Sample dead water

Somebody gave you a sample of water from the Dead Sea containing about 70 g/L NaCl. Could you measure this amount of NaCl in a 50-mL sample adding the same amount of silver nitrate reagent used in this experiment (5 mL 0.01 N) ... 

A new method for measuring environmental tritium levels without enrichment was recently developed by the authors (Cawley t al , 1980). This method is basically a double isotope, external standard count procedure which eliminates the background by measuring tritium free water scimples ("dead water" samples) and applying a difference method. 

The most delicate part of the method developed to measure environmental tritium levels is the elimination of the background. A difference method has been applied for this purpose using "dead water" samples, i.e. tritium free water samples obtained from National Bureau of Standards. 

The environmental and dead water samples exhibit quenching characteristics falling into the range of 0.5 - 0.6 quenched standards (Packard Instrument Co.) for tritium and carbon-14. During each cycle an efficiency calibration using the quenched standards is made. A cycle consists of counting the 15 sample vials, 2 or more vials of dead water, and the 4 quenched standards (two carbon-14 and two tritium standards). The selected count period is 20 minutes. 

The numerous short counting periods, the large number of vials coupled with the efficiency calibration data from the external standard count, the quenched standards, and the vials with mixtures of either scintillator-sample or scintillator-dead water make this a program of data organization and reduction. To eliminate the need to change the source progreun due to different numbers of observations from one sample run to another, the PL/1 feature of dynamic allocation of storage has been used. This allows the user to define the dimensions of the arrays for the input data. It is not uncommon for the arrays for the quenched standards, the dead water, and the sample data to have different dimensions. 

The data from the quenched standards and the AES for the sample and dead water are used to calculate the efficiency of... 

Once the efficiencies for the sample and the dead water and their respective count rates in Channels I and II are determined, the tritium concentrations in pico-Curies per liter and the associated error may be calculated for each sample vial. 

On February 8, it was found that eight drinking wells were contaminated with cyanide (UNEP/OCHA, 2000). A week later, the water appeared to be safe to drink. On March 6, 17 scientists from seven countries finished sampling the water of the Danube River, 800 km downstream from the mine. A total of 180 tons of dead fish were removed from Hungary s Szamos and Tisza Rivers. Aceording to Hungary s Minister of the Environment, the recovered fish represented only 15% of the total fish killed, while an estimated 15% drifted down the Tisza into Yugoslavia and another 15% were still trapped under ice. 

The Waters company recommends a system check of the chromatographic equipment that is used for plate number determination and analyses (2) the columns in the GPC unit used are replaced by a zero dead volume union. Then the test sample is injected under the same conditions such as a plate number determination. The 5a peak width measured on a suitable recorded peak is evaluated this 5or width of a 20-/a1 injection should be lower than 150 /a1. 

Ideally, the sample should be taken from a valve installed specifically for sampling. When sampling valves are not installed the taking of samples from locations where sediment or water can collect, such as dead ends of piping, tank drains, and low points of large pipes and filter bowls, should be avoided if possible. If samples are taken from pipe drains, sufficient fluid should be drained before the sample is taken to ensure that the sample actually represents the system. Samples are not to be taken from the tops of... 

The dead point is obtained by including in the sample a trace of an unretained solute or, more often, one of the components of the mobile phase. For example, when using a methanol water mixture as the mobile phase, the dead point is obtained from the elution of a pure sample of methanol. The pure methanol can often be monitored, even by a UV detector, as the transient change in refractive index resulting from the methanol is sufficient to cause a disturbance that is detectable. 

Benzwi [409] determined lithium in Dead Sea water using atomic absorption spectrometry. The sample was passed through a 0.45 pm filter and lithium was then determined by the method of standard additions. Solutions of lithium in hexanol and 2-ethylhexanol gave greatly enhanced sensitivity. 

By this method the weighed dry product is dissolved in methanol and titrated with the Karl Fischer solution until the color changes from brown to yellow. The visual observation can be replaced by an ammeter, which shows an steep increase in current, when the titration is terminated (dead-stop-titration). The samples can be two to four times smaller than for the gravimetric method. To avoid the visual observation completely, iodine can be produced by electrolyzation and the water content is calculated by Coulomb s law. Such an apparatus (e. g. Fig. 1.97.1 and 1.97.2) is available commercially. The smallest amount of water to be detected by such instruments is 10 pg. Wekx and De Kleijn [1.84) showed, how the Karl Fischer method can be used directly in the vial with the dried product. The Karl... 

Implementation Samples of the river water, sediments, and even some of the dead fish are taken to the contract lab where their chemists use GC-MS, after appropriate sample preparation, to determine that there are no toxic compounds at significant levels i.e., high enough to harm the fish. Your own results for heavy metals are also negative—nothing above safe limits was detected. 

The test organisms are exposed for 24, 48, and 96 hours to different concentrations of testing water. After the exposure period the number of dead organisms is counted. Each test sample container is examined and the number of dead organisms counted (looking for the absence of swimming movements). A test is regarded as valid if the mortality in the control is <10%. Toxicity is calculated as ... 

The LPS silica is prepared by extracting the water from a low solids hydrogel with an organic solvent to avoid the compression of aqueous surface tension. This leaves a fragile catalyst of very high pore volume. Such preparations often provide dramatic examples of the effect of pore volume because the same gel dried directly in an oven will frequently be less active or even completely dead. Invariably, nitrogen sorption shows the inactive silica to contain a low pore volume mainly inside small pores, e.g., less than 60 A diameter. In contrast, the active sample dried by extraction usually has equal or greater volume inside small pores, and, in addition, considerable volume... 

From these equations it can be seen that each mole of water requires one mole of I2. In a visual endpoint Karl Fischer titration, a sample is titrated with the Karl Fischer reagent until a permanent iodine color (indicating that all water has been reacted) is observed. Because of other reaction products, the color change is usually from a yellow to a brownish color, which may be difficult to detect visually. Highly colored samples may affect the visual end point as well. A much sharper end point, known as the dead stop end point, can be obtained if the titration is done electrometrically. Here, two small platinum electrodes dip into the titration cell, a small constant voltage is impressed across these electrodes, and any current that flows is measured with a galvanometer. At the end point of the titration the current either goes to a minimum or else increases suddenly from nearly zero. Commercially available Karl Fischer instruments incorporate semiautomatic microprocessors based on this principle. 

The layered structure and hydrophobic properties of zinc monoglycerate prepared by high-temperature alcoholysis of acetate (in contrast to the properties of the samples obtained from the water solutions at room temperatures) permit it to be applied as a lubricant and alternative to graphite and talc [700], The alkoxides ofmercury were used in the 1970s as fungicides [715, 819] but were found to be too poisonous and were forbidden as they caused the death of birds and small animals in several places in Europe ("The dead spring"). 

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