Precision Measurement Using UV/Vis Spectroscopy Lab Report

This experiment examines the impact of varied dilution volumes and maximum dye absorbance methods and relates the findings to the concept of precision in measurement.

Experiment 2: Precision Measurement Using UV/Vis Spectroscopy Lab Report
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Abstract
This experiment examines the impact of varied dilution volumes and maximum dye absorbence
methods and then relates the findings to concept of precision in measurement. Out of the 3
method of measuring volume, statistical analysis of results obtained in this experiment shows
that bulb pipette is more precise that air-displacement pipette and measuring cylinder.
INTRODUCTION
Background theory
The quantity of solute per solvent solution forms the basis of most chemical solution preparaiton.
Chemical preparation of solutions thus requires accuracy and precision in measuring both the
volume and mass. In most cases, the analytical techniques require standard solution preparation.
The low concentration of hazardous substances (μg/L levels) complicates weighing of small
amount of chemicals in analytical balance. Often, majority of these chemicals are in the form of
crystals and granular where individual crystal has as low weight as milligram thus complicating
the measurement process thus complicating the possibility of getting desired weight in analytical
balance (Pedersen, Gammelgaard, & Halvorsen, 2019).
In these measurement, precision and accuracy are important. Precision is a term that is used to
describe a relationship between a series of measurement to indicate whether they give similar
results (Laksmiwati, Junaidi, & Hakim, 2017). A precise measurement may not necessarily
mean that the measurement is accurate. In reality, no single set of value can be considered
similar (Valcarcel, 2012). Analysts thus usually make reference to the experimentally values
with some uncertainty range
This experiment compares the reliability of air displacement pipette, bulb pipette and measuring
cylinder. The report reports precision in measurement in terms of standard deviation, range of
variance, 95 % confidence interval and relative standard deviation of the impact of various
dilution quantities and methods of maximum absorbance value of a dye and then relates the
obtained findings to the measurement precision.
Aims
 To use an air-displacement piston pipette

 To use analytical balance
 To calibrate glassware
 To provide a demonstration of measurement equipment precision.
 To statistically analyses data
METHODOLOGY
Part 1
The pipette was inspected to familiarize with its correct operation under the supervision of the
operator. The pipette scale was then set at 1.00Ml mark. A capped 20Ml liquid was then placed
in the scintillation vial onto the balance before taring the balance. The vial was then removed
from the balance and then the cap removed with the air displacement pipette, 1mL of water was
then dispensed and the cap via placed on the balance. The weight displayed on the digital display
was then recorded on the LNB. The balance was then tared. The above steps were then repeated
9 more times for the weight of the dispenser.
Part 2
This section of the experiment was carried individually. A stock solution containing methyl
orange in water was provided. For the solution preparation, the desired volume of the stock was
transferred using air displacement pipette or a bulb pipette and then diluted to specified volume
with deionized water.
For solution 1, using an air displacement pipette, 1000uL of the stock solution was take and
diluted to 10.0mL in a volumetric flask and absorbance measured at 473 nm on the UV/Vis
spectrometer. The solution was then discarded and 4 more identical solutions prepared using the
same pipette and volumetric flask and their absorbance measured.
For solution 2, 10mL of the stock solution was then taken using a bulb pippete and the volume
diluted in a 100.0mL volumetric flask before measuring the absorbance at 473 nm on the UV/Vis
spectrometer. 4 replicates were then prepared in different volumetric flask and their absorbance
measured.

For solution 3, 10 ml of the stock solution in 100 ml measuring cylinder was diluted in 100mL
volumetric flask and then absorbance measured at 473nm on the UV/Vis spectrometer. 4
replicates were then prepared in different volumetric flasks and their absorbance measured
RESULTS
Part 1
Part 2
Air Displacement (Own Result)
Mean 0.245
Standard Deviation 0.005099
Range 0.012
Minimum 0.236
Maximum 0.248
Count 5
Confidence Level(95.0%) 0.006331
%RSD 2.081232
Own Result
Mean 1.00279
Standard Deviation 0.002628
Sample Variance 6.91E-06
Range 0.0076
Minimum 0.9993
Maximum 1.0069
Count 10
Confidence Level(95.0%) 0.00188
%RSD 0.262051
Partner Results
Mean 1.00683
Standard Deviation 0.003201
Sample Variance 1.02E-05
Range 0.0098
Minimum 1.0016
Maximum 1.0114
Count 10
Confidence Level(95.0%) 0.00229
%RSD 0.317969
Air Displacement (partner Result)
Mean 0.2262
Standard Deviation 0.003033
Range 0.006
Minimum 0.223
Maximum 0.229
Count 5
Confidence Level(95.0%) 0.003766
%RSD 1.340915

Bulb Own Result
Mean 0.2228
Standard Deviation 0.004025
Sample Variance 1.62E-05
Range 0.011
Minimum 0.218
Maximum 0.229
Count 5
Confidence Level(95.0%) 0.004998
%RSD 1.806518
Bulb Pipette (Partner)
Mean 0.2038
Standard Deviation 0.00228
Sample Variance 5.2E-06
Range 0.006
Minimum 0.201
Maximum 0.207
Count 5
Confidence Level(95.0%) 0.002831
%RSD 1.118916
Volumetric flask (Own Result)
Mean 0.223
Standard Deviation 0.003317
Minimum 0.219
Maximum 0.228
Count 5
Confidence Level(95.0%) 0.004118
%RSD 1.487276

Volumetric Flask (partner)
Mean 0.2262
Standard Deviation 0.003033
Range 0.006
Minimum 0.223
Maximum 0.229
Count 5
Confidence Level(95.0%) 0.003766
%RSD 1.340915
DISCUSSION
From the statistical results shown above, bulb pipette offers more precision than air displacement
pipette. This is because the standard deviation obtained from bulb pipette is < than the standard
deviation of the measurements using air displacement for both data sets. The relative standard
deviations which describes the spread of data with respect to the mean is also less for bulb
pipette for both sets of data (1.8066%<2.0812%) and (1.11892%<1.3409%). This shows that
bulb pipette offers more consistent results compared to air displacement pipette. The 95%
confidence interval that provides a range of values that one can be 95% certain that the true mean
of the measured values by the equipment also support the statement that bulb pipette offers more
precision than the other two methods because (0.004998<0.006331) and (0.002831<0.003766)
Comparison between the data obtained Bulb pipette
t-Test: Paired Two Sample for Means
Variabl
e 1
partne
r
Mean 0.2228 0.2038
Variance 1.62E- 5.2E-

05 06
Observations 5 5
Pearson Correlation
-
0.30507
Hypothesized Mean
Difference 0
df 4
t Stat
8.17629
8
P(T<=t) one-tail
0.00060
9
t Critical one-tail
2.13184
7
P(T<=t) two-tail
0.00121
8
t Critical two-tail
2.77644
5
The average measurement obtained by my partner was slightly less than the data I obtained.
Statistically, the p-value (0.000609<0.05), the absorbance at 473 nm on the UV/Vis spectrometer
measured by my partner and I are equal. In terms of variation from the mean, the relative
standard deviation obtained by one group was greater than that obtained by second group
(partner) (1.8065% and 1.118916%). The two sets of data also varied in terms of range. One data
set had a range of (0.011) while the second data set had a range of (0.006).
The measurement using bulb pipette were thus statistically the same. The slight variation in some
aspects of the data on the absorbance of 473 nm on the UV/Vis spectrometer such as the range
and relative standard deviation. These slight variations can be attributed to the following human
errors in reading the instruments and the slight difference in the volumes of the measuring
instruments.

Throughout the procedure, it is important to use the same pipette and glassware when completing
the 5 repeat measurement to improve precision and accuracy. This is because despite similar
calibration, no single set of two apparatus have the same measurements. Using varied glassware
and pipette would have led to inconsistency making comparison implicit.
CONCLUSION
The experiment was a success because we were able to use an air-displacement piston pipette,
analytical balance. We also managed to calibrate the software besides evaluating the precision of
the three volume measuring apparatus using various statistically analysis tools such as variance.
Of the instruments used, () was found to be the most precise
RECOMMENDATION
Future experiments should include a larger set pf values to make comparison clearer and improve
precision.
Bibliography
Laksmiwati, D., Junaidi, E., & Hakim, A. (2017). Basic Chemitry Laboratory Works Based on
Maritim Culture Analysis. 2nd Asian Education Symposium.
Pedersen-Bjergaard, S., Gammelgaard, B., & Halvorsen, T. G. (2019). Introduction to
Pharmaceutical Analytical Chemistry 2e. Hoboken, NJ: Wiley.
Valcarcel, M. (2012). Principles of Analytical Chemistry: A Textbook. Berlin, Germany:
Springer Science & Business Media.