Injector repeatability

System suitability specifications and tests, Capacity factor (k ), Preci-sion/injector repeatability (RSD), Relative retention (a), Resolution (Rs),Tailing factor (T),Theoretical plate number (N)... 

It should be noted that the tests and specifications listed in Table 7 are provided for guidance and should be set for each individual method based on its application and performance. For example, there may be no resolution requirement for an HPLC dissolution assay. For the same method, it may also be impractical to set the injector repeatability requirement at an RSD of < 1% if the peak response for the API is very small. Again, in the same example it is also impractical to require a check standard to be within 1% of the working standard if the RSD requirement for replicate analyses of the working standard is <2 %. Some ion exchange columns may not provide plate counts of > 2000 or tailing factors of < 2. 

Consider two wells in an infinite, isotropic, homogeneous reservoir, with both having identical volume flow rates. Sketch the streamline pattern when (i) both are producers, and (ii) one is a producer while the other is an injector. Repeat this exercise when the volume flow rates are different. Identify all symmetries that you observe. How would you use this information to simplify the numerical modeling of petroleum reservoirs ... 

Injections using the MARK I kit injectors (or atropine only if directed by the local physician) may be repeated at 5 to 20 minute intervals if signs and symptoms are progressing until three series of injections have been administered. No more injections will be given unless directed by medical personnel. In addition, a record will maintained of all injections given. 

Internal purge gas was again diverted through the reaction cell, which was emptied and rinsed with doubly distilled water. The sodium borohydride solution was withdrawn from the injector tip by reversing the direction of the peristaltic pump. The next sample aliquot was then added to the cell and the measurement process repeated. Replicate measurements could be made every 3-4min. 

Injection samples need to be as concentrated as possible and this leads to problems. A column acts as a sample concentrator. If the solution starts out saturated, it will supersaturate on the column, precipitate, and plug the column. I have seen a column with a 3-cm-deep plug that had to be bored out with a drill bit and a spatula. A couple of injector loops full of the stronger solvent in a mixed mobile phase will clear this if there is still some flow, but the separation will have to be repeated. It is better to dissolve the compound, then add a half volume of additional solvent, ensuring that there will be no precipitation on injection. 

Typically splitless injection is used for trace analysis by capillary GC. Splitless injections can exhibit problems with carryover, poor repeatability, and labile analytes. Penton (1991) reports improved results with the temperature-programmable injector. With a temperature-programmable injector, samples are injected into a glass insert at an injector temperature below the boiling point of the analysis solvent the injector temperature is then rapidly programmed to a higher value. Penton reported this technique offered greater ease of optimization and improved precision. 

In the fiber mode, the sorbent coated fiber is housed in a microsyringelike protective holder. With the fiber retracted inside the syringe needle, the needle is used to pierce the septum of the sample vial. The plunger is depressed to expose the sorbent-coated fiber to the sample. After equilibrium is reached or at a specified time prior to reaching equilibrium, the fiber is retracted into the protection of the microsyringe needle and the needle is withdrawn from the sample. The sorbent is then interfaced with an analytical instrument where the analyte is desorbed thermally for GC or by solvents for HPLC or capillary electrophoresis. For the in-tube mode, a sample aliquot is repeatedly aspirated and dispensed into an internally coated capillary. An organic solvent desorbs the analyte and sweeps it into the injector [68,130,133]. An SPME autosampler has been introduced by Varian, Inc., that automates the entire process for GC analyses. 

FIGURE 4.14 Seven repeated injections (spaced 50 s) of air into the helium carrier flow using a chip with a cross-injector for GC analysis. Detection with capillary plasma detector using the 337-nm N2 band [563]. Reprinted with permission from the Royal Society of Chemistry. 

For contrast agent injection an MR compatible power injector should be used to ensure a high and reproducible injection rate. Injection rate should be at least 3 ml/s. Injection should be started parallel to the dynamic scan. This ensures a sufficient number of measurements for calculation of the pre-contrast baseline and guarantees that the whole first pass is comprised, if the scans are repeated for at least 1 min. 

The improvement in the resolution of a separation is a multiple of the square root of the number of plates which the sample encounters. Even if some band broadening occurs because the sample passes repeatedly through the pump, injector, or detector, it is still possible to attain a distinct separation, as demonstrated in the 14-pass recycle shown in Figure 6-11. 

It is used to eliminate or reduce weld lines. Two separate injectors or one injector with a splitting device are used to move melt in and out of the cavity from opposite sizes. This type action repeats and is programmed to maximize the best melt flow patterns. 

Because the internal standard method eliminates some of the errors found in the external standard method it does not automatically follow that the internal standard method should always be used. The precision of many LC external standard methods is very good (e.g. <0.4% RSD for a purity determination) given that (i) the repeatability of injection volumes in modern injectors is much better than it used to be, especially if the injection is automated and (b) there are many methods for which sample... 

The first outbreak of a disease in which a jet injector was imphcated as the vehicle of transmission has been reported. Thirty-one attendees at a weight-reduction clinic in Southern California experienced hepatitis B after daily parenteral injections of human chorionic gonadotrophin given by jet injectors transmission appeared to have resulted from the multiple repeated jet injections (85). WHO and UNICEF have stated in their Guidehnes for selecting injection equipment for the Expanded Program on Immunization that the use of jet injectors should be restricted to circumstances in which reusable or disposable equipment is not feasible because of the large number of persons to be immunized within a short period of time (83). 

Autosampler precision can be checked by replicate injections of a control sample, with wash injection intervals between every two sample injections. The repeatability of peak areas, mathematically expressed as RSD, is used as a criterion for autosampler precision. For example, when 10 consecutive injections of 10 pL of a solution are performed, the expected RSD for peak area precision ranges from 0.5% to 1.0%. Single injections of different volumes, such as 5, 10, 50, or 80 pL, can also be used, simultaneously checking the linearity of the injector, the detector, and the data system. Another approach to qualify the autosampler involves the gravimetric determination of the average volume of water per injection withdrawn from a tared vial after six 50-pL injections. The procedure... 

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