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Query: UMLS:C0847097 (acidity)
 15,165 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Grated cassava to which tap water was added at levels of 25%, 50% and 75% (v/w) was held at 30 degrees C, 40 degrees C or 50 degrees C and examined over a 6 h period for cyanide content, pH and titratable acidity (TTA). During the come-up time, i.e. the time between addition of water and attainment of desired holding temperature (between 14 and 47 min), reductions in bound cyanide of ca 54-85% occurred, depending on the level of added water and holding temperature. The corresponding losses for the control samples, to which no water was added, were ca 25-33%. The biggest reduction in the bound cyanide of > 99% (from 89.0 to 0.6 ppm) occurred in grated cassava with 75% added water held at 50 degrees C. There was little or no change in pH during the period of study. The reduction of processing time for certain cassava products based on separation into detoxication and flavour development/fermentation stages is discussed.
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PMID:Changes in cassava toxicity during processing into gari and ijapu--two fermented food products. 149 86

Acid precipitation affects the solubility of several metals in aquatic systems and in soil. Cadmium levels in tap water samples from geological areas having low resistance to acidic pollution were significantly higher than those in samples from a neighbouring reference area where there was a different geological structure. The median cadmium levels and pH values were 0.14 microgram l-1 and 5.6 respectively, for the acidic areas compared with 0.07 microgram l-1 and 6.4 respectively for the reference area. Further, there was a significant inverse relationship between both cadmium and lead contents and the pH values of the samples. The mobility of the metals was thus dependent on the acidity. The blood lead levels in 195 subjects from the acidic areas were lower than those in 91 subjects from the reference area (medians 60 vs. 70 micrograms l-1); no significant differences were found in blood cadmium or blood mercury levels. Subjects in the acidic areas had lower plasma selenium levels than those from the reference area (medians 85 vs. 90 micrograms l-1); the difference was mainly attributed to subjects with private wells. The data may indicate a negative effect of the acidic pollution on selenium intake via water and/or foods. There was also a positive relationship between intake of fish on the one hand and blood mercury and plasma selenium on the other, which is in accordance with the role of fish as a source of these metals.
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PMID:Acidic deposition and human exposure to toxic metals. 343 37

The potential impact of acidic precipitation on the environmental mobility of the metalloids arsenic (As) and selenium (Se) has not been given much attention and is poorly understood. As with other elements, the interest here is the potential effect of environmental acidification on environmental behavior in ways that are relevant to human exposure to these metalloids. Available information on acid precipitation and the environmental behavior of these metalloids do, however, permit some preliminary conclusions to be drawn. Both As and Se appear to be mobilized from household plumbing into tap water by the corrosive action of soft, mildly acidic water, while surface water catchment systems in areas impacted by acidic deposition may contain elevated soluble As levels. Acidification of aquatic ecosystems that are drinking water sources may pose the prospect of enhanced release of As from sediment to water as well as reduction in water levels of Se. Acidification of ground waters, where As appears to be especially mobile, is of particular concern in this regard. The potential impact of acidic deposition on As and Se in soils cannot readily be assessed with respect to human exposure, but it would appear that the behavior of these metalloids in poorly buffered, poorly immobilizing soils, e.g., sandy soils of low metal hydrous oxide content, would be most affected. The effect is opposite for the two elements; lowered pH would appear to enhance As mobility and to reduce Se availability. Altered acidity of both soil and aquatic systems poses a risk for altered biotransformation processes involving both As and Se, thereby affecting the relative amounts of different chemical forms varying in their toxicity to humans as well as influencing biogeochemical cycling.
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PMID:Potential impact of acid precipitation on arsenic and selenium. 407 75

Acids and alkalies were instilled into the eyes of 2 groups of rabbits; the eyes of one group were washed with tap water 30 s after exposure. Damage seen in washed and unwashed eyes was not always related to pH. Some strong acids with greater acidity than pH 2.5 produced opacities while 0.3% hydrochloric acid with a pH of 1.28 produced no ocular damage. Phenol (5%) and acetic acid (5%) with pHs greater than 2.5 produced damage equivalent to or greater than that produced by equal concentrations (w/v) of the mineral acids. All alkalies with pHs ranging from 11.5 to 13.5 produced opacities and other ocular damage of different degrees depending upon the alkali and its concentration. For example, low concentrations of some alkalies in the pH range from 11.3 to 12.8 produced no ocular changes. The duration of the corneal opacities produced by phenol, 1% sodium hydroxide, acetic acid and anhydrous sodium carbonate and the onset of corneal opacity produced by 5% sulfuric acid, the weak acids and 1% sodium hydroxide were reduced as a result of washing the test eyes 30 s after instillation of the test material. These data suggest that acidity and alkalinity of the test material are not the only factors to be considered in relation to a substances' capacity to produce severe ocular injury. The concentration of the test chemical and its period of contact with the eye prior to washing are also important.
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PMID:Ocular irritancy responses to various pHs of acids and bases with and without irrigation. 698 67

Bicarbonate-calcic water Ferrarelle has been administered both in the fasting state and during meals to patients suffering from gastro-esophageal reflux disease submitted to computerized pHmetry. Marked and lasting increase of esophageal and gastric pH was observed with significant differences from the effect of tap water. In addition, patients reported improvement of heart burn and acidity after the administration of the bicarbonate-calcic water. The alkalizing effect of the mineral water employed is therefore fully confirmed.
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PMID:[Alkalizing activity of a calcium-bicarbonate-containing water, evaluated for pH, in patients with gastroesophageal reflux]. 822 43

New procedures for the preservation stage of ripe olives from Hojiblanca cultivar were studied. An aerobic fermentative process was used with initial pH correction (0.3% acetic acid) and various NaCl concentrations: 6, 3 and 0% (w/v) in tap water. Treatments were carried out at industrial level and the spontaneous changes monitored. At initial salt concentrations of 6 and 3% (w/v) NaCl, pH rose progressively, reaching 4.3 at equilibrium maintaining during this period a constant free lactic acidity of around 0.4% (w/v). When the initial solution was tap waste, however, the pH decreased rapidly to stabilize at about 3.7, and lactic acidity increased continuously to reach values over 1% (w/v) at the end of the preservation process. In all treatments aeration effectively purged the carbon dioxide from the preservation brines, preventing shrivelling of olives. The microbial growth was strongly influenced by the initial NaCl concentration. At 6 and 3%, only yeasts grew, the most abundant being Pichia membranaefaciens, P. vini, P. fermentans and Hansenula polymorpha. However, when there was no NaCl, lactic acid bacteria colonized the solution. Lactobacillus plantarum and Pediococcus inopinatus were the only species found. In this case there was a co-existence between yeasts and lactic acid bacteria. As the treatment that supported lactic acid bacteria achieved the best final pH and acidity for olive stability, it may help to overcome the obstacles to a lactic fermentative process during the preservation stage of ripe olives from the Hojiblanca cultivar.
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PMID:Microflora of the aerobic preservation of directly brined green olives from Hojiblanca cultivar. 824

A simple, sensitive, highly selective, automatic spectrofluorimetric method for the simultaneous determination of selenium (IV) and (VI) as selenite-selenate by flow injection analysis (FIA) has been developed. The method is based on the selective oxidation of the non-fluorescent reagent 2-(alpha-pyridyl)thioquinaldinamide (PTQA) in acidic solution (1.5-3.0 M H2SO4) by SeIV to give an intensely fluorescent oxidation product (lambda ex =350 nm; lambda em = 500nm). Selenium (VI) is reduced on-line to SeIV, in a reduction coil installed in a photo-reactor, which is then treated with PTQA and the fluorescene due to the sum of SeIV and SeVI is measured; SeVi is determined from the difference in fluorescence values. Various analytical parameters, such as effect of acidity, flow rate, sample size, dispersion coefficient, temperature, reagent concentration and interfering species were studied. The photo-reduction conditions were optimized, with an FIA procedure, for SeVI on the basis of its reduction efficiency. The calibration graphs were rectilinear for 0.1-2.4 micrograms ml-1 of SeVI and 10 ng ml-1-2.2 micrograms ml-1 of SeIV, respectively. The method was applied to the determination of Se in several Standard Reference Materials (alloy, sediments and tea), as well as in some environmental waters (tap and surface water), food samples (flour and egg), a biological sample (human hair), soil sample and in synthetic mixtures. Up to 25 samples per hour can be analysed with an RSD approximately 0.1-2%.
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PMID:Simultaneous spectrofluorimetric determination of selenium (IV) and (VI) by flow injection analysis. 915 38

A method has been developed for the speciation of trace dissolved Fe(II) and Fe(II) in water by on-line coupling of flow injection separation and preconcentration with inductively coupled plasma mass spectrometry (ICPMS). Selective determination of Fe(III) in the presence of Fe(II) was made possible by on-line formation and sorption of the Fe(III)-pyrrolidinecarbodithioate (PDC) complex in a PTFE knotted reactor over a sample acidity range of 0.07-0.4 mol L(-1) HCl, elution with 1 mol L(-1) HNO3, and detection by ICPMS. Over a sample acidity range of 0.001-0.004 mol L(-1) HCl, the sum of Fe(III) and Fe(II), i.e., Fe(III + II), could be determined without the need for preoxidation of Fe(II) to Fe(III). The concentration of Fe(II) was obtained as the difference between those of Fe(III + II) and Fe(III). With a sample flow rate of 5 mL min(-1) and a 30-s preconcentration time, an enhancement factor of 12, a retention efficiency of 80%, and a detection limit (3s) of 0.08 microg L(-1) were obtained at a sampling frequency of 21 samples h(-1). The relative standard deviation (n = 11) was 2.9% at the 10 microg L(-1) Fe(III) level. Recoveries of spiked Fe(III) and Fe(II) in local tap water, river water, and groundwater samples ranged from 95% to 103%. The concentrations of Fe(III) and Fe(II) in synthetic aqueous mixtures obtained by the proposed method were in good agreement with the spiked values. The result for total iron concentration in the river water reference material SLRS-3 was in good agreement with the certified value. The method was successfully applied to the determination of trace dissolved Fe(III) and Fe(II) in local tap water, river water, and groundwater samples.
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PMID:Speciation of dissolved iron(III) and iron(II) in water by on-line coupling of flow injection separation and preconcentration with inductively coupled plasma mass spectrometry. 1078 57

After a topical fluoride application two resulting features can be observed and measured: the formation of calcium fluoride and a decrease in caries incidence. For the formation of solid calcium fluoride the source of calcium may be either the enamel itself or remaining saliva or--in plaque--plaque fluid and calculus. The aim of the present study was to examine whether saliva through its calcium content has any influence on the amount of calcium fluoride formed by a topical fluoride treatment of enamel. The roots and the fissure systems of 64 freshly extracted intact third molars were covered with nail varnish and allocated to eight groups of 8. Half of the groups were put in fresh paraffin-stimulated saliva for 5 min after which surplus of saliva was shaken off whilst the other groups remained in distilled water. The teeth were given a 2-min topical treatment with either distilled water (control), neutral 0.2% NaF, neutral 2% NaF or 2% NaF acidified with 0.1 mol/l H3PO4. After the topical treatment the teeth were rinsed in running tap water for 5 min, dried and revarnished before determination of calcium fluoride. It was found that the amount of calcium fluoride formed depended on the concentration of fluoride (the higher the fluoride concentration, the higher was the amount of calcium fluoride), the acidity of the solution (presumably due to the increase in available calcium through enamel dissolution) and the presence of saliva (presumably due to its calcium content and its mucinous nature). As there was always more calcium fluoride formed in the presence of saliva, thorough drying of the teeth prior to topical treatments may be superfluous.
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PMID:The influence of saliva on the formation of calcium fluoride-like material on human dental enamel. 1112 98

The acid-induced cloud-point extraction (CPE) technique based on sodium dodecylsulfate (SDS) micelles has been used for preconcentration of ten representatives of polycyclic aromatic hydrocarbons (PAHs) for the following fluorescence determination. The effect of the acidity of solution, SDS and electrolyte concentrations, centrifugation time and rate on the two-phase separation process and extraction percentages of PAHs have systematically been examined. Extraction percentages have been obtained for all PAHs after CPE ranged from 67 to 93%. Pyrene was used as a fluorescent probe to monitor the micropolarity of the surfactant-rich phase compared with SDS micelles and this allows one to conclude that water content in micellar phase after CPE is reduced. The spectral, metrological and analytical characteristics of PAH fluorimetric determination after acid-based CPE with sodium dodecylsulfate are presented. Advantages provided by using CPE in combination with fluorimetric determination of PAHs are discussed. The determination of benz[a]pyrene in tap water is presented as an example.
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PMID:Preconcentration and fluorimetric determination of polycyclic aromatic hydrocarbons based on the acid-induced cloud-point extraction with sodium dodecylsulfate. 1599 62


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