Large-volume Injection Technique Research Articles

Reply.

Arshinoff and Modabber5 call into question two assumptions of our mathematical model describing the residence times of moxifloxacin in the anterior segment with two different intracameral injection strategies.1 The authors of the letter agree with us on the underlying principle of our publication but disagree on the volume of the anterior chamber (AC) and the half-life of antibiotics. We selected two representative mean pseudophakic AC volumes (0.19 mL and 0.33 mL), substantiated by the literature,2,3 to demonstrate the principle that injecting the same dose of antibiotics (eg, 500 μg) into ACs with varying volumes produces varying concentrations of antibiotics within the total aqueous humor volume. The larger volume of 0.33 mL of Matsuura was derived from aqueous humor sampling immediately after intracameral injection in humans, before any possible fibrosis of the capsule. Libre and Mathews4 also agree with this volume. Arshinoff and Modabber's5 estimation of 0.5 mL is based on a mean phakic AC volume in the human eye of 0.25 mL; however, measurements of the AC volume in the elderly phakic eye average only 0.15 mL.6,7 With this experimentally derived volume, Arshinoff's estimation of the mean pseudophakic aqueous volume would be 0.4 mL, close to Matsuura and Libre's reported value of 0.33 mL. The AC size is known to vary from patient to patient, which cataract surgeons recognize when operating on smaller eyes and myopic eyes with longer axial lengths and larger chambers. Therefore, attempting to replace the aqueous contents with an antibiotic solution of known concentration will achieve the more consistent final concentration of drug, irrespective of the patient's pseudophakic AC volume. This same principle would have been demonstrated had we chosen two different AC volumes. There is a wide variation in the reported half-life elimination of antibiotics in the AC. Generally speaking, interdrug variation in elimination times, especially in the eye, may be due to factors such as differences in the drug molecular size, tissue binding, active pump mechanisms, and obstructions or reductions to outflow and drug elimination. Asena obtained antibiotic half-lives between 1.2 hours and 13 hours in rabbits, depending on which time points were used8; Lipnitzki et al.9 found between 0.64 hours and 1.8 hours in rabbits. Matsuura et al.3,10 demonstrated a half-life in rabbits and humans that averaged 1.2 hours over most time points. We chose 1.2 hours as it agrees with the 1% per minute aqueous turnover rate noted by Goel et al.11 The varied measures of the intradrug half-life elimination time of moxifloxacin and other antibiotics in the AC may be due to imprecision in injection and sampling techniques, pharmacokinetics that are not single compartment, and variations in individual subject anatomy and physiology. We would caution against the speculation of postantibiotic effects in regard to half-life because efficacy should be related to the target microorganism.12 Furthermore, principles that apply to the multidose administration of antibiotics in the treatment of systemic infections should not be presumptively applied to the scenario of single-dose intraocular injection without empirical evidence. Our study used two different and substantiated aqueous volumes and demonstrated that injecting small volumes of an agent can result in unequal final drug concentrations in the AC. Given the patient-to-patient variations, the “flushing” or large-volume injection technique should offer some degree of standardization and assurance of a more uniform final drug concentration in the pseudophakic AC as compared with smaller-volume–injected aliquots, thereby minimizing the interpatient variable of AC volume differences during cataract surgery.

Deep eutectic solvent magnetic bucky gels in developing dispersive solid phase extraction: Application for ultra trace analysis of organochlorine pesticides by GC-micro ECD using a large-volume injection technique

Novel deep eutectic solvent (DES) magnetic bucky gels (MBG) were formed by choline chloride/urea deep eutectic solvent and magnetic multi-walled carbon nanotube nanocomposite (MMWCNT) and were used in developing dispersive solid-phase extraction (dSPE) method. The hydrophilic DES based MBGs were developed with the features of magnetic susceptibility to permit fast injection of sorbent into the aqueous sample, rapid retrieval of the sorbent, high dispersion of MWCNT in water and compatibility with GC. In this work we investigated the application of DESs as a new class of carriers for CNT based nanofluids. In this gel DES acts simultaneously as a carrier and stabilizer for MMWCNT nanoparticles. By combining the MWCNT nanocomposite and DES, a highly stable (stability against sedimentation) viscous magnetic bucky gel or soft material was prepared without any additional stabilizer. This gel possesses fluidity, stability, magnetic properties and the unique strong sorbing properties of MWCNT simultaneously. We used the advantages of this magnetic DES based soft material in developing a new DES magnetic bucky gel based dispersive solid phase extraction. By coupling this method with GC- micro ECD and using large-volume-injection technique we achieved low LOD values which is a necessity in the ultra trace analysis of organochlorine pesticides (OCPs) in environmental water samples. Under the optimized conditions, the enrichment factors were in the range of 270–340. The limits of detection were between 0.04 and 0.27ng/L and the relative standard deviations were <10%. This method was successfully used for the determination of OCPs with good reproducibility and recovery.

Problemas en el análisis de metilsiloxanos volátiles (VMS): origen y soluciones

Volatile methylsiloxanes (VMS) are pollutants widely distributed in the environment due to its extensive uses and high volatility. The analysis of these compounds is commounly performed by gas chromatography - mass spectrometry (GC-MS), and it is dificult due to the presence of background contamination and volatile losses. Different preconcentration techniques such as purge and trap (P&T), headspace (HS) and headspace - solid phase microextraccion (HS-SPME) have been applied for the analysis of VMS in environmental samples. Alternatively, solvent extraction combined with large volume injection techniques has been an effective method for the analysis of complex matrices (eg. wastewater, sludges). In this review, the efficiency of the different methods reported for the analysis of VMS is discussed, and different solutions are proposed to minimize background contamination and volatilization.

Multi-Pesticide Analysis in Sediment by GC-EI-MS/MS Using Programmed Temperature Vaporization–Large Volume Injection Technique

A sensitive, selective and high throughput gas chromatography–tandem mass spectrometry method using programmable temperature vaporization–large volume injection mode (PTV-LVI-GC-MS/MS) for the analysis of 30 organochlorine pesticides (OCPs) including toxaphenes in sediments was developed. The PTV-LV injection settings, viz. inlet temperature, split flow, injection phase time, and injection speed were optimized for 50 µL injection. A significant increase in sensitivity was accomplished as compared with that obtained by the conventional 1 µL cold splitless injection. Average LVI recoveries for OCPs were in the range 58–133 % with low % RSD in instrument precision (<12 %). The method detection limits achieved were 0.04–0.92 µg kg−1. The method recovery ranged from 80 to 120 % with <10 % RSD for more than 83 % of targeted analytes fortified at 10 µg kg−1 in sediments. The PTV-LVI-GC-MS/MS allows simultaneous determination and unambiguous confirmation of trace OCPs and toxaphene congeners, which significantly streamlines and improves the trace organic analysis in the environmental surveillance and monitoring.

Possibility of Large Volume Injection and Band Focusing in UHPLC

New shell-type stationary phases are widely used in fast chromatographic measurements. These columns provide more efficient separation, when applied in a conventional high-performance liquid chromatography instrument, than columns with fully porous particles, and the volume overload of core-shell particles is 60% of the value obtained for fully porous particles. Additionally, to achieve adequate sensitivity, the injection volume cannot be significantly decreased. This study presents a systematic evaluation of the possibilities of large volume injection onto columns packed with 2.6 µm Kinetex C18 shell particles. The effect of volume overload on performance of columns with different lengths (50, 100 and 150 mm) is studied. Column efficiency is compared under isocratic, pulse gradient and gradient conditions. The application of large volume injection in practice is also reported. The most suitable among the tested large volume injection techniques was the gradient elution, which was applied to determine amino acid enantiomers from fruit juice.

Applications of large-volume injection for environmental analysis

Large-volume injection (LVI) in capillary gas chromatography (CGC) was developed for determining the trace components in environmental samples and for reducing (or even eliminating) the need for cleanup step, also for on-line connection of liquid chromatography (LC) with CGC. The key features of the LVI include sample retained by a large capacity volume liner or a retention gap, and solvent vapor eliminated by solvent vapor exit. There are many kinds of LVI techniques for different analyses, capillary columns and purposes. This review summarizes the recent developments of LVI for environmental analysis, include on column injection (OCI), programmed temperature vaporizer (PTV), AT-column, direct sample introduction/difficult matrix injection, concurrent solvent recondensation large volume splitless injection, and also through oven transfer adsorption desorption interface for on-line connection of LC with CGC.

Analysis of polycyclic aromatic hydrocarbons extracted from air particulate matter using a temperature programmable injector coupled to GC–C–IRMS†

Compound specific isotopic analysis (CSIA) can provide information about the origin of analysed compounds – in this case, polycyclic aromatic hydrocarbons (PAHs). In the study, PAHs were extracted from three dust samples: winter and summer filter dust and tunnel dust. The measurement was performed using the method validated in our laboratory using pure, solid compounds and EPA 610 reference assortment. CSIA required an appropriate clean-up method to avoid an unresolved complex in the gas chromatographic analysis usually found in the chromatography of PAHs. Extensive sample clean-up for this particular matrix was found to be necessary to obtain good gas chromatography–combustion–isotope ratio mass spectrometry analysis results. The sample purification method included two steps in which the sample is cleaned up and the aliphatic and aromatic hydrocarbons are separated. The concentration of PAHs in the measured samples was low; so a large volume injection technique (100 μl) was applied. The δVPDB 13C was measured with a final uncertainty smaller than 1 ‰. Comparison of the δVPDB 13C signatures of PAHs extracted from different dust samples was feasible with this method and, doing so, significant differences were observed.

Comprehensive gas chromatography with Time of Flight MS and large volume introduction for the detection of fluoride-induced regenerated nerve agent in biological samples

Recently, several methods have been developed to verify exposure to nerve agents. Most of these methods, such as the fluoride reactivation technique and the analysis of inhibited phosphonylated butyrylcholinesterase (BuChE), are based on mass spectrometry. The high specificity of the mass spectrometer might also imply a disadvantage, because the acquisition mass, i.e. the identity of the analyte must be known beforehand in order to direct the MS analysis in the most sensitive mode. In real cases, the identity of the nerve agent is not always known beforehand and the mass spectrometer should be operated in a scanning mode, with the consequence that sensitivity of the method will be lower. Comprehensive GC, or GC × GC, is a technique which offers enhanced separation. The implied larger selectivity of the GC separation allows mass spectrometry to be conducted in a less specific, scanning, mode. By the use of this configuration, the identity of the nerve agent does not have to be known beforehand but can be traced. In order to be able to detect lower concentrations and assess lower exposure levels, a large volume injection technique was developed allowing sample sizes up to 100 μL. The technique was tested with plasma samples that had been inhibited with various nerve agents. Subsequently, the cholinesterase-bound nerve agent was regenerated by the fluoride reactivation technique. Using the newly developed comprehensive GC–MS method it was possible to detect nerve agent at an exposure level of 1% BuChE inhibition, which is approximately 70 pg nerve agent/mL. These low exposure levels cannot be verified with a cholinesterase (ChE) activity assay. Moreover, the identity of the regenerated nerve agent was verified by the mass spectrum that was generated by the TOF mass spectrometer. This paper presents a technique able to deliver full-scan data on the analysis of nerve agents in biomedical samples at relevant exposure levels (1% BuChE inhibition). This full-scan data meets for a large part the forensic requirements that are in place for the analysis of biomedical samples in the context of alleged use of Chemical Warfare Agents.

Analysis of part-per-billion level of arsine and phosphine in light hydrocarbons by capillary flow technology and dielectric barrier discharge detector

A practical gas chromatographic procedure has been developed and implemented for the measurement of arsine and phosphine in hydrocarbons such as propylene at the part-per-billion level. The successful measurement of arsine and phosphine at the level mentioned was attained by incorporating a large volume injection technique to increase the mass of solutes delivered for sensitivity improvement, capillary flow technology to keep the matrix from entering the detector by either back-flushing through the inlet vent, or by heart-cutting if required, and dielectric barrier discharge detector operating in argon mode for sensitivity enhancement, as well as offering improved selectivity towards the solutes cited. Using the technique described a complete analysis can be conducted in less than 4 min. A relative standard precision of less than 1.7% was achieved with repeated injections at the concentration level of 25 and 125 ppb (v/v) each of arsine and phosphine in nitrogen with a practical detection limit at the 5 ppb (v/v) level. Correlation coefficients of greater than 0.9999 were obtained for arsine and phosphine over a range from 10 to 2500 ppb (v/v). The analytical methodology was proven to be reliable in continuous operation during the first 6 months of deployment.

Determination of Trace Levels of Bromate in Flour and Related Foods by Ion Chromatography

In this paper, a method of determining trace levels of bromate in flour and related foods by ion chromatography with large volume injection has been proposed. The detection of bromate was performed with a suppressed conductivity detector after separation on an IonPac AS19 column with KOH as the gradient eluent. Parameters affecting the extraction efficiency of bromate, such as the flour-to-water ratio, extraction time, and temperature, were studied in detail. The optimized pretreatment process was then selected. By using the large volume injection technique, the solution detection limit was decreased to 0.5 microg/L. The linear range of this method was from 5 to 1000 microg/L, and the linear correlation coefficient was 0.9998. The method has been applied to the detection of bromate in flour and related foods, and different concentration levels of bromate were detected in various samples. The spiked recoveries ranged from 86 to 110%. The relative standard deviation (RSD) of the bromate peak height for the seven successive injections of the flour sample was 6.4%.

Optimisation of a programmed split–splitless injector in the gas chromatographic–mass spectrometric determination of organochlorine pesticides

Large-volume injection techniques in gas chromatography are used to compensate for the at times limited detection sensitivity of mass spectrometric detection. In this work a programmed split–splitless injector in solvent split mode was employed to determine organochlorine pesticides in environmental samples. The injection conditions were selected by a Plackett-Burman design followed by a central composite design. The LODs obtained in the optimum conditions were compared with those obtained with splitless-MS and splitless-ECD. Finally, the method was applied to a soil sample.

Determination of polybrominated diphenyl ethers and polychlorinated biphenyls in human adipose tissue by large-volume injection-narrow-bore capillary gas chromatography/electron impact low-resolution mass spectrometry.

A new analytical method has been developed for the quantification of polybrominated diphenyl ethers (PBDEs) in human adipose tissue samples. After Soxhlet extraction and a cleanup procedure using two successive solid-phase extraction cartridges containing acid silica and acid silica: neutral silica:deactivated basic alumina (from top to bottom), detection can been achieved by narrow-bore (0.10-mm i.d.) capillary gas chromatography/electron impact low-resolution mass spectrometry using a large-volume injection technique. Using narrow-bore capillaries, it is possible to analyze complex mixtures in a short time (up to 10 min), saving 50% or more of the analysis time of conventional columns while maintaining a similar resolution power. The method allows the determination of five major PBDE congeners (BDE 28, 47, 99, 100, and 153) at concentrations below 1 ng/g lipid weight. Detection limits in the selected ion mode varied between 0.05 and 0.30 ng/g lipid weight, depending on the degree of bromination. The sensitivity of this method can compete with low-resolution mass spectrometry with electron capture ionization, while a much better selectivity is obtained. Levels of PBDEs in 20 Belgian human adipose tissue samples ranged between 2.18 and 11.70 ng/g lipid weight and were similar to previously reported values from Europe.

Quantitative analysis of aroma compounds in carrot (Daucus carota L.) cultivars by capillary gas chromatography using large-volume injection technique.

Dynamic headspace sampling was used to collect aroma compounds from raw samples of four carrot (Daucus carota L.) cultivars (Brasilia, Duke, Fancy, and Cortez). The collected volatiles were analyzed by capillary GC-FID and GC-MS using large-volume cool on-column injection (LVI-COC). Of the 36 compounds identified, 6 had not been previously detected in carrots. Significant differences between the carrot cultivars were found for 31 of the identified volatiles as well as for total monoterpenes, sesquiterpenes, and total volatile content. Mono- and sesquiterpenes accounted for about 98% of the total volatile mass in all cultivars. LVI-COC injection was used to determine the loss of carrot volatiles during concentration of headspace samples under a stream of nitrogen. The loss among major monoterpenes in the concentrated samples varied from 16% for p-cymene to >40% for alpha-pinene as compared to nonconcentrated samples. The loss among high-boiling sesquiterpenes varied from not detectable (beta-caryophyllene, alpha-humulene, and caryophyllene oxide) to approximately 7% for (E)- and (Z)-gamma-bisabolene.

Simultaneous Determination of Acidic and Basic-Neutral Pesticides in Water at ppt Concentration Level by Ion-Interaction Micro-HPLC/MS

A new ion-interaction micro-HPLC method, for the simultaneous separation of acidic and base-neutral pesticides, was coupled to a capillary-scale particle beam LC/MS interface for EI mass spectrometric detection of the analytes. The method was employed for analysis of tap water in which a large number of functionally different pesticides can be determined in a single run. Capillary-scale technology of the LC/MS apparatus yields full compatibility with hexylammonium phosphate, a nonvolatile salt used as ion-interaction reagent in the HPLC mobile phase, and provides an excellent sensitivity with instrument detection limits (IDLs) ranging between 0.07 and 0.7 ng in SIM mode. Method sensitivity lower than 0.1 ppb in water was achieved using a large-volume injection technique specifically developed for capillary columns typical flow rates.

Determination of selected microbial volatile organic compounds by diffusive sampling and dual-column capillary GC-FID--a new feasible approach for the detection of an exposure to indoor mould fungi?

A new, analytically valid procedure is described to assess the exposure of human beings to the so-called microbial volatile organic compounds (MVOCs) in air. The method can be used routinely for large sample numbers and is especially valuable as a basis for further research on the correlation between single MVOCs and indoor mould growth. The procedure is based on the fact that fungi produce a variety of volatile organic compounds, such as 3-methylbutan-1-ol, 3-methylbutan-2-ol, fenchone, heptan-2-one, hexan-2-one, octan-3-one, octan-3-ol, pentan-2-ol, alpha-terpineol, and thujopsene, which they emit into the indoor environment. Using diffusive samplers, these MVOCs are adsorbed onto charcoal during a sampling interval of four weeks. The described method is thus superior to existing methods which use short-term active sampling. After desorption with carbon disulfide, the MVOCs were determined by dual-column gas chromatography with flame ionization detection using the large-volume injection technique for sample introduction. The detection limits ranged between 0.15 and 0.53 microgram m-3, within-series precision was found to range between 6.5 and 19.0%, and recovery was between 77 and 118%. The procedure has been successfully applied in the context of a large field study to measure the indoor MVOC exposure in children's rooms of 132 dwellings. The objective of the study was to examine the relation between indoor mould growth, the indoor MVOC exposure and the prevalence of adverse health effects. Information about mould formation has been obtained by a questionnaire and by the determination of colony forming units of mould fungi in mattress dust. With the exception of 3-methylbutan-2-ol, fenchone, nonan-2-one, octan-2-one, and thujopsene, indoor air concentrations of all MVOCs under investigation were significantly higher inside damp and mouldy dwellings. From the primary MVOCs under investigation, 3-methylbutan-1-ol, hexan-2-one, heptan-2-one, and octan-3-ol were found to be most reliable indicators for mould formation. A correlation was also found between selected MVOCs and the occurrence of mould species in mattress dust. Aspergillus sp. correlated with heptan-2-one, hexan-2-one, octan-3-ol, octan-3-one, and alpha-terpineol, while the occurrence of Eurotium sp. was correlated with higher indoor air concentrations of 3-methylbutan-1-ol, 3-methylbutan-2-ol, heptan-2-one, hexan-2-one, octan-3-ol, and thujopsene. Children living in dwellings with elevated MVOC levels had a higher prevalence of asthma, hay fever, wheezing, and irritations of the eyes. These positive associations persisted after controlling for confounding factors such as age, sex, body-mass index, number of siblings, social status, passive smoking, type of heating, and ventilation habits. However, they were not statistically significant. This lack of significance may be a result of the small number of investigated samples.

Analysis of nonylphenol polyethoxylates and their degradation products in river water and sewage effluent by gas chromatography–ion trap (tandem) mass spectrometry with electron impact and chemical ionization

A method is presented for the analysis of nonylphenol polyethoxylate (NPEO) residues and their degradation products, nonylphenol polyethoxy carboxylates and carboxyalkylphenol ethoxy carboxylates, in the samples of river water and sewage effluent. The method involves extraction of the samples by graphitized carbon black (GCB) cartridge, propylation by a propanol/acetyl chloride derivatization procedure, and separation, identification and quantitation by ion-trap GC–MS with electron impact ionization (EI), liquid-chemical ionization (CI) and CI-MS–MS modes. The large-volume injection technique provides high precision and sensitivity for both NPEO residues and their degradation products, to quantitation at ≥0.01 μg/l in 100 ml of water samples. Dicarboxylic acids of NPEO residues were identified by the CI-MS–MS technique with relatively high concentrations in the samples of river water and sewage effluent. Recovery of nonylphenol and octylphenoxyacetic acid in spiked water samples ranged from 81 to 107%. Relative standard deviations of replicate analyses ranged from 2 to 12%.

HPLC Analysis of Asulam in Water Using an On-Line Solid-Phase Extraction Technique.

HPLC using a large-volume injection technique has been developed to determine trace levels of pesticides in water. To prevent disturbance of the base line from excess water injected, a reversed-phase guard cartridge is substituted for an injection loop as an enrichment column. This procedure is applied to Asulam, N'-methoxycarbonyl sulfanylamide, one of the herbicides used in golf links. One milliliter of sample made up in a solution of 0.5 mM in cetyltrimethylammonium chloride is passed through the cartridge, where Asulam is trapped quantitatively. Asulam is then back flushed from the cartridge onto an analytical column, where the separation is achieved. Asulam below ppb level can be readily detected. The precision of the measurements, evaluated by the analysis of spiked samples, is 3.3% at 1 ppb level.

A comparative study of large volume injection techniques for microbore columns in HPLC

This paper focuses attention on the potentially larger signal-to-noise ratios produced by microbore columns in comparison with conventional columns. The increased chromatographic signals by the application of microbore columns are due to the lower chromatographic dilution of elution profiles which are proportional to the square of the column inner radius. Generally less than 1μl sample should be injected into microbore systems to obtain the full benefit of the column performance. However, since more sample can be loaded on conventional columns compared to microbore columns the advantage of improved signal-to-noise ratio can only be realised in situations where very little sample is available. To inject more than 1μl sample, at the same time avoiding extra band-broadening effects, suitable injection techniques must be available. In this study three injection methods for microbore systems that meet this condition, are studied and compared.