Cadmium standard curve

Figure 10, The change in the slope of the cadmium standardization curves for the various level of sodium in the matrix...

In the presence of cadmium, nitrate (N03 ) is reduced to nitrite (N03). The nitrite produced is diazotized with sulfanilamide. This is followed by coupling with N-(l-naphthyl)-ethylenediamine to form a highly colored azo dye. The intensity of the color developed is measured by a spectrophotometer or a filter photometer at 540 nm. The concentration of oxidized N/L (N03-N plus NO AN) is read from a standard curve prepared by plotting absorbance (or transmittance) of standard against N03-N concentrations. 

To 50 mL of solution passed through cadmium column, add 2 mL of color reagent and mix. Allow the solution to stand for 30 min Measure the absorbance at 543 nm against a distilled water-reagent blank. Read the concentration of N03 -N from the prepared standard curve. Standards should be reduced exactly like samples. 

Pruszkowska et al. [135] described a simple and direct method for the determination of cadmium in coastal water utilizing a platform graphite furnace and Zeeman background correction. The furnace conditions are summarised in Table 5.1. These workers obtained a detection limit of 0.013 pg/1 in 12 pi samples, or about 0.16 pg cadmium in the coastal seawater sample. The characteristic integrated amount was 0.35 pg cadmium per 0.0044 A s. A matrix modifier containing di-ammonium hydrogen phosphate and nitric acid was used. Concentrations of cadmium in coastal seawater were calculated directly from a calibration curve. Standards contained sodium chloride and the same matrix modifier as the samples. No interference from the matrix was observed. 

Stein et al. [673] have described a simplified, sensitive, and rapid method for determining low concentrations of cadmium, lead, and chromium in estuarine waters. To minimise matrix interferences, nitric acid and ammonium nitrate are added for cadmium and lead only nitric acid is added for chromium. Then 10,20, or 50 pi of the sample or standard (the amount depending on the sensitivity required) is injected into a heated graphite atomiser, and specific atomic absorbance is measured. Analyte concentrations are calculated from calibration curves for standard solutions in demineralised water for chromium, or an artificial seawater medium for lead and cadmium. 

Cadmium in acidified aqueous solution may be analyzed at trace levels by various instrumental techniques such as flame and furnace atomic absorption, and ICP emission spectrophotometry. Cadmium in solid matrices is extracted into aqueous phase by digestion with nitric acid prior to analysis. A much lower detection level may be obtained by ICP-mass spectrometry. Other instrumental techniques to analyze this metal include neutron activation analysis and anodic stripping voltammetry. Cadmium also may be measured in aqueous matrices by colorimetry. Cadmium ions react with dithizone to form a pink-red color that can be extracted with chloroform. The absorbance of the solution is measured by a spectrophotometer and the concentration is determined from a standard calibration curve (APHA, AWWA and WEF. 1999. Standard Methods for the Examination of Water and Wastewater, 20th ed. Washington, DC American Public Health Association). The metal in the solid phase may be determined nondestructively by x-ray fluorescence or diffraction techniques. 

To determine the calibration curve, aspirate the Cadmium Calibration Standards and the Calibration Blank Solution. If possible, use the calibration function incorporated in the ICP-AES instrument s soft- or firmware. If necessary, plot instrument response versus concentration of cadmium Fit this line with a linear equation of the form y = mx + b, in which y is instrument response, m is the slope of the best-fit line, x is concentration, and b is the y intercept of the best-fit line. The correlation coefficient for the best-fit line should be >0.99. Concentrations of cadmium in the calibration blanks, calibra-... 

Procedure Set up the instrumental method to measure the area of the 0- ig/mL Working Calibration Standard (blank) peaks and then the net intensities of the 0.050- and 0.250-fig/ mL Working Calibration Standards with the yttrium Internal Standard. The calibration curve should be linear. Examine the spectra of the cadmium and yttrium, and make any necessary adjustments to the exact peak locations and baselines to ensure proper integration of the areas under the respective peaks. Analyze the sample and calculate the concentration, in micrograms per milliliter, of the cadmium in the Sample Solution. 

Plot the absorbance of each standard solution against the concentration of cadmium, reduce the intercept to zero by drawing a parallel line through die origin, and read off the concentration in the sample. The calibration curve should be linear in the range 0 to 0.01 lag/ml. 

In a linear dilution series the concentrations are separated by an equal amount, e.g. a series containing cadmium at 0, 0.2, 0.4, 0.6, 0.8, l.OmmolL" might be used to prepare a calibration curve for atomic absorption spectroscopy (p. 170) when assaying polluted soil samples. Use [Ci]F] =[C2]f2 to calculate the volume of standard solution for each member of the series and pipette or syringe the calculated volume into an appropriately sized volumetric flask as described above. Remember to label clearly each diluted solution as you prepare it, since it is easy to get confused. The process is outlined in Box 4.3. 

For each of the elements examined, an initial suppression in signal is observed with the introduction of sea salts. Figures 1 and 2 show this effect for cadmium and lead respectively. The calculated concentrations, based on the absorbance curve of de-ionized water-acid standards for two series of spiked sample solutions for each element, are plotted against the concentration of sea salt present in solution (expressed as sodium). 

Use a least squares regression program to plot a concentration-response curve of net absorbance reading (or peak area for HGA analysis) versus concentration (ng/mL or ng/mL) of cadmium in each working standard. 

Claeys-Thoreau (1982) and DeBenzo et al. (1990) diluted blood samples at a ratio of 1 10 with a matrix modifier (0.2% Triton X-100, a wetting agent) for direct determinations of CDB. DeBenzo et al. also demonstrated that aqueous standards of cadmium, instead of spiked, whole-blood samples, could be used to establish calibration curves if standards and samples are treated with additional small volumes of matrix modifiers (i.e., 1% HNO3, 0.2% ammonium hydrogenphosphate and 1 mg/ml magnesium salts). 

Limit of Detection. A limit of 100 pg/l urine should be achievable, although the insert to the test kit (Pharmacia 1990) cites a detection limit of 150 pg/l private conversations with representatives of Pharmacia, how ever, indicate that the lower limit of 100 pg/l should be achievable provided an additional standard of 100 pg/l B2M Is run with the other standards to derive the calibration curve (section 3.3.1.1). The lower detection limit is desirable due to the proximity of this detection limit to B2MU values defined for the cadmium medical monitoring program. 

The infrared spectrum of each sample was analyzed with a Fourier transform infrared (FTIR) microspectroscopy (IRT-5000-16/FTIR-6200, Jasco Co., Tokyo, Japan) equipvped with a mercury cadmium telluride (MCT) detector via a transmission technique (Gao Lin, 2010 Lin et al., 2006, 2010). All the FTIR spectra were obtained at a 4 cmi resolution and at 100 scans. The components and relative compositions of each sample were estimated quantitatively within the 1740-1600 cm-i region of FTIR spectra by a curve-fitting algorithm with a Gaussian-Lorenzian function (Cheng et al., 2008 Hu et al., 2002). The best curvefitting procedure was performed by iterative fits toward a minimum standard error. The relative composition of the component was computed to be the fractional area of the corresponding peak, divided by the sum of the area for all the peaks. 

The service life of a sealed nickel-cadmium battery, normalized to unit weight (kilograms) and size (liters), at various discharge rates and temperatures is summarized in Fig. 28.15. The curves are based on a capacity, at the C/5 discharge rate at 2(fC, of 30 Ah/kg and 85 Ah/L, reflecting the performance of standard-type sealed cylindrical batteries. Manufacturers should be contacted for performance characteristics of specific batteries. 

Calibration Curve - The emission counts are plot versus mg/L cadmium in the standard series. 

Figure 22. Typical power-time curve for the action of cadmium intoxication on a freshwater snail Planorbis comeus). At the arrow, contaminated water is introduced to the sorption chamber at a higher flow rate to guarantee for a quick and effective water exchange. The bar near the ordinate indicates the standard deviation for a superposition of 3 individual traces [182].

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