Determination of Inorganic Ions in Parenteral Nutrition Solutions by Ion Chromatography.

A new, simple and sensitive ion chromatography (IC) method for the determination of sodium, potassium, magnesium, calcium and chloride in a parenteral nutrition (PN) solution was developed and validated. Before sample analysis, a sample pretreatment by calcination was applied which could totally remove interference from other constituents of the PN solution. Methanesulfonic acid (MSA) and sodium hydroxide were used as the mobile phase for the determination of cations and anions, respectively. The calibration curves showed good correlation between analyte peak area and concentration (r2 > 0.999). Detection limits ranged from 0.0001 to 0.02 mg/L and quantification limits from 0.0002 to 0.06 mg/L. Relative standard deviation (RSD) values for repeatability and inter-day precision did not exceed 1.0% and the recoveries for all analytes were between 99.1−101.1%. The robustness was verified by using an experimental design.

Headspace gas chromatography for the determination of volatile methylsiloxanes in personal care products.

Most of the reported methods for the analysis of volatile methylsiloxanes focus on their environmental fate or possible health effects, aiming at trace level analysis by using direct injection gas chromatography. However, system contamination as carry over and side reactions at the injector are commonly reported in those cases. In this article, we explore the use of headspace gas chromatography combined with the total vaporization technique as an alternative to avoid such issues for the analysis of linear (L2-L5) and cyclic (D3-D5) volatile methylsiloxanes. The proposed method showed good linearity with R2 values higher than 0.9961 and no significant contribution (α = 0.05) of the intercept. The limit of detection was always below 0.11 µg/vial (0.0025% m/m). Finally, the method was applied to real samples like an adhesive remover, hair oil, shampoo, and cream. After simple sample pretreatment, recoveries higher than 86% were achieved. Graphical abstract.

Overview of sample introduction techniques prior to GC for the analysis of volatiles in solid materials.

Sample preparation and introduction techniques are very critical steps in gas chromatography analysis and particularly in the analysis of volatiles in solid samples. In these cases, they can be divided into two main categories: direct and indirect approaches, based on how the solid sample is treated, i.e. with and without dissolution (or extraction) of analytes from the solid sample. To enable routine application, coupling with sample preparation techniques (especially solid or solvent-based microextractions) is needed to achieve automation. Here, an overview of the most common sample introduction techniques for gas chromatography with their advantages and drawbacks is presented and discussed, including references to relevant examples. So, this review can serve as guidance for new users.

Exploration of the problems and solutions related to reference introduction prior to calibration of thermal desorber-gas chromatography.

Reference introduction in thermal desorption with gas chromatography is a critical aspect. It is mostly performed by offline liquid calibration using a micro syringe to inject a liquid standard solution on the sorbent in the thermal desorption tube. This is based on the assumptions that the adsorption-desorption process is quantitative and that no sample is lost in manipulating the tube. However, for analytical procedures involving thermal extraction of solid matrices, the adsorption-desorption processes for sample and reference differ and the assumptions are not always fulfilled. This is explored in this work. First, issues related to the online liquid calibration were investigated. With tubes containing only quartz filters, a relative loss of over 80% was noticed for some solvents due to tube manipulation processes. Enclosing a bed of mesoporous silica as sorbent limited the losses to about 25% when samples were immediately analysed, and even better results were obtained when tubes were stored for several hours so that proper adsorption could take place. An additional sweep gas during loading boosted the transfer of analytes with recoveries above 95%. Next, an inline injection system was installed on the thermal desorber instrument. This sorbent free, independent calibration tool avoids the drawbacks of other approaches.

Gastric and Duodenal Ethanol Concentrations after Intake of Alcoholic Beverages in Postprandial Conditions.

This study determined intraluminal ethanol concentrations (stomach and duodenum) in fed healthy volunteers after the consumption of common alcoholic beverages (beer, wine, and whisky). The results of this study were compared with a previous study in fasted volunteers. Five healthy volunteers were recruited in a crossover study. The fed state was simulated by ingestion of 250 mL of Nutridrink Compact Neutral. Volunteers subsequently consumed two standard units of beer (Stella Artois, 500 mL, 5.2% ethanol), wine (Blanc du Blanc, 200 mL, 11% ethanol), or whisky (Gallantry Whisky, 80 mL, 40% ethanol). Gastric and duodenal fluids were aspirated through two catheters over time and analyzed for ethanol content by head space gas chromatography. The capability of ethanol to permeate gastric and duodenal rat mucosa was examined in an Ussing chambers setup. A similar average gastric Cmax was observed in the beer and the wine conditions: 3.3% and 3.7% ethanol, respectively. The gastric Cmax in the whisky condition amounted to 8.5% ethanol. Lower ethanol concentrations were observed in the duodenum compared to the stomach. The duodenal Cmax was similar in all three conditions: 1.3%, 1.2%, and 1.6% ethanol for beer, wine, and whisky, respectively. Compared to the fasted state (reported in a previous study), higher gastric ethanol concentrations were observed during a longer time period. In the beer and wine conditions, similar concentrations were observed in the intestine regardless of the prandial state. After intake of whisky, however, the ethanol concentration was lower in the fed intestine. Alcohol was observed to permeate both gastric and duodenal rat mucosa. Higher intragastric ethanol concentrations were maintained for a longer period of time in fed compared to fasted state conditions. However, the observed concentration profiles were not in line with current FDA guidelines for alcohol resistance testing of formulations, stating that in vitro tests should investigate the impact of up to 40% ethanol for 2 h. The presented intraluminal ethanol concentrations may serve as reference data for the further development of relevant in vitro models to assess ethanol effects on formulation performance.

Comprehensive headspace gas chromatographic analysis of denaturants in denatured ethanol.

To discourage consumption, ethanol is often denatured using both volatile (e.g., methyl ethyl ketone and isopropanol) and nonvolatile (e.g., denatonium benzoate) chemical substances. As a result, the analysis of denatured ethanol samples is usually performed by multiple techniques such as gas chromatography for the volatile denaturants and liquid chromatography for the nonvolatile ones. However, the need for multiple techniques increases the cost of analysis and forms a severe obstruction for on-site product control. Using the full evaporation technique combined with gas chromatography and flame ionization detection, only one analytical methodology has to be used here to determine both volatile and nonvolatile denaturants in denatured ethanol. Denatonium benzoate is determined as benzyl chloride following an in-vial reaction. Compared to conventional techniques, the novel method performs equally well, but it is simpler to apply. At the same time, drawbacks of alternative methods are circumvented such as equilibration issues and alterations to the stationary phase when using liquid chromatography with ion pairing agents or matrix effects when applying static headspace gas chromatography. The developed method showed good linearity, repeatability, and recovery toward all analytes and was applied to the analysis of commercial denatured ethanol for disinfection and ethanol-based windscreen washer fluids.

Novel multiple extraction thermal desorption approach prior to gas chromatography for the determination of residual solvents applied to modified cellulose.

In this work, multiple extraction thermal desorption (METD), as a sample introduction method for GC, was developed. This technique was used for the determination of residual solvents (RS) in modified cellulose, because it is practically impossible to dissolve or distribute it uniformly in water and common organic solvents. Moreover, METD facilitates the optimization of the desorption time and it is more sensitive to quantify trace level volatiles in insoluble material, compared to direct dynamic desorption (DDD). In addition, METD provides diagnostic information about the sample-sorbent interaction. Three solvents (methanol, ethanol and tert-butanol) were determined in two types of modified cellulose (dialdehyde cellulose (DAC) and DAC-ethylenediamine (DAC-EDA)). It was shown that good linearity over a wide concentration range was achieved. The limits of detection (LOD) and limits of quantification (LOQ) for the different solvents ranged from 0.1 to 0.3 µg and from 0.3 to 0.9 µg per tube, respectively. Accuracy of the METD method was verified by using an alternative method based on the decomposition of the modified celluloses by Trichoderma reesei cellulase, followed by headspace-trap-GC (HS-trap-GC). The results obtained from the two validated methods were found to be similar (relative deviation < 17.0 %). However, the developed METD-GC method is preferable for the analysis of RS in modified cellulose since it does not require sample pretreatment and possesses higher sensitivity.

Impact of diluents on the calibration of direct dynamic thermal desorption prior to gas chromatography.

A thermal desorber (TD) can be used in different ways to introduce samples in a gas chromatographic (GC) system. Besides its conventional use where the collected analytes are released from the sorbent in the sample tube, direct dynamic desorption (DDD) is an interesting option where a solid sample is put directly in the TD tube. However, since no sorbent is used for the sample, proper calibration is not straightforward. This issue was investigated in the present work using offline liquid calibration (OLC) and inline liquid calibration (ILC). Unexpectedly, ILC yielded a lower response than OLC. This could be related to the adsorption kinetics of the analytes and water on the cold trap of the TD. More insight was gained performing double injection ILC experiments with toluene as diluent for the analytes and injecting water before or after the toluene solution. This revealed a clear influence of the diluent. The influence of water was further explored applying two cold trap temperatures (4 °C and -30 °C). Inserting a LiCl trap in the TD tube to capture the water was found to be an effective solution for the problem. Finally, quantitative aspects of this approach were demonstrated.

Identification of the oxidation products of cysteamine and cystamine by CE-MS interfaced by a noncommercial electrospray ionization source.

Sodium cysteamine phosphate is a prodrug derivative of cysteamine that can be used in cystinosis treatment. Although titrimetric assays are very well established and precise, iodimetric determination of sodium cysteamine phosphate requires considerably more carefulness and time from the analyst than usual. The possibility to assess sodium cysteamine phosphate by CE was evaluated by means of the quantification of its oxidation product, cystamine, which is a more suitable substance to be used as primary standard than sodium cysteamine phosphate. Apparently, this approach should be straightforward, but systematic differences between the results obtained with CE and titrimetric assays were noticed. MS and CE-MS were employed to aid in the investigation of the possible causes of imprecision of the sodium cysteamine phosphate titration and CE determination. For this purpose, a simple and inexpensive ESI source was constructed. It was observed that cystamine is not the final product of the cysteamine and/or sodium cysteamine phosphate iodine-oxidation and other species besides cystamine may be formed depending on the reaction conditions, which explains the difficulties observed in the sodium cysteamine phosphate quantification.

Full evaporation headspace gas chromatography with thermal conductivity detection for the direct determination of water in solid pharmaceutical bulk products.

Headspace gas chromatography (HS-GC) has the potential to be used for water determination in pharmaceutical products. In this article, its use for the determination of water in solid samples is explored without the need of dissolution by means of the full evaporation technique (FET). This way, water is thermally removed from a small amount of sample which is directly weighed in the vial. This simplifies considerably the method since no diluent has to be searched and HS saturation is avoided. Blank corrections were performed to compensate for atmospheric moisture variation. Moreover, the performance of mass spectrometry (MS) and thermal conductivity detection (TCD) was compared. The method showed excellent figures of merit when working with TCD, such as R2> 0.99 and RSD< 5% for each level of the calibration curve. Eight samples were carefully studied at different equilibration temperatures to find the optimal working conditions for each case and the results were compared to the ones obtained by Karl Fischer titration (KFT). Both methods showed restrictions and proper case by case optimization/validation turned out to be mandatory. Hyphenation with a flame ionization detector (FID) in series with the TCD showed the benefit to be useful for testing residual solvents (RS) simultaneously.

Gas chromatographic method with minimal sample consumption for quality control of 13C-mixed triglycerides used in clinical diagnosis.

Exocrine pancreatic insufficiency (EPI) can be comfortably diagnosed by a breath test using the mixed triglyceride 2-octanoyl (1-13C)-1,3 distearoyl glycerol (13C-MTG). However, it is not fully accepted as a routine test yet as no vendor provides a certified product for clinical applications. Current recommended methods for quality control of triglycerides are not compatible with the produced expensive small batches of 13C-MTG. In this article, two procedures were miniaturized and optimized: one to confirm the structure by a regiospecific enzymatic reaction and another to check the purity via a methyl esterification. Both pretreated samples were then analyzed by gas chromatography coupled to mass spectrometry (GC-MS). The proposed methods showed good selectivity for the structure confirmation and good linearity with external standards for the purity control: R2 values were higher than 0.995, accuracy was in the 98-100% range and excellent repeatability (RSD <1.4%) was achieved.

Mixed aqueous solutions as dilution media in the determination of residual solvents by static headspace gas chromatography.

Static headspace (HS) sampling has been commonly used to test for volatile organic chemicals, usually referred to as residual solvents (RS) in pharmaceuticals. If the sample is not soluble in water, organic solvents are used. However, these seriously reduce the sensitivity in the determination of some RS. Here, mixed aqueous dilution media (a mixture of water and an organic solvent like dimethyl formamide, dimethyl sulfoxide or dimethyl acetamide) were studied as alternative media for static HS-gas chromatographic analysis. Although it has been known that mixed aqueous dilution media can often improve sensitivity for many RS, this study used a systematic approach to investigate phase volumes and the organic content in the HS sampling media. Reference solutions using 18 different class 1, 2 and 3 RS were evaluated. The effect of salt addition was also studied in this work. A significant increase in the peak area was observed for all RS using mixed aqueous dilution media, when compared with organic solvents alone. Matrix effects related to the mixed aqueous dilution media were also investigated and reported. Repeatability and linearity obtained with mixed aqueous dilution media were found to be similar to those observed with pure organic solvents.

Characterization and improvement of signal drift associated with electron ionization quadrupole mass spectrometry.

Quadrupole mass spectrometry with electron ionization (EI-QMS) is a very popular detection technique in combination with gas chromatography. It is deployed for the analysis of volatile and semivolatile analytes in many industry domains. Although a very important factor for quantitative analysis, little is known about the stability of ion source performance. Only a few papers and patents report possible signal instabilities due to sample adsorption, degradation, or insulating deposits on the hot stainless steel surface of the ion source. In this study, a conventional stainless steel ion source was used to investigate possible signal drifts. It was observed that the EI-QMS instrument indeed suffered from continuous signal instability. It was found that the key parts which are responsible for the signal instabilities are those that regulate the ion beam toward the mass analyzer: the repeller, exit plate, and focusing lenses. The voltage of the repeller was found to have a major influence on the signal stability. The surface of the repeller, exit plate, and focusing lenses was modified by applying a gold coating. It was demonstrated that the signal stability of the MS dramatically improved when using the gold-coated parts. The contribution of each part to the stability improvement was quantitatively determined and compared with the standard stainless steel source performance. It was assumed that the signal drift observed with the stainless steel EI source originated from charge buildup on the surfaces. This hypothesis was supported by software simulations.

Development and validation of a thermal desorber gas chromatography method for determination of residual solvents in drug loaded albumin.

The conventional approach for residual solvent (RS) analysis is headspace-gas chromatography (HS-GC). This starts from a homogenous sample solution and is based on the equilibrium of the analyte between the sample and the gas phase. Unfortunately, aqueous solutions of albumin form irreversible hydrophobic aggregates when heated above 50 °C. Consequently, the use of HS-GC for RS analysis in albumin becomes problematic due to the presence of an additional solid phase in the HS vial. In this work, a method using a thermal desorber (TD) combined with GC was developed for the determination of RS in drug loaded albumin. Samples were immobilized between two double layers of quartz filter (QF) in a polytetrafluoroethylene (PTFE) insert which was placed in an empty desorption tube prior to TD-GC analysis. The liquid standard mix consisted of ethanol (EtOH), acetone (Ace), dichloromethane (DCM) and chloroform (Chl) dissolved in toluene. Offline liquid calibration (OLC) was applied by introducing 2 µL of the standard mix under counter flow of an inert gas into the TD tube containing a mixed bed of mesoporous silica (MPSi) immobilized between two double layers of QF. The OLC results were verified using the inline liquid calibration (ILC) approach based on a heated GC injector installed on the TD. The validation results revealed that the proposed method has good recovery (> 98 %). R2-values (> 0.998) indicated good linearity over a wide range. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.01 and 0.04 µg on tube, respectively. Repeatability of the method was reported as RSD-values and they were lower than 3 %. A method based on the complete enzymatic digestion of albumin combined with conventional HS-GC was developed to verify the completeness of release of the RS from the albumin. Both the TD-GC and HS-GC methods were applied for the determination of EtOH and DCM in two different albumin samples loaded with experimental drugs. Statistical comparison indicated that there was no significant difference (p > 0.05) between the two methods. However, the HS-GC method following enzymatic degradation is much more expensive and time consuming.

Current application and potential use of GC × GC in the pharmaceutical and biomedical field.

The analysis of volatile samples is mostly performed by GC. However, its separation power may not be enough for some complex samples. Comprehensive gas chromatography (GC × GC) increases the separation power by means of a second separation dimension. Parallel to the great technological advances realised since the early stages of the technique, considerable applications in different fields have emerged. Nonetheless, it is still often seen as a novelty, thus being rarely considered a fully established technique for routine analysis. In this article we review different recent applications of GC × GC in the pharmaceutical and biomedical field, highlighting the obtained results and advantages compared to other methods when possible. We aim to encourage researchers to embrace GC × GC as a possible alternative to improve their results by presenting its great application potential in this area.

Static headspace gas chromatography of (semi-)volatile drugs in pharmaceuticals for topical use.

An analytical method that allows simultaneous analysis of some (semi-)volatile drugs and additives in pharmaceuticals for topical use was developed using classical static headspace as sampling technique combined with gas chromatography (HS-GC). The capillary column used, RSL-200, showed good selectivity towards all the analytes in the samples investigated. Among the different dilution media investigated, dimethyl sulfoxide in combination with sodium chloride solution showed better sensitivity. Using the optimized headspace sample dilution medium, better sensitivities for all the analytes were achieved at low thermostatting temperature (85 degrees C). The optimized HS-GC method with flame ionization detection showed good repeatability, linearity and accuracy.

Evaluation of the European Pharmacopoeia method for control of residual solvents in some antibiotics.

Residual solvents (RS) are volatile organic chemicals that are used or produced during the manufacturing process of drug substances or excipients. The European Pharmacopoeia (Ph. Eur.) limits the amount of RS in pharmaceuticals, considering the International Conference on Harmonization (ICH) of Technical Requirements for Registration of Pharmaceuticals for Human Use guidelines for RS. According to the Ph. Eur. general method, water insoluble samples may be analyzed using DMF as dilution solvent at high equilibration temperatures such as 105 degrees C. This could be problematic in the case of antibiotics, many of which are water insoluble and temperature sensitive. Moreover, antibiotics are complex in nature and beside RS, one can expect several other volatile impurity peaks in the chromatogram. In this study, the Ph. Eur. method for RS analysis was evaluated for selected groups of antibiotics. An alternative dilution medium was proposed (DMSO-water), which offers optimum sensitivity while working at lower equilibration temperatures such as 80 degrees C. The optimized method was investigated for precision, accuracy, linearity and detection limits.

Characterization of mesoporous silica used for drug delivery by sorptive interaction - multiple headspace extraction-gas chromatography.

A multiple headspace extraction experiment coupled to gas chromatography (MHE-GC) is used for the classification and qualification of different mesoporous silica (MPSi) materials used for drug delivery. In this MHE experiment, a pure liquid solvent probe is fully evaporated in a sealed headspace vial in the presence of the MPSi sample, leading to a gas-solid partitioning that is theoretically described. The obtained results matched with the known characteristics of the studied samples, such as adsorption capacity due to differences in porosity and passivation treatments. Moreover, it proves the effectiveness of a poly dimethyl siloxane (PDMS) coating treatment over a thermal one in reducing the specific interactions of the MPSi. In addition, it evidences the important role of confinement effects when the pore diameter is close to the microporosity range. Finally, a simple experiment for fast screening is proposed by comparison of the results obtained for four different probes used as a mixture.

Determination of residual dimethylsulphoxide in drug loaded gelatin using thermal desorber - gas chromatography.

Traditional headspace - gas chromatography (HS-GC) methods for the determination of residual solvents (RS) start from a homogenous sample solution. Subsequently, it is challenging to determine RS using HS-GC techniques from insoluble solid samples like gelatin which is practically impossible to dissolve or distribute uniformly in water and common organic solvents. In this study, a thermal desorber combined with capillary gas chromatography and flame ionization detection/mass spectrometry (TD-GC-FID/MS) was used for quantitative determination of residual dimethylsulfoxide (DMSO) in gelatin without sample pretreatment. A sample of gelatin was sandwiched between two quartz filter double layers in a polytetrafluoroethylene insert which was then placed in its entirety into a thermal desorption tube. Factors affecting the performance of TD-GC including desorption time, desorption temperature, desorption flow and type of adsorbent were studied by applying a standard solution of DMSO in methanol on a blank gelatin bed. Validation results of the proposed method showed good linearity with an R2-value higher than 0.999 for a wide concentration range and good sensitivity with a limit of detection and limit of quantification of 0.1 µg and 0.2 µg on tube, respectively. The proposed method shows recovery values close to 100%. In addition, a conventional HS-GC method following enzymatic degradation of gelatin was developed to verify the proposed TD-GC method. Both methods were applied for the determination of residual DMSO in gelatin that was loaded with an experimental drug. Results were comparable, but the enzyme assisted HS-GC method was more time consuming and expensive.

Investigation of sorbic acid volatile degradation products in pharmaceutical formulations using static headspace gas chromatography.

An analytical method that allows simultaneous analysis of sorbic acid and its degradation products was developed using static headspace gas chromatography (HS-GC). AT-Aquawax-DA, the capillary column used, showed good selectivity and separation towards sorbic acid and its degradation products. Sorbic acid degradation was investigated in both acidic and aqueous media at room and elevated temperatures. In total 12 sorbic acid degradation products were found, 8 of which could be characterized. The method was investigated for its accuracy towards estimation of degradation products. Using the HS-GC method different batches of pharmaceutical preparations such as cold cream, cetomacrogol cream and vaseline were investigated for sorbic acid degradation products which were estimated by applying the standard addition method. Acetaldehyde was found to be the major degradation product. The other identified degradation products were: acetone; 2-methylfuran; crotonaldehyde; alfa-angelicalactone; 2-acetyl, 5-methylfuran; toluene and 2,5-dimethylfuran. Both mass spectrometeric (MS) and flame ionization detection (FID) were used. The qualitative investigation was done on HS-GC-MS and the quantitative work on HS-GC-FID.