Karl-Fischer Method Research Articles

Residual Moisture Determination in Lyophilized Drug Product Samples Using FT-NIR: A Comparison of Data Processing Methods

Introduction: Remdesivir for injection is a Gilead Sciences manufactured drug product approved by the FDA to treat COVID-19. One of the critical attributes of this drug product, which is lyophilized, is its water moisture content. The current method used to determine the water content of remdesivir is the Karl Fischer titration method. The Karl Fischer method is considered the gold standard for determining the residual water moisture content of lyophilized drug products in the pharmaceutical industry. However, it is timeconsuming, can at times be sensitive to difficult-to-control techniques, and most importantly is destructive. The purpose of this study was to create a non-destructive residual water moisture determination method using FT-NIR. Methods: Three FT-NIR methods were proposed as a non-destructive alternative to Karl Fischer method: partial least squares regression, Beer’s law and area under the curve, and Beer’s law and peak height. Results were statistically validated using RMSEC, RMSEP, and R2, and the percent differences of predicted and accepted residual moisture values were compared with external validation vials. Results: Results showed that the partial least squares regression method produced a 0.999 correlation coefficient and a 95% performance index score, highlighting the accuracy between the actual Karl Fischer moisture values and the predicted FT-NIR moisture values. The Beer’s law methods produced acceptable correlation coefficients of 0.996 and 0.982 for the peak area and height, respectively, but comparisons between the actual and predicted values were not as closely matched as the partial least squares method. Conclusion: Our results support the use of a non-destructive partial least squares FT-NIRbased moisture contest method, which is a useful alternative to the destructive Karl Fischer method for determining residual water moisture of lyophilized drug products. Only an FTNIR instrument and chemometric statistical software along with the appropriately trained/educated analysts, and routine Karl Fischer instrumentation to measure/determine moisture content values of either water spiked or lyo-thieved and normal lyophilized samples are required.

Quantitative Determination of Water in Organic Liquids by Ambient Mass Spectrometry.

This study uses a rapid tandem mass-spectrometry method to determine water content in complex organic solutions. Emphasis is placed on trace-water analysis by a fast and accurate alternative to the Karl-Fischer method. In this new method, water is captured by a charge-labeled molecular probe. Water binds strongly with high specificity to the strongly electrophilic aldehyde site in a charge-labelled molecule (N-methylpyridinium); competitive binding by other analytes is effectively discriminated against in the mass-measurement step. Quantitative determinations are made over a wide concentration range, 0.001 % (10 ppm) to 99 %, with better than 10 % relative standard deviation, along with short (1 min) analysis times using small sample volumes (several μL). Applications include water measurement in simple organic solvents, for example, deuterated solvents, as well as in complex mixtures, for example, organic reaction mixtures. Additionally, this method allows for water monitoring in levitated droplets. Mechanistic investigations into the impact of water on important chemical processes in organic synthesis and environmental science are reported.

Fast quantification of water content in glycols by compact 1H NMR spectroscopy

Glycols are key chemicals for many applications in different fields of activities. Being highly hydroscopic, glycols contain usually water. The presence of water, even in tiny amounts, can affect their chemical and physical properties. Therefore, the accurate determination of water content is essential for any intended applications. In this context, a novel method using low-field Nuclear Magnetic Resonance (NMR) spectroscopy is introduced. The proposed approach offers a straightforward, fast, low-cost, and versatile solution for water quantification in glycols without the need for reagents or calibration data. It is demonstrated by quantifying the water concentration up to 11 wt% in aqueous ethylene glycol (EG) and triethylene glycol (TEG) mixtures with the help of lineshape analysis of the corresponding proton spectra. The limit of detection, achieved within 1 min of measuring time, was 0.05 wt% for water in EG and 0.15 wt% in TEG. The excellent agreement between the NMR results and those from the Karl-Fischer titration indicates that the proposed NMR-based approach has a great potential to be used as an alternative to the Karl-Fischer method. In addition, it is expected that the same methodology can be applied for water quantification in more complex glycolic solutions and other mixtures.

Enhanced & effective phosphate recovery from water by indium fumarate & zirconium fumarate metal-organic frameworks: Synthesis, characterization, adsorption, kinetic and isotherm studies

Eutrophication has been an important environmental issue for the last decade. Agricultural and industrial actions cause high concentrations of phosphate discharging to surface and ground waters, and high levels of phosphate concentration causes eutrophication. The decreasing of the phosphate concentration is an essential matter and adsorption is one of the most effective solutions for this purpose. In this study, indium fumarate (In-fum) and zirconium fumarate (Zr-fum) were prepared. Surface characterizations of these adsorbents were applied by XRD, FTIR, SEM, TGA, DSC, and BET surface analysis. The surface areas of In-fum and Zr-fum were determined as 181.19 m2/g and 527.96 m2/g, respectively. Water absorption abilities of adsorbents were tested by Karl-Fischer method. The water contents inside the pores of water-treated Zr-fum and In-fum are 0.0560% (w/w) and 0.0694% (w/w), respectively. Phosphate adsorption performances of In-fum and Zr-fum particles were studied by parametric research, investigating the effects of adsorbent quantity, contact time, solution pH, initial solution concentration, adsorption temperature, and co-existing ions. The phosphate adsorption uptake (qe) of Zr-fum is 33.52 mg/g and qe value of In-fum is 31.29 mg/g when adsorbent quantity is 1 mg. The kinetic studies reveal that both adsorbents follow pseudo second-order kinetic model according to the R2 values. These values are 0.93 for In-fum and 0.98 for Zr-fum. The rate constants are 0.15 g/mg min (In-fum) and 0.14 × 10−2 g/mg min (Zr-fum). Theoretical maximum phosphate adsorption uptake (qm) of In-fum is 93.40 mg/g at 318 K. The qm value of Zr-fum is 67.44 mg/g at 308 K. Phosphate adsorption over In-fum is strongly dependent on temperature change whereas the effect of temperature on adsorption performance of Zr-fum is insignificant. The pH of the phosphate solution should be below 7 to obtain an appropriate surface and phosphate ion charge combination. The presence of co-existing chloride ions does not dramatically affect phosphate adsorption capacity.

Determination of Moisture in Olive Oil: Rapid FT-NIR Spectroscopic Procedure Based on the Karl-Fischer Reference Method.

According to CODEX, moisture and volatile matter are olive oil quality parameters and the development of a rapid screening method for the determination of moisture is of interest. We recently demonstrated for the first time that the weak near-infrared (NIR) band near 5260 cm-1 is primarily attributed to a water O-H combination band. To determine the intensity of this band, we measured the peak-to-peak (p-p) height of its first derivative and generated exponential calibration curves for p-p height versus gravimetrically determined concentrations of spiked water in olive oils that had been purged of their initial moisture contents. To further optimize this univariate calibration method, calibration curves were generated in the present study based on plotting the moisture band first derivative p-p heights for neat olive oils (that were neither purged nor spiked) versus the moisture concentrations obtained by the Karl-Fischer (KF) primary reference method. To enhance the speed of FT-NIR data collection, measurements were carried in the transmission mode using disposable glass tubes. We also developed and compared a multivariate partial least squares approach to the univariate one. All the spectra were collected in two separate laboratories using two FT-NIR spectrometers of the same brand and model and no significant difference (p > 0.05) was found between the two laboratory determinations and the KF reference values at a 95% confidence interval. High accuracies were found with the two FT-NIR instruments used, as indicated by the low root mean squared error (RMSE, %) for predicted values obtained with the univariate procedure (RMSE = 0.008% and 0.010%) and the multivariate one, which yielded an even lower value (RMSE= 0.007% for both instruments). These results suggest that, once validated, the FT-NIR approach could potentially be a rapid substitute for the KF method.

Freeze-dried meningococcal vaccine: Total error assessment of a near-infrared method for water content determination

Accuracy of reference values obtained by the reference method is essential to ensure the quality of a near-infrared (NIR) model. The purpose of this study was to assess the accuracy of a newly developed NIR analytical method for the determination of water content in a freeze-dried meningococcal vaccine by evaluating not only uncertainties associated with the calibration model and NIR measurement procedures but also systematic error arising from the reference Karl-Fischer method. An experimental design based on the standard addition method (SAM) in freeze-dried vaccines is proposed for total error assessment of the NIR analytical system. The accuracy profile showed that the NIR model successfully determined water content over the 1.0–6.7% range. The SAM enabled overall proportional error assessment, which yielded a slope of 1.01. The present study confirmed the suitability of the proposed NIR analytical method for the determination of water content in the freeze-dried meningococcal vaccine. Furthermore, assessment of the overall proportional error proved that the NIR analytical method could be used to accurately estimate differences in water content, therein surpassing the reference method as the method of choice for determining intra- or interbatch variability as well as stability.

Measurement of the Water Content in Semi-solid Formulations Used to Treat Pressure Ulcers and Evaluation of Their Water Absorption Characteristics.

We investigated the water contents in commercial semi-solid preparations used for pressure ulcer (PU) treatment using near-IR spectroscopy (NIRS) and compared the results with those measured using the Karl Fischer (KF) method. The aim of this study was to determine a standard method and select the appropriate topical preparation with the optimal moisture for PU treatment. The water absorption properties of bases and formulations were evaluated with a time-dependent factor using Transwell as the model membrane. KF and NIRS were applicable as measurement methods of the water content in semi-solid formulations. NIRS was shown to be a useful, simple, nondestructive tool that is more advantageous than the KF method. The water absorption characteristics tested using Transwell revealed that the rate of and capacity for water absorption are determined not only by the absorption ability of the polymer base but also by other factors, such as the osmotic pressure exerted by additives. KF and NIR measurements can be used to choose external skin preparations to control the amount of water in PU treatment.

Moisture content determination in an antibody-drug conjugate freeze-dried medicine by near-infrared spectroscopy: A case study for release testing

The use of Near-infrared spectroscopy (NIRS) as a fast and non-destructive technique was employed for moisture content (MC) determination in Antibody-drug conjugates (ADCs) in replacement to Karl Fischer (KF) method. The lab analysis of ADCs, high potent medicines, should be performed in conditions ensuring the operator’s safety and using secured analytical tools like NIRS. A NIRS method was first developed and validated in compliance with current guidelines. The novelty of this work first lies in the large number of samples prepared for a wide moisture calibration range of 0.51%–4.01%. Then, the classical Partial Least Square (PLS) regression was used as chemometric tool for the computation of the model. Excellent predictive calibration results were shown. A coefficient of correlation (r) value of 0.99 was obtained. An intercept value of 0.02 and a slope of 0.99 were observed, while the root mean square error of calibration (RMSEC) and the root mean square error of prediction (RMSEP) were respectively 0.10% and 0.12%. In addition, instrumentation, model performances and robustness of the method were evaluated, demonstrating the validation results. Calibration transfer issue and impact of the number of samples were also evaluated. Consequently, a validation strategy was introduced as a basis for submission to the health authorities’ for release and stability activities in a cGMP environment in replacement of the KF method.

Effects of Adsorbed Water on Nano Silicon for Lithium-Ion Battery

Silicon has been developed as a promising anode in the next generation lithium-ion batteries due to its high gravimetric capacity density of 3580mAh g−1 at room temperature. However, the lithiation and delithiation reactions are accompanied by large volume changes, resulting in the fracture and pulverization of Si particles and leading to the failure of electrical contacts and poor cycleability. To suppress the physical stress due to its large volume change, we have reported Si Leaf Powder® (Si-LP, Oike & Co., Ltd.), which is amorphous Si nano-flake powder exhibited a good cycleability.1-3 Another serious problem for Si-LP anode such as a large irreversible capacity in the initial and during cycleability remain to be solved for practical use. In previous studies, we have reported Li pre-doping technique using direct contact method with Li foil and Li-naphthalene complex solutions, which completely compensated a initail large irreversible capacity. 4-5Unfortunately, irreversible capacity was continually generated during cycleability and coulombic efficiency was hovered at 97.9 % even after 10 cycle, where part of charging Li was considered to be consumed for the decomposition of electrolyte solution as solid electrolyte interface (SEI). In this study, the effects of adsorbed water on nanolized amorphous silicon and its electrodes were investigated by meas of analysis of Karl-Fischer method and in-situgas generation measurement under different drying condition. In addition, their electrochemical properties including the charge and discharge characteristics were carried out to elucidate the effects of containing water. 1,743 ppm of water in nano-flake amorphous silicon powder were detected at 250°C Karl-Fischer method even after 1 hour drying at 120°C under 3Pa. This result indicated that nano-flake amorphous silicon were strongly bonded with water and the water was not easy to remove in electrode drying process, which were usually conducted around 100°C in practical CMC/SBR binder electrode. In coparision with graphite electrode, more than twenty times of adsorbed water were observed in nano-flake amorphous silicon electrodes and considerred to track inside the cell, leading to low coulombic efficiency not only initial but during cycleability. Actually, H2 gas generation was increased and initial coulombic efficiency was enhanced after dried at 180°C under 3Pa. In addition, remarkable coulombic efficiency improvement of 99.9 % (2140 mAh g− 1) was observed after 10 cycles. The results of this study show that nanoized silicon strongly adsorbed water , which continuously caused the decomposition of electrolyte solution.

On the Determination of Water Content in Biomass Processing

Processing of lignocellulosic materials to fuels such as methane and bioethanol may involve several processing steps including pretreatment, saccharification, fermentation, and anaerobic digestion. The amounts of substrate used in these processes are usually based on dry matter content, and the processes themselves typically lead to a change in dry matter content. Thus, it is of great importance to be able to measure dry matter accurately. Dry matter content is commonly determined by measuring loss of water during oven drying. We have used Karl Fischer (KF) titration to measure the water content in a wide range of biomass fractions and have compared these data to results obtained by oven drying. This revealed considerable differences for all tested materials. For lignocellulosic materials, oven drying tends to overestimate dry matter content for untreated material. On the other hand, oven drying generally underestimates dry matter content in pretreated materials due to loss of organic volatiles. These differences have major consequences for the calculation of mass balances and yields in bioprocessing. The KF method gives more accurate water determination than oven drying due to the unique selectivity of the analysis. The method is suitable for the analysis of lignocellulosic biomasses and is particularly useful for determination of water content in pretreated materials, where oven drying usually underestimates the dry matter content due to loss of volatiles.

A copper interdigitated electrode and chemometrical tools used for the discrimination of the adulteration of ethanol fuel with water

A new approach for the discrimination of the adulteration process of ethanol fuel with water is reported using a copper interdigitated electrode and chemometrical tools. The sensor was constructed using copper sheets with non-chemical modification of the electrode surface. The discrimination process was performed using capacitance values recorded at different frequencies (1000Hz to 0.1MHz) as the input data for non-supervised pattern recognition methods (PCA: principal component analysis and HCA: hierarchical cluster analysis). The relative standard deviation for the capacitance signals obtained from ten independent interdigitated sensors was below 5.0%. The ability of the device to differentiate non-adulterated ethanol samples from those adulterated with water was demonstrated. In all analysed cases, there was good separation between the different samples in the score plots and the dendrograms obtained from PCA and hierarchical cluster analyses, respectively. Furthermore, the water content was quantified using a PCA approach. The results were consistent with those obtained using the Karl–Fischer method at a 95% confidence level, as measured using Student's t-test.

(2-Hydroxyethyl)ammonium Lactates—Highly Biodegradable and Essentially Non-Toxic Ionic Liquids

(2-Hydroxyethyl)ammonium lactates have been prepared by reactions of the corresponding (2-hydroxyethyl) amines with lactic acid and characterized by their 1H NMR, IR, and mass spectra. They have been quantita- tively analyzed by HPLC, and their water contents have been determined by the Karl-Fischer method. The title salts are low-melting solids or viscous liquids, and they belong to the class of polar, hydrophilic ionic liquids. The toxicity and chemical and biological degradation of the synthesized ionic liquids have been evaluated by methods described in European Standards. The measurements showed these ionic liquids to be highly biodegradable and only slightly toxic substances. Condensation reactions of benzaldehyde with ethyl cyanoacetate and with acetophenone have been performed in these materials as solvents. The possibility of simultaneously applying these ionic liquids as both solvents and catalysts for the mentioned reactions has been demonstrated, as well as repeated use of the same ionic liquid for a number of condensation reactions without any purification.

Towards a robust water content determination of freeze-dried samples by near-infrared spectroscopy

The possibility for determination of the water content in pharmaceutical samples by near-infrared (NIR) spectroscopy has been more widely investigated in the past few years. However, many studies claim that changes in sample composition will require the establishment of a new method. The aim of this study was several fold: firstly to investigate validation aspects of water content determination in samples with varying composition and furthermore to see if a model based solely on freeze-dried mannitol–sucrose mixtures can be established that will be able to predict water contents for samples containing proteins, excipients or having a lower density of freeze-dried solids. Samples were measured by NIR, standard normal variate (SNV) corrected and the obtained spectra were compared with the results from a conventional Karl–Fischer titration by means of multivariate analysis, namely principal component analysis (PCA) and partial least square regression (PLS). For the overall sample set, a highly linear correlation between the NIR and the Karl–Fischer method with a slope of 1.00, an R 2 value of 0.98 and a root mean square error of cross-validation (RMSECV) of 0.15% were found. In a second step samples solely consisting of mannitol and sucrose mixtures were used to build a calibration set, which resulted in a RMSECV of 0.16%. The prediction of the remaining samples, which included protein or excipient containing samples, as well as lower density samples, resulted in a root mean square error of prediction (RMSEP) of 0.19%. Thus the present study demonstrated, that a general model for the determination of the water content by NIR could be established, within the limits investigated.

Comparison of Standard Moisture Loss-on-Drying Methods for the Determination of Moisture Content of Corn Distillers Dried Grains with Solubles

This study quantified the variability among 14 standard moisture loss-on-drying (gravimetric) methods for determination of the moisture content of corn distillers dried grains with solubles (DDGS). The methods were compared with the Karl Fischer (KF) titration method to determine their percent variation from the KF method. Additionally, the thermo-balance method using a halogen moisture analyzer that is routinely used in fuel ethanol plants was included in the methods investigated. Moisture contents by the loss-on-drying methods were significantly different for DDGS samples from three fuel ethanol plants. The percent deviation of the moisture loss-on-drying methods decreased with decrease in drying temperature and, to a lesser extent, drying time. This was attributed to an overestimation of moisture content in DDGS due to the release of volatiles at high temperatures. Our findings indicate that the various methods that have been used for moisture determination by moisture loss-on-drying will not give identical results and therefore, caution should be exercised when selecting a moisture loss-on-drying method for DDGS.

Comparison between Karl Fischer and refractometric method for determination of water content in honey

The aim of this work was to compare refractometric index (RI) and Karl Fischer (KF) titration methods for water content measurement in honeys. In addition, the effectiveness of two different solvents (methanol (M) and methanol:formamide in the ratio 1:1 (M + F)) was evaluated. Results indicated that RI and KF methods yielded similar results for water content determination in honeys; mainly, when the solvent M + F was used. This solvent mixture (M + F) also allowed a reduction in titration time which may be a potential advantage for measuring water content in honey.

Thermal analysis of the influence of water content on glass transitions

Starch is an important natural substance in which the water content has a significant influence on its structure and properties. In the present study, the effect of the water content on glass transition temperatures Tg and heat capacities Cp of wheat, maize and potato starches were investigated by high-sensitivity differential scanning calorimetry (temperature modulated TMDSC and conventional DSC). Thermal analysis measurements were performed on starch samples with different water contents. The exact water mass percentage of each sample was determined using the Karl-Fischer method.

Determination of total water content in inulin using the volumetric Karl Fischer titration

A new sample preparation method for the water content determination of inulin by volumetric Karl Fischer (KF) titration was developed and compared to the usual method of introducing the sample directly in the methanol-based working medium, modified or not by formamide (1:3, v/v) in order to increase sample solubility. In the proposed method, inulins were externally prepared by dissolving them in pure formamide (2.5:7.5, w/w). The time of analysis of the liquid/liquid reaction of the new method between the dissolved sample and the reaction medium is about 1–2 min, while the usual KF method is stopped after the 10 min delay time. The developed method permits the determination of water included in the crystals of the sample, confirmed by analysing both crystalline and amorphous inulin samples. Another advantage of this new method is its applicability for the water content determination of other polysaccharides that are not readily soluble in the working medium. Moreover, water content determination can be done by any type of volumetric KF titrator, as this proposed technique is not dependent on any additional tools such as a built-in homogeniser or a heatable titration beaker.

Determination of water content in powdered milk

The determination of the water content in foodstuff is one of the most frequently performed analyses in the food industry ( Isengard, 2001). In dried milk IDF method 26A in which the sample is dried at 102.0 ± 2.0 °C in a standard air drying oven has been used for many years as reference method. The method exhibits excellent repeatability but reproducibility is insufficient. Therefore the IDF working group on water developed an alternative drying method which involves drying the sample in a column at 87.0 ± 1.0 °C under a stream of dried air passing trough the column. The drying conditions were chosen to obtain equivalent results to the standard method. As the physico-chemical properties of the food might influence the outcome it is doubtful that any of the drying techniques allow a well-defined cut between adsorbed and bound water. On the contrary it is possible to define the total water content in milk powder as all water molecules present in whatever form. This is usually measured by the Karl–Fischer (KF) method ( Rüegg & Moor, 1987). In this study we measured samples the moisture or water content of a large number of milk powders by several techniques (IDF 26A, desiccation by P 2O 5, KF) and used water activity and near infrared spectroscopy to further understanding. We show how the measurement techniques relate to each other and demonstrate that the KF technique seems to be the most precise and best-defined method. This results, when the KF method is applied properly, in the best reproducibility of the tested methods.

Efficiency of methods for Karl Fischer determination of water in oils based on oven evaporation and azeotropic distillation.

The efficiency of azeotropic distillation and oven evaporation techniques for trace determination of water in oils has recently been questioned by the National Institute of Standards and Technology (NIST), on the basis of measurements of the residual water found after the extraction step. The results were obtained by volumetric Karl Fischer (KF) titration in a medium containing a large excess of chloroform (> or = 65%), a proposed prerequisite to ensure complete release of water from the oil matrix. In this work, the extent of this residual water was studied by means of a direct zero-current potentiometric technique using a KF medium containing more than 80% chloroform, which is well above the concentration recommended by NIST. A procedure is described that makes it possible to correct the results for dilution errors as well as for chemical interference effects caused by the oil matrix. The corrected values were found to be in the range of 0.6-1.5 ppm, which should be compared with the 12-34 ppm (uncorrected values) reported by NIST for the same oils. From this, it is concluded that the volumetric KF method used by NIST gives results that are much too high.

Comparison of water measurement results in polyol ester‐based lubricating fluids determined by the coulometric karl fischer method and a thin‐film polymer capacitive water sensor

AbstractField samples of MIL‐PRF‐23699 and DOD‐L‐85734, both polyol ester‐based fluids, were evaluated for water concentration by the coulometric Karl Fischer (KF) method according to ASTM D 6304 and with a prototype thin‐film polymer capacitance‐based sensor at Naval Air Systems Command (NAVAIR). The NAVAIR KF results showed a consistent negative bias, 190 ppm on average, compared to the results obtained with the water sensor. Since the calibration of the water sensor was performed by the sensor manufacturer using a different KF instrument and reagent/co‐solvent system, the ∼190 ppm negative bias probably reflects the difference in KF results between sensor manufacturer and NAVAIR. A limited round robin test, involving several laboratories using different instruments, reagents, solvents, and techniques, showed that water concentrations determined by the KF method can vary significantly from laboratory to laboratory. A larger round robin test was conducted to assess more accurately the variability in water measurement results. The results of the two round robin tests show that the particular KF instrument, reagents/solvents, and procedures being utilised by the various participating laboratories lead to a KF measurement variability of 20–30% for polyol ester‐based lubricating fluids. The results show that it is possible to obtain ∼190 ppm difference, observed between the water sensor and KF measurements at NAVAIR, between two laboratories. The results of the round robin tests showed a maximum repeatability of 9%. The significant difference between the repeatability and reproducibility indicates that there is potential for improved reproducibility of KF measurements through standardisation of, for example, instrument type, reagent/solvent system, test method, and laboratory procedure. Further work is required to determine the optimum KF test parameters for polyol.