Palladized aluminum electrode covered by Prussian blue film as an effective transducer for electrocatalytic oxidation and hydrodynamic amperometry of N-acetyl-cysteine and glutathione

The mediated oxidation of N-acetyl cysteine (NAC) and glutathione (GL) at the palladized aluminum electrode modified by Prussian blue film (PB/Pd–Al) is described. The catalytic activity of PB/Pd–Al was explored in terms of Fe^III[Fe^III(CN)₆]/Fe^III[Fe^II(CN)₆]¹⁻ system by taking advantage of the metallic palladium layer inserted between PB film and Al, as an electron-transfer bridge. The best mediated oxidation of NAC and GL on the PB/Pd–Al electrode was achieved in 0.5 M KNO₃ + 0.2 M potassium acetate of pH 2. The mechanism and kinetics of the catalytic oxidation reactions of the both compounds were monitored by cyclic voltammetry and chronoamperometry. The charge transfer-rate limiting step as well as overall oxidation reaction of NAC or GL is found to be a one-electron abstraction. The values of transfer coefficients α, catalytic rate constant k and diffusion coefficient D are 0.5, 3.2 × 10² M⁻¹ s⁻¹ and 2.45 × 10⁻⁵ cm² s⁻¹ for NAC and 0.5, 2.1 × 10² M⁻¹ s⁻¹ and 3.7 × 10⁻⁵ cm² s⁻¹ for GL, respectively. The modifying layers on the Pd–Al substrate have reproducible behavior and a high level of stability in the electrolyte solutions. The modified electrode is exploited for hydrodynamic amperometry of NAC and GL. The amperometric calibration graph is linear in concentration ranges 2 × 10⁻⁶–40 × 10⁻⁶ for NAC and 5 × 10⁻⁷–18 × 10⁻⁶ M for GL and the detection limits are 5.4 × 10⁻⁷ and 4.6 × 10⁻⁷ M, respectively.     

Adsorption of bovine serum albumin on fused silica: Elucidation of protein–protein interactions by single-molecule fluorescence microscopy

The adsorption of bovine serum albumin (BSA) on fused silica at pH 4.7 was studied at the single molecules level by total-internal-reflection fluorescence microscopy. This pH value was the isoelectric point of BSA. At low [BSA] of 20 pM, protein molecules adsorbed as monomers. At intermediate [BSA] of 500 pM, protein molecules adsorbed as clusters of about five monomers on average. Both monomers and clusters had adsorption rate coefficients of the order 10⁻⁷ m s⁻¹ and desorption rate coefficients of about 2 × 10⁻² s⁻¹. The respective steady-state coverage was about 10× higher than that at neutral pH, presumably because of the more favorable BSA–silica electrostatics. At pH 4.7 and with [BSA] higher than 100 nM, adsorption begot further adsorption to produce nonlinear isotherms. The coverage at 1 μM BSA was 2.5× that of the linearly extrapolated coverage. This suggests that at pH 4.7, solute–adsorbate affinity was the dominant factor that explains the enhanced adsorption observed in ensemble measurements.     

Positronium inhibition and quenching by organic electronic acceptors and charge transfer complexes

Positron lifetime measurements were performed on a series of organic electron acceptors and charge-transfer complexes in solution. The acceptors cause both positronium (Ps) inhibition (with maybe one exception) and quenching, but when an acceptor takes part in a charge-transfer complex the inhibition intensifies and the quenching almost vanishes. The reaction constants between ortho-Ps and the acceptors were determinded to be: 1.5 × 10¹⁰ M⁻¹ s⁻¹ for SO₂ in dioxane 3.7 × 10¹⁰ M⁻¹ s⁻¹ for SO₂ in n-heptane, 3.4 × 10¹⁰ M⁻¹ s⁻¹ for tetracyanoquinodimethane in tetrahydrofurane and 1.6 × 10¹⁰ M⁻¹ s⁻¹ for tetracyanoethylene in dioxane. From the ortho-Ps lifetimes in solutions containing charge-transfer complexes complexity constants were determined that were in reasonable agreement with constants obtained from optical data. The influence of acceptors and charge-transfers complexes on the Ps yield was interpreted in terms of the spur reaction model of Ps formation. Correlation was also made to gas phase reaction between electron acceptors and free electron, as well as to pulse radiolysis data.     

Binding of 6-propyl-2-thiouracil to human serum albumin destabilized by chemical denaturants

We compared the binding affinity of 6-propyl-2-thiouracil (PTU) with native and destabilized human serum albumin (HSA) as a model to assess the binding ability of albumin in patients suffering from chronic liver or renal diseases. Urea (U) and guanidine hydrochloride (Gu·HCl) at a concentration of 3.0 M were used as denaturation agents.Increasing the concentration of PTU from 0.8 × 10⁻⁵ to 1.20 × 10⁻⁴ M in the systems with HSA causes a decrease in fluorescence intensity of the protein excited with both 280 and 295 nm wavelengths. The results indicate that urea and Gu·HCl bind to the carbonyl group and then to the NH-group. To determine binding constants we used the Scatchard plots. The presence of two classes of HSA–PTU binding sites was observed. The binding constants (K_b) are equal to 1.99 × 10⁴ M⁻¹ and 1.50 × 10⁴ M⁻¹ at λ_ex = 280 nm, 5.20 × 10⁴ M⁻¹ and 1.65 × 10⁴ M⁻¹ at λ_ex = 295 nm. At λ_ex = 280 nm the number of drug molecules per protein molecule is a_I = 1.45 and a_II = 1.32 for I and II binding sites, respectively. At λ_ex = 295 nm they are a_I = 0.63 and a_II = 1.54 for the I and II binding sites.The estimation of the binding ability of changed albumin in the uremic and diabetic patients suffering from chronic liver or renal diseases is very important for safety and effective therapy.     

Spectrofluorimetric quantification of bromazepam using a highly selective optical probe based on Eu–bromazepam complex in pharmaceutical and serum samples

A rapid, simple and sensitive spectrofluorimetric method for determination of trace amount of bromazepam is developed. In phosphate buffer of pH 7.4. The bromazepam enhance the luminescence intensity of the Eu³⁺ ion in Eu³⁺–bromazepam complex at λ_ex = 390 nm. The produced luminescence intensity of Eu³⁺–bromazepam complex is in proportion to the concentration of bromazepam. The working range for the determination of bromazepam is 2.3 × 10⁻⁸ to 6.2 × 10⁻⁷ M with detection limit (LoD) and quantitative detection limit (LoQ) of 3 × 10⁻⁹ and 1.2 × 10⁻⁸ M, respectively. While, the working range, detection limit (LoD) and quantitative detection limit (LoQ) in case of the quantum yield calculations are 3.7 × 10⁻⁸ to 3.4 × 10⁻⁷ M with of 3.4 × 10⁻⁹ and 9.2 × 10⁻⁸ M, respectively. The enhancement mechanism of the luminescence intensity in the Eu³⁺–bromazepam system has been also explained.     

Synthesis, characterization and radiolytic properties of bis(oxalato)borate containing ionic liquids

Previously unreported bis(oxalato)borate (BOB) ionic liquids (ILs) containing imidazolium, pyridinium, and pyrrolidinium cations were prepared from the corresponding halide salts by reaction with sodium bis(oxalato)borate (NaBOB), and their properties are reported. Pulse radiolysis experiments revealed that the BOB anion scavenges solvated electrons with rate constants of 3×10⁸ M⁻¹ s⁻¹ in the ionic liquid C₄mpyrr NTf₂ and 2.8×10⁷ M⁻¹ s⁻¹ in water. This reactivity indicates that BOB ILs may be too sensitive to be used as neat solvents for nuclear separations processes in high radiation fields but may still be useful for preventing criticality while processing relatively “cold” fissile actinides.     

A new Tb-selective fluorescent sensor based on 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-henylhydrazinecarbothioamide

A novel fluorescent chemosensor 2-(5-(dimethylamino)naphthalen-1-ylsulfonyl)-N-phenylhydrazinecarbothioamide (L) has been synthesized, which revealed an emission of 530 nm and when excited at 360 nm. The fluorescent probe undergoes a fluorescent emission intensity quenching upon binding to terbium ions in MeCN solution. The fluorescence quenching of L is attributed to the 1:1 complex formation between L and Tb(III) which has been utilized as the basis for the selective detection of Tb(III). The linear response range covers a concentration range of Tb(III) from 4.0 × 10⁻⁷ to 1.0 × 10⁻⁵ M and the detection limit is 1.4 × 10⁻⁷ M. The association constant of the 1:1 complex formation for L–Tb⁺³ was calculated to be 6.01 × 10⁶ M⁻¹, and the fluorescent probe exhibits high selectivity over other common metal ions mono-, di-, and trivalent cations indicate good selectivity for Tb(III) ions over a large number of interfering cations.     

Pulse radiolysis study of ion-species effects on the solvated electron in alkylammonium ionic liquids

The spectra and kinetic behavior of solvated electrons (e_sol⁻) in alkyl ammonium ionic liquids (ILs), i.e. N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEMMA-TFSI), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium tetrafluoroborate (DEMMA-BF₄), N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI), N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13-TFSI), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P13-TFSI), and N-methyl-N-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide (P14-TFSI) were investigated by the pulse radiolysis method. The e_sol⁻ in each of the ammonium ILs has an absorption peak at 1100 nm, with molar absorption coefficients of 1.5–2.3×10⁴ dm³ mol⁻¹ cm⁻¹. The e_sol⁻ decayed by first order with a rate constant of 1.4–6.4×10⁶ s⁻¹. The reaction rate constant of the solvated electron with pyrene (Py) was 1.5–3.5×10⁸ dm³ mol⁻¹ s⁻¹ in the various ILs. These values were about one order of magnitude higher than the diffusion-controlled limits calculated from measured viscosities. The radiolytic yields (G-value) of the e_sol⁻ were 0.8–1.7×10⁻⁷ mol J⁻¹. The formation rate constant of e_sol⁻ in DEMMA-TFSI was 3.9×10¹⁰ s⁻¹. The dry electron (e_dry⁻) in DEMMA-TFSI reacts with Py with a rate constant of 7.9×10¹¹ dm³ mol⁻¹ s⁻¹, three orders of magnitude higher than that of the e_sol⁻ reactions. The G-value of the e_sol⁻ in the picosecond time region is 1.2×10⁻⁷ mol J⁻¹. The capture of e_dry⁻ by scavengers was found to be very fast in ILs.     

Determination of trace amounts of mercury(II) in water samples using a novel kinetic catalytic ligand substitution reaction of hexacyanoruthenate(II)

A simple, sensitive, selective and rapid kinetic catalytic method has been developed for the determination of Hg(II) ions at micro-level. This method is based on the catalytic effect of Hg(II) ion on the rate of substitution of cyanide in hexacyanoruthenate(II) with nitroso-R-salt (NRS) in aqueous medium and provides good accuracy and precision. The concentration of Hg(II) catalyst varied from 4.0 to 10.0 × 10⁻⁶ M and the progress of reaction was followed spectrophotometrically at 525 nm (λ_max of purple-red complex [Ru(CN)₅NRS]³⁻,  = 3.1 × 10³ M⁻¹ s⁻¹) under the optimized reaction conditions; 8.75 × 10⁻⁵ M [Ru(CN)₆⁴⁻], 3.50 × 10⁻⁴ M [nitroso-R-salt], pH 7.00 ± 0.02, ionic strength, I = 0.1 M (KCl), temp 45.0 ± 0.1 °C. The linear calibration curves, i.e. calibration equations between the absorbance at fixed times (t = 15, 20 and 25 min) versus concentration of Hg(II) ions were established under the optimized experimental conditions. The detection limit was found to be 1.0 × 10⁻⁷ M of Hg(II). The effect of various foreign ions on the proposed method has also been studied and discussed. The method has been applied to the determination of mercury(II) in aqueous solutions.     

Simultaneous determination of hydroquinone and catechol at PASA/MWNTs composite film modified glassy carbon electrode

A poly-amidosulfonic acid and multi-wall carbon nanotubes composite (PASA/MWNTs) modified electrode has been constructed by electropolymerization on glassy carbon electrode (GCE). The electrochemical behaviors of hydroquinone (HQ) and catechol (CC) were investigated using cyclic and differential pulse voltammetries (DPVs) at the prepared electrode. Separation of the reductive peak potentials for HQ and CC was about 120 mV in pH 6.0 phosphate buffer solution (PBS), which makes it suitable for simultaneous determination of these compounds. In the presence of 1.0 × 10⁻⁴ mol L⁻¹ isomer, the reductive peak currents of DPV are proportional to the concentration of HQ in the range of 6.0 × 10⁻⁶ to 4.0 × 10⁻⁴ mol L⁻¹, and to that of CC in the range of 6.0 × 10⁻⁶ to 7.0 × 10⁻⁴ mol L⁻¹. When simultaneously changing the concentration of both HQ and CC, the linear concentration range of HQ (or CC) is 6.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹ (or 6.0 × 10⁻⁶ to 1.8 × 10⁻⁴ mol L⁻¹), and the corresponding detection limits are 1.0 × 10⁻⁶ mol L⁻¹. The proposed method has been applied to simultaneous determination of HQ and catechol in water sample, and the results are satisfactory.     

Interactions of thioflavin T with serum albumins: Spectroscopic analyses

The interaction of thioflavin T (ThT) with serum albumins from four different mammalian species i.e. human, bovine, porcine and rabbit, has been investigated by circular dichroism (CD), fluorescence spectroscopy and ITC. The binding constant (K) for HSA was found to be 9.9 × 10⁴ M⁻¹, 4.3 × 10⁴ M⁻¹ for RSA, 1.07 × 10⁴ M⁻¹ for PSA and 0.3 × 10⁴ M⁻¹ for BSA and the number of binding sites (n) were 1.14, 1.06, 0.94 and 0.8, respectively, which is very significant. By using unfolding pathway of HSA in the presence of urea, domain II of HSA has been assigned to possess binding site of ThT. Its binding constant is comparable to many drugs that bind at domain II of HSA, like salicylate, warfarin, digitoxin, etc. Acting force between HSA and ThT is showing that both hydrophobic and electrostatic forces have contributed for the interaction. ΔG_binding, ΔH and ΔS were calculated to be −28.46 kJ mol⁻¹, −3.50 kJ mol⁻¹ and 81.04 J K⁻¹ mol⁻¹, respectively. The data described here will help to increase our understanding about the interaction of ThT with native proteins. The results also indicate that care must be taken while using ThT as a probe for detecting amyloid fibrils.     

Voltammetric determination of N-acetylcysteine using a carbon paste electrode modified with copper(II) hexacyanoferrate(III)

The preparation and electrochemical characterization of a carbon paste electrode modified with copper(II) hexacyanoferrate(III) (CuHCF) as well as its behavior as electrocatalyst toward the oxidation of N-acetylcysteine were investigated. The electrochemical behavior of the modified electrode and the electrooxidation of N-acetylcysteine were explored using sweep linear voltammetry. The best voltammetric response was observed for a paste composition of 20% (w/w) copper(II) hexacyanoferrate(III) complex, acetate buffer solution at pH of 6.0 as the electrolyte and scan rate of 10 mV s^− 1. A linear voltammetric response for N-acetylcysteine was obtained in the concentration range from 1.2 × 10^− 4 to 8.3 × 10^− 4 mol L^− 1, with a detection limit of 6.3 × 10^− 5 mol L^− 1. The proposed electrode is useful for the quality control and routine analysis of N-acetylcysteine in pharmaceutical formulations.     

Piezoelectric Sensor in Situ Monitoring Adsorption of Fibrinogen and Surfactant onto a Self-Assembled Monolayer of Alkanethiols

This report describes the use of a piezoelectric quartz crystal (PQC) sensor to investigate the nonspecific adsorption of fibrinogen (FN) and sodium dodecyl sulfate (SDS) onto a self-assembled monolayer (SAM) of alkanethiols on gold. The change in adsorption mass was monitored in situ by the PQC sensor. A kinetics model was proposed to describe the adsorption of the FN and SDS on the hydrophobic SAM surface. The adsorption kinetics parameters were determined from the responses of the PQC. The adsorption and desorption rate constants of the FN on the SAM surface were estimated to be (6.18 ± 0.53) × 10³ M⁻¹ s⁻¹ and (6.74 ± 0.72) × 10⁻³ s⁻¹, respectively. The rate constants for the adsorption and desorption of SDS on the SAM are (24.3 ± 1.4 M⁻¹ s⁻¹) and (1.52 ± 0.11) × 10⁻² s⁻¹, respectively. The adsorption of SDS on the SAM was reversible. The fractional coverage of the FN on the SAM surface was estimated from kinetics analyses to be 42–86% for the FN concentration range 25–400 μg/ml. Over 80% of the FN is irreversibly adsorbed on the SAM surface with respect to dilution of the bulk phase. The fraction of FN reversibly adsorbed increases with the bulk concentration of FN.     

Fluorescence enhancement effect for the determination of DNA with calcein-cetyl trimethyl ammonium bromide system

A new spectrofluorimetric method was developed for the determination of trace amounts of DNA using the calcein as a fluorescent probe. In the presence of appropriate amounts of the cationic surfactant cetyl trimethyl ammonium bromide (CTAB), the anionic dye calcein dimerizes. The weak fluorescence intensity of the dimer was enhanced by adding DNA at pH 6–7. The interaction between calcein–CTAB and DNA was studied on the basis of this behavior and a new method was developed for determining DNA. Under the optimal conditions, the enhanced fluorescence intensity was in proportion to the concentration of DNA in the range of 4.0 × 10⁻⁶ to 8.0 × 10⁻⁵ g L⁻¹ for fsDNA and thermally denatured ctDNA (4.5 × 10⁻⁶ to 9.0 × 10⁻⁵ g L⁻¹). The detection limits (S/N = 3) were 2.0 × 10⁻⁶ and 2.2 × 10⁻⁶ g L⁻¹, respectively. This method was used for determining the concentration of DNA in synthetic samples with satisfactory results.     

Differential pulse polarography as a tool for the determination of trace levels of nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+) in aqueous solution

The differential pulse polarographic behavior of NAD⁺ and NADP⁺ has been investigated in phosphate buffer. The peaks obtained at pH 8.0 are recommended for the trace determination of these compounds. Linear calibration curves are obtained over the concentration ranges from 2.6 × 10⁻⁷ to 2.6 × 10⁻⁵M for NAD⁺ and from 2 × 10⁻⁶ to 4 × 10⁻⁵ for NADP⁺.     

Novel lipoate-selective membrane sensor for the flow injection determination of alpha-lipoic acid in pharmaceutical preparations and urine

A potentiometric lipoate-selective sensor based on mercuric lipoate ion-pair as a membrane carrier is reported. The electrode was prepared by coating the membrane solution containing PVC, plasticizer, and carrier on the surface of graphite electrode. Influences of the membrane composition, pH, and possible interfering anions were investigated on the response properties of the electrode. The sensor exhibits significantly enhanced response toward lipoate ions over the concentration range 1 × 10⁻⁷ mol L⁻¹ to 1 × 10⁻² mol L⁻¹ with a lower detection limit of (LDL) of 9 × 10⁻⁸ mol L⁻¹ and a slope of −29.4 mV decade⁻¹, with S.D. of the slope is 0.214 mV. Fast and stable response, good reproducibility, long-term stability, applicability over a pH range of 8.0–9.5 is demonstrated. The sensor has a response time of ≤12 s and can be used for at least 6 weeks without any considerable divergence in its potential response. The proposed electrode shows good discrimination of lipoate from several inorganic and organic anions. The CGE was used in flow injection potentiometry (FIP) and resulted in well defined peaks for lipoate ions with stable baseline, excellent reproducibility and reasonable sampling rate of 30 injections per hour. The proposed sensor has been applied for the direct and FI potentiometric determination of LA in pharmaceutical preparations and urine; and has been also utilized as an indicator electrode for the potentiometric titration of LA.     

Recombination of KrD and XeD ions with electrons

Recombination rate coefficients of protonated and deuterated ions KrH⁺, KrD⁺, XeH⁺ and XeD⁺ were measured using Flowing Afterglow with Langmuir Probe (FALP). Helium at 1600 Pa and at temperature 250 K was used as a buffer gas in the experiments. Kr, Xe, H₂ and D₂ were introduced to a flow tube to form the desired ions. Because of small differences in proton affinities of Kr, D₂ and H₂ mixtures of ions, KrD⁺/D₃⁺ and KrH⁺/H₃⁺ are formed in the afterglow plasma, influencing the plasma decay. To obtain a recombination rate coefficient for a particular ion, the dependencies on partial pressures of gases used in the ion formation were measured. The obtained rate coefficients, α_KrD+(250 K) = (0.9 ± 0.3) × 10⁻⁸ cm³ s⁻¹ and α_XeD+(250 K) = (8 ± 2) × 10⁻⁸ cm³ s⁻¹ are compared with α_KrH+(250 K) = (2.0 ± 0.6) × 10⁻⁸ cm³ s⁻¹ and α_XeH+(250 K) = (8 ± 2) × 10⁻⁸ cm³ s⁻¹.     

Fabrication of a template-synthesized gold nanorod-modified electrode for the detection of dopamine in the presence of ascorbic acid

Gold nanorods (GNRs) with suitable aspect ratio were synthesized with a template technique and then dispersed in a saturated sodium citrate solution by ultrasonication to form a GNR suspension. A GNR-modified electrode was fabricated using the GNR suspension. The oxidation of dopamine at the GNR/GC electrode exhibited surprisingly high electrocatalytic activity and adsorption-controlled characteristics. Square-wave voltammetry was used to detect dopamine. At the GNR/GC electrode, the linear concentration range of DA is from 1 × 10⁻⁸ M to 1 × 10⁻⁷ M and the detection limit (s/n = 3) is as low as 5.5 × 10⁻⁹ M. The current sensitivity is 3.280 μA/μM, and 1000-fold ascorbic acid (AA) cannot interfere with the determination of DA. All these performances are greatly superior to those of the bare GC electrode.     

The reduction mechanism of the C=O group. Part 2. The electrochemical reduction of p-diacetylbenzene in aqueous medium

A detailed study of the electrochemical reduction of diacetylbenzene A in aqueous medium between H_o = −5 and pH 14 is presented. The reactants are strongly adsorbed, so that the reactions are of a surface nature. From H_o = −5 to pH 6, a global 2e⁻ reduction yielding an enediol-type intermediate occurs. Analysis using the theory of the square schemes with protonations at equilibrium shows that, up to pH 4, the reaction is controlled by the first electron uptake, the paths being successively H⁺e⁻ and e⁻H⁺. The elementary electrochemical surface rate constants are 9.6 × 10⁷ s⁻ and 1.2 × 10⁶ s⁻ for AH⁺ and A respectively. From pH 6 to 14, a le⁻ adsorption wave, corresponding to the formation of (a) monoradical(s), appears and is followed by a le⁻ wave due to the reduction of the radical(s). A dimerization occurs, due to the coupling A⁻ + AH, as in the case of the monocarbonyl compounds. The rate of this surface process, k_d = 5 × 10¹³ cm² mol⁻¹ s⁻¹, is markedly smaller than the rate of the homogeneous reaction obtained in alkaline ethanol by Savéant et al. for the coupling of the radicals of benzaldehyde, benzophenone and acetophenone.     

Electrochemical behavior and voltammetric determination of tryptophan based on 4-aminobenzoic acid polymer film modified glassy carbon electrode

Herein, a novel electrochemical method was developed for the determination of tryptophan based on the poly(4-aminobenzoic acid) film modified glassy carbon electrode (GCE). The electrochemical behaviors of tryptophan at the modified electrode were investigated. It was found that the oxidation peak current of tryptophan at the modified GCE was greatly improved compared with that at the bare GCE. The effects of supporting electrolyte, pH value, scan rate, accumulation potential and time were examined. The oxidation peak current of tryptophan was proportional to its concentration over the range from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol L⁻¹. The limit of detection was evaluated to be 2.0 × 10⁻⁷ mol L⁻¹. The proposed method was sensitive and simple. It was successfully employed to determine tryptophan in pharmaceutical samples.