Cadmium calibration standards

Cadmium Calibration Standards Tare three clean, dry 4-oz polyethylene bottles (or equivalent). Add approximately 50 g of High-Purity Water to each. Slowly add 28 1 g of concentrated nitric acid, mix thoroughly, slowly add 12 1 g of concentrated hydrochloric acid, and mix thoroughly again. Using a precision micropipet, add 10, 50, and 500 pL, respectively, of Cadmium Stock Solution to one of each of the bottles. Dilute each solution to 100.0 0.1 g with High-Purity Water, and mix thoroughly to obtain calibration standards with 0.1, 0.5, and 5.0 mg/kg, respectively. 

Subsequently analyze all three Cadmium Calibration Standards, from lowest concentration to highest. Results for each of the calibration standards should indicate concentrations of 100 5 mg/kg, 500 25 mg/kg, and 5000 250 mg/kg, respectively. If the results are not as indicated, repeat the analysis. In the event that reanalysis is unsuccessful, take steps consistent with the manufacturer s recommendations to identify and remediate the sources of contamination or interference. Do not proceed with the analysis until the sources of contamination or interference have been identified and addressed. After successful calibration of the instmment for cadmium, reanalyze the Calibration Blank Solution to demonstrate that there is no carryover of the cadmium. 

Next, analyze the prepared samples, digestion blanks, and digestion fortification samples in groups of no more than ten. At a minimum, each group should contain a digestion blank, a prepared sample, a second replicate of the prepared sample, and that same sample prepared as a fortification sample. Analyze the Calibration Blank Solution followed by any of the Cadmium Calibration Standards between each group of ten samples. 

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. 

Cepria and coworkers used the voltammetry of immobilized microparticles to detect and quantify the cadmium pigments (e.g., cadmium sulfide and cadmium sulfoselenide) used in artists paints, as well as in glasses, plastics, ceramics, and enamels [141]. For this, a simple, fast and reliable technique was developed that proved to be especially applicable for valuable art objects, as it was minimally invasive and required only nanogram quantities of material (see also Section 6.4.1). For quantification purposes, an abrasive stripping scan was used from + 0.3 V to —1.0 V, following a 10 s pre-treatment step at —1.5 V. The Cd oxidation peak was evaluated with respect to an internal AgCl calibration standard. 

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. 

A standard cell produces a precise voltage and, before the advent of reliable voltmeters, was needed to calibrate medical and laboratory equipment. It is generally agreed that the first standard cell was the Clark cell (see p. 299), but the most popular was the Weston saturated cadmium cell, patented in 1893. 

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. 

Lopez Garcia et al. [2] have described a rapid and sensitive spectrophotometric method for the determination of boron complex anions in plant extracts and waters which is based on the formation of a blue complex at pH 1 - 2 between the anionic complex of boric acid with 2,6-dihydroxybenzoic acid and crystal violet. The colour is stabilised with polyvinyl alcohol. At 600 nm the calibration graph is linear in the range 0.3-4.5 xg boron per 25 ml of final solution, with a relative standard deviation of 2.6% for xg/l of boron. In this procedure to determine borate in plant tissues, the dried tissue is treated with calcium hydroxide, then ashed at 400 °C. The ash is digested with 1N sulfuric acid and heated to 80 °C, neutralized with cadmium hydroxide and then treated with acidic 2,6-dihydroxybenzoic acid and crystal violet, and the colour evaluated spectrophotometrically at 600 nm. Most of the ions present in natural waters or plant extracts do not interfere in the determination of boron complex anions by this procedure. Recoveries of boron from water samples and plant extracts were in the range of 97 -102%. 

The resulting metal, in the salt state, is dissolved in nitric acid and diluted to a known volume with double distilled water. The solution is analyzed by Atomic Absorption for the metals of interest. Metals such as Cadmium, Berylium and Nickel have very low threshold limit values which are set by OSHA and are frequently present in the sample in very low quantities. Many Atomic Absorption units are equipped with a hollow graphite tube atomizer which increases the sensitivity dramatically making it easier for the analyst to obtain reliable results for species present in the sample in very low concentrations. The validity of the metal fume data depends on sampling train calibration and the precision and accuracy of the analytical procedure. NIOSH has reported a 2% relative standard deviation in the analytical method which has been collaboratively tested. 

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 cadmium, one participant remarked that without using standard additions, only 50% of the Cd content was recovered. A strong requirement is therefore to perform calibration by standard additions for estuarine water analysis. As mentioned earlier, the participants stressed that the extraction efficiency has to be verified, particularly for Cd, as it depends on the content of complexing agents present in estuarine water matrices. The risk of incomplete extraction should be checked by repeated extractions. The problem raised by the presence of organic matter may be overcome in many cases by the use of UV irradiation or addition of acids. This possible pretreatment should... 

Metallic ions can be assayed by ICP-AES or ICP-MS and by electrothermal atomization-AAS (FETA-AAS) as well as by polarographic methods. These methods assure reliable information for determination of metallic ions. For example, cadmium is analyzed in baby food with ETA-AAS with a tube and a L vov pyrolytic graphite platform.114 The results obtained for cadmium assay are then compared with the levels of a national standard. There are many standards containing quality requirements for laboratories, but the most important and widely accepted international quality standard for testing laboratories is the ISA/IEC Guide 25 1990 "General requirements for the competence of calibration and testing laboratories."32... 

Calibration. Adjust the base line to zero absorbance while aspirating 0.6N hydrochloric acid. Aspirate each standard cadmium solution in turn and record the reading. Plot the readings obtained against cadmium concentration. 

The above calculation contains two dangerous assumptions. It assumes a linear calibration of peak height with concentration. This could be checked by making several such standard additions. It also assumes that the reagent contain no cadmium traces. A blank would have to be run on any reagents used, to check and allow for this. 

In addition to these defining and secondary temperature standards, a thermocouple wire (SRM 733, a silver-28 at.% gold alloy) has been certified, which serves to compare manufactured wire to standard reference thermocouple tables between 4 and 273 K. SRM 767, a superconductive thermometric fixed-point device, provides temperature calibration in the range 0.5 to 7.2 K This device incorporates five high-purity elements (lead, indium, aluminum, zinc, and cadmium) in long, thin cylinders whose superconductive transition temperatures are certified to be reproducible within 1 mK. 

The spatial distributions of thermal and epithermal neutron flux in the 2.94-kg pile, the 3.95-kg pile, and in the various experimental holes of the mock-up assembly, as indicated in the listing below, were measured. These measurements were made with indium foils, used alternately bare and cadmium covered, as described previously. A calibration. of foils in the standard (sigma)reactor indicated that the absolute flux (nv) is obtained from the measured saturated activities, shown in the attached figures by the following relations, ... 

Three sets of spiked MCEF samples were prepared by injecting 15 pL of 5, 10 and 20 pg/mL dilute cadmium stock solutions on 37 mm diameter filters (part no. AAWP 037 00, Millipore Corp., Bedford, MA) with a calibrated micropipet. The dilute stock solutions were prepared by making appropriate serial dilutions of a commercially available certified 1,000 pg/mL cadmium standard stock solution (Fisher Chemical Co., Lot 913438-24) with the diluting solution (4% HNO3, 0.4% FICI). Each set contained six samples and a sample blank. The amount of cadmium in the prepared sets were equivalent to 0.5, 1 and 2 times the Action Level TWA target concentration of 2.5 pg/m for a 60 L air volume. 

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. 

---