Acceptability of HPV vaccine among a national sample of gay and bisexual men.
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- Extraction into chloroform of the lanthanides, using 2,5-dimethyl-2hydroxyhexanoic acid .
- The extracted metal species is highly aggregated.
II. LANTHANIDE EXTRACTIONS
- A variety of extracting agents have been investigated for use in the solvent extraction separation of the rare earths.
- These agents can be roughly placed into the following classifications: 1) neutral phosphates, 2) acidic phosphates, 3} amines, 4) carboxylic acids, and 5) other.
- For this reason this chapter, in addition to reviewing lanthanide extractions, will discuss some of the more pertinent applications to nuclear waste processing.
- Extractant, is the liquid phase that extracts.
- Distribution ratio (D), is the ratio of the total equilibrium concentration of all f'orms o!' the substance in the e..v..taac t to total equilibrium concentration of all forms in the aqueous phase.
A. Neutral Phosphorus Agents
- Tributylphosphate (TBP) has been one of the most thoroughly studied extracting agents for the lanthanides.
- At higher acidities partial anion coextraction occurs, which lowers the separation factors (14, 15) .
- Its lanthanide separation factors are better than those of HDEHP, but problems with the coextraction of other metals has prevented its use in waste reprocessing (27) .
- Monoacidic phosphinates are also strong extracting agents.
III. CARBOXYLIC ACID LANTHANIDE EXTRACTION
- This chapter is divided into two sections.
- The first section concerns itself with the mechanisms and equilibria involved in extractions using carboxylic acids.
- The second section reviews lanthanide carboxylate extractions in detail.
- Some of the equilibria discussed in the first section have been em~loyed in the evaluation of such extractions.
A. Extraction Equilibria
- Extraction of metals by carboxylic acids involves the formation of metal carboxylates and can be represented by: (1) where the subscripts a and o denote the aqueous and organic phases, respectively.
- This assumption is not valid if: 1) the acid is appreciably soluble in the aqueous phase; 2) the acid dimerizes in the organic phase; or 3) the initial metal concentration is of the same order of magnitude as the organic acid concentration.
- When the value of x obtained from a log D vs pH plot is The extraction of a single aggresated species (MAx)J(HA)n yields the following expression: K = D[Mx+Jl-J.l[H+].
- As applied to extraction, the method consists of varying the proportions of two reacting species while keeping the s~m of the two concentrations constant and measuring the amount of extraction.
- Though useful for simple systems, the molar ratio method suffers from similar drawbacks as those inherent in the isomolar series method.
B. Extraction of Lanthanides
- In the previous chapter, a variety of extracting agents for the lanthanides was reviewed.
- In the latter, the ketone probably helps to solvate the complex.
- In a series of papers Korpusov et al. (56) and Danilov et al. (57, 58) have reported on extractions using a,adisubstituted carboxylic acids, usually containing eight or nine carbons.
- With an increase in solvent polarity, KD 0 decreased and PHA increased.
- Applying these constants , in analyzing lanthanide extractions, the extracting species were all found to be LnA 3 (HA) 3.
Comparison of log
- The hydrate number varied between one and two, but approached one at increasing lanthanide salt concentrations.
- At salt concentrations greater than 10-3 M, the extracting species may be aggregated.
- For lanthanide separations, these a,adisubstituted carboxylic acids showed better selectivity than either the naphthenic or normal carboxylic acids.
- Have been noted by Mikhailichenko" et al.
- About 300 g of crude product (45% yield) were kindly provided by the above and were recrystallized from a 1:1.
C. Acid Anion Protonation Constant
- The acid anion protonation constant was obtained from pH measurements on a series of independently prepared DMHHA c solutions, each containing a different amount of added KOH.
- This KN0 3 amount was calculated from an estimated protonation .
- In one method, the metal was re-extracted into J M HCl and then titrated with EDTA.
- Gave reasonably good analyses, but neither was well~suited for small samples.
- In some of the distribution experiments, the acid content of the aqueous phase was needed.
C. Acid Distribution Studies
- The distribution behavior of DMHHA between chloroform and water is depicted in Figure 1 , where E is defined as the ratio of the concentrations of total unionized organic acid to total unionized aqueous acid.
- As can be seen, The typical infrared spectrum of DMHHA displayed a sharp band at 2960 cm-l on top of a broad but not intense band ranging from 3~bo to 28bo ~m-1.
A. Neodymfum-DMHHA Stability Constants
- The main point of interest in most metal extraction studies is the means by which the metal extracts, that is, the nature of the extracting species.
- The aqueous phase interaction between the metal and the extracting agent should be invP.Rt1iated.
- X X Rather than studying all of the lanth~nides, one was chosen for detailed analysis in this investigation.
- The stability constant calculations will now be discussed.
- 0 X All of the quantities except the 8's are known or directly measurable.
•ment and the equation [A]= ([H]tot-[H])/~[H]. Measuring
- The pH valu~ unde~ i different conditions givea i equations.
- (At this point for further simplification, the. value of x is made equal to 3).
- This .system of i equations and 3 unknowns is solved by a least-squares multiple linear regression.
- The least-squares analysis proceeds by minimizing the sum of the squares of the individual residuals Ei.
- In a series of experiments holding the pH constant, the distribution ratios were measured.
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