Solubility of Tricalcium Citrate in Solutions of Variable Ionic Strength and in Milk Ultrafiltrates

Summary Solubility of tricalcium citrate has been determined at 21 and 95° C. by dissolution in water and by precipitation from supersaturated solutions containing various proportions of calcium to citrate and at pH 4.4 to 8.8. Solubility product in solutions at equilibrium varied with ionic strength, according to the relation pks = 17.63 − 10.84 μ , but was unaffected by variations in pH and temperature and by the presence of magnesium or phosphate ions. Milk ultrafiltrates were shown to be saturated with tricalcium citrate, i.e., the calculated pk s values agreed with the solubility product in all but two of the 15 samples tested, and composition of two ultrafiltrates was unaffected by agitation with crystals of tricalcium citrate

Direct Analysis of Lactose in Milk and Serum

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Analysis for Citric Acid in Presence of Casein

Summary Factors affecting citric acid determination in the presence of casein were studied with the pyridine-acetic anhydride method. Although the opalescence in skimmilk tests affected results by only 2%, the turbidity introduced by solutions of isolated casein could cause gross overestimation. A pH above 12.3 in the test aliquot assured a clear reaction mixture with both skimmilk and casein solutions. It is, therefore, recommended that test aliquots containing casein should comprise sufficient alkali to insure a clear reaction. Acid casein required seven resuspensions in fresh washing solution at pH 4.5 for complete removal of occluded citrate, lactose, and calcium. Adsorption of citric acid by casein precipitated at the iso-electric point, or with trichloroacetic acid, was demonstrated and appears to account for the lower citrate concentration in acid sera, as compared to skimmilk. These results extend the conclusions of a previous paper

Direct determination of citric acid in milk with an improved pyridine-acetic anhydride method.

Summary The determination of citric acid with pyridine and acetic anhydride has been investigated at reaction temperatures from 17 to 60° C. The optimum proportions of pyridine, acetic anhydride, water, and acetic acid for maximum color intensity and stability are given for each temperature. The procedure has been modified to eliminate the violent nature of the reaction, even when the analysis is done at a reaction temperature of 60° C. Details of a method for the determination of 25–200 μ g. of citric acid, at a reaction temperature of 32° C., are presented. In comparison with previously published methods based on the reaction, the recommended technique results in improved sensitivity, stability, and reproducibility without requiring careful timing. The method has been successfully applied to the routine analysis of milk and milk products. Milk and serum can be analyzed directly, after suitable dilution. Corrections for the interference caused by fat in homogenized milk, and by trichloroacetic acid in T.C.A. serum, can be made easily. Results of direct analysis of milk were from 5 to 15% higher than those for the corresponding sera and are believed to represent the true values for the citric acid content of milk

Incomplete Release of Citrate During Acid Precipitation of Casein

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Turbidimetric Micro-Determination of Magnesium in Milk

Summary From 5 to 40 μ g. of magnesium can be determined by measuring the turbidity formed when the potassium salt of erucic acid is added in the presence of potassium oxalate. Preliminary removal of calcium as oxalate is achieved rapidly at room temperature; other milk components do not interfere. Analysis of various samples of milk and serum by the present technique showed that, compared with ashed samples, direct analysis gave results which agreed within±3.3%. The method is simple, convenient, and suitable for routine analysis

Preparation of a Standard for Citric Acid Analysis

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The impact of selected contextual factors on experts' clinical reasoning performance (does context impact clinical reasoning performance in experts?).

Item does not contain fulltextContext specificity, or the variation in a participant's performance from one case, or situation, to the next, is a recognized problem in medical education. However, studies have not explored the potential reasons for context specificity in experts using the lens of situated cognition and cognitive load theories (CLT). Using these theories, we explored the influence of selected contextual factors on clinical reasoning performance in internal medicine experts. We constructed and validated a series of videotapes portraying different chief complaints for three common diagnoses seen in internal medicine. Using the situated cognition framework, we modified selected contextual factors--patient, encounter, and/or physician--in each videotape. Following each videotape, participants completed a post-encounter form (PEF) and a think-aloud protocol. A survey estimating recent exposure from their practice to the correct videotape diagnoses was also completed. The time given to complete the PEF was randomly varied with each videotape. Qualitative utterances from the think-aloud procedure were converted to numeric measures of cognitive load. Survey and cognitive load measures were correlated with PEF performance. Pearson correlations were used to assess relations between the independent variables (cognitive load, survey of experience, contextual factors modified) and PEF performance. To further explore context specificity, analysis of covariance (ANCOVA) was used to assess differences in PEF scores, by diagnosis, after controlling for time. Low correlations between PEF sections, both across diagnoses and within each diagnosis, were observed (r values ranged from -.63 to .60). Limiting the time to complete the PEF impacted PEF performance (r = .2 to .4). Context specificity was further substantiated by demonstrating significant differences on most PEF section scores with a diagnosis (ANCOVA). Cognitive load measures were negatively correlated with PEF scores. The presence of selected contextual factors appeared to influence diagnostic more than therapeutic reasoning (r = -.2 to -.38). Contextual factors appear to impact expert physician performance. The impact observed is consistent with situated cognition and CLT's predictions. These findings have potential implications for educational theory and clinical practice.1 maart 201

A Design Task Advisor. Artificial Intelligence Education

NRC publication: Ye