Mercury blanks

Nitric acid washing of glassware, even if not previously used for mercury determinations, often did not remove all traces of mercury. Large, variable mercury contamination can be encountered during determinations, but the contamination appears constant on a given day. To avoid the effects of mercury contamination, a mercury-free oil—e.g., a white oil—must be carried through the procedure until an acceptable mercury blank is obtained. 

Gill and Fitzgerald [481] determined picomolar quantities of mercury in seawater using stannous chloride reduction and two-stage amalgamation with gas-phase detection. The gas flow system used two gold-coated bead columns (the collection and the analytical columns) to transfer mercury into the gas cell of an atomic absorption spectrometer. By careful control and estimation of the blank, a detection limit of 0.21 pM was achieved using 21 of seawater. The accuracy and precision of this method were checked by comparison with aqueous laboratory and National Bureau of Standards (NBS) reference materials spiked into acidified natural water samples at picomolar levels. Further studies showed that at least 88% of mercury in open ocean and coastal seawater consisted of labile species which could be reduced by stannous chloride under acidic conditions. 

The film formed during the blank test was left on the glassy carbon surface. Upon addition of further mercury nitrate, 20-50 til of a 5 g/1 solution were... 

In their proposed method, contamination only from the ammoniacal glutathione solution is expected. However, any inorganic mercury in this solution will be adsorbed on the glass container walls with a half-life about 2d, i.e. the blank value becomes zero if the solution is left to stand for more than a week. This method for mercury in sediments does not distinguish between the different forms of organomercury. Results are calculated as methylmercury. 

Procedure Weigh accurately about 0.17 g of amoxycillin trihydrate and dissolve in sufficient DW to produce 500 ml. Now, transfer 10 ml of this solution into a 100 ml volumetric flask, add 10 ml of buffer solution pH 9.0 followed by 1 ml of acetic anhydride-dioxan solution, allow to stand for 5 minutes, and add sufficient water to produce 100 ml. Pipette 2 ml of the resulting solution into each of the two stoppered tubes. To tube 1 add 10 ml of imidazole-mercury reagent, mix, stopper the tube and immerse it in a water-bath previously maintained at 60 °C for exactly 25 minutes, with occasional swirling. Remove the tube from the water-bath and cool rapidly to 20 °C (Solution-1). To tube 2 add 10 ml of DW and mix thoroughly (Solution-2). Immediately, measure the extinctions of Solutions 1 and 2 at the maximum at about 325 nm, as detailed above, employing as the blank a mixture of 2 ml of DW and 10 ml of imidazole-mercury reagent for Solution-1 and simply DW for Solution-2. 

The instrumentation adds this device on-hne with the standard units for mercury analysis and is also controlled by the software. Steps have been taken to minimize the blank levels of mercury in the solutions, gases and reagents. 

The effects of mercury compression and the compressive heating of the hydraulic oil are thermodynamically compensated. Therefore, the need to make blank runs is unnecessary for all but the most exacting analysis. Blank runs made on cells filled with mercury show less than 1 % of full-scale signal over the entire operating range from 0 to 60000psi. 

Three samples per patient, each with 200 pi blood, are mixed with double-distilled water prewarmed to 37°C for 10 min. To one of the tubes with the diluted hemoly-sate, add 1 ml mercury chloride/trichloracetic acid solution and 1 ml ALA solution for determination of the blank value. The enzyme reaction is performed in duplicate To each of the 200-pl hemolysate samples add 1 ml prewarmed ALA solution. All three tubes are mixed and incubated for 1 h at 37°C. To stop the reaction, 1 ml mer-... 

FTIR Microspectroscopy.3 A microscope accessory coupled to a liquid-nitrogen-cooled mercury-cadmium-telluride (MCT) detector can be used to obtain an IR spectrum. This is possible in both the transmission and reflectance modes. Several beads are spread on an IR-transparent window (NaCl, KBr, diamond) and possibly flattened via a hand-press or a compression cell. The IR beam is focused on a single bead using the view mode of the microscope. The blank area surrounding the bead is isolated using an adjustable aperture, and a spectrum is recorded using 32 scans (<1 min). A nearby blank area of the same size on the IR transparent window is recorded as the background. 

After the firing was completed, the permanganate solution was analyzed by the same procedure used for the volatile mercury samples. Mercury in coal samples from the National Bureau of Standards and the United States Bureau of Mines were analyzed simultaneously as controls. At least duplicate analyses were performed on all samples. Empty crucibles were fired into acidic permanganate solutions by an identical procedure to obtain solutions for blank determinations. 

The permanganate solutions obtained from both the coal and ash samples were analyzed by the direct aeration flameless atomic absorption procedure. The concentration in each sample was calculated from the measured mercury value, the blank concentration in the permanganate solutions, and the weight of the samples. 

Optimization of System Variables. The dependence of the blank level and the total signal (blank + analyte response) on the liquid flow rate is shown in Figure 10. The conditions are the same as those for Figure 9 except that 10"6 M Hg2(N03)2 at pH 4 is used. Down to the lowest flow rate studied (1500 / L/min), the net response to 5 ppbv S02 is essentially constant. Unfortunately, this flow rate dependence was examined fairly late in the study and the other data reported here were obtained with a liquid flow rate of 2600 pL/min. It is clear, however, that down to at least 1500 nL/min, the response/blank ratio improves it may be advantageous to use a lower flow rate. This behavior also strongly suggests that the transport of mercury from the bulk solution (liberated due to the intrinsic disproprotionation equilibrium) to the carrier air stream is controlled by liquid phase mass transfer. 

One of the filtered water samples was acidified on the same day as collection by the addition of 1.0 ml of concentrated HN03 acid using a droplet bottle. The sample for mercury analysis was acidified and preserved by adding 5 ml of a prepared solution of concentrated HN03 acid and potassium dichromate solution. Bottles were then stored in a refrigerator and sent to the laboratory soon after sampling. A blank water was collected, filtered, and preserved in the same manner as the actual samples after every 20th sample. 

In a closed system with a circulating air pump, connect a calcium chloride drying tube and an aerator inserted in a 300-mL reaction vessel so that air passed through the treated preparation contained in the reaction vessel evaporates any metallic mercury present. In a similar manner, treat 100 mL of the Test Solution and 100 mL of water (reagent blank), and determine the maximum absorbances at the same wavelength. The absorbance of the solution from the Test Solution does not exceed that of the solution from the Standard Solution. 

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