Dilute samples,injection

The simplest mode of IGC is the infinite dilution mode , effected when the adsorbing species is present at very low concentration in a non-adsorbing carrier gas. Under such conditions, the adsorption may be assumed to be sub-monolayer, and if one assumes in addition that the surface is energetically homogeneous with respect to the adsorption (often an acceptable assumption for dispersion-force-only adsorbates), the isotherm will be linear (Henry s Law), i.e. the amount adsorbed will be linearly dependent on the partial saturation of the gas. The proportionality factor is the adsorption equilibrium constant, which is the ratio of the volume of gas adsorbed per unit area of solid to its relative saturation in the carrier. The quantity measured experimentally is the relative retention volume, Vn, for a gas sample injected into the column. It is the volume of carrier gas required to completely elute the sample, relative to the amount required to elute a non-adsorbing probe, i.e. 

A stream of ethylene is fed into the reactor by use of quaternary LC pumps and subsequently dissolved in a 1.90 ml h toluene stream [1]. Ethylene is handled at 60 °C, well above the critical temperature. Catalyst additions are fed via HPLC-type sample injection valves. Various combinations of precatalysts and activators were sampled and loaded by an autoinjector. Catalyst solutions typically were diluted 20-fold within the micro reactor. 

The attractive features of spllti ess injection techniques are that they allow the analysis of dilute samples without preconcentration (trace analysis) and the analysis of dirty samples, since the injector is easily dismantled for cleaning. Success with individual samples, however, depends on the selection of experimental variables of which the most Important sample... 

Sample preparation, injection, calibration, and data collection, must be automated for process analysis. Methods used for flow injection analysis (FLA) are also useful for reliable sampling for process LC systems.1 Dynamic dilution is a technique that is used extensively in FIA.13 In this technique, sample from a loop or slot of a valve is diluted as it is transferred to a HPLC injection valve for analysis. As the diluted sample plug passes through the HPLC valve it is switched and the sample is injected onto the HPLC column for separation. The sample transfer time typically is determined with a refractive index detector and valve switching, which can be controlled by an integrator or computer. The transfer time is very reproducible. Calibration is typically done by external standardization using normalization by response factor. Internal standardization has also been used. To detect upsets or for process optimization, absolute numbers are not always needed. An alternative to... 

Solvent venting, without splitting Liquid sample from syringe into cold inlet. Solvent is vented at low temperature, condensing nonvolatiles. Heat programming subsequently vaporises the residues, which enter column as in splitless injection Dilute samples thermally labile Broad, some focusing required 1-1000 80-95... 

In ESMS (Figure 11.2), a dilute solution of the analyte is pumped through the capillary at a flow rate of typically 0.1 to lOpl/min. A high voltage (typically 2-5 kV) is applied to a narrow bore sample injection tube (capillary) relative to its surrounding, which generally includes a counter electrode that is... 

Animal infectivity methods Some viruses do not cause recognizable effects in cell cultures but cause death in the whole animal. In such cases, quantification can only be done by some sort of titration in infected animals. The general procedure is to carry out a serial dilution of the unknown sample, generally at ten-fold dilutions, and samples of each dilution are injected into numbers of sensitive animals. After a suitable incubation period, the fraction of dead and live animals at each dilution is tabulated and an end point dilution is calculated. This is the dilution at which, for example, half of the injected animals die. Although such serial dilution methods are much more cumbersome and much less accurate than cell culture methods, they may be essential for the study of certain types of viruses. 

Aqueous simulants — HPLC with UV detection. Olive oil extracted with dilute sodium hydrogen carbonate and the aqueous extract acidified and examined by HPLC Headspace GC with automated sample injection and specific nitrogen detector. Confirmation by GC-MS if required Headspace GC of the polymer dissolved in N,N-dimethylacetamide. 

The linearity of the detector can be obtained by diluting the analyte stock solution and measuring the associated responses, while the linearity of the analytical method can be determined by making a series of concentrations of the analyte from independent sample preparations (weighing and spiking) [15]. It is also essential that the basic calibration linear curve be obtained by using independent samples, and not by using samples that have been prepared by dilution and injected into HPLC/GC, or spotted on one TLC plate. 

Column diameter is an important parameter to consider in life science applications in which sample amounts are very limited and the components of interest may not be abundant. Researchers have reviewed micro HPLC instrumentation and its advantages.910 Nano LC-MS offers 1000- to 34,000-time reductions in the dilution of a sample molecular zone eluted from nano LC columns of 25 to 150 [Mi IDs in comparison to a 4.6 mm ID column. This represents a large enhancement of ion counts in comparison to counts obtained for the same amount of sample injected into a conventional 4.6 mm column. Solvent consumption for an analysis run or sample amount required for injection in a nano LC application may be reduced 1000 to 34,000 times compared to amounts required by an analytical column operated at a 1 mL/min flow rate. 

Ponceau 4R, E-124 and Erythrosine, E-127) using a buffered mobile phase. Separation of dyes was performed in an ODS column (150 X 3.9 mm i.d. particle size 3 pm). Components of the mobile phase were methanol (eluent A) and 0.1 M NaH2P04/Na2HP04 buffer (pH = 7). The gradient elution started with 20 per cent A and reached 100 per cent in 2 min, final hold 4 min. The flow rate was 2 ml/min and dyes were detected at 520 nm. The baseline separation of dyes in 6 min is illustrated in Fig. 3.34. Commercial samples were diluted and injected into the analytical column without any pretreatment. The amounts of dyes found in the samples are compiled in Table 3.20. It was concluded from the good validation parameters that the technique is specific, sensitive, accurate and rapid. Consequently, its application for the determination of these synthetic dyes in drinks was proposed [112],... 

Chiral or achiral assay and purity determinations are done according to an external calibration calculation procedure, either with or without internal standardization. The calibration is performed against a 10% w/w (compared to the nominal concentration of the sample solution at 100% w/w) reference standard solution. The sample solution for the purity determination remains at the 100% w/w level, while that of the assay determination is diluted 10 times. The reason for the difference in concentration levels is similar to the purity method. A suggested sample injection sequence can be... 

The manual procedure for determination of total nitrogen by chemiluminescence involves preparing the standards from a stock solution, diluting the samples, injecting the standards into the combustion furnace for analysis, and calculation of the nitrogen content of the samples. The calculation is based on the signal from the diluted sample compared to the standard curve and the dilution factor for the sample. 

Sugars were estimated by using a Beckman 344 gradient high-pressure liquid chromatograph with an Altex 156 refractive index detector and a Spherogel 7.5% carbohydrate column with a flow rate of 0.5 ml/min in the mobile phase of water at 80 C. The sugar samples were appropriately diluted before injection. 

Filtration injection of sample directly dilution and injection elution from reverse-phase HPLC column with methanol/water... 

Inject the diluted sample solution into the HPLC system. Replicates of the sample preparation and of the injection of the sample in HPLC may be carried out sample preparation procedures are more likely to give rise to imprecision than instrumental variation. 

Carryover. Small amounts of analyte may get carried over from the previous injection and contaminate the next sample to be injected [10]. The carryover will affect the accurate quantitation of the subsequent sample. The problem is more serious when a dilute sample is injected after a concentrated sample. To avoid cross-contamination from the preceding sample injection, all the parts in the injector that come into contact with the sample (the injection loop, the injection needle, and the needle seat) have to be cleaned effectively after the injection. The carryover can be evaluated by injecting a blank after a sample that contains a high concentration of analyte. The response of the analyte found in the blank sample expressed as a percentage of the response of the concentrated sample can be used to determine the level of carryover. Caffeine can be used for the system carryover test for assessing the performance of an injector and serves as a common standard for comparing the performance of different injectors. 

AB-labelled oligosaccharides are resolved in 50 pi 65% acetonitrile/35% 80 mM ammonium formate (pH 4.4). Aliquots (50 pi) of 1 10 diluted samples are injected onto the HPLC column. Analysis of the eluate is carried out by fluorescence detection (excitation at 330 nm, emission at 420 nm). Peak fractions are further investigated by mass spectrometry. 

For the isotope dilution, mass spectrometry method samples are injected directly into the gas sample injection port of the mass spectrometer [27]. These techniques do not allow concurrent analysis of TMA and TMA N-oxide in the sample. TMA N-oxide is quantified indirectly by measuring the increase in TMA after chemical reduction. 

When working with capillary columns, the splitless mode is used for very dilute samples. In this mode, the injection is made very slowly, leaving valve no. 2 in the closed position (Fig. 2.5) for approximately 0.5 to 1 min. This allows vaporisation of the compounds and solvent in the first decimetre of the column by a complex mechanism of dissolution in the stationary phase, which is saturated with solvent. Compound discrimination is very weak using this method. The proper use of this injection mode, which demands some experience, requires a temperature program that starts with a colder temperature so that the solvent can precede the analytes in the column. This mode is typically used for trace analyses. The opening of valve no. 2 eliminates, from the injector, compounds which are less volatile and that can interfere with the analyses. 

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