Solid sampling techniques Calibration curve

Another unique approach is to produce a dry aerosol from a standard aqueous solution with a pneumatic nebulizer and desolvator. The aerosol produced by this apparatus is combined with the aerosol from the ablation cell using a dual gas-flow sample introduction system and a gas-mixing cell. By varying the concentration of the analyte in the standard aqueous solution, calibration curves can be created by this procedure. The composition of the standard solution can be adjusted to match the matrix composition of the bulk material of the solid sample, thereby simulating the behavior of the ablated solid in the plasma. Secondary standards can be created by this technique from selected samples. Future calibration curves can be prepared from ablating these secondary standards. 

It is known that Selenium catalyzes reaction of some dye reduction by Sulphide. On this basis spectrophotometric and test-techniques for Selenium determination are developed. Inefficient reproducibility and low sensitivity are their deficiencies. In the present work, solid-phase reagent on silica gel modified first with quaternary ammonium salt and then by Indigocarmine was proposed for Selenium(IV) test-determination. Optimal conditions for the Selenium determination by method of fixed concentration were found. The detection limit of Se(IV) is 10 ftg/L = 2 ng/sample). Calibration curve is linear in the range 50-400 ftg/L of Se(IV). The proposed method is successfully applied to the Selenium determination in multivitamins and bioadditions. 

Conditioning of the manganese oxide suspension with each cation was conducted in a thermostatted cell (25° 0.05°C.) described previously (13). Analyses of residual lithium, potassium, sodium, calcium, and barium were obtained by standard flame photometry techniques on a Beckman DU-2 spectrophotometer with flame attachment. Analyses of copper, nickel, and cobalt were conducted on a Sargent Model XR recording polarograph. Samples for analysis were removed upon equilibration of the system, the solid centrifuged off and analytical concentrations determined from calibration curves. In contrast to Morgan and Stumm (10) who report fairly rapid equilibration, final attainment of equilibrium at constant pH, for example, upon addition of metal ions was often very slow, in some cases of the order of several hours. 

Fig. 2 Calibration curve in Round No. 73. Calibration data are shown by dots, the calibration curve obtained by the ordinary least squares technique, by the solid regression line 5 the limits of the regression corridor by dotted lines 4 and 6 the result of the ethanol determination in the sample by the dotted lines 1 and 8 the calibration curve for 3-times increased uncertainty of the certified value by the solid regression line 3, and the limits of its corridor by thin lines 2 and 7...

The use of NMR spectroscopy as an analytical technique is well established ( 1 8). In order to quantitate our spin-echo height to the number of protons present, we performed an independent calibration using standard solutions of naphthalene in carbon tetrachloride. Concentrations for the standards were chosen to correspond to the anticipated supercritical C02 solubilities, and all calibration measurements were performed using a sample cell of the same dimensions as the solubility sample cell previously described. The response of our spectrometer to the standard solutions was linear over the concentration range. The reproducibility for independent measurements of the calibration curve was 3 . Throughout the experiment, all spectrometer conditions (pulse lengths, phases, receiver amplifier gain, etc.) were closely monitored, and frequent checks on the calibration of the spectrometer were performed. In this way we were able to obtain the molar solubility of solid naphthalene in supercritical carbon dioxide to an estimated experimental accuracy of 6%. 

Calibration is carried out using standard calibration curves. The simplicity, repeatability, and low cost of the method have allowed its use for routine determination of trihalomethanes in tap water. SOME has also been compared with solid phase microextraction (SPME), purge and trap (P T), and direct aqueous injection (DAI) [10]. This technique offers accuracy comparable with that obtained using P T and DAI. With respect to conventional LEE, the SDME method is more accurate. In contrast to DAI and P T, it requires no special equipment. SDME has been used for extraction of chlorophenols [II], pesticides [12, 13], warfare agents [14], and butanone derivatives [15], and for control of food products [16]. The low costs of the SDME method (typical GC syringe and 2-3 pL of solvent), simplicity, and short extraction time (approximately 15 min) make it particularly suitable for preliminary analyses of organic pollutants in water samples. It can also be an effective alternative to SPME, as it does not require the use of expensive instrumentation. 

The ultimate development in the field of sample preparation is to eliminate it completely, that is, to make a chemical measurement directly without any sample pretreatment. This has been achieved with the application of chemometric near-infrared methods to direct analysis of pharmaceutical tablets and other pharmaceutical solids (74-77). Chemometrics is the use of mathematical and statistical correlation techniques to process instrumental data. Using these techniques, relatively raw analytical data can be converted to specific quantitative information. These methods have been most often used to treat near-infrared (NIR) data, but they can be applied to any instrumental measurement. Multiple linear regression or principal-component analysis is applied to direct absorbance spectra or to the mathematical derivatives of the spectra to define a calibration curve. These methods are considered secondary methods and must be calibrated using data from a primary method such as HPLC, and the calibration material must be manufactured using an equivalent process to the subject test material. However, once the calibration is done, it does not need to be repeated before each analysis. 

If the mean diameter of the particles is very small (1-2 fxm), standard calibration curves can be prepared using an aqueous standard, direct calibration technique (see Chapter 7). One or more suitable internal standard elements are required to compensate for the difierences in sensitivities of analytes that occur between the aqueous standards and the solid sample matrix.The use of internal standards ensures maximum accuracy of the calibration process. 

TGA has been used with some success to determine the extent of sublimation of volatile solid materials. TGA-DSC can be applied to determine the corresponding sublimation enthalpies, which are usually difficult to determine by conventional methods. The determination of sublimation enthalpies is notoriously difficult since with most volatile solids, the effusion process is rarely smooth and continuous and thus the use of STA for this purpose is a most welcome adjunct to many less reliable analytical techniques which rely on an ideal sublimation process. For sublimation studies, the sample is sealed in a container with a small pin-hole in the lid. The TGA curve shows a progressive mass loss until the sample is exhausted. The corresponding DSC curve shows a deviation from the base-line equivalent to the sublimation enthalpy which can be correlated with the rate of mass loss. Calibration of the... 

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