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Absorbance readings

The unknown solution (which should contain between 0.5 and 2.0mg phenol L 1) is treated in the manner described above, and by reference to the calibration curve the absorbance reading will determine the phenol content of the unknown sample. [Pg.717]

Procedure. Place 80 mL of the arsenic/antimony solution in the titration cell of the spectrophotometer. Titrate with standard bromate/bromide solution at 326 nm taking an absorbance reading at least every 0.2 mL. From the curve obtained calculate the concentration of arsenic and antimony in the solution. [Pg.724]

Procedure. Charge the titration cell (Fig. 17.24) with 10.00 mL of the copper ion solution, 20 mL of the acetate buffer (pH = 2.2), and about 120mL of water. Position the cell in the spectrophotometer and set the wavelength scale at 745 nm. Adjust the slit width so that the reading on the absorbance scale is zero. Stir the solution and titrate with the standard EDTA record the absorbance every 0.50 mL until the value is about 0.20 and subsequently every 0.20 mL. Continue the titration until about 1.0 mL after the end point the latter occurs when the absorbance readings become fairly constant. Plot absorbance against mL of titrant added the intersection of the two straight lines (see Fig. 17.23 C) is the end point. [Pg.725]

If necessary, the test solution must be suitably diluted using a pipette and a graduated flask, so that it too gives absorbance readings in the range 0.1-0.4. [Pg.800]

Aqueous solutions may sometimes be analysed directly without any pretreatment, but it is a matter of chance that the given solution should contain the correct amount of material to give a satisfactory absorbance reading. If the existing concentration of the element to be determined is too high then the solution must be diluted quantitatively before commencing the absorption measurements. Conversely, if the concentration of the metal in the test solution is too low, then a concentration procedure must be carried out by one of the methods outlined at the end of this section. [Pg.801]

Separation techniques may have to be applied if the given sample contains substances which act as interferences (Section 21.10), or, as explained above, if the concentration of the element to be determined in the test solution is too low to give satisfactory absorbance readings. As already indicated (Section 21.10), the separation methods most commonly used in conjunction with flame spectrophotometric methods are solvent extraction (see Chapter 6) and ion exchange (Chapter 7). When a solvent extraction method is used, it may happen that the element to be determined is extracted into an organic solvent, and as discussed above it may be possible to use this solution directly for the flame photometric measurement. [Pg.802]

A double-beam atomic absorption spectrophotometer should be used. Set up a vanadium hollow cathode lamp selecting the resonance line of wavelength 318.5 nm, and adjust the gas controls to give a fuel-rich acetylene-nitrous oxide flame in accordance with the instruction manual. Aspirate successively into the flame the solvent blank, the standard solutions, and finally the test solution, in each case recording the absorbance reading. Plot the calibration curve and ascertain the vanadium content of the oil. [Pg.808]

About 5 ml of sample is withdrawn for every 4-6 hours. The absorbance reading of the sample at 580 nm was measured using a Hitachi U-2000 spectrophotometer. The sample is filtered in a vacuum through Whatman filter paper with a pore size of 2.5 pin and diameter of 47 mm. The dry weight of cells is measured to monitoring microbial cell population and cell density. A plot of optical density reading from the spectrophotometer against cell dry... [Pg.257]

Data for the reaction of nitrous acid with hydrogen peroxide1 follow Eq. (4-22), with kf = 3.76 s"1 and ks = 0.0854 s"1. We now show that either kf or ks may be k or k2. That is, an absorbance reading that rapidly rises and slowly declines does not necessarily imply the first step is fast and the second slow. Inspection of the expression for [P]f, Eq. (4-8), and that for Yt, Eq. (4-18), shows their symmetry upon interchange of A i and k2. Absent other information, the two rate constants cannot be assigned. [Pg.75]

Absorbance Reading [AU] Tablet Weight [mg] Assay [mg] Calibration Factor Type of Result... [Pg.267]

Another common problem is that the detector registers very high or offscale absorbance readings all the time, ie the uv radiation is being absorbed strongly when it should not be. [Pg.56]

To continue the derivation, the next step is to determine the variation of the absorbance readings starting with the definition of absorbance. The extension we present here, of course, is based on Beer s law, which is valid for clear solutions. For other types of measurements, diffuse reflectance for example, the derivation should be based on a suitable function of T that applies to the situation, for example the Kubelka-Munk function for diffuse reflectance should be used for that case ... [Pg.235]

To construct a standard curve of various biotin concentrations, first zero a spectrophotometer at an absorbance setting of 500 nm with sample and reference cuvettes filled with 0.05M sodium phosphate, 0.15M NaCl, pH 6.0. Remove the buffer solution from the sample cuvette and add 3 ml of the (strept)avidin solution plus 75 pi of the HABA-dye solution. Mix well and measure the absorbance of the solution at 500nm. Next add 2 pi aliquots of the biotin solution to this (strept)avidin-HABA solution, mix well after each addition, and measure and record the resultant absorbance change at 500 nm. With each addition of biotin, the absorbance of the (strept)avidin-HABA complex at 500 nm decreases. The absorbance readings are plotted against the amount of biotin added to construct the standard curve. [Pg.923]

Experiments were then designed in which absorbance readings were acquired over the full time course of the reaction. These experiments employed a low concentration of PyO as the limiting reagent and a large excess of phosphine. The data fit a precise pseudo-second-order analysis, and gave kcat = 1.5xl04Lmol 1 s-1 in benzene at 298 K a precision of 5% was estimated. [Pg.167]

When using a spectrophotometer for a colorimetric analysis, both the 0% and 100% transmittance (oo and 0 absorbance) readings must be set. Once the instrument has warmed up, with the light beam blocked and with nothing in the sample compartment, the readout is set to 0% transmittance (oo abs.). Again, this measurement is done to set / in the absorbance equation shown earlier. A blank, a solution containing all the components used in the analysis except the analyte being measured, is placed in a cuvette, placed in the sample... [Pg.310]

Using one of your standards and the Spectronic 20, or other single-beam visible spectrophotometer, obtain an absorption (or transmittance) spectrum of the Fe-o-phenanthroline complex ion (instructor will demonstrate use of instrument). Determine the wavelength of maximum absorbance from the spectrum and use this wavelength to obtain absorbance readings of all the solutions. (Use the blank for the 100% transmittance setting.)... [Pg.198]

A sample in a 1-cm cuvette gives an absorbance reading of 0.558. If the absorptivity for this sample is 15,000 L mob1 cnP1, what is the molar concentration ... [Pg.201]

Problems with the mechanics of a procedure can involve an improperly diluted sample (perhaps manifested by an absorbance reading that is greater than specified or expected), an obstruction in the sample or reference beam, an improperly aligned source or mirror, the incomplete programming of a scan, or improper or inappropriate software entry. In these cases, the operator will need to carefully examine his or her technique or procedure, or instrumental parameters, such as the optical path, perhaps with the help of the instrument troubleshooting guide, to solve the problem. [Pg.215]

Discuss troubleshooting procedures for spectrophotometers for 1) failure of electrical components, 2) unexpectedly high absorbance readings, and 3) an unexpected peak in an absorption spectrum. [Pg.238]

Quantitative analysis in flame atomic absorption spectroscopy utilizes Beer s law. The standard curve is a Beer s law plot, a plot of absorbance vs. concentration. The usual procedure, as with other quantitative instrumental methods, is to prepare a series of standard solutions over a concentration range suitable for the samples being analyzed, i.e., such that the expected sample concentrations are within the range established by the standards. The standards and the samples are then aspirated into the flame and the absorbances read from the instrument The Beer s law plot will reveal the useful linear range and the concentrations of the sample solutions. In addition, information on useful linear ranges is often available for individual elements and instrument conditions from manufacturers and other literature. [Pg.256]

Set up the atomic absorption instrument and obtain absorbance readings for all solutions using the extracting solution for the blank. Follow the instructions provided for instrument shutdown. [Pg.270]

Some of the AP recommended experiments require the use of a spectrophotometer. A spectrophotometer is an instrument that is used to measure the amount of light absorbed (or percentage transmitted) by a particular solute in a solution. In order to determine the absorbance (A) of a sample, the instrument is set to a particular wavelength a solution, contained in a holder called a cuvette, is placed in a sample chamber and an absorbance reading is taken. This procedure may be repeated for other solutions or wavelengths. The cuvette is a standard size to ensure a given path length (b). [Pg.289]

The Milton Roy Spectronic(R)-20 definitely provides a low-cost and easy to operate instrument, that is still capable of achieving absorbance readings accurate to 1 or 2%. [Pg.304]

The use of flow cells may generate variability in absorbance readings. Air bubbles can become caught in the cell, either introduced via a water source containing bubbles or by air entering inadvertently into poorly secured sample lines. Flow rate and dwell time should be evaluated so that the absorbance reading can be determined to have reached a steady plateau. Cells need to be cleaned frequently to avoid build up of drug, excipient, surfactant, or buffer salts from the dissolution medium. [Pg.65]


See other pages where Absorbance readings is mentioned: [Pg.694]    [Pg.707]    [Pg.715]    [Pg.806]    [Pg.807]    [Pg.253]    [Pg.74]    [Pg.15]    [Pg.207]    [Pg.485]    [Pg.250]    [Pg.224]    [Pg.313]    [Pg.270]    [Pg.360]    [Pg.362]    [Pg.534]    [Pg.310]    [Pg.266]    [Pg.261]    [Pg.261]    [Pg.268]    [Pg.269]    [Pg.269]    [Pg.269]    [Pg.269]   
See also in sourсe #XX -- [ Pg.293 ]




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