Chemical Buffering Capacity Research Articles

Binding Acanthamoeba to mannose-glycoproteins of corneal epithelium: effect of injury: ERRATUM

PURPOSE. The buffering action of human tears is thought to be important to keep its pH constant. We measured the change in pH in the precorneal tear film in vivo when the acidic solution is challenged, using a fluorophotometric technique. METHODS. Twelve eyes from 6 healthy subjects were entered in this study. Each subject was pretreated with either one drop of 0.4% oxybuprocaine for once (light anesthesia), three times (deep anesthesia), or none (controls). The measurement was initiated by instilling 20 µl of 0.067 M phosphate buffer at pH 5.5 containing 2 mM bis-carboxyethyl-carboxyfluorescein free acid, a pH sensitive dye, into the subject's eye. The pH was determined by the ratio of fluorescent intensities at two excitation wavelengths (490 and 430 nm). pH recovery time (PHRT) as defined by the time required for pH to reach 95% of pH at equilibrium was used for the marker of tear buffering action. Tear turnover rate was also determined using the fluorescent decay curve at 430 nm, which was independent of pH, but dependent on dye concentration. RESULTS. Immediately after the instillation, the pH value in the tear film was around 6.0–6.5 in all cases. The tear film rapidly became more alkaline, reaching its normal value in 2.3 ± 0.5 min in untreated eyes. The pretreatment with 0.4% oxybuprocaine retarded the neutralization process. A single regression analysis revealed that the PHRT had a significant negative correlation with the tear turnover rate (r = -0.78). CONCLUSIONS. Our results suggest that the neutralization process of tears largely depends on the tear turnover rate. The buffering action of tears in vivo consists of the tear turnover as well as its chemical buffering capacity.

Fluorophotometric measurement of the buffering action of human tears in vivo

PURPOSE. The buffering action of human tears is thought to be important to keep its pH constant. We measured the change in pH in the precorneal tear film in vivo when the acidic solution is challenged, using a fluorophotometric technique. METHODS. Twelve eyes from 6 healthy subjects were entered in this study. Each subject was pretreated with either one drop of 0.4% oxybuprocaine for once (light anesthesia), three times (deep anesthesia), or none (controls). The measurement was initiated by instilling 20 µl of 0.067 M phosphate buffer at pH 5.5 containing 2 mM bis-carboxyethyl-carboxyfluorescein free acid, a pH sensitive dye, into the subject's eye. The pH was determined by the ratio of fluorescent intensities at two excitation wavelengths (490 and 430 nm). pH recovery time (PHRT) as defined by the time required for pH to reach 95% of pH at equilibrium was used for the marker of tear buffering action. Tear turnover rate was also determined using the fluorescent decay curve at 430 nm, which was independent of pH, but dependent on dye concentration. RESULTS. Immediately after the instillation, the pH value in the tear film was around 6.0–6.5 in all cases. The tear film rapidly became more alkaline, reaching its normal value in 2.3 ± 0.5 min in untreated eyes. The pretreatment with 0.4% oxybuprocaine retarded the neutralization process. A single regression analysis revealed that the PHRT had a significant negative correlation with the tear turnover rate (r = -0.78). CONCLUSIONS. Our results suggest that the neutralization process of tears largely depends on the tear turnover rate. The buffering action of tears in vivo consists of the tear turnover as well as its chemical buffering capacity.

Efeito da aplicação de efluente da fábrica de celulose junto com fosfogesso na correção da acidez do solo

Foram coletados vários efluentes alcalinos da fábrica de celulose a fim de estudar a utilização destes junto com fosfogesso na correção da acidez do solo. Avaliou-se o poder de neutralização dos efluentes e a lixiviação de sódio na presença de fosfogesso numa coluna de terra. A aplicação do efluente eleva o pH do solo e o volume de efluente necessário para atingir pH 6,5 depende da sua composição química e o poder tampão de acidez do solo. A lixiviação de sódio é maior quando o fosfogesso é incorporado ao solo. A combinação do efluente com o fosfogesso corrige a acidez do solo, aumenta o teor de cálcio e, ao mesmo tempo, reduz o acúmulo de sódio no solo.

Measuring Alkalinity Accurately in Aqueous Systems Containing High Organic Acid Concentrations

ABSTRACT Alkalinity is one of the most important parameters in biological waste management systems. It is a measurement of the chemical buffering capacity and its level therefore is an indication of the biological health of aqueous waste treatment processes. Alkalinity is based primarily on the carbonate-bicarbonate-carbonic acid complex as the major contributor. The measurement of alkalinity for years has been based on the fact that titration to a pH endpoint of 4.3 or 3.7 {Standard Methods, 1985, 1980) would measure all the carbonic acid system. While this is true, in waste management processes where organic acids are significant, titration to this pH also measures much of the organic acid complex. This is a false alkalinity since the pKa of most organic acid systems is below 4.75. Jenkins et al. (1983) first expressed concern about this phenomenon. Described here is a simple titrametric procedure for determining alkalinity in wastewater samples that is approximately 10 times more accurate than the Standard Methods (1985) procedure. The study used synthetic controlled chemical solutions. The levels of organic acid, true bicarbonate alkalinity and endpoint titration pH were closely controlled and their influence on the measured alkalinity was determined. The results show that titration to pH 4.3, when organic acids are present, can result in great error (ca. 600%) in measured alkalinity. Using the procedure proposed here, the error is much less (<45%).

Optimal Parameters of Silver Metal Based Air-Gap Cyanide Sensors

Analytical characteristics of air-gap cyanide sensor incorporating metallic silver as indicator electrode have been investigated as function of chemical composition, pH, buffer capacity, concentration and volume of the absorbent electrolyte film covering the indicator electrode. Simple silver nitrate electrolyte provides results equivalent to those obtained with a dicyanoargentate(l) electrolyte, but its preparation is easier. The pH of absorbing solution should be kept at pKHCN=9.3. Convenient buffer capacity can be assured by a medium concentrated (10-1 M) appropriate buffer system (e.g. borax-borate). Optimal electrolyte concentration is about 10"* mol/l, while the volume of electrolyte must be of several microlitres for assuring good reproducibility. For interpretation of the results an equation correlating equilibrium activity of the acidified sample solution with that of the absorbing film has been determined, and the relationship between the e.m.f. and the pH of the film has been derived. Thus, the entire 4-phase system (sample solution, air-gap, absorbing film, potentiometric sensor) can be described as a closed equilibrium system.