Assessment of sample preservation techniques for pharmaceuticals, personal care products, and steroids in surface and drinking water

Proper collection and preservation techniques are necessary to ensure sample integrity and maintain the stability of analytes until analysis. Data from improperly collected and preserved samples could lead to faulty conclusions and misinterpretation of the occurrence and fate of the compounds being studied. Because contaminants of emerging concern, such as pharmaceuticals and personal care products (PPCPs) and steroids, generally occur in surface and drinking water at ng/L levels, these compounds in particular require such protocols to accurately assess their concentrations. In this study, sample bottle types, residual oxidant quenching agents, preservation agents, and hold times were assessed for 21 PPCPs and steroids in surface water and finished drinking water. Amber glass bottles were found to have the least effect on target analyte concentrations, while high-density polyethylene bottles had the most impact. Ascorbic acid, sodium thiosulfate, and sodium sulfite were determined to be acceptable quenching agents and preservation with sodium azide at 4 °C led to the stability of the most target compounds. A combination of amber glass bottles, ascorbic acid, and sodium azide preserved analyte concentrations for 28 days in the tested matrices when held at 4 °C. Samples without a preservation agent were determined to be stable for all but two of the analytes when stored in amber glass bottles at 4 °C for 72 h. Results suggest that if improper protocols are utilized, reported concentrations of target PPCPs and steroids may be inaccurate.     

Determination of trace chlorine dioxide based on the plasmon resonance scattering of silver nanoparticles

A plasmon resonance scattering (PRS) method for chlorine dioxide is reported based on the oxidization of silver nanoparticles (NPs) by it, in pH 9.1 ammonia-ammonium nitrate buffer solutions. Silver NPs exhibit strong PRS signals at 470nm, and can be oxidized by ClO(2), which results in PRS quenching at 470nm. It was found that the PRS quenching intensity is proportional to the concentration of chlorine dioxide over the range of 0.0011-0.185microg/mL, with a detection limit (3sigma) of 0.00050microg/mL and the correlation coefficient of 0.9995. The method is simple, rapid and cost effective. It was applied to the determination of chlorine dioxide in drinking water, with satisfactory results.     

Use of Potentiometry with Imposed Current for the Determination of Chlorine in Breakpoint Chlorination

Abstract

An investigation of the use of potentiometric titrations with imposed current, in order to identify break-point curves, has been carried out. The influence of temperature and/or conctact times has been evaluated. In ammonia chlorine mixtures determination of ammonia have been performed before and after addition of sulfite, as dechlorination agent, and results have been compared with potentiometric titrations of combined chlorine.     

Rapid determination of total trihalomethanes index in drinking water

A method for the rapid determination of total trihalomethanes (THMs) index in drinking water has been developed by using a headspace-mass spectrometry (HS-MS) system and partial least squares (PLS) multivariate regression approach. Due to the presence of residual amounts of chlorine and organic matter in the drinking water, the use of a quenching reagent in order to avoid THM generation during the sample manipulation is necessary. The optimization experiments revealed that ascorbic acid was the best quenching reagent compared with sodium thiosulfate and ammonium sulfate. The use of a classification chemometric technique as soft independent modeling of class analogy before the PLS regression improved the results obtained in the prediction of the total THMs index, lowering the relative standard error of prediction (RSEP) from 11.4% to lower than 6.0%. The results obtained by the proposed HS-MS method were compared with those provided by a conventional chromatographic method after analyzing 20 real drinking water samples. A good agreement in the results was observed and no systematic differences were found, which corroborates the good performance of the proposed method.     

Evaluation of a Novel Dechlorination Reaction as an Analytically Useful Derivatization Reaction Part 1. Stoichiometry,Mechanism and Yield Optimization

Abstract

A novel reaction for the dechlorination of polychlorinated biphenyls (PCBs) as well as most other chlorinated aromatic and aliphatic compounds is evaluated and discussed in terms of its potential for analytical purposes. The active dechlorinating agent is prepared through the reaction of molten sodium or potassium with polyethylene glycols (MW >200), in the absence of oxygen, to form the corresponding alkali metal glycolate, a powerful nucleophilic agent. Special emphasis is given to the mechanistic aspects of the reaction and their importance in terms of achieving high and reproducible yields with analytical quantities of substrate, in short periods of time. The contribution of the techniques: ESR, NMR, IR, UV, MS, GC-ECD, LC-EC, CIDNP-NMR, conductimetry and chloride analysis (amperometric) in elucidating the reaction mechanism and providing valuable kinetic data is illustrated. This reaction can potentially be applied to the determination of PCBs in waste oils.     

Microdetermination of sulfite with a piezoelectric crystal detector

A piezoelectric method is proposed for the determination of sulfite in concentration range 1 × 10^–7–1 × 10^–5 mol/1. The method is based on the redox reaction of sulfite with iodine followed by measuring frequency change of the piezoelectric crystal caused by the unreacted iodine. The method is applied to the determination of sulfite in liquor.     

Simultaneous kinetic determination of sulfite and sulfide using artificial neural networks

Artificial neural networks (ANNs) are proposed for the determination of sulfite and sulfide simultaneously. The method is based on the reaction between Brilliant Green (BG) as a colored reagent and sulfite and/or sulfide in buffered solution (pH 7.0) and monitoring the changes of absorbance at maximum wavelength of 628 nm. Experimental conditions such as pH, reagents concentrations, and temperature were optimized and training the network was performed using principal components (PCs) of the original data. The network architecture (number of input, hidden and output nodes), and some parameters such as learning rate (η) and momentum (α) were also optimized for getting satisfactory results with minimum errors. The measuring range was 0.05-3.6 μg ml⁻¹ for both analytes. The proposed method has been successfully applied to the quantification of the sulfite and sulfide in different water samples.     

Study of Six Polycyclic Aromatic Hydrocarbons by Chemical Deoxygenation Microemulsion-Stabilized Room Temperature Phosphorimetry

Six polycyclic aromatic hydrocarbons (PAHs) are studied by chemical deoxygenation microemulsion-stabilized room temperature phosphorimetry with sodium sulfite as an oxygen scavenger and thallous nitrate as a heavy atom perturber in sodium dodecyl sulfate medium. Several factors influencing room temperature phosphorescence such as the concentration of sodium dodecyl sulfate, the heavy atom concentration, the pH, and the concentration of sodium sulfite are discussed and the quenching effect of NO₂⁻on room temperature phosphorimetry of PAHs was compared in the microemulsion and micelle media.     

High performance liquid chromatographic determination of bound sulfide and sulfite and thiosulfate at their low levels in human serum by pre-column fluorescence derivatization with monobromobimane.

A sensitive and specific high performance liquid chromatographic method for the determination of sulfide, sulfite, and thiosulfate was established. Inorganic sulfur anions were converted into fluorescent derivatives with monobromobimane. The derivatives were separated on a coupled column chromatography with a reversed-phase octadecyl silica column connected with a weakly basic anion exchanger column by isocratic elution with acetic acid solution (pH 3)-acetonitrile (13:3, v/v) containing 25 mM NaClO4. The method was applied to the determination of bound sulfide and sulfite and thiosulfate in normal human serum. Thiosulfate could be determined directly by use of an ultrafiltered sample. For the determination of bound sulfide and sulfite, the pretreatment step with continuous flow gas dialysis was effective for the sample after releasing sulfide and sulfite by reduction with dithiothreitol. The limits of quantification by the present method were 0.05 microM for thiosulfate, 0.5 microM for bound sulfide, and 0.2 microM for bound sulfite.     

Identification of disinfection by‐products of selected triazines in drinking water by LC‐Q‐ToF‐MS/MS and evaluation of their toxicity

During the development of an on‐line solid phase extraction‐liquid chromatography‐ultraviolet detection (SPE‐LC‐UV) analytical method for determination of eight selected triazines; ametryn, atrazine, cyanazine, metrybuzine, prometryn, propazin, simazine, and terbutryn, in drinking water, it was observed that the retention times of three of them (ametryn, prometryn, and terbutryn) in Milli‐Q water were different from those in chlorinated Milli‐Q water, indicating the formation of new products. The cause of this change was found in the oxidation of the molecules as a result of chlorination with sodium hypochlorite. Experiments performed at varying concentrations of triazines and hypochlorite showed that the extent of the reaction depended on their relative concentrations. At the maximum admissible level of 100 ng/l for individual pesticides in drinking water, no apparent transformation was observed in the absence or at low concentrations (0.05 mg/l) of hypochlorite; however, on increasing the concentration of hypochlorite to the level typically present in drinking water (0.9 mg/l) the transformation was complete. The reaction is quite fast; within 1 h the parent compound is completely degraded and after 22 h the concentrations of the by‐products are constant. Investigation of the by‐products by ultra performance liquid chromatography‐quadrupole‐time of flight‐ tandem mass spectrometry (UPLC‐Q‐ToF‐MS/MS) has shown that all three triazines follow a similar transformation pathway, forming four new molecules whose structure have been elucidated. The acute toxicity of the new products was investigated using a standard method based on the bioluminescence inhibition of Vibrio fischeri, and the by‐products showed a higher toxicity than that of the parent compounds. Copyright © 2008 John Wiley & Sons, Ltd.     

Trace-level determination of triazines and several degradation products in environmental waters by disk solid-phase extraction and micellar electrokinetic chromatography

An analytical method combining disk solid-phase extraction with micellar electrokinetic chromatography has been developed for the determination of atrazine, simazine, hydroxyatrazine, deisopropylatrazine, deethylatrazine, propazine and prometryn in water samples. The influence of the buffer and sodium dodecyl sulfate (SDS) concentration, pH and organic modifier on the separation has been studied. Baseline separation of the seven triazines was achieved under the following conditions: 10 mM borate buffer, 60 mM SDS, 20% methanol and pH 9.2. C18-bonded silica and poly(styrene-divinylbenzene) (PS-DVB) disks were evaluated for solid-phase extraction of the selected pesticides (11 of water sample). Using two PS-DVB disks, quantitative recoveries were obtained for all pesticides tested. The method was successfully applied for the determination of the seven triazines in drinking and well water at the 0.1 microg l(-1) and 0.5 microg l(-1) concentration levels, respectively. The detection limits for these analytes using the proposed analytical method were within the 0.02-0.06 microg l(-1) range in drinking water and the 0.06-0.30 microg l(-1) range in well water.     

Factorial designs applied to the development of a capillary electrophoresis method for the analysis of zinc, sodium, calcium and magnesium in water samples

The aim of this work was to study the influence of several both chemical and instrumental variables for the development of a new capillary electrophoresis (CE) method for the determination of zinc, sodium, calcium and magnesium in water samples by using 1,10-phenanthroline as complexing agent and UV photometric detection at 214 nm. Due to the number of parameters involved and their interactions, factorial experimental designs at two levels have been applied to investigate the influence of several experimental variables (concentration of complexing agent, concentration of a visualisation agent, pH, sample introduction, applied voltage and capillary length) in sets of several capillary electrophoretic responses. The method was applied to the simultaneous determination of Na(I), Ca(II), Mg(II) and Zn(II) in drinking water with satisfactory results and a detection limit of 32 ng ml⁻¹ for Zn(II) was obtained.     

Flow-through fluorescence immunosensor for atrazine determination

A new flow-through fluoroimmunosensor for atrazine determination based on the use of protein A immobilized on controlled pore glass as immunoreactor is reported. The support, placed in the optical path of the flow cell, allows the ‘in situ’ quantification of atrazine by on-line antigen–antibody binding upon successive injections of both substances. The immunosensor has a detection limit of 2.1 μg l⁻¹, a sample speed of about 10 samples per hour, and provides high reproducibility both within-day (3.2% for 5 μg l⁻¹ and 2.2% for 30 μg l⁻¹) and between days. The optimum working concentration range was 2.1–50 μg l⁻¹. Possible interferences of other triazines like simazine, desethylatrazine (DEA) and desisopropylatrazine (DIA) were evaluated. Simazine and DIA were not cross-reactive; however, the cross-reactivity for DEA was CR=7.7%. The proposed immunosensor was successfully applied to the determination of atrazine in drinking water and citrus fruits.     

Fabrication of Sensitive Membrane Electrodes and their Application in Electrochemical Quantification of Ibandronate in Dosage Form

A new, highly selective, simple and accurate method was adopted and validated for the direct quantification of ibandronate sodium monohydrate (IBN) in tablets using sensitive polyvinyl chloride membrane electrodes. Three membranes were fabricated using dibutyl sebacate, nitrophenyl octyl ether and dioctyl phthalate. The fabricated electrodes showed fast response, capability of application in wide pH range and direct determination of IBN in turbid solutions. The most important advantage of the proposed analytical method is that it successfully allows direct determination of IBN in dosage form. The proposed analytical methodology can be applied for the direct quantification of IBN in pharmaceutical formulations.     

Selective Complexometric Determination of Titanium(IV) Using Sodium Potassium Tartrate or Ascorbic Acid as Masking Agent

 A simple, rapid and accurate complexometric method is proposed for the determination of titanium(IV) where sodium potassium tartrate or ascorbic acid were used as masking agents. In the presence of diverse metal ions, titanium is first complexed with excess of EDTA and surplus EDTA is then titrated at pH 5–6 with zinc sulfate, xylenol orange being used as indicator. An excess of 5% aqueous sodium potassium tartrate is then added to displace the complexed EDTA from the Ti-EDTA complex quantitatively, which is titrated with zinc sulfate. Also, ascorbic acid may be used as the releasing agent. The methods work well in the range 1–53 mg of Ti(IV) for sodium potassium tartrate with relative errors ± 0.28% and standard deviations ≤ 0.16 mg. For ascorbic acid the range is 1.00–30.00 mg of Ti(IV) with relative errors of ± 0.40% and standard deviations of ≤ 0.05 mg Received October 9, 2001; accepted August 2, 2002     

Application of direct thermometric analysis in iodometry

Elementary chlorine was determined by a thermometric method using potassium iodide as reagent. The temperature rise corresponding to the heat of reaction was proportional to the chlorine content. Iodine formed in the reaction was also determined with sodium thiosulphate. The heat of the chlorine-iodide reaction is about five times that of the iodine-thiosulphate reaction. Direct determination with potassium iodide is simpler and more rapid than the indirect one.     

A spectroscopic investigation into the reaction of sodium tetrathionate with cysteine

A spectroscopic investigation into the reaction of sodium tetrathionate with cysteine at pH 5 both at the boil and at room temperature has been carried out. The Raman and infrared spectra of the model compounds cysteine, cysteine-S-sulfonate, cysteine-S-thiosulfonate, sodium thiosulfate and sodium sulfite were also obtained and vibrations involving the sulfur atoms were analyzed in detail. These results were utilized in the interpretation of the spectra obtained from tetrathionate-cysteine reaction mixtures. The reaction supernatants were analyzed by high performance thin layer chromatography while the precipitates were analyzed gravimetrically. It was found that during the reaction, the thiol groups of cysteine are oxidised to give predominantly cysteine-S-sulfonate. Cystine was also detected but was determined gravimetrically to be a minor reaction product. No significant amounts of cysteine-S-thiosulfonate were detected. The reaction is accompanied by the formation of elemental sulfur and a small amount of sulfite. Major reaction pathways are put forth that are consistent with the experimental data.     

Simultaneous spectrophotometric determination of cyanide and thiocyanate after separation on a melamine-formaldehyde resin

A simple indirect spectrophotometric method for the determination of cyanide, based on the oxidation of the cyanide with chlorine (Cl(2)) is described. The residual chlorine is determined by the color reaction with o-tolidine (3,3'-dimethylbenzidine). The maximum absorbance for Cl(2) is at 437 nm. A linear calibration graph (0-4.0x10(-5) M CN(-)) is obtained under optimal reaction conditions at room temperature and pH 11-12. The stoichiometric mole ratio of chlorine to cyanide is 1:1. The effective molar absorptivity for cyanide is 5.87x10(4) l mol(-1) cm(-1) at pH 1.6. The limit of quantification (LOQ) is 3.6x10(-7) M or 9.4 ppb. Effects of pH, excess reagent, sensitivity, reaction time and tolerance limits of interferent ions are reported. The method was applied to the determination of cyanide in a real sample. The basic interferent usually accompanying CN(-), i.e. thiocyanate, is separated from cyanide by sorption on a melamine-formaldehyde resin at pH 9 while cyanide is not retained. Thiocyanate is eluted with 0.4 M NaOH from the column and determined spectrophotometrically using the acidic FeCl(3) reagent. The initial column effluent containing cyanide was analyzed by both the developed chlorine-o-tolidine method and the conventional barbituric acid-pyridine (Spectroquant 14800) procedure, and the results were statistically compared. The developed method is relatively inexpensive and less laborious than the standard (Spectroquant) procedure, and insensitive to the common interferent, cyanate (CNO(-)).     

Square-wave voltammetric (SWV) determination of Captopril in reconstituted serum and pharmaceutical formulations

A simple, fast and sensitive square-wave voltammetric (SWV) method for the determination of trace amounts of Captopril in pharmaceutical formulation and reconstituted serum is reported. A three-electrode system containing the static mercury drop electrode (SMDE) working electrode, Pt auxiliary electrode and Ag/AgCl reference electrode was used throughout. Sodium sulfite was used as both supporting electrolyte and oxygen removing agent. No nitrogen purging is needed for oxygen removal from sample solution. Calibration graph showed good linearity in the concentration range of 0.5-50.0 μg mL⁻¹ of Captopril and regression coefficient of 0.9957 is obtained. R.S.D. for eight replicate measurements and LOD of the proposed method are 1.2% and 6.28 × 10⁻³ μg mL⁻¹, respectively. The effect of various parameters (equilibration time, scan increment, pulse height, drop size, frequency and sodium sulfite concentration) on the determination were investigated. The procedure was successfully applied to the determination of Captopril in pharmaceutical formulation and reconstituted serum.     

Simple and rapid determination of the drug naproxen in pharmaceutical preparations by heavy atom-induced room temperature phosphorescence

A simple, selective and sensitive heavy atom-induced room temperature phosphorimetric method (HAI-RTP) is described for the determination of naproxen (NAP) in pharmaceutical preparations. The phosphorescence signals are a consequence of intermolecular protection when analytes are, exclusively, in presence of a heavy atom salt and sodium sulfite as an oxygen scavenger to minimize RTP quenching. These variables selection constitute the basis of a HAI-RTP method for the determination of naproxen (detection limit 17.6 ng ml(-1); 1.71% relative standard deviation at 250 ng ml(-1)). The method has been applied satisfactorily to the analysis of pharmaceutical preparations.