Baki B. M. Sadi

Trace humic and fulvic acid determination in natural water by cloud point extraction/preconcentration using non-ionic and cationic surfactants with FI-UV detection.

A preconcentration and determination method for humic and fulvic acids at trace levels in natural water samples was developed. Cloud point extraction was successfully employed for the preconcentration of humic acid (HA) and fulvic acid (FA) prior to the determination by using a flow injection (FI) system coupled to a spectrophotometric UV-Vis detector. The quantitative extraction of HA and FA within the pH range 1-12 was obtained by neutralization of the anionic charge on the humic substances with a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB). This generated a hydrophobic species that was subsequently incorporated (solubilized) into the micelles of a non-ionic surfactant polyethylene glycol, tert-octylphenyl ether (Triton X-114). The FI method for HA and FA determination was developed by injection of 100 microl of the extracted surfactant-rich phase using an HPLC pump with spectrophotometric detection at 350 nm. A 50 ml sample solution preconcentration allowed an enrichment factor of 167. The limit of detection (LOD) obtained under the optimal conditions was 5 microg l(-1). The precision for ten replicate determinations at 0.2 mg l(-1) HA was 3.1% relative standard deviation (RSD), calculated from the peak heights. The calibration using the preconcentration system for HA and FA was linear with a correlation coefficient (r2) of 0.9997 at levels near the detection limits up to at least 1 mg l(-1). The method was successfully applied to the determination of HA and FA in natural water samples (river water).

Reversed phase ion-pairing HPLC-ICP-MS for analysis of organophosphorus chemical warfare agent degradation products

The separation and analysis of three organophosphorus chemical warfare degradation products is described. Ethyl methylphosphonic acid (EMPA, the major hydrolysis product of VX), isopropyl methylphosphonic acid (IMPA, the major hydrolysis product of Sarin (GB)), and methylphosphonic acid (MPA, the final hydrolysis product of both) were the analytes and were separated by reversed phase ion-pairing high-performance liquid chromatography (RP-IP-HPLC) with the use of myristyl trimethylammonium bromide as ion-pairing reagent and an ammonium acetate–acetic acid buffer system (pH 4.85). An Agilent 7500ce inductively coupled plasma mass spectrometer (ICP-MS) equipped with collision/reaction cell technology was coupled to the chromatographic system for detection of 31P and 47PO+. Historically, ICP-MS detection of phosphorus has been limited due to its high first ionization potential (10.5 eV) and the presence of severe nitrogen polyatomic interferences (such as 14N16O1H+ and 15N16O+) overlapping its only isotope at m/z = 31. Implementation of an octopole reaction cell with helium as the cell gas allowed for removal of the nitrogen polyatomic interferences and reduction of background signal. Detection limits for EMPA, IMPA, and MPA were found to be 263, 183 and 139 pg mL−1, respectively, with separation in less than 15 min. The developed method was successfully applied to the analysis of spiked environmental water and soil samples.

Emergency Radiobioassay Method for Determination of 90Sr and 226Ra in a Spot Urine Sample

A new radiobioassay method has been developed for simultaneous determination of (90)Sr and (226)Ra in a spot urine sample. The method is based on a matrix removal procedure to purify the target radionuclides from a urine sample followed by an automated high performance ion chromatographic (HPIC) separation of (90)Sr and (226)Ra and offline radiometric detection by liquid scintillation counting (LSC). A Sr-resin extraction chromatographic cartridge was used for matrix removal and purification of (90)Sr and (226)Ra from a urine sample prior to its introduction to the HPIC system. The HPIC separation was carried out through cation exchange chromatography using methanesulfonic acid (75 mM) as the mobile phase at 0.25 mL/min flow rate. The performance criteria of the method was evaluated against the American National Standard Institute ANSI/HPS N13.30-2011 standard for the root mean squared error (RMSE) of relative bias (Br) and relative precision (SB) at two different spiked activity levels. The RMSE of Br and SB for (90)Sr and (226)Ra were found to be satisfactory (≤0.25). The minimum detectable activity (MDA) of the method for (90)Sr and (226)Ra are 2 Bq/L and 0.2 Bq/L, respectively. The MDA values are at least 1/10th of the concentrations of (90)Sr (190 Bq/L) and (226)Ra (2 Bq/L) excreted in urine on the third day following an acute exposure (inhalation) that would lead to an effective dose of 0.1 Sv in the first year. The sample turnaround time is less than 8 h for simultaneous determination of (90)Sr and (226)Ra.