Element stock solutions, preparation

Standard solutions - Prepare at least three standard solutions by combining appropriate volumes of stock standard solutions or intermediate standard solutions in volumetric flasks. Dilute to volume with 1 % nitric acid. Chemical compatibility (i.e., of analytes, acids, etc.) must be considered to avoid the formation of analyte precipitates when mixing single element stock solutions to prepare standard solutions. 

ICP-AES element solutions with appropriate specifications, which may be used as stock solutions, are available commercially. They should be prepared according to the producer s instructions. Generally, hydrochloric or nitric stock solutions are provided which can be stored for several months. The formulations of element stock solutions are compiled in Table c. 

In flame spectrophotometric measurements we are concerned with solutions having very small concentrations of the element to be determined. It follows that the standard solutions which will be required for the analyses must also contain very small concentrations of the relevant elements, and it is rarely practicable to prepare the standard solutions by weighing out directly the required reference substance. The usual practice therefore is to prepare stock solutions which contain about 1000 ig mL 1 of the required element, and then the working standard solutions are prepared by suitable dilution of the stock solutions. Solutions which contain less than 10 igmL 1 are often found to deteriorate on standing owing to adsorption of the solute on to the walls of glass vessels. Consequently, standard solutions in which the solute concentration is of this order should not be stored for more than 1 to 2 days. 

Working solutions (1 litre) which were 10 7 mol/1 in one of the elements to be studied were prepared by appropriate addition of the radioactive stock solutions to pH-adjusted artificial seawater. After the pH had been checked, 100 ml portions were transferred to the bottles to be tested. The filled bottles were shaken continuously and gently in an upright position, at room temperature and in the dark. At certain time intervals, ranging from 1 min to 28 d, 0.1 ml aliquots were taken. These aliquots were counted in a 3 x 3 in Nal (TI) well-type scintillation detector, coupled to a single-channel analyser with a window setting corresponding to the rays to be measured. 

Calcium stock solution, 1000 jg Ca + mh - stock solutions of many elements for determination by AAS are available commercially. Details for in-house preparation will also be given. Anhydrous calcium nitrate, CafNOjfj, is dried for 1 h at 105°C, then cooled in a desiccator. Transfer 2.05 g to a 100-ml beaker containing water and stir to dissolve. Immediately add 1 ml HCI (36% m/m) to prevent hydrolysis, add with washings to a 500 ml volumetric flask, make up to the mark with water, and mix by shaking. 

A TLC system comprises three elements. As its name implies, one of the elements is thin layer coated mostly on a glass or plastic plate, which acts as a stationary phase. Such a plate is termed chromatoplate . The most popular materials (adsorbent) used to form the thin layer are silica gel and alumina powder. The other elements are a sample, and a solvent or solvent mixture (developer) which acts as a mobile phase to develop (elute) the sample. A stock solution of sample is prepared in advance of the TLC experiment and applied to the thin layer to form a spot. After removal of solvent contained in the spot, the sample is eluted with an appropriate... 

The concentration of humic acid was determined by TOC analysis. TOCs for the humic stock solutions were normally 2.3 0.1 g/L. Elemental analysis showed that the powdered humic substance was 52 carbon weight. This result indicates that the theoretical maximum of TOC for an 800-mL solution prepared from 4.0 g of humic substances is 2.6 g/L. 

Standard Lead Solution Prepare all lead solutions in 0.1% nitric acid. Use a single-element 1000 p,g/mL lead stock solution to prepare (weekly) an intermediate stock solution (1 p,g/ mL). Prepare (daily) a Standard Lead Solution (10 ng/mL) by diluting the intermediate stock solution 1 100 with 0.1 A nitric acid. 

For calibration, a series of standard solutions is prepared which differ in their concentration of the element to be determined but which are equal in their concentration of all other elements. When calibrating with a pure-element solution a stock solution which contains a high concentration of the element to be determined and which only has to be diluted in certain ratios is used. However, in the case of an analytical sample interferences have to be expected. It is recommended that a model solution is prepared... 

Sample Solutions. The urine sample solutions all originated from one composite urine sample. The latter was made by combining 150-mL aliquots of the entire first-morning voids of 16, presumably healthy, male subjects. Aliquots of the composite were used to prepare three sets of sample solutions as indicated in Table IV. The solutions in each set were "spiked with internal reference elements and with appropriate volumes of multielement stock solution to make a (multiple) standard addition series (12). The final gallium and yttrium internal reference-element concentrations were 1.0 and 0.1 mg/L, respectively, for both the reference and standard addition solutions. The added analyte concentrations for both the reference and standard addition solutions were 0, 2, 4, 10, and 20 times the approximate "normal analyte concentrations for urine, as listed in Table II. 

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. 

If there is no available salt of constant composition, such as copper(II) sulphate or iron(III), aluminium or chromium alums, it is advisable to prepare first a stock solution of an approximate concentration, slightly higher than required and to determine the concentration by a gravimetric or volumetric method. After suitable calculations the solution is diluted with pure solvent to obtain a solution containing exactly, e.g., 1 mg/ml of the given element. In some cases, standard solutions are obtained by dissolving a precisely weighed amount of the element in its pure form. 

Procedures are given for the preparation of stock standard solutions of elements of concentration 1 mg/ml. If no other statement is given, the working solutions (of concentration 100, 10, or 1 pg/ml) are prepared by appropriate dilution of the stock solutions. 

A stock solution of 140 meq/L Na and 4.1 meq/L K (20 times the concentration in the standard solution) can be prepared by dissolving 8.1 g NaCl and 0.21 KCl in 1 L water. This contains the normal levels of Na and K in serum and compensates for ionization interference due to these elements in the serum. Dilute this solution 1 20 in the standards. 

Stock solutions Nos. 1 and 2 contain those elements whose sulfides are precipitated from strongly acid solution. High-purity oxides of all these elements except antimony are readily soluble in hydrochloric acid. Antimony must be prepared as a separate stock solution because of its tendency to hydrolyze and precipitate as a basic chloride in dilute hydrochloric acid solution. This stock solution is stable for at least 30 days. 

Two series of standard solutions were prepared, each containing from 0.1 to 500 /ig./liter of each element. In the first series, prepared from stock solutions Nos. 1 and 2, only those elements which were expected to precipitate completely, or nearly completely, from acid solution were included (Table I). Similarly the second series, prepared from stock solutions Nos. 3 and 4, contained only those expected to precipitate completely, or nearly so, from ammoniacal solution (Table II). 

The extractants (0.05 mol L EDTA and 0.43 mol acetic acid) were prepared as laid out in the Annex (Section 11.7). All precautions were taken to avoid contamination during the extraction procedures. The trace element contents (Cd, Cr, Cu, Ni, Pb and Zn) in the extracts were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). Cali-brant solutions were prepared from stock solutions (1000 mg L ) of the individual elements in 0.5 mol HNO3. 

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