Splitless injections

Split injection Splitless injection On-column injection... 

There are three injection techniques for introducing a sample into a GC equipped with a capillary column split injection, splitless injection, and on-column injection. Split injection is the most often used injection technique. When a certain amount of FAME sample (1 to 3 ll) is introduced into the GC injector that is normally set at a temperature much higher than the boiling point of the solvent, the solvent vaporizes instantly in the carrier gas and creates a large volume of gas that contains all of the injected FAME in it. The carrier gas that contains the FAME is then divided into two streams from the injector one is directed onto the column, and the second is vented to the atmosphere, clearing the sample out of the injection chamber momentarily. This way, only a limited amount of sample is introduced into the column, to avoid column overloading, and injection time is short, to avoid peak broadening. 

Injection Splitless mode, 30 sec splitless period Gases Carrier gas (helium) inlet pressure 8 p.s.i.g. Split flow 1 50 mL/min ... 

Column Fused silica capillary column, Durabond DB-1 (0.1 xm film thickness), 30 m x 0.32 mm inner diameter (ID) (J. W. Scientific, Folsom, CA, USA). Injection Splitless mode (1 min) ... 

The three principal modes of operation are named split cold injection, splitless cold injection and injection with elimination of solvent. 

Co., Palo Alto, CA.) One rL of each extract was injected (splitless mode 30 s valve delay 200 0 injector temperature) into a capillary column (DB-wax or DB-Sms. 60 m length x 0.25 mm i.d. x 0.25 pm film thickness (d,) J W Scientific, Poison, CA). Helium was u.scd as carrier gas at a constant How rate of 0.96 mI7min. Oven temperature was programmed from 40 C to 200 0 at a rate of 3 Omin with initial and final hold times of 5 and 60 min, re.speclively. MSD conditions were as follows capillary direct interface temperature, 280 C ionization energy, 70 eV mass range, 33-350 a.in.u. BM voltage, 1956 (Atune + 200V) scan rate, 2.2 scans/s. Bach SDB or DE extract was analyzed in duplicate. 

Injection splitless split relay opened after 1.5 min. 

Split injection, splitless injection, SPME, headspace SPME, gas valve injection, tenax trapping with thermal desorption, purge and trap sampling... 

Chemical Analysis. The quantity of gas chromatographable organic compounds were determined as described previously (4, 5). For GC/MS analysis, a Finnigan model 4023 gas chromato-grapH/mass spectrometer and I NCOS data system were used to obtain 70 ev electron impact mass spectra of gas chromatographable compounds. A 25 m OV-101 quartz capillary column was used. Carrier gas was helium with a flow velocity of 30 cm/sec. The temperature program was 50 C for two minutes and then 5 per minute to 270 . The final temperature was held for 15 minutes. Samples were injected (splitless injection) in 1 uL of dichloromethane at a concentration of 2 yg per yL. 

Different sample introduction methods can be used in GC. If the sample is a liquid or a solid dissolved in an appropriate solvent, it may be introduced by a syringe into the injector. The choice of injection system depends on the column type and the sample composition. In packed columns, the sample is injected directly into the column inlet (Figure 2.3). In smaller inner diameter columns, split injection, splitless injection, and on-column injection techniques are used for liquid samples. 

Figure 25 Selected ion recording of QA-HFIP and [ 0]QA-HF iP at m/z 467 and 471. Sample, rat frontal cortex including the [ 0]QA internal standard. Conditions column, DB-5 (30 m X 0.25 mm i.d. column temperature, 95°C for 1 min 170°C, 30°C/min carrier gas, helium flow rate, not described sample injection, splitless injection mode. (From Ref. 68.)...

Figure 13 Gas chromatography-mass spectrometry TIC of the aromatic fraction of an Arabian crude oil. While the TIC of the whole oil yields a chromatographically unresolved "hump, this sample, which has had approximately 95% of the saturates removed by a fast silica SPE cleanup procedure, shows good resolution of the aromatic components, due to the fact that there are far more isomers at a given carbon number of saturates than aromatics. Conditions 100 mg oil deposited on 1-g silica SPE cartridge 2 ml pentane, followed by 2 ml ethyl ether. The ether fraction was partially evaporated and injected splitless into a Varian 3400 gas chromatograph (Varian, Palo Alto, CA) using a 100 m X 0.25 mm ID DB5-MS (0.1 pm film thickness) capillary GC column (special order fiom J W Scientific, Folsom, CA). Colutim temperature ramp 35 to 350°C at 2°C/mln. Mass spectrometer Finnigan (San Jose, CA) SSQ710 in 70-eV FI full-scan mode.

It is described in the Dutch test method that a first identification of the additives can be performed by determination of the gas-chromatographic retention times. Therefore we provide the retention times of the additives which could be analysed by GC. The GC analysis was carried out on a Perkin Elmer autosystera XL with the following conditions. The column was a Hewlett Packard Ultra 1 column. 50 m x 0.32 mm with a film thickness of 0.52 fim of crosslinked methylsiloxane. The temperature program was 5 min at SO C then raised at 5 C/min to 320"C and held for 26 min. The carrier gas was helium at 3.5 mL/min. The temperature of the injector was 260 C and injections of I firL of substance dissolved in dlethylether were injected splitless. The flame ionisation detector used was held at 325 C. Under these conditions the retention times of the hydrocarbon markers were 20.1, 38.5 and 45.2 min for C12, C20 and C24 respectively. Retention indexes of the reference substances can be calculated on basis of these retention times [12J. 

Split injection is used for volatile to semi-volatile compounds, and is one of the easiest injection techniques. With this technique, the flow of carrier gas is split between the capillary column and the atmosphere. This split does not occur in case of splitless injection. Splitless injection is used in case residual solvents remain in the sample at low eon-centrations, due to increased sensitivity compared to split injection. Other possibilities of direct injection are on-column injection and Programmed Temperature Vaporisation (PTV) injection. Both techniques allow detection limits to achieve put levels but are large volxune injection techniques. In on-column injection systems, the sample is injected on a pre-colmnn and then the solvent is vented, leaving only the analytes to be injected on the coltunn. In PTV, after the sample injection, the solvent is evaporated at a low temperature in a packed chamber and then removed. This leaves the solutes on the packing. When the injection port is heated the analytes are transferred to the analytical column. ... 

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