Aliquot measurement

An injector valve operates in two modes— the fixed-loop mode or the partial-loop mode. In the fixed-loop mode, a sample is overfilled into the loop at 2-4 times the loop volume and the entire loop content is injected. In the partial-loop fill mode, a variable sample aliquot, measured precisely by a syringe at <50% of the loop volume, is injected. Note that the sample slug is introduced into the end of the sample loop and is back flushed onto the column to minimize band dispersion by the sample loop (Figure 9). Due to the emphasis on productivity, manual injectors are seldom used in the pharmaceutical laboratory except for preparative applications. 

Consider a system containing an unknown amount q of some active substance A whose specific activity A cannot be measured. Take two equal aliquots of this unknown substance A. Add r milligrams of inactive A to one aliquot and p milligrams of inactive A to the other aliquot. Measure the specific activities of the two aliquots, Sr and SPi respectively. For the first sample of specific activity Sn we have... 

It is common to measure only a small number of objects or aliquots, and so one has to rely upon the central limit theorem to see that a small set of data will behave in the same manner as a large set of data. The central limit theorem states that as the size of a sample increases (number of objects or aliquots measured), the data will tend towards a normal distribution. If we consider the following case ... 

Fig. 2. Radiolabeling (iodination) of nucleic acids, (a, a ) Plasmid DNA and siRNA concentrations and -radioactivity (CPM/20 gl aliquots) measured in the fractions after purification of the labeled nucleic acids on a Sephadex column G25 PD10. (b, b ) Fraction probes (ca. 1 pg nucleic acid) were electrophoresed (100 V 30 min for sIRNA and 90 min for plasmid DNA) on an EtBr/1% agarose gel in TBE buffer. Lane 1. Unlabeled nucleic acid. Lane 2. (b) Supercoiled DNA Ladder and (b ) peqGold DNA Ladder. Lanes 3,4, and 5. Erections of the J-labeled nucleic acids...

Software designed for spot optimization should enable the difference between aliquot measurement of a band (without this optimization) and measurement of a spot to be determined experimentally. 

The skewness of the histogram of sample 47/2 indicates that the calculated age is too high, caused by palaeodose overestimation. The true palaeodose cannot be accurately deducted because it is not known whether the skewness is caused by a large amoxmt of partly bleached grains, by a smaller amount of much older unbleached grains or by a combination of these two factors. The aliquot measurements can be a mix of the age of mineral (2D)... 

A standard solution of Mn + was prepared by dissolving 0.250 g of Mn in 10 ml of concentrated HNO3 (measured with a graduated cylinder). The resulting solution was quantitatively transferred to a 100-mL volumetric flask and diluted to volume with distilled water. A 10-mL aliquot of the solution was pipeted into a 500-mL volumetric flask and diluted to volume, (a) Express the concentration of Mn in parts per million, and estimate uncertainty by a propagation of uncertainty calculation, (b) Would the uncertainty in the solution s concentration be improved... 

The concentration of Ca + in a sample of sea water is determined using a Ca ion-selective electrode and a one-point standard addition. A 10.00-mL sample is transferred to a 100-mL volumetric flask and diluted to volume. A 50.00-mL aliquot of sample is placed in a beaker with the Ca ion-selective electrode and a reference electrode, and the potential is measured as -0.05290 V. A 1.00-mL aliquot of a 5.00 X 10 M standard solution of Ca + is added, and a potential of -0.04417 V is measured. What is the concentration of Ca + in the sample of sea water ... 

The concentration of NO3 in a water sample is determined by a one-point standard addition using an N03 ion-selective electrode. A 25.00-mL sample is placed in a beaker, and a potential of -t0.102 V is measured. A 1.00-mL aliquot of a 200.0 ppm standard solution of N03 is added, after which the potential is found to be -t0.089 V. Report the concentration of N03 in parts per million. 

Determine the parts per million of F in the tap water, (b) For the analysis of toothpaste a 0.3619-g sample was transferred to a 100-mL volumetric flask along with 50.0 mL of TISAB and diluted to volume with distilled water. Three 20.0-mL aliquots were removed, and the potential was measured with an L ion-selective electrode using a saturated calomel electrode as a reference. Live separate 1.00-mL additions of a 100.0-ppm solution of L were added to each, measuring the potential following each addition. 

With conventional nonspectroscopic detectors, other methods must be used to identify the solutes. One approach is to spike the sample by adding an aliquot of a suspected analyte and looking for an increase in peak height. Retention times also can be compared with values measured for standards, provided that the operating conditions are identical. Because of the difficulty of exactly matching such conditions, tables of retention times are of limited utility. 

The complication of matching the matrix of the standards to that of the sample can be avoided by conducting the standardization in the sample. This is known as the method of standard additions. The simplest version of a standard addition is shown in Figure 5.5. A volume, V, of sample is diluted to a final volume, Vf, and the signal, is measured. A second identical aliquot of sample is... 

To find the best a priori conditions of analysis, the equilibrium analysis, based on material balances and all physicochemical knowledge involved with an electrolytic system, has been done with use of iterative computer programs. The effects resulting from (a) a buffer chosen, (b) its concentration and (c) complexing properties, (d) pH value established were considered in simulated and experimental titrations. Further effects tested were tolerances in (e) volumes of titrants added in aliquots, (f) pre-assumed pH values on precision and accuracy of concentration measured from intersection of two segments obtained in such titrations. 

When the eleetroehemieal oxidation has been finished the analyzable solution is boiled till almost removal of bromine. Then the halogenation of fluoreseein by two aliquots of determined solution at pH 5.5 is earned out. Abundanee of iodide-ions is added to one of the aliquots and abundanee of bromide-ions - to the other. The dependenee A(X) is measured for every solution. C(T) is ealeulated from reeeived data supposing that two lightabsorbing forms - fluoreseein and dihalide-fluoreseein are present at this eondition. 

Procedure To an aliquot of the sample solution containing 12.5 - 305 p.g of platinum(IV) were added 5 ml of hydrochloric acid - sodium acetate buffer of pH 2.1, 1 ml of O.IM Cu(II) sulphate solution, and 3.0 ml of 0.5% propericiazine solution. The solution was diluted to 25 ml with distilled water, mixed thoroughly, and the absorbance measured at 520 nm against a reagent blank solution after 10 min. The platinum concentration of the sample solution was determined using a standar d calibration curve. 

Historically, measurements have classified ambient hydrocarbons in two classes methane (CH4) and all other nonmethane volatile organic compounds (NMVOCs). Analyzing hydrocarbons in the atmosphere involves a three-step process collection, separation, and quantification. Collection involves obtaining an aliquot of air, e.g., with an evacuated canister. The principal separation process is gas chromatography (GC), and the principal quantification technique is wdth a calibrated flame ionization detector (FID). Mass spectroscopy (MS) is used along with GC to identify individual hydrocarbon compounds. 

Procedure. Weigh out accurately about 4 g of the pure organic acid, dissolve it in the minimum volume of water (Note 1), or 1 1 (v/v)ethanol/water mixture, and transfer the solution to a 250 mL graduated flask. Ensure the solution is homogeneous and make up to the required volume. Use a pipette to measure out accurately a 25 mL aliquot and transfer to a 250 mL conical flask. Using two drops of phenolphthalein solution as indicator, titrate with standard 0.2M (approx.) sodium hydroxide solution (Note 2) until the colourless solution becomes faintly pink. Repeat with further 25 mL volumes of the acid solution until two results in agreement are obtained. 

Procedure. Use a solution containing 0.15-1.8 mg antimony per 100 mL it should be slightly acidic with sulphuric acid (1.2-1.5M). Transfer a 10 mL aliquot to a 50 mL graduated flask, add 25 mL of the potassium iodide-ascorbic acid reagent, and dilute to the mark with 25 per cent v/v sulphuric acid. Mix thoroughly and measure the absorbance at 425 nm or at 330 nm using a reagent blank as reference solution. 

Procedure. Dissolve the sample in distilled water and take an aliquot which should contain not more than 50 pg of phenolic compound. Use the aqueous ammonia to adjust the pH of the solution to 9.7-10.3 (pH meter), and then dilute to 500 mL with distilled water. Transfer the solution to a large separatory funnel, add 1.0 mL of solution A followed by 10 mL of solution B. Shake well to ensure thorough mixing, and then carry out three extractions with successive portions of 15 mL, 10 mL and 5 mL of chloroform (trichloromethane). Combine the chloroform extracts and make up the volume to 30 mL. Measure the absorbance of the extract against a blank of chloroform at a wavelength of 460 nm (blue filter), using 1 cm cells. The colour may tend to fade after 10 minutes and so speed is essential. 

Pipette a 25 mL or 50 mL aliquot of the clear sample solution into a 250 mL conical flask, add 5 mL concentrated sulphuric acid, 5 mL 85 per cent phosphoric(V) acid, and 1-2 mL of 0.1 M silver nitrate solution, and dilute to about 80 mL. Add 5 g potassium persulphate, swirl the contents of the flask until most of the salt has dissolved, and heat to boiling. Keep at the boiling point for 5-7 minutes. Cool slightly, and add 0.5 g pure potassium periodate. Again heat to boiling and maintain at the boiling point for about 5 minutes. Cool, transfer to a lOOmL graduated flask, and measure the absorbances at 440 nm and 545 nm in 1 cm cells. 

Fig. 8.2 Gel filtration on a column of Sephadex G-100 at pH 8 (both panels) of the crude extract of Gonyaulax polyedra cells prepared at pH 8 (upper panel) and prepared at pH 6 (lower panel). The activities of the 35 kDa and 130 kDa luciferases are measured by the addition of an excess of luciferin at pH 6.3 ( ) or at pH 8(A). The activity of the luciferin-bound LBP (luciferin-binding protein) in the upper panel is measured after the addition of an excess of 35 kDa luciferase at pH 6.3 ( ). In the lower panel, the LBP activity can be obtained by the addition of an excess of luciferin at pH 8, followed by the removal of unbound luciferin with a small column of Sephadex G-25 before the luminescence assay of bound luciferin at pH 6.3 (see the Section 8.2.8). The Overlap in the upper panel is the light emission resulting from the mixing of an aliquot of the fractions with pH 6.3 buffer. From Fogel and Hastings, 1971, with permission from Elsevier.

Accurate quantitation in GC/MS requires the addition of a known quantity of an internal standard to an accurately weighed aliquot of the mixture (matrix) being analyzed. The internal standard corrects for losses during subsequent separation and concentration steps and provides a known amount of material to measure against the compound of interest. The best internal standard is one that is chemically similar to the compound to be measured, but that elutes in an empty space in the chromatogram. With MS, it is possible to work with isotopically labeled standards that co-elute with the component of interest, but are distinguished by the mass spectrometer. 

Three related methods based on the quasiisostatic method are used to measure permeability. The most commonly used technique allows the permeant gas or vapor to flow continuously through one chamber of the permeability cell. The gas or vapor permeates through the sample and is accumulated in the lower-concentration chamber. At predetermined time intervals, aliquots are withdrawn from the lower cell chamber for analysis. The total quantity of accumulated permeant is then determined and plotted as a function of time. The slope of the linear portion of the transmission-rate profile is related to the sample s permeability. 

A soil sample was taken from a field, transported back to the laboratory by road and stored for three weeks prior to analysis. The analytical procedure consisted of drying the soil in an oven at 100°C for 24 h before the analyte was extracted using 200 cm of dichloromethane. This extract was reduced in volume to 200 til and a 20 p.l aliquot then analysed by HPLC. A calibration was set up by measuring the response from a number of solutions containing known concentrations of the analyte. The resnlt obtained from the unknown , after suitable mathematical manipulation, indicated the original soil sample contained 20 0.05 mgkg of the analyte. Comment on the accuracy of this result. 

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