Monograph pubs.acs.org/doi/book/10.1021/acsreagents
Pararosaniline Hydrochloride (4-[(4-Aminophenyl)(-4-imino-2,5-cyclohexadien-1-ylidene)methyl]benzenamine Monohydrochloride) Part 4, Monographs for Reagent Chemicals: General Descriptions, Specifications, and Tests eISBN: 9780841230460 Tom Tyner Chair, ACS Committee on Analytical Reagents James Francis Secretary, ACS Committee on Analytical Reagents
ABSTRACT This monograph for Pararosaniline Hydrochloride provides, in addition to common physical constants, a general description including typical appearance, applications, and change in state (approximate). The monograph also details the following specifications and corresponding tests for verifying that a substance meets ACS Reagent Grade specifications including: Assay and Suitability for SO.
C19H17N3 • HCl
Formula Wt 323.82
CAS No. 569-61-9
GENERAL DESCRIPTION Typical appearance . . . . . . . . . . . . . . . . . . . green crystalline solid Applications . . . . . . . . . . . . . . . . . . . . . . . . determination of sulfur dioxide Change in state (approximate) . . . . . . . . . . . . melting point, 268–270 °C
SPECIFICATIONS Assay . . . . . . . . . . . . . . . . . . . . . . . . . . . . ≥99.0% C19H18N3Cl Suitability for SO2 determination:
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4255 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
Absorbance of reagent blank . . . . . . . . . . . . . ≤0.170 Calibration (µg/mL) . . . . . . . . . . . . . . . . . . . 0.706–0.786
TESTS Assay (By spectrophotometry at 540 nm).
For the Assay
S a m p l e S t o c k S o l u t i o n . Weigh accurately 0.200 g of sample. Dissolve completely by shaking with 1 N hydrochloric acid in a 100 mL volumetric flask, and dilute to volume (1 mL = 0.002 g).
Dilute 1.0 mL of sample stock solution with water to the mark in a 100 mL volumetric flask. Pipette 5.0 mL into a 50 mL volumetric flask, add 5 mL of 1 M sodium acetate–acetic acid buffer solution (described below), and dilute with water to volume. Allow to stand for 1 h at room temperature, and determine the absorbance at 540 nm with a spectrophotometer, using 1 cm cells at a slit width of 0.04 mm.
where A = absorbance and W = weight, in grams, of sample in 1.0 mL of sample stock solution.
For the Assay
S o d i u m A c e t a t e – A c e t i c A c i d B u f f e r S o l u t i o n , 1 M . Dissolve 13.61 g of sodium acetate trihydrate in water in a 100 mL volumetric flask. Add 5.7 mL of glacial acetic acid, and dilute to volume with water.
Suitability for SO2 Determination Note: All absorbance measurements using this procedure are temperature-dependent (0.015 AU/°C) and should be performed at 22 °C.
A b s o r b a n c e o f Re a g e n t B l a n k . Pipette 10 mL of 0.04 M potassium tetrachloromercurate and 1 mL of 0.6% sulfamic acid solution (both described below) into a 25 mL volumetric flask. Allow to stand for 10 min, then add from a pipette 2.0 mL of 0.2% formaldehyde solution (described below) and 5.0 mL of pararosaniline reagent (described below). Dilute to volume with water, allow to stand for 30 min, and determine the absorbance at 548 nm in 1 cm cells, using water as the reference. C a l i b r a t i o n C u r v e S l o p e . Pipette 1.0 mL of sulfite standard solution (described below) into a 25 mL volumetric flask. Add 9 mL of 0.04 M potassium tetrachloromercurate and 1 mL of 0.6% sulfamic acid, allow to stand for 10 min, then add from a pipette 2.0 mL of 0.2% formaldehyde solution and 5.0 mL of pararosaniline reagent. Dilute to volume with water, allow to stand for 30 min, and determine the absorbance at 548 nm in 1 cm cells, using water as the reference.
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4255 ACS Reagent Chemicals, Part 4
ACS Reagent Chemicals
Monograph
pubs.acs.org/doi/book/10.1021/acsreagents
where As = absorbance of sample; Ab = absorbance of reagent blank; and W = weight, in micrograms, of SO2 in 1 mL.
Reagents and Solutions for Testing Suitability for SO2 Determination All six reagents cited should be freshly prepared.
F o r m a l d e h y d e S o l u t i o n , 0 . 2 % . Dilute 0.5 mL of 36–38% formaldehyde with water to 100 mL. Prepare this solution daily. Pa r a r o s a n i l i n e Re a g e n t . Pipette 20.0 mL of sample stock solution of pararosaniline (described above in the assay) into a 250 mL volumetric flask. Add an additional 0.2 mL of stock for each percent the pararosaniline assay is below 100%. Add 25 mL of 3 M phosphoric acid, and dilute to volume with water. Po t a s s i u m Te t r a c h l o r o m e r c u r a t e , 0 . 0 4 M . Dissolve 10.86 g of mercuric chloride in water in a 1 L volumetric flask. Add 5.96 g of potassium chloride and 0.066 g of EDTA, dissolve, and dilute with water to volume. The pH of this reagent should not be less than 5.2. S u l f a m i c A c i d S o l u t i o n , 0 . 6 % . Dissolve 0.6 g of sulfamic acid in 100 mL of water. This solution can be kept for a few days if protected from air. S u l fi fitte S t a n d a r d S o l u t i o n . Immediately after its standardization, pipette a 2 mL aliquot of sulfite stock solution (described below) into a 100 mL volumetric flask, and dilute to volume with 0.04 M potassium tetrachloromercurate. This solution is stable for 30 days if stored at 5 °C. S u l fi fitte S t o c k S o l u t i o n . Dissolve 0.40 g of sodium sulfite or 0.30 g of sodium metabisulfite in 500 mL of deaerated water (purged with high-purity nitrogen gas or by boiling). This solution contains 320–400 µg/mL as sulfur dioxide. The actual concentration is determined by adding excess iodine solution and back-titrating with sodium thiosulfate solution that has been standardized against potassium iodate or potassium dichromate. Sulfite solutions are unstable. Standardize as follows: For blank solution A, in the back-titration, transfer 25 mL of water to a 500 mL iodine flask, and add from a pipette 50.0 mL of 0.01 N iodine. For sample solution B, in a second 500 mL iodine flask, add successively from a pipette 25.0 mL of sulfite stock solution and 50.0 mL of 0.01 N iodine. Stopper the flasks, allow to react for 5 min, and titrate each with 0.01 N sodium thiosulfate to a pale yellow color. Add 5 mL of starch indicator solution, and continue the titration to the disappearance of the blue color. Calculate the concentration of sulfur dioxide as follows:
© 2017 American Chemical Society
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DOI:10.1021/acsreagents.4255 ACS Reagent Chemicals, Part 4
