Chromotropic acid-formaldehyde reaction in strongly acidic media. The role of dissolved oxygen and replacement of concentrated sulphuric acid

The procedure for formaldehyde analysis recommended by the National Institute for Occupational Safety and Health (NIOSH) is the Chromotropic acid spectrophotometric method, which is the one that uses concentrated sulphuric acid. In the present study the oxidation step associated with the aforementioned method for formaldehyde determination was investigated. Experimental evidence has been obtained indicating that when concentrated H₂SO₄ (18 mol l⁻¹) is used (as in the NIOSH procedure) that acid is the oxidizing agent. On the other hand, oxidation through dissolved oxygen takes place when concentrated H₂SO₄ is replaced by concentrated hydrochloric (12 mol l⁻¹) and phosphoric (14.7 mol l⁻¹) acids as well as by diluted H₂SO₄ (9.4 mol l⁻¹). Based on investigations concerning the oxidation step, a modified procedure was devised, in which the use of the potentially hazardous and corrosive concentrated H₂SO₄ was eliminated and advantageously replaced by a less harmful mixture of HCl and H₂O₂.     

Spectrophotometric determination of traces of formic acid and formaldehyde in effluent waters with or without preconcentration

Formic acid plus formaldehyde are determined after reducing the acid with nascent hydrogen; formaldehyde alone is determined without reduction. The chromotropic acid method is used in 6–7.5 M sulfuric acid. The limit of determination is 0.05 μg ml^-1 without preconcentration and 0.05 ng ml^-1 with preconcentration by extraction with diethyl ether. Analysis time is 30 min by the direct method and 1 h with preconcentration.     

Flow-injection determination of hydrogen peroxide based on fluorescence quenching of chromotropic acid catalyzed with Fe(II)

Flow-injection analysis system (FIA system), which was based on Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide, was developed for the determination of hydrogen peroxide. The chromotropic acid has a fluorescence measured at λ_em = 440 nm (emission wavelength) with λ_ex = 235 nm (excitation wavelength), and the fluorescence intensity at λ_em = 440 nm quietly decreased in the presence of hydrogen peroxide and Fe(II), which was caused by Fe(II)-catalyzed oxidation of chromotropic acid with hydrogen peroxide. By measuring the difference of fluorescence intensity, hydrogen peroxide (1.0 × 10⁻⁸-1.0 × 10⁻³ mol L⁻¹) could be determined by the proposed FIA system, whose analytical throughput was 40 samples h⁻¹. The relative standard deviation (RSD) was 1.03% (n = 10) for 4.0 × 10⁻⁸ mol L⁻¹ hydrogen peroxide. The proposed FIA technique could be applied to the determination of hydrogen peroxide in rain water samples.     

N-(Trifluoromethylsulfonyl)trifluoromethanesulfinimidic acid and its salts

Lithium, sodium and potassium N-(trifluoromethylsulfonyl)trifluoromethanesulfinimidates were obtained by the reaction of the corresponding sulfinimidoyl chloride with alkali metal trimethylsilanolates. The potassium and sodium salts were converted to the free acid, having predominantly the amidic tautomeric structure, CF₃S(O)NHSO₂CF₃, by treatment with concentrated H₂SO₄ or with H⁺-cationite.     

A greener microwave-assisted extraction method for rapid spectroscopic determination of selected metals in river and freshwater sediment certified reference materials

The current study describes development of novel, cost-effective, rapid and greener microwave-assisted extraction (MW-AE) method using diluted hydrogen peroxide (H₂O₂) and 400 µL of concentrated aqua-regia for the extraction of 10 selected metals (Ba, Cr, Cu, Co Fe, Mn, Ni, Pb, V and Zn) in sediment certified reference materials (CRMs), prior to inductively coupled plasma-optical emission spectroscopic analysis. The optimum extraction conditions were achieved when 0.2 g of sediment was extracted with 1 mol L^?1 of H₂O₂ (12.00 mL) and 400 µL of concentrated aqua-regia, at 180°C microwave extraction temperature for 30 min. Accuracy of the proposed MW-AE method was evaluated by using river (LGC6187) and freshwater (CRM015-050) sediment CRMs. Quantitative extraction recoveries of 80–120% in LGC6187 and 74–124% in CRM0150-050 were obtained with acceptable precision (0.4–1.0%). The proposed extraction method has a clear advantage over classical approaches as 1 mol L^?1 H₂O₂ was used instead of notorious acidic mixture (Hydrochloric acid/ nitric acid/ hydrofluoric). The method detection limits (MDLs) of 0.03–0.9 μg g^?1 were obtained for all the investigated metals and were fairly comparable with the MDLs of the published literature reports. Therefore, the proposed MW-AE method can be routinely used for monitoring of metal ions in various river and fresh water sediments.     

Cyclothiomethylation of carboxylic acid hydrazides with aldehydes and H<Subscript>2</Subscript>S

The cyclothiomethylation of carboxylic acid hydrazides RCONHNH₂ (R = C₅H₄N, Ph, 2-MeOC₆H₄, or 4-HOC₆H₄CH₂) with formaldehyde and H₂S at 70 °C affords predominantly the corresponding N-(1,3,5-dithiazinan-5-yl)amides, whereas this reaction at 0–−50 °C gives a mixture of the latter compounds with 3-acyl-1,3,4-thiadiazolidines. N-(1,3,5-Dithiazinan-5-yl)-amides were selectively synthesized by the reaction of carboxylic acid hydrazides with formaldehyde and H₂S in the presence of BuONa in BuOH.     

Gas-diffusion flow injection assay for the selective determination of chlorine dioxide based on the fluorescence quenching of chromotropic acid

The present work reports the first spectrofluorimetric gas-diffusion flow injection (GD-FI) assay for the determination of chlorine dioxide in water samples (tap, mineral and soda water). The method is based on the fluorescence quenching of chromotropic acid (CA) (λ_ex. = 347 nm, λ_em. = 371 nm) caused by the analyte. The chemical and instrumental variables of the system were studied in terms of maximum sensitivity. The gas-diffusion cell was thermostated at 40 °C to enhance the vaporization of chlorine dioxide and thus the sensitivity of the method. The quenching effect of chlorine dioxide on CA was linear in the range 0.09-3.41 mg l^− 1, while the precisions either close to the quantitation limit or near to the middle of the linear section of the calibration graph were satisfactory in both cases (s_r = 2.6% and 1.5% (n = 10) at 0.17 and 1.71 mg l^− 1 level, respectively). The developed method proved to be adequately selective and sensitive with 3σ limit of detection equal to c_L = 0.03 mg l^− 1. The application of the assay to spiked tap, mineral and soda water samples yielded accurate results with recovery values in the range 94.1-105.9%.     

Extraction—spectrophotometric determination of boric acid with 1,8-dihydroxynaphthalene-4-sulfonic acid and zephiramine

l,8-Dihydroxynaphthalene-4-sulfonic acid (DHNS) is described as a new reagent for the extraction—spectrophotometric determination of boric acid. The reagent and its boron complex are extracted into 1,2-dichloroethane as ion-associates with tetradecyldimethyl-benzylammonium chloride (zephiramine). The extracted complex of boron—DHNS—zephiramine has the composition 1:2:3 and is stable to back-washing with 1 M sodium chloride solution (pH 9.2), whereas the excess of reagent co-extracted is removed to the aqueous phase. The apparent molar absorptivity of the complex in the organic phase is 2.45 × 10⁴ l mol^-1 cm^-1 at 341 nm, which is 1.7 times larger than that with chromotropic acid. Addition of EDTA prevents most interferences. The improved method with DHNS is successfully applied to the determination of boron as boric acid in waters. The exchange equilibrium constants,

, for the reagent and complex were also determined for four monovalent anions (X^- = Cl^-, Br^-, NO₃^-and I^-). Some of these constants are compared with those pertaining to chromotropic acid and 1,8-dihydroxynaphthalene.     

Synthesis of a diastereomeric mixture of deuterium-labeled lovastatin and its acid ammonium salt

In this communication, a facile synthesis for (2S/2R)-[²H₃]lovastatin and (2S/2R)-[²H₃]lovastatin acid ammonium salt was described. The stable isotope-labeled (2S/2R)-lovastatin and its acid ammonium salt were prepared from butyric acid via several reaction steps with 11.1 and 6.3 % overall yield, respectively.     

o-phthalic acid as a standard substance for calibrations of hydrogen ion concentrations with a glass electrode

o-Phthalic acid is proposed as a standard substance for buffer solutions of known hydrogen ion concentration (I ? 0.2 M KCl, p[H⁺] = 3.0–5.4, 25°C). Its crystallinity, purity and slightly wide buffer range afford advantages over acetic acid. Empirical relationships between measured pH (pH_m) and calculated [H⁺] were derived for sequences of buffer solutions at several ionic strengths: pH_m - Mp[H⁺] + C. These calibration lines were parallel and of unit slope as required by theory. A table of p[H⁺] values for o-phthalic acid buffer solutions at I = 0.1 M (KCl) is presented and the method of calculation of p[H⁺] values for a buffer series generated by additions of potassium hydroxide is outlined.     

Spectrophotometric and fluorimetric determinations of trichothecene mycotoxins with reagents for formaldehyde

Several trichothecene mycotoxins, such as fusarenone-X (F-X) and T-2 toxin (T-2), readily liberate formaldehyde on heating with sulfuric acid. Spectrophotometric and fluorimetric methods for the determination of trichothecenes with reagents for formaldehyde are therefore possible. F-X (or T-2) can be determined in the 50–1000 mg l^-1 (or 50–1500 mg l^-1) range by the chromotropic acid method, in the 30–1200 mg l^-1 (or 50–2000 mg l^-1) range by the phenyl J acid method, and in the 1.25–25 mg l^-1 (or 2–40 mg l^-1) range by the J acid method. Other trichothecenes, neosolaniol, nivalenol, tetraacetylnivalenol, diacetoxyscirpenol and HT-2 toxin, etc. also give positive reactions but trichothecin and dihydronivalenol do not.     

Flow injection direct spectrophotometric assay for the speciation of trace chromium(III) and chromium(VI) using chromotropic acid as chromogenic reagent

A new rapid and sensitive FI assay is reported for the simultaneous direct spectrophotometric determination of trace Cr(VI) and Cr(III) in real samples. The method is based upon the reaction of Cr(VI) with chromotropic acid (CA) in highly acidic medium to form a water-soluble complex (λ_max = 370 nm). Cr(III) reacts with CA only after its on-line oxidation to Cr(VI) by alkaline KIO₄. The determination of each chromium species in the sample was achieved by absorbance differences. The calibration curves were linear over the range 3-4000 μg l⁻¹ and 30-1200 μg l⁻¹ for Cr(VI) and Cr(III), respectively, while the precision close to the quantitation limit was satisfactory in both cases (s_r = 3.0% for Cr(VI) and 4.0% for Cr(III) (n = 10) at 10 and 50 μg l⁻¹ level, respectively). The method developed proved to be adequately selective and sensitive (c_L = 1 and 10 μg l⁻¹ for Cr(VI) and Cr(III), respectively). The application of the method to the analysis of water samples (tap and mineral water) gave accurate results based on recovery studies (93-106%). Analytical results of real sample analysis were in good agreement with certified values.     

Selective stopped-flow sequential injection method for the spectrophotometric determination of titanium in dental implant and natural Moroccan phosphate rock

The present work reports the first sequential injection (SI) method for the spectrophotometric determination of Ti(IV). The method is based upon the reaction of Ti(IV) with chromotropic acid (CA) in acidic medium to form a water-soluble complex (λ_max = 420 nm). The chemical and instrumental variables of the system that affected the reaction were studied. Selectivity was greatly enhanced using ascorbic acid. A linear calibration graph was obtained in the range 0.2-10.0 mg l⁻¹ Ti(IV) at a sampling frequency of 24 h⁻¹. The precision was satisfactory (s_r = 1.5% at 5.0 mg l⁻¹ Ti(IV), n = 12) and the 3σ limit of detection, c_L, was 0.7 mg l⁻¹ (n = 10). The developed method proved to be adequately selective and was applied successfully to the analysis of real samples (dental implant and natural Moroccan phosphate rock) giving accurate results based on recovery studies (98-105%).     

Synthesis and characterization of four new manganese(III) complexes and amino acid (L-aspartic acid, L-asparagine, L-glutamic acid, L-glutamine) Schiff bases

New series of manganese(III) complexes and amino acid Schiff bases have been prepared from 2-hydroxy-1-naphthaldehyde and α-amino acids [L-aspartic acid (Asp), L-asparagine (Asn), L-glutamic acid (Glu) and L-glutamine (Gln)]. The structures of the ligands and manganese complexes were identified using elemental analyses, i.r, electronic spectra, ¹H-n.m.r spectra, magnetic moment measurements and thermogravimetric analyses (t.g.a). The results suggest that H₂L¹: [N-(2-hydroxy-1-naphthylidene) aspartic acid] and H₂L³: [N-(2-hydroxy-1-naphthylidene)glutamic acid] Schiff bases behave as trianionic tetradentate species and coordinate to Mn(III) ion according to the general formula [MnL] · xH₂O complexes. But, H₂L²: [N-(2-hydroxy-1-naphthylidene) asparagine] and H₂L⁴: [N-(2-hydroxy-1-naphthylidene)glutamine] Schiff bases behave as dianionic tridentate and coordinate to Mn(III) ion in the general formula for [MnL(OOCH₃)] · xH₂O complexes.     

Carbon-13 kinetic isotope effects in the decarbonylation of lactic acid of natural isotopic composition in phosphoric acid medium

The¹³C kinetic isotope effect fractionation in the decarbonylation of lactic acid (LA) of natural isotopic composition by concentrated phosphpric acids (PA) and by 85% H₃PO₄ has been studied in the temperature interval of 60–150°C. The values of the¹³C₍₁₎ isotope effects in the decarbonylation of lactic acid in 100% H₃PO₄, in pyrophosphoric acid and in more concentrated phosphoric acids are intermediate between the values calculated assuming that the C₍₁₎–OH bond is broken in the rate-controllin gstep of dehydration and those calculated for rupture of the carbon-carbon bond in the transition state. In the temperature interval of 90–130°C the experimental¹³C fractionation factors determined in concentrated PA approach quite closely the¹³C fractionation corresponding to C₍₂₎–C₍₁₎ bond scission. the¹³C₍₁₎ kinetic isotope effects in the decarbonylation of LA in 85% orthophosphoric acid in the temperature range of 110–150°C coincide with the¹³C isotope effects calculated assuming that the frequency corresponding to the C₍₁₎–OH vibration is lost in the transition state of decarbonylation. A change of the mechanism of decarbonylation of LA in going from concentrated PA medium to 85% H₃PO₄ has been suggested. A possible secondary¹⁸O and a primary¹⁸O kinetic isotope effect in decarbonylation of lactic acid in phosphoric acids media have been discussed, too.     

Dichromate dosimetry: The effect of acetic acid on the radiolytic reduction yield

The radiation chemical yield for the reduction of dichromate, Cr(VI) → Cr³⁺, in an acidic aqueous perchloric acid solution of potassium dichromate, may be increased from 0.04 to >0.2 μ mol J^-1 by adding acetic acid. The increased yield, G[-(Cr₂O₇)^2-] is about the same in N_2- and O₂-saturated solutions. The molar linear absorption coefficient at 350 nm also is the same in both solutions (ϵ_m = 2800 M^-1cm^-1) at pH 0.4. The proposed mechanism to explain the enhanced response in N₂-saturated solutions involves the efficient reaction of acetic acid with hydroxyl radicals by the abstraction of H from the methyl group; the resulting acid radicals react with relatively high yield to reduce Cr(VI). In O₂-saturated solution, the acetic acid radical apparently goes through an acetic acid peroxyl radical by a bimolecular reaction to the tetroxide intermediate of acetic acid, which releases H₂O₂ with relatively high yield by a Bennett-type reaction. This additional H₂O₂, as a reducing agent, reacts slowly with dichromate and boosts the value of G[-(Cr₂O₇)^2-]. The negative slope of the response (ΔA vs dose) continues to increase during the period immediately after irradiation of oxygenated solution, due to slow reaction of radiolytically-produced H₂O₂ with dichromate. There is also in both O₂- and N₂-saturated solution a long-term slow reaction involving oxidation of the organic substrate (in this case, acetic acid). Because of these instabilities, the solutions cannot readily be used for dosimetry without the presence of silver ions, which in the oxidized state, Ag²⁺, act to stabilize the solution after irradiation. The addition of silver dichromate at a concentration of 0.1 mM decreases the yield to G[-(Cr₂O₇)^2-] = 0.17 μmolJ^-1, but greatly improves the stability of the solution after irradiation. The absorbed dose range for the modified dichromate dosimeter when analyzed spectrophotometrically at 350 nm wavelength is approx. 2 × 10²-2 × 10³ Gy.     

Chemiluminescence flow-through sensor for pipemidic acid using solid sodium bismuthate as an oxidant

A novel chemiluminscence (CL) flow-through sensor for pipemidic acid is described. It was based on the sensitizing effect of pipemidic acid on the CL oxidation of sulfite by sodium bismuthate in H₂SO₄ media. The solid-phase sodium bismuthate was mechanicially immobilized on the sponge rubber inside of the CL flow cell as CL oxidant. The calibration graph is linear in the range 0.1-10 μg/ml with a detection limit of 6.2×10⁻⁸ g/ml (3σ). A complete analysis could be performed in 1 min with a relative standard deviation (R.S.D.) of 2.5% for 2 μg/ml pipemidic acid (n=8). This method has been successfully applied to determine pipemidic acid in pharmaceutical preparation.     

A New Method for the Measurement of Airborne Formaldehyde Using Derivatization with 3,5-Bis(Trifluoromethyl) Phenylhydrazine and Analysis by GC-ECD and GC-MS/SIM

Abstract

A new method was developed and described for the measurement of airborne formaldehyde using derivatization with 3,5-bis(trifluoromethyl)phenylhydrazine (TFMPH) coated onto silica solid phase extraction cartridges. Analysis by GC-ECD provides a detection limit of 74 ng formaldehyde per sample. A field study was conducted to compare the use of TFMPH to 2,4-dinitrophenylhydrazine (DNPH) and NIOSH method 3500 (chromotropic acid, CTA). Samples were collected from indoor and outdoor environments known or suspected to contain formaldehyde. Use of TFMPH with GC-ECD analysis correlates well with both methods (R²=0.93, slope=1.07 vs. DNPH; R²=0.99, slope=1.06 vs. CTA). Spiked samples were shown to be stable at least 7 days when stored at –20 °C. Analysis of samples by GC-MS with selected ion monitoring (GC-MS/SIM) also proved feasible. Laboratory and field results show the use of TFMPH to be viable for quantifying airborne formaldehyde in occupational and environmental samples.     

Carbon-13 kinetic isotope effects in the decarbonylation of formic acid of natural isotopic composition in phosphoric acid media

The¹³C kinetic isotope effect (K.I.E.) in the decarbonylation of formic acid of natural isotopic composition in 85% orthophosphoric acid, in 100% H₃PO₄, and in pyrophosphoric acid has been measured in different temperature intervals ranging from 19 to 133 °C. In 85% H₃PO₄ the carbon-13 K.I.E. is determined by the fractionation of carbon isotopes expected for C–O bond rupture (k ₁₂/k ₁₃=1.0531 at 70°C). In 100% H₃PO₄ the¹³C K.I.E. indicates that C–H bond rupture is the major component of the reaction coordinate motion (thek ₁₂/k ₁₃ lay in the range of 1.026–1.017 over the range 30–70 °C). In pyrophosphoric acid the fractionation factor for¹³C equals 1.010 at 19 °C. Activation parameters for the decarbonylation of H¹²COOH in phosphoric acid media have been determined also and suggestions concerning the intimate mechanisms of decarbonylation of formic acid in dilute and concentrated phosphoric acids are made.     

Chiral fluoroacetic acid: synthesis of (R)- and (S)-[2H1]-fluoroacetate in high enantiopurity

A two-step synthesis of (R)- and (S)-[²H₁]-fluoroacetate (sodium salts) in high enantioselectivity is reported. The synthesis is the development of a previous one in which the enantioselectivity has been increased from ～38% ee to >95% ee. The improvement in enantioselectivity applied Bio’s methodology, which involved a deoxyfluorination reaction with DAST on either enantiomer of [²H₁]-benzyl alcohol, adding TMS-morpholine to the reaction. The additive promotes an S_N2 inversion process, and suppresses a competing non-stereospecific S_N1 reaction course, and as a result significantly improves the stereointegrity of the C–F bond formation. The intermediate [²H₁]-benzyl alcohols, [²H₁]-benzyl fluorides and the product [²H₁]-fluoroacetates as their hexyl esters were separately assayed for their stereochemical integrity, using the Courtieu method. This method involved measuring their ²H NMR spectra in a chiral matrix of poly-γ-benzyl l-glutamate. The chiral assay demonstrated that there was no significant loss in stereointegrity during the deoxyfluorination reaction and showed that the enantiomers of [²H₁]-fluoroacetate were generated with high enantiomeric purity (95% ee).