Multi-element standard solutions

Multi-element analysis by ETV-ICP-MS using ultrasonic slurry sampling of silicon based minerals such as talc or quartz is described by Rodriguez et al.33 The calibration was performed in the standard addition mode, where slurries were spiked with different weights (volumes) of a multi-element standard solution of the analytes of interest.33... 

Fig. 9.8. Relative sensitivity coefficients in LA-ICP-MS [ La,0,/SrCO,/MnOi stoichiometric mixture perovskite (La , 5Sr ,MnO,)] compared to ICP-MS [A 0.7 ppm multi-element standard solution]. (Reproduced with permission of Springer-Verlag.)...

Fig. 12-21. Multi-element spectra from a multi-element standard solution using Mo and W excitation, respectively. The peaks arise from an amount of 1 ng per element. The different peak heights reflect different sensitivities.

Check for spectral overlap by comparing a one element standard with a multi-element standard solution. 

Calibration was achieved with an ICP multi-element standard solution of 19 elements (Merck), to which known amounts of five other elements (K, Na, Ca, Mg and Hg) were added to complete it with all the desired standard elements. Mo could not be added because it provoked precipitation of other elements. Analytical data result from the average of 3 integrations. 

Standards are prepared from high purity salts dissolved with high purity acids or can be obtained as commercial solutions with a certified element content. These solutions are then diluted in order to obtain the desired concentration levels in the elements and an identical acidity to that of the sample solutions with which they are compared. Multi-element standards can be manufactured by mixing single-element solutions taking care to assure compatibility of the chemical species so as not to produce precipitates. 

Method for Preparation of Samples. To three 100.0 ml volumetric flasks accurately weigh approximately 10.0 g of metal free conostan oil 20 blend and dissolve one in 50 ml kerosene, the second in 50 ml tetralin and the third in 50 ml decalin. Repeat this for the metal free conostan 75 blend. To each of the six flasks add 1.0 ml of 500 ppm certified oil based multi-element standard containing the elements Cu, Fe, V, Ni, Na, Ti and Co and dilute to mark with the respective solvent. Each solution is shaken to dissolve the sample and spiked with standards to give 5.0 ppm of each metal for each solution. 

Method. The sample (in this case the metal-free blank Conostan 75 viscosity oil is spiked with known concentration of metals listed in Table 5.7 and is divided into four aliquots. To the four flasks add known increasing concentrations of the standard control stock solution (500 ppm of each metal) to 10.0 g of sample of to give 0.0, 2.5, 5.0 and 10.0 pgg-1 of multi-elemental standard when diluted to 100 ml in each solvent. The preparation is carried out using the solvents kerosene, tetralin and decalin made up to 100 ml. The samples are analysed and the linear curve is extrapolated to the negative concentration line to determine the concentration of each metal in the original spiked sample. 

Weigh accurately approximately 0.75 g of Conostan 75 high viscosity oil blend into a shallow platinum dish which is placed on a wire sample holder attached to the lid of the bomb. A 10 cm length of nichrome or platinum wire is connected between the electrodes. Then 5.0 ml of water or 0.05 M NaOH is added to the bottom of the vessel. To the aqueous solution add 0.125 ml of 100 ppm multi-element standard containing As, Hg and Se, respectively (MBH Cat. No. 255C 100) and 0.025 ml (25 pi) of 500 ppm multi-element standard containing Cd, Pb, Cr, and Sn, respectively (MBH 252C 12-500). 

Along with the matrix RMs, a series of other quality control tools such as calibrants and standard solutions was also produced. On the occasion of the first set of reference materials, calibrants for trace elements and major components were also prepared and sent to the laboratories in order to minimize the differences in results produced by the use of different calibrants. For the other two sets of materials, multi component standard solutions for PAHs and pesticides were prepared and distributed in order to check the analytical performance of the chromatographic methods used. 

Filter standards used for calibration and method assessment were prepared by adding 2 pL drops of standard solutions with concentration of 0-100 mg L onto blank filters. The solutions were prepared in 100 mL acid washed flasks by dilution of a multi-element standard (Merck CertiPUR, 1,000 mg L ) in 18 MQ cm water obtain from a Milli-Q Gradient system (Milhpore, Bedford, MA) with 7 mL eoneentrated nitric acid (65% HNO3, suprapure grade) and 2 mL of a Rhodamine B dye solution (prepared by dissolution of 0.125 g Rhodamine B... 

One half of the PTFE filters were used for the WS trace metal analysis. The WS metals were extracted by ultrasonicating for an hour at room temperamre with 20 ml of ultrapure water. The extracts were passed through a 0.45 mm pore size filter before analysis. Both extracts were analyzed for 14 metals, i.e., Al, Co, Cr, Cu, Fe, Mn, Pb, Cd, Ni, As, Ag, Ti, Zn and V, with the ELAN 6100 Inductive Coupled Plasma Mass Spectrometer (ICP-MS, PerkinEhner, Inc., MA, U.S.A.). Prior to each analytical batch, the ICP-MS was cafibrated with multi-element standards at different concentrations, prepared from serial dilution of 1,000 mg/1 of individual standard solutions, and its response was regularly verified by a calibration standard. The instmmental settings used for the analysis were similar to those recommended by the manufacturer. 

Prepare multi-element reference solutions which cover the working range from the stock and standard solutions corresponding to the element concentrations expected. 

Multi-element standard stock solutions are useful and permit more rapid determination of several elements of interest. 

Multi-element Standard—Using the aqueous standard solutions, prepare a multi-element standard containing 100 mg/L each of vanadium, nickel, and iron. 

Internal standard of Rh with 2 ppb concentration was added to all the solutions. Three certified Multi-element solutions (CLMS-1,-2,-4, SPEX, USA) were employed for constmcting calibration graphs. 

As discussed before, quadrupole based ICP-MS allows multi-element determination at the trace and ultratrace level and/or isotope ratios in aqueous solutions in a few minutes as a routine method with detection limits of elements in the sub pgml-1 range and a precision for determined trace element concentration in the low % range (RSD - relative standard deviation). The precision for isotope ratio measurements varies between 0.1% and 0.5% RSD. This isotope ratio precision is sufficient for a multitude of applications, e.g., for evidence of contamination of sample with depleted or enriched uranium in urine (this technique is used in the author s laboratory in a routine mode14) or the isotope dilution technique for the quantitative determination of trace element and species concentration after doping the sample with enriched isotope spikes. 

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