Alkalinity samples

Protein False positives may occur with highly buffered or alkaline samples or from contamination with quaternary ammonium compounds (antiseptics, detergents). 

Other halide ions, especially bromide and iodide, are interference in this analysis. Acidity alkaline samples before analysis. Fe3+, CrO, . and SOT at concentrations above 10 mg/L are often used to interfere with the analysis. 

The above procedure is similar to the analysis of total cyanide in the alkaline distillate described in the preceding section, except that the sample pH are different. In the above method, chlorination is done on the alkaline sample at a pH between 11.5 and 12. On the other hand, in the determination of cyanide (total), the pH of the distillate is maintained below 8 with acetate buffer before adding chloramine-T solution. 

Sampler 2 collects the pH and conductivity/alkalinity samples immediately after the filtered water samples. Like the filtered samples, they should be collected from the mid-stream flow, on the upstream side of the sampler. Thoroughly rinse the sample containers and caps with stream water three times. Submerge the containers in the stream to fill then seal underwater, ensuring that all air has been expelled. Place the unfiltered samples into a clean, self-seal polythene bag along with the knotted bag containing the filtered water samples. 

Tsalev et al. [3] explored the advantages of using V(V) as a chemical modiber in ETAAS, particularly when determining As. This modiber is compatible with alkaline sample solutions, samples solubilized in TMAH, and slurries. 

A nonoxidative alkaline sample digestion procedure using TMAH and a high-pressure, MW-assisted autoclave-digestion system was developed [16]. The Si concentrations of the solubilized samples were measured by ICP-AES. The method was developed and tested using Si-spiked ascorbic acid and applied to samples of animal tissue and organs. 

Early protocols to measure ATP from cell cultures involved an acid or alkaline sample extraction step to precipitate proteins and inhibit ATPases (Lundin et al. 1986 Crouch et al. 1993). This was followed by removal of debris by centrifugation or filtration and a step to neutralize the pH of the sample prior to addition of luciferin and firefly luciferase to generate a flash of light proportional to the amount of ATP. Early reagents that created flash kinetics required luminometers with injection capabilities that hindered their use for HTS. 

The primary scintillator converts excitation energy into light. Two commonly used primary scintillators are PPO (2,5-diphenyl-oxazole) and butyl-PBD (2-(4 -tert-butyl-phenyl)-5-(4 -biphenyl)-l,3,4-oxadiazole). The pulse voltage produced by butyl-PBD is about 20% greater than that produced by PPO, but its usefulness is reduced because of its limited solubility. Suitable concentrations of PPO and butyl-PBD are about 5 g/1 and 7 g/1 respectively. With alkaline samples butyl-PBD produces a brownish colour in the scintillation cocktail. In highly quenched samples, a higher concentration may be required for optimum efficiency. 

Alkaline sample dialyzed with solvent, dialyzates separated and concentrated. HR6C-MS 3-4 pg 60-70% Kosaka et al. 1984... 

To a slightly alkaline sample solution (pH 8-9), containing not more than 25 pg of Mg and free from the Group I-Hl metals add, in a 25-ml volumetric flask, 10 mg of ascorbic acid and 10 mg of potassium cyanide (to mask possible traces of Fe, Ni, Cu, Zn, and other metals). After 5 min, add 1 ml of buffer solution and 25 ml of the Eriochrome Black T reagent. Dilute the solution with water to volume in a 25-ml standard flask and measure the absorbance at 520 nm against a reagent blank. 

Haddad, Laksana and Simons [3] described a device for off-line neutralization of strongly alkaline samples. The method uses an electrodialysis cell comprising three compartments separated from each other by cation-exchange membranes (Fig. 9.2). 

Cations can pass through the membrane but anions cannot. The cathode compartment of the cell was typically filled with 20 mL of 0.1 M sodium hydroxide, the anode compartment with 10 mL of 0.05 M sulfuric acid, and the sample compartment contained 2 mL of highly alkaline sample. Application of power (< 3 W) resulted in currents of 100-200 mA. As shown in the figure, water is reduced to H2 -t- OH" in the cathode and is oxidized to O2 + H" in the anode compartment. To complete the electric circuit cations must be carried from the anode through the sample solution to the cathode. 

S. Laksana and P. R. Haddad, Dialytic clean-up of alkaline samples prior to ion chromatographic analysis,/. Chromatogr., 602, 57,1992. 

Yamamoto et al. (1980) reported incomplete recovery of both inorganic and total mercury when the Magos method (see Differentiation between inorganic and organic mercury ) was applied on blood, liver, and spleen of mice, which had been simultaneously injected with equal molar doses of mercuric chloride and sodium selenite. The recovery increased to the expected level when the alkalinized samples were heated to 40 °C for at least 30 min. 

Speciation analysis of iodine in human urine samples has also been carried out by ion chromatography (IC) combined with ICP-MS (Stark etai, 1997). Because of the possible interconversion of the iodine species, depending on the pH value, different eluent—column combinations were used for acidic or alkaline sample solutions. Iodide, iodate and several unidentified, presumably organo-iodine species could be separated and detected. 

Sample preparation with methanol in an acid medium causes partial methylation of benzoylecgonine, which is determined as cocaine. The morphine is acetylated by the acetic anhydride to give heroin. If alkaline sample preparation is used, it is not possible to determine THC and secobarbital. Separate sample preparations would be necessary to enable these components to be analyzed. 

Fig. 13-7. Gas chromatogram of the interlaboratory test of Sample A. Alkaline sample pretreatment by solid phase extraction.

Fig. 13-9. Gas chromatogram of die interlaboratory test of Sample B. Alkaline sample pretreatment with solid phase extraction.

On taking the sample, convert the free, dissolved carbon dioxide and hydrogen carbonates into carbonates by adding sodium hydroxide. In closed apparatus in the laboratory, add acid to the weakly alkaline sample to... 

Evaporate the weakly alkaline sample to less than 1000 ml, allow to cool, and acidify with 25 % hydrochloric acid until all the soluble substances... 

Active Donnan dialysis is employed most commonly with ion chromatography and is useful for clean-up of sample solutions at extreme pHs. Electrodialysis can be used with ion chromatography for the off-hne analysis of strongly alkaline samples containing trace amounts of common inorganic anions. ... 

Haddad, P.R. Laksana, S. On-line analysis of alkaline sample with a flow-through electrodialysis device coupled to an ion chromatography. J. Chromatogr. 1994, 671, 131 139. 

R. G. Simons, Electrodialysis for cleanup of strongly alkaline samples in ion chromatography./. Chromatogr., 640, 135,1993. 

The efficiency of the extraction methods in acid-aqueous media (0.1 M HCl, or 0.1 M HCl-methanol) or in chloroform solution (for pre-alkaline samples) was investigated. Various devices (ultrasound device, shaking machine, Soxhlet-apparatus) were used for the extraction. The best method was the extraction with 0.1 M HCl- methanol (1 1, v/v) in ultrasound device. 

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