Mercury calibration curve

Scope. This method is applicable to the determination of mercury in petroleum and petroleum products (except leaded gasoline) which can be burned in a Wickbold apparatus. The method is capable of measuring the amount of mercury in a sample down to the 5-ng/g level. The upper limit of the method as presented is determined by the linearity of the mercury calibration curve (Figure 1.2). Three to four samples can be analyzed conveniently at one time, and the average analysis time is about 2 hr. 

With these facts in mind, it seems reasonable to calculate the pore volume from the calibration curve that is accessible for a certain molar mass interval of the calibration polymer. A diagram of these differences in elution volume for constant M or AM intervals looks like a pore size distribution, but it is not [see the excellent review of Hagel et al. (5)]. Absolute measurements of pore volume (e.g., by mercury porosimetry) show that there is a difference on principle. Contrary to the absolute pore size distribution, the distribution calcu-... 

In addition, the AAS requires a calibration curve to be constructed to convert readings of ahsorhence to nanograms of mercury whereas the Jerome provides direct readings in nanograms. 

Both Ksec <1 pore size distribution have been measured experimentcilly for hard-sphere column packing materials (9), but for soft gel packing materials there does not seem to be ciny reliable information presumably because the accepted method of pore structure characterisation in porous materials, mercury porosime-try, cannot be used. However, Ep Ccin be measured for gels without great difficulty from the column calibration curve (as is mcinife-st from Equation 12) provided the calibration is made on the basis of the peak mean position, i.e. the first moment of the peak... 

Determination of Pore Size Distributions. The shape and range of a GPC calibration curve are, in part, a reflection of the pore size distribution (PSD) of the column packing material. A consideration of the nature of PSDs for the ULTRASTYRAGEL columns to be used in this work is therefore appropriate. The classical techniques for the measurement of PSDs are mercury porisimetry and capillary condensation. The equipment required to perform these measurements is expensive to own and maintain and the experiments are tedious. In addition, it is not clear that these methods can be effectively applied to swellable gels such as the styrene-divinylbenzene copolymer used in ULTRASTYRAGEL columns. Both of the classical techniques are applied to dry solids, but a significant portion of the pore structure of the gel is collapsed in this state. For this reason, it would be desirable to find a way to determine the PSD from measurements taken on gels in the swollen state in which they are normally used, e.g. a conventional packed GPC column. 

Hg2 ion-selective electrode calibration curve from J. A. Shatkin, H. S. Brown, and S. licht, Composite Graphite Ion Selective Electrode Array Potentiometry for the Detection of Mercury and Other Relevant Ions in Aquatic Systems, Anal. Chem. 1995, 67,1147. It was not stated in the paper, but we presume that all solutions had the same ionic strength. 

The volume inside this tensimeter varies with pressure. Therefore, in situations which require a knowledge of the number of moles of gas, it is necessary to construct a calibration curve relating the internal volume of the tensimeter to the mercury level. The procedure for calibrating a manometer and attached volume has been described in Section 5.3.H. 

The concentration of mercury vapor is determined from the calibration curve. Typical calibration curve is shown in Fig. 15.3. Detection limit corresponds to about lng/1 and can probably be improved by using differential configuration and/or temperature stabilization. 

Fig. 20.4. Calibration curve for inhibition of invertase (0.05 pg/mL) by methyl mercury after 10-min incubation using biphasic system (phosphate buffer/ toluene mixture) and glucose oxidase biosensor. Eapp — +0.60 V vs. Ag/AgCl and reaction time = 5 min.

Calibration standards are made from a soluble mercury salt, such as, mercuric chloride. The standard solutions are analyzed first prior to the sample, following acid digestion, oxidation, and reduction, as described above. A standard calibration curve is constructed by plotting absorbance vs. concentrations of Hg (or mg Hg). The concentration of Hg in the sample is then determined by comparing the absorbance with that in the calibration curve. 

Figure 2. Wavelength calibration curve of the microspectrofluorometer using mercury and helium...

Repeat the procedure using 5 ml of each of the diluted standard solutions and 5 ml of water (blank). Plot the absorbance of each standard solution against the concentration of mercury, and read off the concentration in the sample. The calibration curve should be linear for concentrations in the range 0 to 0.15 lag/ml. 

Figure 2. A composite calibration curve for mercury in seawater samples measured over a three-week period. The mercury spike quantities are in ng and the mercury absorption in arbitrary units (21).

Analytical Curves. Appropriate spikes of mercmric chloride standards were added to the sample matrix, and the sample determination procedmre was repeated. Three spike additions were usually made. A sample blank is measmred and the mercury concentration determined from an individual calibration curve for each sample. The working calibration curve for a seawater sample is prepared by plotting the gas phase absorption of mercury (arbitrary units) against the mercury spike concentration (ng/1.). Using log-log coordinates, the mercury response is linear over... 

In Figure 2, a composite calibration curve for seawater is reproduced. This curve is based on the response obtained for spike additions of 1.0, 2.5, 5.0, and 10 ng Hg to different 100-ml seawater samples analyzed over three weeks. The number of spikes making up this composite graph are 3, 19, 20, and 9, for the 1.0-, 2.5-, 5.0-, and 10-ng mercury additions, respectively. The average value for each addition was plotted, and the brackets indicate the standard deviation. The precision of analysis reported as a coefficient of variation for these spike additions is 30% at 5 ng Hg/L, 20% at 10 ng Hg/L, 15% at 25 ng Hg/L, and 10% at 50 ng Hg/L... 

This composite calibration curve for seawater demonstrates the applicability of the cold-trap pre-concentration technique to low concentration ranges of mercury. Approximately 0.2 ng of mercury can be determined with a 25x scale expansion. Since the response depends on the vaporization and elution of trapped mercury from the column, the calibration curves were similar for other aqueous media including acidified (nitric acid) distilled deionized water. Therefore, this cold-trap procedure appears to separate effectively reducible mercury species from interfering substances that might be associated with differing solution matrices. 

All samples are analysed for Cd, Pb, Cr against standard calibration curves prepared from 0.0, 0.5, 2.5, 5.0 and lO.Oppm of each metal in 0.25 M HNO3. The ultrasonic nebuliser is used for the determination of Cd, Pb and Cr while the continuous cold vapour trap method is used for the determination of Hg. The recovery of each metal is determined for each metal. The Hg forms the vapour ion of the metal in solution after reduction with SnCl2(Sn2+ + Hg2+ > Sn4+ + Hg°) and the metallic mercury is swept to the plasma torch by the argon gas. This method is sensitive for Hg and has the advantage that it removes the analyte from the main solution and has very low limits of detection. 

The reduction of phenylmercuric cations to elemental mercury has previously been reported (21, 22). The average relative precision of the method was 1.8Z. Linear calibration curves for DPM and PMA were obtained for almost the entire solubility ranges of these compounds in seawater (Figure 2). The calibration curve for DPM became nonlinear near the solubility limit (3.5 ppm for DPM and >5.0 ppm for PMA). The detection limits for DPM and PMA were 0.10 ppm and 0.04 ppm respectively, in seawater. Because of the relatively high detection limits for DPM and PMA, it was not possible to work in the ppb or lower concentration range which would be environmentally more relevant. 

A person has the symptoms of chronic mercury poisoning, but there is no logical explanation of where the contamination is occurring. The problem is to determine if the person is in fact being slowly exposed to mercury vapors or a mercury compound. This will be done by testing for Hg in head hair. You are given a sample of hair to determine the Hg in it. However, you have never done this before, and you need a blank, in any case. You obtain some hair from a known healthy person and determine the Hg present. You run two samples one as a blank and the other spiked with 10 ppb Hg to make sure you can detect it. You also run a set of five standards. This allows you to prepare a calibration curve and to determine the % recovery. 

Convert the absorbance to micrograms of mercury from the calibration curve and calculate the mercury content of the sample ... 

The use of gold coated piezoelectric crystals as sensors for mercury in air was investigated by Scheide et al.(47). The crystal was incorporated into a variable oscillator circuit, and changes in the frequency due to the increase in mass resulting from the ability of gold to amalgamate mercury facilitated the measurement of mercury in air at sub-part-per billion level. Calibration curves were obtained from part-per-million to subpart-per-billion concentration of mercury. Reversibility was achieved by heating the crystal in an oven to 150°C. 

The mercury vapor produced by bubbling the sulfur dioxide through a mercurous nitrate solution was detected by the gold-coated crystal due to the formation of a mercury amalgam. The optimum conditions were temperature = 27°C flow rate = 55 ml/min [Hg2 ] = 4 x 10 M purge time = 10 min. The sensitivity of the detector depended on the sample size, and linear calibration curves in the concentration... 

Data from the analyses are collected by a PC running "Mercury MD-1" data analysis software. This software can store multiple calibration curves and raw data finm the samples. The mercury response can be measured using either peak height or integration over time. The PC software is strictly for data acquisition and does not control the instrument start or any operating parameters. 

After choosing the appropriate instrument range and working standard, as shown in Table 1, the analyst measures aliquots of standard into the cooled boats using an adjustable pipettor with disposable tips. Instrument heating mode "1" is chosen for the aqueous standards or samples of a similar nature. Several heating modes are available, and examples of the samples for which each mode may be used are shown in Table 2. A calibration curve is established from the instmment response to various known mercury concentrations. 

Next, curves are recorded for solutions containing samples to be analyzed in the same supporting electrolyte as was used for the construction of the calibration curve. It is essential that the curves for the sample analysis be recorded under exactly the same conditions as those used in the construction of the calibration curve. In particular, one uses the same capillary, the same pressure of mercury, the same... 

The pressure of mercury is kept constant by maintaining the mercury in the reservoir at a constant level. Somewhat more difficult to guarantee is the use of the same capillary. This implies that when a capillary is broken, or behaves erratically (commonly, as a result of penetration of impurities into the bore), a new calibration curve must be constructed. If the highest accuracy is aimed at, the temperature of the electrolytic cell must also be controlled by using a water-jacket or by immersing the cell in a thermostatted bath. 

FIGURE 11-4. Calibration curve for the fluorescence analysis of zinc. [From J. D. Wine-fordner and R. A. Staab, Determination of Zinc, Cadmium, and Mercury by Atomic Fluorescence Spectrometry, Anal. Chem., 36, 165 (1964). Used by permission of the American... 

This is called the Ilkovic equation. For a particular capillary and pressure head of mercury, is a constant. Also, the value of n and that of the diffusion coefficient for a particular species and solvent conditions are constants. Thus, (l is proportional to the concentration C of the electroactive species, and this is the basis for quantitative analysis. The Ilkovic equation is accurate in practice to within several percent, and routinely 1% precision is possible. It is commonplace to use standard additions to obtain a calibration curve or an internal standard. Internal standards are useful when chemical sampling and preparation procedures involve the possibility of losses. The principle is that the ratio of the diffusion currents due to the sample and the added standard should be a constant for a particular electrolyte. 

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