Injection, sample valve syringe

The basic difference between this type of valve and the normal external loop sample valve is the incorporation of an extra port at the front of the valve. This port allows the injection of a sample by a syringe directly into the front of the sample loop. Position (A) shows the load position. Injection in the front port causes the sample to flow into the sample loop. The tip of the needle passes through the rotor seal and, on... 

Sample injection system. Introduction of the sample is generally achieved in one of two ways, either by using syringe injection or through a sampling valve. 

Split vent. The sample vapors that do not enter the column are ejected through the split vent. A needle valve on this line regulates the total flow of carrier gas into and from the inlet, generating the split ratio, which determines the portion of sample that enters the column. The split ratio is the ratio of the split vent flow to the column flow and provides a measure of the amount of sample that actually enters the column from the injection. A split ratio of 100 1 indicates that a lpl injection from the syringe results in approximately 10 ml of liquid sample reaching the column. 

An HPTC injector allows the introduction of a precise sample volume onto the column. A typical manual injector consists of a 6-port valve with a rotor, a sample loop and a needle port (Eigure 9). A sample solution is introduced into the sample loop using a 22-gauge blunt tip syringe in the TOAD position. The sample is then injected into the column by switching the valve to INJECT. The typical external sample loop size ranges from 6 pT to 2 mT. For many years, the Rheodyne 7125 injector was the industry-standard. In the early 1990s, it was replaced by the Rheodyne 7725 injector, which injects samples without momentary flow disruptions. ... 

Inject sample (syringe pump off) and divert the Row to waste (path B) for the first 10-25% of the assay run time then switch the divert valve to send the eluant into the MS/MS system (path A) for the analysis of the sample. 

GAS SAMPLE VALVE. With all the problems associated with syringe injection of gas samples, it is not surprising that a more accurate way of injecting gas samples has been found. This system makes use of a gas sampling valve. There are a number of these valves on the market using either rotary or push-pull actuation and interchangeable volumes are standard. A schematic for a rotary valve is shown in Figure 4.15. In the load position the volume of the valve is connected to the in and out load ports. 

Fig. 9.6. Schematic representation of die BEST system (Brnker Biospin see also [21]). 1, Bottle with transport liquid 2, dilutor 402 single syringe (5mL) with 1100 iL tube 3, dilutor 402 3-way valve 4, sample loop (250-500 pL) 5, 6-way valve (standard version) loading sample 6, 6-way valve (standard version) injecting sample 7, injection port 8, XYZ needle 9, rack for sample vials 10, rack for recovering vials 11, rack for washing fluids and waste bottle (3 glass bottles) 12, external waste bottle 13, flow probe with inner lock container 14, inert gas pressure canister for drying process.

A simple method for the analysis of small volumes of gas from single-breath samples from humans was described by Zarling and Clapper (1987). Total breath samples were collected into a gas-tight bag and 50 ml aliquots withdrawn into polyethylene/polypropylene syringes. Alveolar breath samples collected by use of a Haldane-Priestly tube were also collected in this way. Gas samples were injected directly into the GLC via a gas-sampling valve. 

Sample injection in hplc is a more critical operation than in gc. Samples may be injected either by syringe or with a valve injector although the former is now rarely used. Valves, which can be used at pressures up to about 7 000 psi (500 bar), give very reproducible results for replicate injections (<0.2% relative precision) and are therefore ideal for quantitative work (p. 129). They consist of a stainless steel body and rotating central block into which are cut grooves to channel the mobile phase. from the pump to the column (figure 4.27). The sample is loaded into a stainless steel loop incorporated... 

Figure 11.24 Rheodyne Type SO mplc injection valve the vent (green). Thus with the solvent flow by-passing the load loop, sample can be injected from a syringe onto the loop, displacing any residual solvent out of the vent. On switching the valve clockwise to the alternative inject position, the solvent stream is diverted through the load loop, introducing the sample onto the column (Fig. 11.25).

A successful sampling valve is that due to Pratt and Purnell (Fig. 58) . A dead-space sample is first withdrawn, followed by a reacted sample. Cundall et claim a better valve is the push-pull type (Fig. 59), a variation of the valve used on some commercial glc instruments. For sample injections after fractionation, a constant volume and manometer is employed for gases, and precision microlitre syringes for liquids. 

Gas samples are injected by a gas-tight syringe or gas-sampling valve called a stream-splitter [Figure 13.4(b)]. In the simplest form, the stream-splitter is merely... 

Samples can be introduced manually into the valve with a syringe to fill the sample loop. Automated sampling valves are routinely used today in which samples are taken from an autosampler for unattended operation. The major limitation of valve injectors is that the sample size is fixed, and the loop must be changed in order to vary the injected sample size. There are automated motor-driven adjustable syringes that provide enough pressure to inject the sample past a check valve that prevents backflow. 

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