Original sample

Now assume that a subsequent measurement of the component of angular momentum along the lab-fixed z-axis is to be measured for that sub-population of the original sample found to be in the P-state. For that population, the wavefunction is now a pure P-function ... 

Equation 5.7 can be solved for the concentration of analyte in the original sample. 

A third spectrophotometric method for the quantitative determination of the concentration of in blood yields an Sjamp of 0.193 for a 1.00-mL sample of blood that has been diluted to 5.00 mb. A second 1.00-mL sample is spiked with 1.00 )J,L of a 1560-ppb Pb + standard and diluted to 5.00 mb, yielding an Sspike of 0.419. Determine the concentration of Pb + in the original sample of blood. 

The concentration of Pb + in the original sample of blood can be determined by making appropriate substitutions into equation 5.7 and solving for C. Note that all volumes must be in the same units, thus Vj is converted from 1.00 )J,L to 1.00 X 10-3 mb. 

II. 5 (arbitrary units). A second 50-mL aliquot of the sample, which is spiked with 1.00-mL of a 10.0-ppm standard solution of the analyte, gives a signal of 23.1. What is the concentration of analyte in the original sample ... 

Construct an appropriate standard additions calibration curve, and use a linear regression analysis to determine the concentration of analyte in the original sample and its 95% confidence interval. 

As a final example, the determination of carbon in steels and other metal alloys can be determined by heating the sample. The carbon is converted to CO2, which is collected in an appropriate absorbent trap, providing a direct measure of the amount of C in the original sample. 

Each of these titrations was conducted on a 50.00-mF aliquot of the original 250.0-mF sample. The mass of each analyte, therefore, must be corrected by multiplying by a factor of 5. Thus, the grams of Ni, Fe, and Cr in the original sample are... 

A sample of Crystal Pepsi, analyzed as described here, yields an absorbance of 0.565. What is the concentration of phosphorus, reported as parts per million of P, in the original sample of Crystal Pepsi ... 

This represents the amount of Na2S203 in a 10.00-mF portion of a 100-mF sample, thus 0.1325 g of Na2S203 is present in the original sample. The purity of the sample, therefore, is... 

This analysis is an example of a concentration technique. Once the original sample is brought to volume in the 100-mL volumetric flask, any portion of the sample solution, even that obtained on filtering, may be used for the analysis. 

The concentration of insulin in a production vat is determined by the method of isotope dilution. A 1.00-mg sample of insulin labeled with with an activity of 549 cpm, is added to a 10.0-mL sample taken from the production vat. After homogenizing the sample, a portion of the insulin is separated and purified, yielding 18.3 mg of pure insulin. The activity for the isolated insulin is measured at 148 cpm. How many milligrams of insulin are in the original sample ... 

An important feature of isotope dilution is that it is not necessary to recover all the analyte to determine the amount of analyte present in the original sample. Isotope dilution, therefore, is useful for the analysis of samples with complex matrices, when a complete recovery of the analyte is difficult. 

Schematic illustrations of the effect of temperature and surface density (time) on the ratio of two isotopes, (a) shows that, generally, there is a fractionation of the two isotopes as time and temperature change the ratio of the two isotopes changes throughout the experiment and makes difficult an assessment of their precise ratio in the original sample, (b) illustrates the effect of gradually changing the temperature of the filament to keep the ratio of ion yields linear, which simplifies the task of estimating the ratio in the original sample. The best method is one in which the rate of evaporation is low enough that the ratio of the isotopes is virtually constant this ratio then relates exactly to the ratio in the original sample.

The thermospray inlet/ion source does not produce a good percentage yield of ions from the original sample, even with added salts (Figure 11.2). Often the original sample is present in very tiny amounts in the solution going into the thermospray, and the poor ion yield makes the thermo-spray/mass spectrometer a relatively insensitive combination when compared with the sensitivity attainable by even quite a modest mass spectrometer alone. Various attempts have been made to increase the ion yield. One popular method is described here. 

This thermal ionization process requires fiiament temperatures of about 1000-2000°C. At these temperatures, many substances, such as most organic compounds, are quickiy broken down, so the ions produced are not representative of the structure of the original sample substance placed on the filament. Ionization energies (1) for most organic substances are substantially greater than the filament work function (( )) therefore 1 - ( ) is positive (endothermic) and few positive ions are produced. 

Eventually, not only neutral solvent molecules but also ions start to desorb from the surface of each droplet, Ions, residual droplets, and vapor formed by electrospray are extracted through a small hole into two evaporation chambers (evacuated) via a nozzle and a skimmer, passing from there into the analyzer of the mass spectrometer, where a mass spectrum of the original sample is obtained. 

Thermal decomposition of perchlorate salts to chloride, followed by the gravimetric determination of the resulting chloride, is a standard method of determining quantitatively the concentration of perchlorates. Any chlorates that are present in the original sample also break down to chloride. Thus results are adjusted to eliminate errors introduced by the presence of any chlorides and chlorates in the original sample. 

Radioactivity in environmental waters can originate from both natural and artificial sources. The natural or background radioactivity usuaUy amounts to <100 mBq/L. The development of the nuclear power industry as weU as other industrial and medical uses of radioisotopes (qv) necessitates the deterrnination of gross alpha and beta activity of some water samples. These measurements are relatively inexpensive and are useful for screening samples. The gross alpha or beta activity of an acidified sample is deterrnined after an appropriate volume is evaporated to near dryness, transferred to a flat sample-mounting dish, and evaporated to dryness in an oven at 103—105°C. The amount of original sample taken depends on the amount of residue needed to provide measurable alpha or beta activity. 

Ash. After the sample is heated ia a cmcible over a hot plate to drive off volatile solvents and moisture, it is charred over a Bunsen burner and then transferred to a muffle furnace where final ignition is completed. The weight of the ash is determined and reported as a percentage of the weight of the original sample. 

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