Hiiii,, I want to understand this experimemnt can u help me :( also i want to un

Question

Hiiii,,

I want to understand this experimemnt can u help me :(

also i want to understand the result and discussion :lllll

Fluorescence Determination of Quinine in Tonic Water Experiment 2

Author: Laura Clesi Lab Partner: Julie Ngo

Objective

The purpose of this introductory experiment is to become familiar with a technique often used
in quantifying the concentration of unknown substances: fluorescence determination. More specifically,
the analysis of quinine concentration in tonic water which makes famous night club drinks fluoresce
blue.

IV. Experimental Procedure

Preparing Stock Solutions. The first step for this experiment involved preparing three stock
solutions. The calibration standards were prepared by diluting the stock solution of quinine with a
diluted H2SO4. The H2SO4 was diluted to 100 mL of 1 M solution according to the following sample
calculation:
SC 1 m1v1 = m2v2
(17.6 M) * (x mL) = (1M) * (100 mL)
x = 5.68 mL  
Fig. 3 Schematic of an optical system for obtaining total luminescence spectra with a CCD detector.[2]
From this, a 0.05 M solution of H2SO4 was prepared according to the following calculation:
SC 2 m1v1 = m2v2 (to get a 0.05M H2SO4 solution)
(1 M) * (x mL) = (0.05 M) * (500 mL)
x = 25 mL
The quinine stock solution was prepared according to the following cocktail: 10 mg quinine, 5 mL of 1 M
H2SO4, and filled to the mark with deionized water.
Preparing the Fluorometer. The fluorometer had to be appropriately set in order to progress
with the quinine standards’ readings. In Simple Reads mode, the excitation wavelength was set to 350
nm. In Scan mode, the emission wavelength was manually identified as “corrected” at 455 nm by the
maximum wavelength identified as the peak of the resulting bell-shaped curve, and set accordingly.
Detection limit was also determined by reading the same blank 20 times.
Gathering Data: Standards. After preparing a set of quinine standards with concentrations of
0.5, 1.0, 2.0, 3.0, and 4.0 ppm, each solution was poured in a cuvette and placed inside the fluorometer
for a rapid reading. Initially, the readings were done with a detector at medium voltage. Based on the
extremely high readings, the detector was exchanged for one that could analyze the sample within a
reasonable fluorescence percentage.  
Gathering Data: Quinine. The tonic water sample was then examined at various dilutions (10x,
20x, 50x, and 100x) in order to find which dilution would be within the range of standards in order to
have this unknown value fit within a calibration plot.  
Fluorescence Quenching. In order to investigate a property of fluorescence not associated with
the results being manipulated called “quenching,” we ran quinine samples (5 mL) with various amounts
of NaCl (0, 0.1, 1.0, 3.0, and 5.0 mL) added to them.  
  

V. Data and Results

Quinine Standards. The quinine calibration standards’ data are presented in Table 1 (medium
voltage) and Table 2 (low voltage). A calibration plot is presented in Graph 1 based on the more
reasonable readings from the low voltage detector. This plot has a slope of 8.4624 and a regression
coefficient (R2) of 0.9997.  
Detection Limit. Table 3 shows the data from the 20 readings of the “blank” trial, as well as the
pertinent information involved in solving for the limit of detection. Quenching trends are shown in Table
4. These values were solved according to the following calculations:
SC 3 Average of “blank” trials (Xbl) = (0.064)/20 = 0.003  
Conf. Int. (95%): Xavg ± (ts)/sqrt(n) = 0.003 ± (1.729*0.094)/sqrt(20) = 0.003 ± 0.036  
Standard deviation of “blank” trials (sbl ) = 0.094, based on Excel
Minimum detectable signal (SM) = Xbl + 3sbl = 0.285
Slope of calibration plot (m) = 8.4624
Limit of Detection (LD) = (SM-Xbl) / m = (0.285-0.003) / 8.4624 = 0.033
After determining these statistics, we found the concentration of quinine in the tonic water using the
best-fit line equation using the 20x dilution.
SC 4 y = 8.4624x – 0.2022
22.641 = 8.4624x – 0.2022
x = 2.699
Concentration of quinine = 20x = 53.99 ppm or mg/L



VI. Discussion and Analysis of Results

Quinine Concentration. Unfortunately, the amount of quinine is not listed on the product’s
nutrition facts.[3] However, it’s interesting to note that the FDA limits the amount of quinine in tonic
water to 83 ppm or 83 mg/L.[4] The experimental value we found of 54 ppm is within this range.
Quenching Trends. The experimental values for our quenching portion of this study (Table 4)
show the same trend as expected. With increasing concentrations of NaCl—despite constant
concentrations of quinine—the intensity of the readings decrease dramatically. In fact, once 5 mL of the
NaCl solution was added to 5 mL of the quinine solution, the % fluorescence decreased by half.
General Assessment. Overall, this data met the objectives for this experiment and were of good
quality. The regression coefficient reading (0.9997) is very high and shows that the best-fit line is of good
quality and represents the data well. This is important because we used the slope of this best fit line in
later analysis, so this lends to the quality of the calculations as a whole. In addition to manually
correcting for emission wavelength setting, a set of quinine standards was used in order to determine an
appropriate sensitivity level. These QC methods assisted in the accuracy and precision of our data.
Additional ways to improve would be to perform more trials when taking data for the quinine calibration
plot (Table 2, Chart 1).

Explanation / Answer

plz check this paper from journal of chemical education to guide you

http://pubs.acs.org/doi/pdf/10.1021/ed052p610

Journal of chemical education, Volume 52. Number 9. September 1975,page 610

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