Splitless injection of large volumes of aqueous samples – A basic feasibility study

Experiments with splitless injection of large volumes of aqueous samples by the overflow technique have shown that an organic co-solvent is necessary to help the packing material (Tenax) retain the liquid. With 25–30% propanol or 15–20% 2-butoxyethanol, some 800 μl can be injected into a 5 mm i.d. liner. The application of the method is restricted to components eluting above ca 200 °C.     

Splitless injection of large volumes of aqueous samples: Further experience. Experiments on analyzing triazines by direct injection of drinking water

Conditions were optimized for the introduction of large volumes of drinking water by splitless injection with vapor overflow, experimenting with the determination of triazines. No co-solvent was added, and the maximum injection volume was 400 μl. A vapor outlet beyond a coated precolumn was used to discharge water vapors released belatedly from the packing. Using alkali flame ionization detection (AFID), detection limits were around 0.5 μg/l.     

Direct injection of large sample volumes into capillary columns with packed column injector

A direct injection method for large volume samples which avoids severe tailing of the solvent peak has been developed using a packed column injector (up to 100 μl) leading into an ordinary capillary column (0.3 mm i.d.). Modifications are made to the cooler zones of the inlet port and on the carrier gas flow control system. This injection technique is based on the effective use of phase soaking and cold trapping using a retention gap. The large volume of solvent vapor is rapidly purged out of the injector with a higher flow of carrier gas while the solutes trapped at the head of the column are subsequently analyzed with another optimum flow rate. The proposed carrier gas flow regulation system is also compared with conventional split/splitless injection methods.     

Splitless injection of up to hundreds of microliters of liquid samples in capillary GC: Part II,experimental results

Sample evaporation in splitless injection of large volumes is rapid: depending on the experiment, results indicate that 200 μl of hexane, for instance, evaporates in 2–10 s, producing vapor at a rate of many hundreds of milliliters per minute. A 60 × 4 mm packed bed of 20–35 mesh Tenax TA enabled injection of 200 μl volumes of all solvents tested, and even 1 ml injections were possible provided they were performed over a period of 30 s. Retention of volatile sample components depends on the sample solvent, the injection volume, and the injection speed, but only little on the injector temperature. Losses of n-tridecane varied from hardly 15 % (when dissolved in pentane) to ca 60 % (ethyl acetate); losses of n-heptadecane were usually below 20 %. The column temperature during injection should be at least ca 20–30°C above the standard solvent boiling point.     

Splitless injection of up to hundreds of microliters of liquid samples in capillary GC: Part 1, concept

If a sample evaporates by flash vaporization in an empty injector insert, the solute material is well mixed with the expanding solvent vapors and the maximum injection volume is determined by the requirement that no vapors must leave the vaporizing chamber. If evaporation occurs from a surface (e.g., of Tenax packing), however, the solvent evaporates first. The site of evaporation is cooled to the solvent's boiling point, and the cool island formed in the hot injector retains solutes of at least intermediate boiling point (visually observed for perylene). Solvent vapors, free from such solutes, may now expand backwards from the injector insert and leave through the septum purge exit. When solvent evaporation is complete, the site of evaporation warms up, causing the high boiling solutes to evaporate and to be carried into the column by the carrier gas. The technique somewhat resembles PTV injection, but is performed using a classical vaporizing injector.     

The effects of inlet liner configuration and septum purge flow rate on discrimination in splitless injection

An unmodified split/splitless inlet system using forward-pressure controlled pneumatics was operated in splitless injection mode with several inlet liners under a range of septum purge flow rates. The relative recovery (discrimination) of hydrocarbons ranging from n-C₈ to n-C₂₀ depended strongly upon the injected sample volume with open-ended liners at high septum purge flow rates of e.g. 50 mL/min. Little or no discrimination was observed at septum purge flows of 2–3 mL/min. The same inlet was also operated in a back-pressure regulated configuration that produced mass discrimination similar to that observed with the higher septum purge flows in the forward-pressure configuration. An inlet liner with a restricted inlet and outlet gave mass-discrimination levels independent of septum purge flow rate, but in the reverse sense of that observed with open-ended liners. Preferential volatile-component losses out of the inlet liner to the septum purge vent are principally responsible for the observed mass discrimination with openended liners, while mass-dependent losses with doubly-restricted liners seem due to slow sample evaporation.     

PTV splitless injection of sample volumes up to 20 μl

PTV splitless injection cannot compete with on-column injection as far as simplicity, reliability, and accuracy of quantitative analysis is concerned. However, PTV splitless injection is attractive for trace analysis of samples containing high concentrations of involatile sample by-products. Maximum injection volumes are limited by the amount of liquid that can be retained within the PTV injector chamber and are around 20–30 μl injected at once. Solvent evaporation must be carried out in such a way that injector overflow is avoided.     

An automated large volume on-column injection technique for capillary gas chromatography

Automated large volume (25-200 μl) on-column injections into a gas chromatograph with a capillary column were successfully performed by coupling a retention gap technique with an air actuated rotary valve. The linearity, injection precision, and carryover were evaluated. Slight boiling point discrimination was observed. This technique is compatible with commonly used chromatographic detectors (FID, ECD, MS) and conditions, while requiring very little instrument modification. The work is directed at the eventual reduction of manpower and turnaround time for sample collection and extraction, and Kuderna-Danish concentration when dealing with methods similar to EPA 625.     

Optimization of conditions for high temprature capillarary gas chromatography using a split-mode programmable temprature vaporizing injection system

This paper discribes an investigation into the effects of various operating conditions applied in a PTV-based gas chromatographic system on the performance observed in high temperature analyses. The work comprises a combination of physical and chromatographic measurements, and conclusions are drawn as to the most effective way of using the equipment under evaluation.     

Assay of the nerve agent Soman in serum by capillary gas chromatography with nitrogen-phosphorus detection and splitless injection

Summary A procedure is described for the determination of the nerve agent Soman in serum. The nerve agent is separated from the serum on C₁₈ modified silica and then eluted with benzene. The concentrated sample, to which butylacetate is added, is injected splitless into a polyethylene glycol (CP Wax 57) coated fused silica column. Solvent trapping of the analytes occurs due to the added butyl-acetate. The detection is performed with a nitrogen-phosphorus detector (NPD). The determination limit of the method is 40 pg/ml.     

Capillary gas chromatography of tert-butyldimethlysilylamino acids with PTV injection

The programmable temperature vaporizing injector (PTV) has been used to study the effects of injection temperature and initial heating period on the FID response factors of TBDMS derivatives of 17 protein amino acids. The relative response factors were calculated for injection temperatures of 50°C, 90°C, 160°C, 220°C, and 260°C with different initial heating periods (1 s, 5 s, and 10 s) and the results compared with the values obtained for the calculated response factors obtained under classical split injection conditions (300°C, continuous). Except for expected peak broadening effects, the initial heating period does not seem to have significative effects on relative peak areas. The response to the derivatives of alanine, glycine, α-aminobutyric acid, valine, proline, methionine, cysteine, phenylalanine, asparagine, and arginine was only slightly affected by increasing the injection temperature whereas the response factors for the derivatives of serine, threonine, glutamic acid, lysine, histidine, tyrosine, and tryptophan were strongly dependent upon initial injection temperatures, decreasing rapidly at temperatures above 160°C. The cold split-splitless injection is clearly advantageous over the classical hot injection techniques for the analysis of this type of aminoacid derivative.     

Flow of the carrier gas in open-tubular capillary columns in temperature-programmed gas chromatography

A second-order non-linear partial different equation was derived to describe the dependence of carrier gas pressure in the column on the column distance and the time under temperature programmed conditions. This equation was solved numerically by the modified finite difference method for various column parameters. Constant inlet and outlet pressures were used as boundary conditions. The retention times calculated on assumption of a constant pressure profile along the column. Significant differences between retention times of corresponding solutes calculated by the two methods were found, especially when relatively long columns(L>50m) with small internal diameter(d<0.3mm)and high temperature program rates (r>5°/min)are used.     

The variation of carrier gas viscosities with temperature

After describing simplified equations exspressing the temparature dependency of the viscosity of carrier gases (helium, nitrogen and hydrogen ) relative to a base value, absolute relationships based on the kinetic theory of gases are discussed. Comparative data obtained using various calculation methods are given and are compared to measured values. Based on the kinetic relationshipsm, of viscosity. Finally, the influence of pressure on the viscosity is also briefly discussed. As a supplement, Viscosity data are tabulated for the three gases in the range of 0°C to 400°C in increments of 2 K, calculated using the kinetic relationships.     

Selection of carrier gas velocity in the analysis of a multicomponent sample

Summary The selection of the average linear carrier gas velocity in the analysis of a multicomponent mixture under isothermal and programmed-temperature conditions is discussed. It is shown that one shouls always select a velocity which is at least equal but preferably higher than the optimum average gas velocity of the earliest peak at the initial column temperature.These symbols essentially correspond to those specified by the British Standard [6], ASTM [7] and IUPAC [8] GC nomenclastures.     

Multiresidue determination of thermolabile insecticides in cereal products by gas chromatography-mass spectrometry: evaluation with on-column injection and conventional hot splitless injection

This communication presents a study on the simultaneous determination of thermolabile N-methylcarbamate and organophosphorus insecticides in cereal products by gas chromatography-mass spectrometry. The thermal stability of the multiple insecticides was evaluated with conventional hot splitless injection and on-column injection. The results obtained by GC-MS with these two injection techniques were compared in terms of the recovery, the limit of detection, the limit of qualification, and the reproducibility. With on-column injection, the pesticide recoveries in cereal samples were better than 82%, with relative standard deviations lower than 5.4%. The limits of qualification for most insecticides were in the range of 0.009-0.08 mg/kg, i. e. lower than the maximum residue limits established for insecticides in cereal products by the European Union. The long-term stability using on-column injection for analysis of insecticides in real samples was evaluated and normal chromatographic performance could be obtained within 50 analyses. The results revealed that it was possible for application of on-column injection in the analysis of thermolabile multiple insecticides in food sample after comprehensive sample clean-up, despite the highly contaminated nature of the column system.