Applications of a GC autosampler modified for headspace sampling

A GC autosampler designed for liquid injection was modified for static headspace sampling. The modification was very simple and involved replacement of the standard 10-μL syringe with a 100-μL gas-tight syringe. Liquid samples (0.2-1.0 mL) were placed in 2-mL vials, normally used for liquid sampling and an aliquot of the head-space above the liquid was withdrawn and injected into the GC. All parts of the sampling system were at ambient temperature. The system was found to be useful for several applications. Among those discussed in this paper are determination of ethanol in the blood or urine of individuals suspected of driving while intoxicated, residual organic solvents in pharmaceuticals, and screening of effluent waters from industrial plants for acrylonitrile.     

Determination of residual solvent in pharmaceutical preparations by static headspace GC

Static headspace GC, a simple, clean technique which is easily automated, appears to be a good approach to the determination of solvent residues in pharmaceutical preparations. The feasibility of this approach has been studied with an automated system. Data is presented for the solvents designated as impurities in pharmaceutical preparations by the United States Pharmacopeia. It was found that the static headspace technique meets the United States Pharmacopeia criteria for sensitivity. The absolute area count precision was <5% relative standard deviation and correlation coefficients to a linear response were >0.999. It was concluded that the technique is viable for this application.     

Determination of benzene series compounds and chlorobenzenes in water sample by static headspace gas chromatography with flame ionization detection

A simple, efficient, solvent‐free, and readily commercially available approach for the determination of eight benzene series compounds and 12 chlorobenzenes in water samples using the static headspace sampling and gas chromatography with flame ionization detection has been described in this paper. The proposed static headspace sampling method was initially optimized, and the optimum experimental conditions explored were 10 mL water sample containing 20% w/v sodium chloride placed in a 20 mL vial and stirred at 70°C for 43 min. The linearity of the method ranged from 1 to 200 μg/L for 20 analytes, with correlation coefficients ranging between 0.9962 and 0.9994. The limits of detection were in the μg/L level, ranging between 0.15 and 0.4 μg/L. The relative recoveries of spiked benzene series and chlorobenzenes with external calibration method at different concentration levels in pure, tap, and sea water samples were 84–113, 78–115 and 85–119%, respectively, with relative standard deviations of 3.8–6.8, 4.1–5.8, and 4.8–5.4% (n = 5), respectively. That this method can be successfully applied to the determination of benzene series compounds and chlorobenzenes in pure, tap, and sea water samples, simultaneously.     

Determination of chlorobenzenes in pure,tap, and sea water by static headspace gas chromatography‐electron capture detection

A simple, efficient, solvent‐free, and commercial readily available approach for determination of 11 chlorobenzenes (CBs) in water samples using the static headspace (HS) sampling and gas chromatography‐electron capture detector has been described. The proposed static HS sampling method was initially optimized and the optimum experimental conditions found were 10 mL water sample containing 20% (w/v) sodium chloride placed in a 20 mL vial and stirred at 70°C for 30 min. The linearity of the method ranged from 0.16 to 8.0 μg/L for dichlorobenzene isomers, 0.0176～0.88 μg/L for trichlorobenzene isomers, 0.004～0.2 μg/L for tetrachlorobenzene isomers, and from 0.001 to 0.05 μg/L for pentachlorobenzene and hexachlorobenzene, with correlation coefficients ranging between 0.9992 and 0.9999. The limits of detection were in the low μg/L level, ranging between 0.0002 and 0.04 μg/L. The relative recoveries of spiked CBs with external calibration or standard addition method at different concentration levels in pure, tap, and sea water samples were 83～116%, 89～108%, and 93～112%, respectively, and with relative standard deviations of 1.9～6.3%, 1.6～5.4%, and 2.5～5.7% (n = 5), respectively. It is concluded that this method can be successfully applied for the determination of CBs in pure, tap, and sea water samples.     

Comparison of quantitative analytical methods in headspace gas chroamtography of residual solvents

Summary The aim of this work was to compare quantitative methods used for headspace gas chromatographic analysis of residual solvents in standard aqueous solutions and to apply the methods to the analysis of medicines. We found that all three quantitative methods (external standard, ESTD; internal standard, ISTD; and standard addition, ASTD) enable determination of the total amount of solute in the equilibrated system by analysis of defined volumes of headspace gas. The results showed that the ISTD method is more precise than ESTD and ASTD when there is no strong interaction between the residual solvents and the pharmaceutical base material. When, however, there is a strong polarpolar interaction between them, the ESTD and ISTD methods give worse results than the ASTD method, because the ASTD method can eliminate the matrix effect. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Determination of volatile chlorinated hydrocarbons in water samples by static headspace gas chromatography with electron capture detection

A simple, efficient, solvent‐free, and commercial readily available approach for determination of five volatile chlorinated hydrocarbons in water samples using the static headspace sampling and gas chromatography with electron capture detection has been described. The proposed static headspace sampling method was initially optimized and the optimum experimental conditions found were 10 mL water sample containing 20% w/v sodium chloride placed in a 20 mL vial and stirred at 50ºC for 20 min. The linearity of the method was in the range of 1.2–240 μg/L for dichloromethane, 0.2–40 μg/L for trichloromethane, 0.005–1 μg/L for perchloromethane, 0.025–5 μg/L for trichloroethylene, and 0.01–2 μg/L for perchloroethylene, with coefficients of determination ranging between 0.9979 and 0.9990. The limits of detection were in the low μg/L level, ranging between 0.001 and 0.3 μg/L. The relative recoveries of spiked five volatile chlorinated hydrocarbons with external calibration method at different concentration levels in pure, tap, sea water of Jiaojiang Estuary, and sea water of waters of Xiaomendao were in the range of 91–116, 96–105, 86–112, and 80–111%, respectively, and with relative standard deviations of 1.9–3.6, 2.3–3.5, 1.5–2.7, and 2.3–3.7% (n = 5), respectively. The performance of the proposed method was compared with traditional liquid–liquid extraction on the real water samples (i.e., pure, tap, and sea water, etc.) and comparable efficiencies were obtained. It is concluded that this method can be successfully applied for the determination of volatile chlorinated hydrocarbons in different water samples.     

Quality control in residual solvent analysis: the static headspace gas chromatographic method

 Residual solvent testing of raw materials and drug products constitutes part of a quality control programme. Static headspace gas chromatography (HS/GC) is suggested in current pharmacopoeias as a general tool for residual solvent testing. But the main obstacles to using HS/GC procedures are the absence of performance tests, suitable reference solvents and matrix standards, and reference methods. Harmonized regulations for residual solvent testing allow the use of a cumulative approach to estimate the residual solvent content in drug products. The supplier data may be appropriate. Therefore, in a quality control programme the main accent is put on the definition of specification limits (in accordance with toxicological data, and the influence of residual solvents on the physical properties and stability of the product) and supplier qualification. This paper focuses on two main problems linked to supplier qualification: system performance and matrix effect. HS/GC of a mixture containing solvents of different volatility and polarity is proposed as a performance test. The test can be done in three ways in accordance with the residual solvents characteristics, the test sample solubility and the specification levels required. The use of the test as a diagnostic tool is demonstrated and sources of uncertainty of the recovery determination are discussed. Received: 12 December 1998 · Accepted: 25 January 1999     

Improved sensitivity of headspace gas chromatography for organic aromatic compounds

Summary The effect of adding an electrolyte and increasing the temperature on the preconcentration of volatile compounds in headspace analysis has been investigated. Quantification of the interactive effects of temperature and addition of salt on the vapor concentration is of interest for the determination of trace organic impurities in pharmaceutical base materials. This study was undertaken to investigate the quantitative effects of the addition of salts alcohols, and acetone, and of increasing the temperature on the vapor concentrations and distribution coefficients of volatile aromatic compounds (benzene, toluene, ando-xylene). It was found that the concentration of aromatic compound residues in the headspace could be increased by adding an inert salt to the water, but this effect was not very significant because of the low orginal solubility of the aromatic compounds in water. The reverse effect can be achieved by use of polar organic additives; this can be explained by the high polarizability of aromatic compounds and their greater solubility in the presence of these solvents. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999.     

Comparison of two systems for sample preparation and injection by dynamic headspace GC analysis

The performance of two commercially available systems employing dynamic headspace techniques for collection, enrichment, and injection of volatile compounds has been compared by GC analysis of test mixtures and dairy products. For technical reasons, it has not been possible to crate identical sorbent materials for both kinds of trap were not available, the most similar adsorbent available were chosen. The total quantity of volatile compounds from a test mixture at the column head was calculated using a theoretical model which enables comparable working conditions to be obtained. Under these circumstances special attention was paid to the repeatability of the data obtained from a test mixture in order to ensure reliable results in quantitative analysis. Significant differences in repeatability between the two systems seemed to originate from their distinctly different technical designs. A qualitative comparison of the systems has been performed using a sample of Swiss cheese. On the basis of the results obtained the systems have been dedicated to different applications in the laboratory of the FAM.     

Possibilities of dynamic headspace analysis coupled with capillary GC for the investigation of solid samples

The advantages of the dynamic headspace method for the analysis of solid samples, as compared with the static head space method, are discussed. Examples of dynamic headspace analyses are given to illustrate its possibilities.     

Analysis of thermolabile residual solvents in a spray dried dispersion using static headspace gas chromatography

In this study, we discuss the development of a static headspace gas chromatography method for the analysis of residual acetone as well as its enriched impurities including mesityl oxide and diacetone alcohol, in a spray dried dispersion. The major challenges include the instability of mesityl oxide and diacetone alcohol at high temperature and peak tailing of diacetone alcohol. It was found that the headspace oven temperature has to be controlled to 150°C or below to prevent degradation beyond an acceptable level (< 1%). The peak tailing of diacetone alcohol was attributed to the “Phase Soaking” effect due to excessive diluent, which may condense and temporarily modify the stationary phase. The peak shape of diacetone alcohol is dependent on the column loading capacity and the peak area of N‐methyl pyrrolidone, the solvent that elutes after diacetone alcohol. The headspace oven temperature was set at 140°C, where the highest response ratio of diacetone alcohol/N‐methyl pyrrolidone at 1.46 and thus the best sensitivity was obtained. The calculated quantitation limits were 1 ppm for acetone, 3 ppm for mesityl oxide and 31 ppm for diacetone alcohol. The method successfully passed validation criteria for specificity, linearity, accuracy, and precision.     

Static headspace and purge-and-trap gas chromatography for epichlorohydrin determination in drinking water

Epichlorohydrin (ECH) can enter drinking-water supplies due to leaching from epoxy resins in contact with water and/or through the use of flocculating water treatment agents. Potential human exposure from drinking waters poses a particular concern on account of toxicological studies showing severe acute and long-term toxic effects of ECH. Recently a parametric value of 0.1 μg/L for ECH in drinking water has been established by European Union.A few methods for ECH determination in water are available. However, they usually adopt cumbersome procedures for sample preparation and provide sensitivity not matching the EU criteria for water monitoring purposes.In this study we investigated the analytical performance of gas extraction techniques, such as static headspace (HS) and purge and trap (P&T), coupled to gas chromatography (GC) with an electron capture detector (GC-ECD) for the determination of ECH in drinking water. The influence of different parameters affecting the analytical response was studied in details in order to enhance the method sensitivity, thus fulfilling the regulatory requirements.The P&T GC-ECD method was proved capable of determining ECH in water for human consumption at a detection limit of 0.01 μg/L fully complying the regulatory levels. On the contrary, the HS GC-ECD method is far less sensitive (LOD≅40 μg/L) than the previous cited method. The P&T GC-ECD method is simple, rapid, automated, safe for operators and does not require large sample volumes. Therefore, it is useful for routine laboratory activities both for control and research actions.     

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.     

Residual solvents determination in drug products by static headspace-gas chromatography

Summary Two static headspace selective methods for residual solvents belonging to Class I, II and III have been developed, optimized and validated for drug products, which are insoluble in water. The methods give very good sensitivities (detection limits under 10 ppm) and precision (under 5.5% RSD) for all solvents. The detection limit for benzene was 0.1 ppm, in concordance with Pharmacopoeia requirements. During method optimization we found that sample volume and water content have a critical influence on the sensitivity. From our data, it is beneficial to choose low sample volume. If sample solubility in the organic solvent allows it, the optimum sample volume is between 0.1 and 0.3 mL. For drug products with water content greater than 7%, the increase in sensitivity produced by water presence should be taken into consideration, otherwise inconsistent recovery data and underestimation of residual solvent content will happen. The headspace vial volume has a critical influence on system precision. Presented at Balaton Symposium '01 on High-Performance Separation Methods, Siófok, Hungary, September 2–4, 2001     

Development of a static headspace gas chromatographic/mass spectrometric method to analyze the level of volatile contaminants biodegradation

Volatile compound biodegradation analysis usually requires the time-consuming step of extraction of the analytes from the matrix using organic solvents or costly radioactive-compounds. Thus, it is desirable to have a simple and fast technique to generate a good evaluation of bacterial biodegradation. The goal of this research was to develop a methodology on the basis of static headspace-gas chromatography/mass spectrometry (HS-GC/MS) to evaluate the level of volatile contaminant biodegradation. The effects of the following parameters were studied: temperature and time of equilibration. The biodegradation experiments were carried out with bacteria inoculation in mineral media in presence of volatile hydrocarbon compounds (toluene, p-xylene, nonane and naphthalene). Autoclaved inoculates were used as control and reference sample. The optimal headspace conditions were observed when the vials were heated at 80 degrees C for 20 min, the syringe at 81 degrees C and an injection volume of 0.4 mL was used. This methodology has the advantage of being relative free from matrix effects.     

Novel techniques for enhancing sensitivity in static headspace extraction-gas chromatography

Static headspace extraction-gas chromatography (SHE-GC) is one of the most commonly used techniques for the analysis of volatile compounds. It is considered by most to be a mature technique and to an extent this is true: there are many users from outside the traditional chromatography research community developing and publishing SHE-GC methods and there are numerous instruments and devices for SHE-GC commercially available. However, research on new SHE-GC methods continues. In this review, several interesting new developments in SHE-GC are described using examples from the past three years’ literature. First, the fundamental theory of SHE-GC is reviewed to provide a basis and common theme for the discussion of new methods. Next, several areas of SHE-GC research are explored: new sampling configurations, analyte derivatization and ionic liquids as solvents. These are all means for enhancing partitioning of the analyte into the vapor phase, thus improving analytical sensitivity of the overall SHE-GC method. Ideally, partitioning of analytes into the vapor phase is increased while partitioning of matrix components is not, or is decreased. There are many aspects of the seemingly straightforward process in SHE-GC that require further fundamental research to extend the application range of SHE-GC and to make method development more systematic.     

Dynamic headspace capillary gas chromatography: A versatile analytical technique

The applicability of dynamic headspace analyses for viscous liquids and solid samples is demonstrated. Some comments on the usefulness of this technique for quantifying volatiles in polymeric matrices are made.     

Dynamic headspace analysis of solid waste materials

A dynamic headspace stripping technique for the extraction of volatile organic compounds has been applied to a variety of solid and semisolid waste materials. A simple glass apparatus accommodates a wide range of sample sizes and allows for the volatiles to be stripped at elevated temperatures. Concentration on Tenax, followed by thermal desorption and analysis by fused silica capillary gas chromatography provides detailed information on the volatile content of waste samples of widely differing matrix composition.     

Analysis of volatile aromatic compounds in gasoline-contaminated ground water samples by static headspace sampling and high speed gas chromatography

A 15 second, high speed, gas chromatographic determination has been performed on the volatile aromatic compounds in gasoline-contaminated ground water following manual, static headspace sampling. Retention time reproducibility of the seven peaks studied ranged from 0.25 to 0.67 per cent (average relative standard deviation). Excellent linear correlations were obtained for plots of either peak height or peak area against the concentration of the compounds. Comparison was made between the results obtained from the analysis of three replicate samples of gasoline-contaminated ground water by the high speed GC, by two field-portable GCs, and by a laboratorybased GC. It is worthy of note that all the high speed GC analyses required for this study were accomplished in one day.