Author Archives: David Harvey

Using a Control Chart to Detect Problem in Analysis

Suppose  you are working at your local sewage treatment facility.  One of your responsibilities is to monitor the effluent’s biological oxygen demand (BOD), which is a measure of the amount of biologically available organic material in the effluent.  Basically, a … Continue reading

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Kinetic Determination of Ascorbic Acid

One method for determining the concentration of glucose in fruit juices is to take advantage of its enzymatic oxidation in the presence of glucose oxidase: β-D-glucose + O2 + H2O → δ-D-gluconolactone + H2O2 To follow the kinetics of this … Continue reading

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Kinetic Method for Manganese

Trace levels of manganese can be determined by measuring its catalytic effect on the oxidation of diethylamine by sodium periodate.  The rate of formation of the oxidation product is followed spectrophotometrically.  A series of external standards are prepared by adding … Continue reading

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Standardization of a Kinetic Method of Analysis

Shown below is a plot of initial rate vs. substrate concentration for an enzyme-substrate reaction that follows Michaelis-Menton kinetics. An analyst developing a quantitative method for the substrate wishes to use a one-point standardization. The standard selected by the analyst, … Continue reading

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HPLC Separation of Phenacetin, Salicylic Acid, Nicotine, Methylamphetamine, and Phenobarbatuic Acid

The graph shown below is a plot of retention time vs. pH for the reverse-phase HPLC separation of a mixture containing phenacetin, salicylic acid, nicotine, methylamphetamine, and phenobarbituic acid. Based on the structures of these compounds and their pKa values, … Continue reading

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Separation of Amino Acids

In ion-exchange chromatography, a solution containing a mixture of compounds is passed through a column packed with a resin containing covalently attached anionic and/or cationic functional groups. One use of ion-exchange chromatography is the separation of compounds based on differences … Continue reading

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Analysis of Anaerobic Sediments for Sulfides

A paper in the Journal of Chemical Education describes an experimental method for determining the concentrations of both insoluble metal sulfides, such as FeS2, and gaseous H2S in anaerobic sediments. Samples of sediment are placed in a flask along with … Continue reading

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Neocuproine Method: Analysis of Procedure

One method for determining copper is the “Neocuproine Method”. In this method, copper in a +1 oxidation state reacts with neocuproine (2,9-dimethyl-1,10-phenanthroline) to form a complex of Cu(neocuproine)2.  The complex is extracted into a chloroform-methanol mixture, giving a yellow solution … Continue reading

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Standards and Samples

The spectrophotometric methods for analyzing Mn and for analyzing glucose use a chemical reaction to produce a useful signal. In the analysis for Mn in steel, colorless Mn2+ is oxidized to give the purple MnO4– ion, while in the analysis for … Continue reading

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Standards for the Spectrophotometric Analysis of Acetone

Suppose you need to prepare a set of calibration standards for the spectrophotometric analysis of acetone at a wavelength of 211 nm using a 1.00 cm cell. The molar absorptivity for acetone at this wavelength is 562. To maintain an … Continue reading

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