Metal calibration standards

Both the solution used to spike the filters and the mixed metal calibration standard were prepared from deliquescent Ni(. 6LL0 and had to be standardized (standard addition technique) to establish concentration. 2 ... 

Prepare calibration standards of the selected metal, with concentrations suggested by your instructor, from a 1000 ppm stock solution. Dilute each to the mark with distilled water and shake well. 

A convenient method is the spectrometric determination of Li in aqueous solution by atomic absorption spectrometry (AAS), using an acetylene flame—the most common technique for this analyte. The instrument has an emission lamp containing Li, and one of the spectral lines of the emission spectrum is chosen, according to the concentration of the sample, as shown in Table 2. The solution is fed by a nebuhzer into the flame and the absorption caused by the Li atoms in the sample is recorded and converted to a concentration aided by a calibration standard. Possible interference can be expected from alkali metal atoms, for example, airborne trace impurities, that ionize in the flame. These effects are canceled by adding 2000 mg of K per hter of sample matrix. The method covers a wide range of concentrations, from trace analysis at about 20 xg L to brines at about 32 g L as summarized in Table 2. Organic samples have to be mineralized and the inorganic residue dissolved in water. The AAS method for determination of Li in biomedical applications has been reviewed . 

This yields 0.5%, 1%, 5%, 10%, 20%, 30%, 40%, and 50% trans calibration standards, respectively. Neat fat should not be stored in glass vials, as trace metals in the glass will accelerate the oxidation process. 

Calibration standards are prepared by single or multiple dilutions of the stock metal solutions. A reagent blank and at least three calibration standards should be prepared in graduated amounts in the appropriate range of the linear part of the curve. The calibration standards must contain the same acid concentration as in the samples after processing. 

The ICP was a Perkin-Elmer 3000DV with an AS90 Autosampler, which has an instrument detection limit of about 1 ppb (for most elements) with a linear calibration up to 100 ppm (for most elements). Solid samples were prepared via microwave digestion in concentrated nitric and hydrochloric acids, then diluted to volume. The ICP was calibrated and verified with two independent, certified standard sets. Spikes and dilutions were done for each batch of samples to check for and/or mitigate any matrix effects. The ICP process ran a constant pump rate of 1.5 mL/min for all samples and standards during analysis. A 3 mL/min rinse and initial sample flush were used to switch between each sample and standard. The plasma was run at 1450 W with argon flow. Trace metal-grade (sub-ppb) acids and two independently NIST-certified calibration standard sets were used for calibration and method verification. 

The metrological complex including the hydrogen analyzer and the calibration standards allows realization of the principle of unity of measurement means in conducting analysis of various metals and alloys and obtaining additional information on the volume and structure of bulk and surface mechanical defects. 

The optimization of the atomic absorption method of determining metals in particulates found in the air of workplace is described. The Plackett-Burman Youden-Steiner balanced incomplete block designs as well as single-factor experiments were utilized with ten metals Be, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, and Pd. Of the parameters tested, perchloric acid digestion, flame-stoichiometry, and the composition of the calibration standards were the most significant. Perchloric acid affected the recoveries of chromium. This was attributed to the formation of volatile chromylchloride. Flame-related phenomena and interelemental effects were brought under control using lanthanum flame buffer. 

Using either commercially available metal in oil standards or organometallic standards, prepared as described in Section III, prepare calibration standards by dilution with white spirit. Standards for Ca, Ba and Mg must contain 1000/igKml-1 as ionisation suppressant. Choose a concentration range for each element which exhibits an approximately linear response. 

The analyst uses ICP-OES (inductively coupled plasma, optical emission spectroscopy) to measure twenty different metal ions in solution. To fully calibrate the instrument requires the preparation and measurement of 100 individual calibration standards (five point calibration per element). It would be impracticable for an analyst to calibrate the instrument daily. The instrument is calibrated at regular intervals (say fortnightly) by the analyst. In the intervening time, the calibration for each metal ion is checked by the use of a set of drift correction standard solutions. Minor corrections can then be made to the calibration to allow for day-to-day drift. 

Metallic foils can be conveniently measured in absorption geometry. An a-Fe foil of 25 tim thickness and an area of 1 cm is often used as a calibration standard. With such a foil and using a Co source with an activity of 50mC, it is possible to acquire a decent spectrum at room temperature in less than 1 h. 

Serious consideration and time must be given to whether the component of interest is in exceptionally high concentration which, in such cases, may have to be diluted to fit calibration standards or, if low, may require pre-concentration. In some cases it may be necessary to carry out a trial-and-error to ascertain the approximate concentration of metals in samples. The low value must at least be at quantitative limits (i.e. ten times the standard deviation of baseline noise, to be confident of results see Section 3.8.1.7). If it is lower than ten times standard deviation of the baseline the sample may have to be preconcentrated prior to analysis to a level that can be comfortably detected and is suitable for reproducible measurements. The following is a list of common methods of sample preparation techniques. Choosing the correct method is of primary importance and poses a challenge to most analysts, particularly for unknown samples ... 

Sample dissolution is probably one of the most common operations in analytical chemistry and is carried out by dissolving in a suitable solvent to a suitable concentration that the analyte of interest can be reproducibly measured. If the composition of the non-aqueous solution is amenable to combustion in a flame or plasma, direct aspiration is possible. Unfortunately, ICP-AES instruments do not have the same solvent tolerance as AAS and require that the solvent selected be stable, non-quenching and non-interfering. Calibration standards are usually prepared in the same metal-free solvent, keeping in mind the effect of sample in the solvent. If the nebulisation efficiency of sample/solvent mixture is different to standards prepared in the same solvent only, then corrective actions must be taken so this anomaly can be taken into consideration. 

Typical plastics used in electronic and electrical appliances are polyethylene, polypropylene or polyethene terphthalate, and these are studied here as part of the RoHS requirement for the presence of toxic metals. This method is to show that analysis of these plastics used in electrical and electronic equipment is essential, especially if the origin of the plastic is unknown and the supplier is unable to state whether or not they are free of these metals. The metals are measured against calibration standards curves for each metal and may also include additional attachments for improving limits of detection such as ultrasonic nebulisers for Cd, Pb and Cr and the cold trap method for Hg. 

The application of atomic spectroscopy methods to the analysis of petroleum products is important to the oil industry. All oil samples must be prepared in solution form and be at a concentration so as to be detected to quantify all metals of interest with accuracy and precision. Solutions containing petroleum products in organic solvents may be measured directly or with the use of internal standards to correct for viscosity effects. It is important that the selected solvent dissolves the oil and products and does not cause erratic flickering of the plasma, or quenches it. It is also important that the same solvent can be used to prepare calibration standards. The following methods are common sample preparation methods for metal analysis of crude and lubricating oils. 

Table 5.9 shows the results of analysis of the low viscosity 75 oil spiked with 5.0 pg mI 1 (ppm) for metals against standard calibration curves generated for each metal. 

Analysis. Multi-element calibration standards of 0.0, 5.0 and 10.0 ppm Fe, Ca, B, Cu and A1 are prepared by dissolving 0.5 and 1.0 ml of 1000 ppm multi-element standard control stock in tetralin solvent to 100 ml with the same concentration yttrium internal standard as for samples A and B. Both samples are stirred and nebulised to determine the metal content against a standard calibration curve and corrected with an internal standard using ICP-OES. 

Table 7.5 Results of analysis of effects of low viscosity lubricating oil (Conostan 20) spiked with and without enhancing agents for the analysis of 0.5 (igmC1 of each metal against standard calibration curves, similar to Figure 7.13. All analyses were carried out using scandium as internal standard. Nl, no increase in signal...

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