Thermodynamic studies for adsorption of ionizable pharmaceuticals onto soil

Although pharmaceutical compounds (PCs) are being used more and more widely, and studies have been carried out to assess their presence in the environment, knowledge of their fate and behavior, especially under different environmental conditions, is still limited. The principle objective of the present work, therefore, is to evaluate the adsorption behavior of three ionizable, polar compounds occurring in different forms: cationic (propranolol - PRO), anionic (sulfisoxazole - SSX) and neutral (sulfaguanidine - SGD) onto soil under various temperature conditions. The adsorption thermodynamics of these researched compounds were extensively investigated using parameters such as enthalpy change (ΔH°), Gibbs free energy change (ΔG°) as well as entropy change (ΔS°). These calculations reveal that sorption of PRO is exothermic, spontaneous and enthalpy driven, sorption of SGD is endothermic, spontaneous and entropy driven whereas sorption of SSX is endothermic, spontaneous only above the temperature of 303.15K and entropy driven. Furthermore, we submit that the calculated values yield valuable information regarding the sorption mechanism of PRO, SGD and SSX onto soils.

Column and batch tests of sulfonamide leaching from different types of soil

Sulfonamides (SAs) and their metabolites present severe hazards to human health and the environment, mainly because of antibiotic resistance. Knowledge of their bioavailability, including their sorption to soils and their impact on the soil-groundwater pathway, is crucial to their risk assessment. Laboratory batch and column leaching tests are important tools for determining the release potential of contaminants from soil or waste materials. Batch and column tests were carried out with soils differing in particle size distribution, organic matter content and pH, each spiked with sulfonamides (sulfadimethoxine (SDM), sulfaguanidine (SGD), sulfisoxazole (SX)). In order to test the applicability of leaching tests to polar contaminants batch and column tests were also compared. In the column tests, release was found to depend on the properties of both soil and sulfonamides. The fastest release was observed for coarse-grained soil with the smallest organic matter content (MS soil; 100% decrease in concentration until liquid-to-solid ratio (L/S) of 0.9 L kg(-1) for all SAs). The slowest release was established for sulfadimethoxine (24.5% decrease in concentration until L/S 1.22 L kg(-1)). The results of the batch and column tests were comparable to a large extent, with slightly higher concentrations being obtained in the column test experiments of fine-grained soils with a high organic matter content.

Sulfadimethoxine and sulfaguanidine: their sorption potential on natural soils

Sulfonamides (SAs) are one of the oldest groups of veterinary chemotherapeutic agents. As these compounds are not completely metabolized in animals, a high proportion of the native form is excreted in feces and urine. They are therefore released either directly to the environment in aquacultures and by grazing animals, or indirectly during the application of manure or slurry. Once released into the environment, SAs become distributed among various environmental compartments and may be transported to surface or ground waters. The physicochemical properties of SAs, dosage and nature of the matrix are the factors mainly responsible for their distribution in the natural environment. Although these rather polar compounds have been in use for over half a century, knowledge of their fate and behavior in soil ecosystems is still limited. Therefore, in this work we have determined the sorption potential of sulfadimethoxine and sulfaguanidine on various natural soils. The influence on sorption of external factors, such as ionic strength and pH, were also determined. The sorption coefficients (K(d)) obtained for the sulfonamides investigated were quite low (from 0.20 to 381.17 mL g(-1) for sulfadimethoxine and from 0.39 to 35.09 mL g(-1) for sulfaguanidine), which indicated that these substances are highly mobile and have the potential to run off into surface waters and/or infiltrate ground water. Moreover, the sorption of these pharmaceuticals was found to be influenced by OC, soil solution pH and ionic strength, with higher K(d) values for soils of higher OC and lower K(d) values with increasing pH and ionic strength.

[Synthesis and identification of artificial antigens for sulfaguanidine and sulfathiazole]

OBJECTIVE

To prepare artificial antigens of sulfaguanidine and sulfathiazole for detecting sulfaguanidine and sulfathiazole in foods of animal origin.

METHODS

The artificial antigens were synthesized by the diazotization methods of coupling sulfaguanidine and sulfathiazole with bovine serum albumin (BSA), and the coupling ratio was 10 : 1 and 9 : 1 respectively. The anti-serum of Balb/c mice was obtained after 5 injections of artificial antigens and the antibody titles were detected by iELISA method.

RESULTS

The artificial antigens were identified by infrared spectra, ultraviolet spectra and immunized experimental animals.

CONCLUSION

The antigens for sulfaguanidine and sulfathiazole were acquired successfully. The results have laid basis for the specific immunoassay of sulfaguanidine and sulfathiazole.

Fluorimetric Determination of Sulphaguanidine and Sulphamethoxazole by Host-Guest Complexation in β-Cyclodextrin and Partial Least Squares Calibration

The host-guest inclusion complexes of sulphamethoxazole (SMTX) and sulphaguanidine (SGN) with beta-cyclodextrin, in aqueous solutions, have been investigated. A 1:1 stoichiometry of the complexes was established, the association constants were calculated by different methods, and the influence of several chemical variables on the complexation processes were established. According to the results obtained, a spectrofluorimetric method for the determination of these sulphonamides has been proposed. The individual and binary mixtures of both sulphonamides have been determined in human urine samples, at representative therapeutic ranges, by application of a first-order multivariate calibration partial least squares (PLS-1) model. The calibration set was designed with 9 samples, containing different concentrations of the two sulphonamides, and 8 blank urine samples, with the aim of modelling the variability of the background. The concentration ranges for the sulphonamides were up to 0.5 microg mL(-1) for SMTX and 1.0 microg mL(-1) for SGN. Figures of merit as selectivity, analytical sensitivity and limit of detection (LOD) were also calculated. The proposed procedure was validated by comparing the obtained results with a HPLC method, with satisfactory results for the assayed method.

Hyphenation of Raman spectroscopy with gravimetric analysis to interrogate water–solid interactions in pharmaceutical systems

A moisture sorption gravimetric analyzer has been combined with a Raman spectrometer to better understand the various modes of water-solid interactions relevant to pharmaceutical systems. A commercial automated moisture sorption balance was modified to allow non-contact monitoring of the sample properties by interfacing a Raman probe with the sample holder. This hybrid instrument allows for gravimetric and spectroscopic changes to be monitored simultaneously. The utility of this instrument was demonstrated by investigating different types of water-solid interactions including stoichiometric and non-stoichiometric hydrate formation, deliquescence, amorphous-crystalline transformation, and capillary condensation. In each of the model systems, sulfaguanidine, cromolyn sodium, ranitidine HCl, amorphous sucrose and silica gel, spectroscopic changes were observed during the time course of the moisture sorption profile. Analysis of spectroscopic data provided information about the origin of the observed changes in moisture content as a function of relative humidity. Furthermore, multivariate data analysis techniques were employed as a means of processing the spectroscopic data. Principle components analysis was found to be useful to aid in data processing, handling and interpretation of the spectral changes that occurred during the time course of the moisture sorption profile.

Determination of sulfonamide antibiotics in wastewater: A comparison of solid phase microextraction and solid phase extraction methods

In recent years, pharmaceutical and personal care products (PPCPs) have been detected in diverse environments (including groundwater, river water, and municipal wastewater). In order to evaluate their environmental impact, PPCPs must first be accurately determined. In this study, we focused on developing methods to accurately determine 10 sulfonamide antibiotics: sulfaguanidine, sulfacetamide, sulfadiazine, sulfathiazine, sulfapyridine, sulfamerazine, sulfamethazine, sulfamethoxazole, sulfadimethoxine, and sulfasalazine. While sulfonamides can easily be determined in pure water, wastewater influent and effluent collected from sewage treatment plants in Burlington and Toronto (Ontario) were found to generate confounding matrix effects. In an effort to overcome these matrix effects, we developed a solid phase microextraction (SPME) method to determine sulfonamides. Of the five different fiber assemblies investigated, the carbowax/divinylbenzene (CW/DVB) fiber produced the optimal response to sulfonamides. The SPME method was further optimized for sorption time (20min), solution salinity (10%, w/v, KCl), pH (4.5), and static desorption time (30min). When compared to solid phase extraction (SPE) using MCX cartridges, we observed that despite having higher MDLs and poorer sensitivity, SPME possessed the advantage of speed and reduced solvent usage. Most importantly, in contrast to SPE, when we applied the SPME method to fortified wastewater samples, we were generally able to accurately determine (i.e., recover) those sulfonamides that were present. Therefore, we conclude that SPME is a viable method for overcoming matrix effects in environmental samples.

Spectrofluorimetric determination of sulphonamides in pharmaceutical compounds and foods

Spectrofluorimetry and room temperature photochemically-induced fluorescence (RTPF) have been applied to the determination of sulphacetamide (SAC), sulphaguanidine (SG) and sulphamethazine (SMT) in milk and pharmaceutical formulations. The methods are suitable for determining 0.02-0.10 micrograms ml of SAC, 0.10-0.50 micrograms ml of SG, and 0.40-1.00 micrograms of SMT.

[Fluorometric determination of sulfanilamide and sulfaguanidine residues in animal tissues with high-performance-liquid chromatography]

A high-performance liquid chromatographic method is presented for the selective analysis of sulphanilamide (SA) and sulphaguanidine (SG) residues in animal tissues (muscle, liver), egg and milk at the 0.01-0.1 mg/kg level. A 25-g amount of the samples was extracted with 90 ml acetonitrile at pH 8.5 to which 2 ml saturated sodium carbonate had been added. After centrifugation, co-extracted water was separated by saturating the extract with sodium chloride and adding 50 ml dichloromethane. The residue of the dried and evaporated organic layer was partitioned between methanol, n-hexane and mobile phase (1 ml each). A 20-microliter volume of the aqueous layer was injected onto a Nucleosil 5 SA column [mobile phase 0.05 M sodium dihydrogenphosphate (adjusted to pH 2.0 with 85% orthophosphoric acid)-methanol, 85:15, v/v]. SA and SG were detected by their native fluorescence (excitation 275 nm, emission 340 nm) at retention times of 7 and 13 min, respectively, without interference of co-extractives. Parallel detection by ultraviolet absorption (275 nm) allowed on-line confirmation of the results. Recovery of spiked samples (0.1 mg/kg) was 80% (coefficient of variation, C.V. = 5%) for SA and 62% (C.V. = 6%) for SG. Concentrations of 0.27 mg/kg for SA and 0.05 mg/kg for SG were analyzed in muscle meat of a swine which received a single intramuscular injection of 2.1 g SA and 0.6 g SG and was slaughtered 24 h later.