Molybdenum calibration curve

The above procedure may be adapted to the determination of molybdenum in steel. Dissolve a 1.00 g sample of the steel (accurately weighed) in 5 mL of 1 1 hydrochloric acid and 15 mL of 70 per cent perchloric acid. Heat the solution until dense fumes are evolved and then for 6-7 minutes longer. Cool, add 20 mL of water, and warm to dissolve all salts. Dilute the resulting cooled solution to volume in a 1 L flask. Pipette 10.0 mL of the diluted solution into a 50 mL separatory funnel, add 3 mL of the tin(II) chloride solution, and continue as detailed above. Measure the absorbance of the extract at 465 rnn with a spectrophotometer, and compare this value with that obtained with known amounts of molybdenum. Use the calibration curve prepared with equal amounts of iron and varying quantities of molybdenum. If preferred, a mixture of 3-methylbutanol and carbon tetrachloride, which is heavier than water, can be used as extractant. 

Add to the sample solution (containing 1 -25 g of Mo) 4 mL of 1 3 sulphuric acid, 3 drops of 85 per cent phosphoric(V) acid, and 0.5 g of citric acid. Dilute with water to 20 mL and add 2 mL of dithiol solution. Allow to stand at room temperature for 2 hours. Extract the molybdenum complex with 13 mL and 10 mL portions respectively of re-distilled butyl acetate, and make up to 25.0 mL with this solvent in a graduated flask filter through glass wool if not entirely clear. Determine the absorbance of the solution at 670 nm. Prepare a calibration curve as detailed in Section 6.14. 

As some other sugars are also present in blood sample, and besides the above reaction not being absolutely stoichiometric, it has become necessary in actual practice to establish an emperical calibration curve using known concentrations of glucose. The above reaction is allowed to proceed for exactly 8 minutes at 100°C. To the resulting solution phosphomolybdic acid is added, which is subsequently reduced by Cu20 to give rise to an intensely coloured molybdenum blue that is measured at 420 nm accurately. 

Figure 7.13 Calibration curves for boron, tungsten and molybdenum from 0.0 to 4.0gg/ml (ppm) using scandium Sc as an internal standard. The units on the Y axis are flask numbers of standards 0.0, 1.0, 2.0, 3.0 4.0 ppm metal respectively...

A calibration curve for the colorimetric determination of phosphorous in urine is prepared by reacting standard solutions of phosphate with molybdenum(VI) and reducing the phosphomolybdic acid complex to produce the characteristic blue color. The measured absorbance A is plotted against the concentration of phosphorous. From the following data, determine the linear least-squares line and calculate the phosphorous concentration in the urine sample ... 

Recommended Methods. Two methods are suitable. In one, a large sample (usually 100 g) is dry ashed in a porcelain crucible. The resulting carbonaceous residue is ignited in a muffle furnace at 480°C. The ash is dissolved in dilute nitric acid, and potassium chloride and aluminum chloride are added to the solution. The molybdenum is measured by atomic absortion in a nitrous oxide-acetylene flame and related to a calibration curve. 

The quantitative reliability of inductively coupled plasma high-resolution mass spectrometry for phosphorus determinations was judged by comparing it to the standard total filterable phosphorus method (Gooper et al., 1999). That method includes a persulphate oxidation step to convert all forms of phosphorus to phosphate, which is then suitable for the molybdenum blue reaction. Using the same set of standards, calibration curves for both methods were developed over a range of 0-200 pg P/1. Fig-... 

In order to prepare the calibration curve take increasing quantities of molybdenum reference solution containing between 0.005 and 0.25 mg of molybdenum, dilute with distilled water to approximately equal volume and treat according to the method described under "Determination". This begins with the addition of the 2 m sodium hydroxide solution to the solution containing sulphuric acid after destruction of the organic matter, and continues with the addition of 15 ml of 20 % sulphuric acid and transfer to the separating funnel. 

Read off the appropriate molybdenum content from the calibration curve on the basis of the extinction measured for the solution under analysis. Taking account of the blank test and the initial quantity of water used, recalculate for 1 litre of the water sample. Correction may also be... 

Another example is a fully computerized MSFIA system for the spectrophotometric determination of available phosphorus in soil extracts. The molybdenum blue method is chosen for the colorimetric determination, using ascorbic acid as reducing agent, antimony to accelerate the reduction to the blue complex and applying the Egner-Riehm method to extract phosphorus from soil samples. It presents a hnear calibration curve between 0.75 and 15 mg/1. A determination frequency of 15/h may be achieved, with good repeatability for 12 consecutive injections of soil extracts (RSD <1.7%). Results obtained from 12 soil samples were statistically comparable to those attained by the usual batch method [102]. 

The determination of silica and phosphorus as mol5djdenum heteropolyacids by ion-pair reversed-phase HPLC is described. The chromatographic behavior of molybdenum heteropolyacids of silicon and phosphorus in the form of its association with tetrabutylam-monium bromide on a reversed-phase column C18 is investigated using ion-pair reversed-phase HPLC (UV detection at 310 nm). Optimal conditions for the separation of the polyacids for the determination of silicon and phosphorus in water were foimd. The calibration curve has a linear behavior in the concentration range of 0.01-0.1 pg/mL silicon and 0.02—0.15 pg/mL phosphorus. The detection limit of silicon and phosphorus is (1.4 0.3)10 and (6.7 1.2)10 pg/mL, respectively. 

A tungsten electrode may be used to indicate the hydrogen ion concentration in solution the E-pH curve for tungsten is linear over the pH range 4-9, but may be calibrated for use from pH 2-12. The E-pH curve for a molybdenum electrode, which behaves in a similar manner, is linear in the pH range 3-13. Both electrodes are poisoned reversibly by hydrogen and irreversibly by copper ions. They are reliable only when cleaned regularly. 

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