycyclic aromatic hydrocarbons in water samples was demonstrated. This nanoporous calcium carbonate was used as sorbent in dispersive micro-solid-phase extraction method. In this approach 50 mg of the calcium carbonate material having about 25 nm pores was placed in a 5mL of water sample and ultrasonicated for 30min. The cloudy sample was centrifuged at 13500 rpm for 2 min. The aqueous layer was then discarded and the CaCO3 material was dabbed dry with a lint-free tissue. The analytes were then desorbed with 100 µL of dichloromethane by ultrasonication for 5 min. Finally, the extract was analyzed by gas chromatography flame ionization detector. Experimental parameters affecting the extraction recoveries were optimized. Using optimum extraction conditions, calibration curves were linear with correlation coefficients of 0.9853 to 0.9973 over the concentration range of 0.05 to 30 ng/mL. This method showed a detection limit as low as 0.004 ng/mL (at signal-to-noise ratio of 3). Performance of the dispersive micro-solid-phase extraction was compared with a previously optimized solid-phase extraction technique. The developed method displayed good extraction recoveries (85 ± 8-110 ± 4%) with high enhancement factors (388- 1433-fold) and good repeatability (% RSD < 13) and involved the use of minimal solvents. Analysis of seawater from Dammam Port revealed the presence of the analytes at concentrations between 0.15 ± 0.01 and 13.43 ± 1.54 ng/mL.

Determination of phenoxy herbicides in water samples using phase transfer microextraction with simultaneous derivatization followed by GC-MS analysis.

A sensitive and accurate method for the determination of two model phenoxy herbicides, 4-chloro-2-methylphenoxy acetic acid and 4-chloro-2-methylphenoxy propanoic acid, in water is explained. This method utilizes a simple phase transfer catalyst-assisted microextraction with simultaneous derivatization. Factors affecting the performance of this method including pH of the aqueous matrix, temperature, extraction duration, type and amount of derivatization reagents, and type and amount of the phase transfer catalyst are examined. Derivatization and the use of phase transfer catalyst have proven to be especially vital for the resolution of the analytes and their sensitive determination, with an enrichment factor of 288-fold for catalyzed over noncatalyzed procedure. Good linearity ranging from 0.1 to 80 μg L(-1) with correlation of determination (r(2) ) between 0.9890 and 0.9945 were obtained. Previous reported detection limits are compared with our new current method. The low LOD for the two analytes (0.80 ng L(-1) for 4-chloro-2-methylphenoxy propanoic acid and 3.04 ng L(-1) for 4-chloro-2-methylphenoxy acetic acid) allow for the determination of low concentrations of these analytes in real samples. The absence of matrix effect was confirmed through relative recovery calculations. Application of the method to seawater and tap water samples was tested, but only 4-chloro-2-methylphenoxy propanoic acid at concentrations between 0.27 ± 0.01 and 0.84 ± 0.06 μg L(-1) was detected in seawater samples.

Determination of Haloacetic Acids in Bottled and Tap Water Sources by Dispersive Liquid-Liquid Microextraction and GC-MS Analysis

Haloacetic acids are toxic organic pollutants that can be formed as by-products of disinfection of water by chlorination. In this study, we developed a fast and efficient method for the determination of six species of these compounds in water using dispersive liquid-liquid microextraction followed by GC-MS analysis. To be suitable for GC analysis, the acidic analytes were derivatized using n-octanol. One-factor-at-a-time optimization was carried out on several factors including temperature, extraction time, amount of catalyst, and dispersive solvent. The optimized conditions were then used to determine calibration parameters. Linearity, as demonstrated by coefficient of determination, ranged between 0.9900 and 0.9966 for the concentration range of 0.05–0.57 µg/L. The proposed method has good repeatability; intraday precision was calculated as %RSD of 2.38–9.34%, while interday precision was 4.69–8.06%. The method was applied to real samples in bottled water and tap water sources. Results indicated that the total concentrations of the analytes in these sources (2.97–5.30 µg/L) were far below the maximum contaminant levels set by both the World Health Organization and the United States Environmental Protection Agency. The proposed method compared favorably with methods reported in the literature.

3.34 Sample Preparation of Complex Biological Samples in the Analysis of Trace-Level Contaminants

Determination of trace-level contaminants in complex biological samples has been of increasing demand. Conventional means of this determination for matrices such as urine, blood, and milk may involve multistep sample preparations with a high probability of loss of analytes, and are mostly time-consuming. As a result, simple minimized microextraction procedures such as solid-phase microextraction, stir bar sorptive extraction, liquid-phase microextraction, and electromembrane extraction, which are mostly carried out in one or two steps, are preferred. Recently a number of tailored solid-phase extraction and molecularly imprinted polymer extraction procedures for nonviscous biological liquid samples have been reported. However, for animal tissues and other solid, semisolid, and highly viscous samples, extraction methods may encounter greater difficulties than those for conventional liquid samples. Consequently the preferred sample preparations are simple, step-minimized methods such as pressurized liquid extraction, supercritical fluid extraction and the like. The main advantages of these modern techniques are that they can be customized for simultaneous extraction and cleanup. To date, these techniques have been successfully applied as sample preparation and preconcentration steps in the determination of various analytes of toxicological importance in different biological matrices.

Analytical method development using functionalized polysulfone membranes for the determination of chlorinated hydrocarbons in water.

In this study, functionalized polysulfone membrane has been utilized as a sorbent for the extraction of chlorinated hydrocarbons (CHCs) in water samples. Two different functionalized polysulfones (i) phosphonic acid functionalized polysulfone (PPSU-A) with different forms (cross-linked and non cross-linked) membranes and (ii) phosphonic ester functionalized polysulfone (PPSU-E) with different forms (cross-linked and non cross-linked) were evaluated for the extraction of CHCs in water. A 10 ml of spiked water sample was extracted with 50mg piece of the functionalized membrane. After extraction, the membrane was desorbed by organic solvent and the extract was analyzed by gas chromatography-mass spectrometry. Eight CHCs, 1,3,5-trichlorobenzene (1,3,5-TCB), 1,2,3-trichlorobenzene (1,2,3-TCB), 1,1,2,3,4,4-hexachloro-1,3-butadiene (HCBD), 1,2,4-trichloro-3-methylbenzene (TCMB), 1,2,3,4-tetrachlorobenzene (1,2,3,4-TeCB), 1,2,4,5-tetrachlorobenzene (1,2,4,5-TeCB), pentachlorobenzene (PeCB) and hexachlorobenzene (HCB) were used as model compounds. Experimental parameters such as extraction time, desorption time, types of polymer membrane as well the nature of desorption solvent were optimized. Using optimum extraction conditions calibration curves were linear with coefficients of determination between 0.9954 and 0.9999 over wide range of concentrations (0.05-100 μgl(-1)). The method detection limits (at a signal-to-noise ratio of 3) were in the range of 0.4-3.9 ng l(-1). The proposed method was evaluated for the determination of CHCs in drinking water samples.