Ion chromatography of alkylamines and alkanolamines using conductivity detection

Simultaneous quantification of alkanolamines and their dehydrogenation products in aqueous samples using high-performance liquid chromatography with pre-column derivatization with 2,4-dinitrofluorobenzene

BACKGROUND

Diethanolamine, monoethanolamine, iminodiacetic acid, and glycine are important fine chemical intermediates, often requiring simultaneous quantitative analysis in various applications. This presents the challenge of accurately quantifying multiple substances within a single sample. The catalytic dehydrogenation of diethanolamine and monoethanolamine has garnered significant research interest, yet no analytical method has been reported for the simultaneous quantification of reactants and products in the dehydrogenation reaction mixtures of different alkanolamines.

RESULTS

A high-performance liquid chromatography (HPLC) method has been developed for the simultaneous quantification of diethanolamine (DEA), iminodiacetic acid (IDA), glycine (Gly), and monoethanolamine (MEA) in aqueous solutions using 2,4-dinitrofluorobenzene (DNFB) for pre-column derivatization. The method demonstrated excellent linearity, with correlation coefficients (R2) of 0.9999, 0.9997, and 0.9998 for IDA, DEA, and Gly, respectively. The detection limits (LODs) were 0.02, 0.08, and 0.01 mg L-1, respectively. The quantification limits (LOQs) were 0.06, 0.24, and 0.03 mg L-1, respectively. Spiked recovery rates ranged from 96.99 % to 104.32 %, with relative standard deviations (RSDs) between 0.70 % and 3.03 %. For MEA and Gly, the R2 values were 0.9970 and 0.9990, the LODs were 0.12 and 0.01 mg L-1, the LOQs were 0.36 and 0.03 mg L-1, and spiked recoveries ranged from 96.24 % to 104.82 %, with RSDs between 1.22 % and 3.68 %. Compared to other methods, this HPLC approach offers superior sensitivity, accuracy, and precision.

SIGNIFICANCE

This method provides a robust reference for the individual or simultaneous quantification of alkanolamines, glycine, and iminodiacetic acid in aqueous matrices. It offers new insights into the simultaneous analysis of alkanolamines with multiple organic acids in complex matrices. Additionally, the method can guide the optimization of catalytic dehydrogenation processes for alkanolamines, potentially extending the advantages of dehydrogenation catalysts to other reactions.

Towards a generic method for ion chromatography/mass spectrometry of low-molecular-weight amines in pharmaceutical drug discovery and development

RATIONALE

Low-molecular-weight amines are encountered in pharmaceutical analysis, e.g. as reactants in chemical syntheses, but are challenging to analyse using ultrahigh-performance liquid chromatography/mass spectrometry (UHPLC/MS) due to their high polarity causing poor retention. Ion chromatography/mass spectrometry (IC/MS) is an emerging technique for polar molecule analysis that offers better separation. A generic IC/MS method would overcome problems associated with using UHPLC/MS in drug discovery and development environments.

METHODS

Amine standards were analysed using IC/MS with gradient elution (variety of column temperatures evaluated). An electrospray ionisation (ESI) quadrupole mass spectrometer was operated in positive ion polarity in scanning mode. The make-up flow composition was evaluated by assessing the performance of a range of organic modifiers (acetonitrile, ethanol, methanol) and additives (acetic acid, formic acid, methanesulfonic acid). The ESI conditions were optimised to minimise adduct formation and promote generation of protonated molecules.

RESULTS

The performance attributes were investigated and optimised for low-molecular-weight amine analysis. Organic solvents and acidic additives were evaluated as make-up flow components to promote ESI, with 0.05% acetic acid in ethanol optimal for producing protonated molecules. The hydrogen bonding capability of amines led to abundant protonated molecule-solvent complexes; optimisation of source conditions reduced these, with collision-induced dissociation voltage having a strong effect. The detection limit was ≤1.78 ng for the amines analysed, which is fit-for-purpose for an open-access chemistry environment.

CONCLUSIONS

This study demonstrates the value of IC/MS for analysing low-molecular-weight amines. Good chromatographic separation of mixtures was possible without derivatisation. Ionisation efficiency was greatest using a make-up flow of 0.05% acetic acid in ethanol, and optimisation of ESI source conditions promoted protonated molecule generation for easy determination of molecular weight.

Novel Rapid Screening of Basic Immobilized Amine Sorbent/Catalyst Water Stability by a UV/Vis/Cu2+ Technique

Time-consuming thermogravimetric analysis (TGA) decomposition study is a typical practice to assess the stability of fresh and water-treated basic immobilized amine sorbents (BIAS)/catalysts. This work presents a faster and more precise spectroscopic UV/Vis/Cu²⁺ sorbent screening technique that quantifies aqueous amines washed from the BIAS by using UV-active amine/Cu²⁺ complexes. Six BIAS-based catalysts, containing different amine species and a crosslinker within silica, were treated with ultrapure water and then analyzed for their CO₂ capture performance and amine leach resistance/stability by using TGA (catalysts, approximately 4 h) and UV/Vis/Cu²⁺ techniques (wash solution, few minutes). A comparative analysis revealed that directly quantifying washed amines with UV/Vis/Cu²⁺ is 9-127 times more precise than indirect testing of the sorbents by TGA. Similar trends in the H₂ O stability profiles of the catalysts [organic content retained values (OCR)] were reported by both analysis methods, allowing UV/Vis/Cu²⁺ to replace TGA for quantifying unstable leached amines. The UV/Vis/Cu²⁺ OCR results could be used to predict the CO₂ -capture stability profile of the sorbents, confirming the reliability of this technique to rapidly screen catalyst stability and performance.

Quantification of short chain amines in aqueous matrices using liquid chromatography electrospray ionization tandem mass spectrometry

A new liquid chromatography-electrospray ionization-tandem Mass Spectrometry (LC-ESI-MS/MS) method was developed for the determination of more than 20 C₁-C₆ alkyl and alkanolamines in aqueous matrices. The method employs Hydrophilic Interaction Liquid Chromatography Multiple Reaction Monitoring (HILIC-MRM) with a ZIC-pHILIC column and four stable isotope labeled amines as internal standards for signal normalization and quantification of the amines. The method was validated using a refinery process water sample that was obtained from a cooling cycle of crude oil distillation. The averaged within run precision, between run precision and accuracy were generally within 2-10%, 1-9% and 80-120%, respectively, depending on the analyte and concentration level. Selected aqueous process samples were analyzed with the method.

A simple gas chromatography method for the analysis of monoethanolamine in air

A simple method determining airborne monoethanolamine has been developed. Monoethanolamine determination has traditionally been difficult due to analytical separation problems. Even in recent sophisticated methods, this difficulty remains as the major issue often resulting in time-consuming sample preparations. Impregnated glass fiber filters were used for sampling. Desorption of monoethanolamine was followed by capillary GC analysis and nitrogen phosphorous selective detection. Separation was achieved using a specific column for monoethanolamines (35% diphenyl and 65% dimethyl polysiloxane). The internal standard was quinoline. Derivatization steps were not needed. The calibration range was 0.5-80 μg/mL with a good correlation (R(2) = 0.996). Averaged overall precisions and accuracies were 4.8% and -7.8% for intraday (n = 30), and 10.5% and -5.9% for interday (n = 72). Mean recovery from spiked filters was 92.8% for the intraday variation, and 94.1% for the interday variation. Monoethanolamine on stored spiked filters was stable for at least 4 weeks at 5°C. This newly developed method was used among professional cleaners and air concentrations (n = 4) were 0.42 and 0.17 mg/m(3) for personal and 0.23 and 0.43 mg/m(3) for stationary measurements. The monoethanolamine air concentration method described here was simple, sensitive, and convenient both in terms of sampling and analytical analysis.

Vaporization and Conversion of Ethanolamines used in Metalworking Operations

OBJECTIVES

This study examined how ethanolamines (EAs) with the same functional alcohol group (HOCH(2)CH(2)), such as mono-EA (MEA), di-EA (DEA), and tri-EA (TEA), in water-based metalworking fluids (wbMWFs) are vaporized, condensed, and transformed by heat generated during metalworking.

METHODS

Two types of experimental apparatus were manufactured to achieve these objectives.

RESULTS

Vaporization tests using a water bath showed that the vaporization rate increased markedly from 0.19 mg/m(2)·min at 23.5℃ to 8.04 mg/m(2)·min at 60℃. Chamber tests with a heat bulb revealed that "spiked" MEA was fully recovered, while only 13.32% of DEA and no TEA were recovered. Interestingly, non-spiked types of EAs were detected, indicating that heat could convert EAs with more alcohol groups (TEA or DEA) into other EAs with fewer group(s) (DEA or MEA). The EA composition in fresh fluid was 4% DEA, 66% TEA, and 30% MEA, and in used fluids (n = 5) was 12.4% DEA, 68% TEA, and 23% MEA. Conversion from TEA into DEA may therefore contribute to the DEA increment. Airborne TEA was not detected in 13 samples taken from the central coolant system and near a conveyor belt where no machining work was performed. The DEA concentration was 0.45 mg/m(3) in the only two samples from those locations. In contrast, airborne MEA was found in all samples (n = 53) regardless of the operation type.

CONCLUSION

MEAs easily evaporated even when MWFs were applied, cleaned, refilled, and when they were in fluid storage tanks without any metalworking being performed. The conversion of TEA to DEA and MEA was found in the machining operations.

6-Oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl)fluorescein as a new fluorescent labeling reagent for aliphatic amines in environmental and food samples using high-performance liquid chromatography

6-Oxy-(N-succinimidyl acetate)-9-(2'-methoxycarbonyl)fluorescein (SAMF), a new fluorescein-based amine-reactive fluorescent probe was well designed, synthesized and used as a pre-column derivatizing reagent for the determination of aliphatic amines in HPLC. It exhibited relatively pH-independent fluorescence (pH 4-9) and excellent photostability. The derivatization was performed at room temperature in 6min. On a C18 column, the derivatives of SAMF with eight aliphatic amines were baseline separated in 28 min with a mobile phase of methanol-water (57:43, v/v) containing 10 mmol l(-1) pH 5.0, H3Cit3-NaOH buffer. With fluorescent detection at lambda(ex)/lambda(em) = 484/516 nm, the detection limit could reach 2-320 fmol (signal-to-noise = 3), which was equivalent to or better than the detection limits obtained from other analytical methods of aliphatic amines. The proposed method has been applied to the determination of the aliphatic amines in environmental and food samples such as lake water, red wine, white wine, and cheese with satisfying recoveries varying from 95 to 106%.

Determination of diethanolamine or N-methyldiethanolamine in high ammonium concentration matrices by capillary electrophoresis with indirect UV detection: application to the analysis of refinery process waters

Alkanolamines such as diethanolamine (DEA) and N-methyldiethanolamine (MDEA) are used in desulfurization processes in crude oil refineries. These compounds may be found in process waters following an accidental contamination. The analysis of alkanolamines in refinery process waters is very difficult due to the high ammonium concentration of the samples. This paper describes a method for the determination of DEA in high ammonium concentration refinery process waters by using capillary electrophoresis (CE) with indirect UV detection. The same method can be used for the determination of MDEA. Best results were achieved with a background electrolyte (BGE) comprising 10 mM histidine adjusted to pH 5.0 with acetic acid. The development of this electrolyte and the analytical performances are discussed. The quantification was performed by using internal standardization, by which triethanolamine (TEA) was used as internal standard. A matrix effect due to the high ammonium content has been highlighted and standard addition was therefore used. The developed method was characterized in terms of repeatability of migration times and corrected peak areas, linearity, and accuracy. Limits of detection (LODs) and quantification (LOQs) obtained were 0.2 and 0.7 ppm, respectively. The CE method was applied to the determination of DEA or MDEA in refinery process waters spiked with known amounts of analytes and it gave excellent results, since uncertainties obtained were 8 and 5%, respectively.

Ion chromatography of amylamine and tert.-butylamine in pharmaceuticals

Ion chromatographic (IC) methods have been developed for the assay of amylamine in BMS-181 866-02 and tert.-butylamine (TBA) in BMS-188 494-04. BMS-181 866-02 is the penultimate intermediate in the synthesis of a novel thromboxane antagonist, BMS-180 291-02, which is undergoing clinical trials. Amylamine may be present as a trace impurity in BMS-181 866-02. BMS-188 494-04 is the TBA salt of the prodrug ester of BMS-187 745, a novel oral hypocholesterolemic agent. Chromatographic separations were accomplished under isocratic conditions using a Dionex CS-14 column with conductivity detection. The methods differ only in the composition of the methanesulfonic acid-acetonitrile mobile phase. The detection limit and minimum quantifiable levels for amylamine were 0.01% and 0.02%, respectively. The method was linear over the range studied (1-12.5 micrograms/ml, n = 7, r = 0.9993). The method for TBA was linear from 5 to 30% (w/w) (50-300 micrograms/ml, n = 8, r = 0.9993) of working sample concentration (1 mg/ml BMS-188 494-04). The precision and accuracy of the methods are presented.