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CIH Analytical Chemistry Questions and Answers 100% Solved
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CIH Analytical Chemistry
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CIH Analytical ChemistryAccuracy - answer How well you come to hitting the mark, i.e., how often you get the
right answer. It is affected by controllable sources of error and include method error,
personal error, and instrument error.
Accuracy Errors - answer Known as systematic errors and include incorrect
calculations, personal carelessness, poorly calibrated equipment, and use of
contaminated reagents. They contribute to a consistent bias to the results that renders
them inaccurate.
Precision - answer How closely clumped together your results are, i.e., the ability to get
the same answer over and over again. Not as important as accuracy.
Precision Errors - answer Affected by indeterminate or random errors, which cannot be
controlled. These include intra or inter day fluctuations, sampling equipment variations
such as random pump flow fluctuations, and analytical method fluctuations such as
variation in reagent addition or instrument response.
Precisions Errors Continued - answer These factors cause variability among the sample
results. Statistical techniques are used to account for random error. For example,
increasing the number of samples taken minimizes the effect of random error.
Lab Blanks/Media Blanks - answerSamples that have not been sent to the field. Used
for quality control to determine if there is contamination at factory or via transport.
NIOSH recommends analyzing 6 media blanks from same sample lot.
Field Blanks - answerSample media taken to the field but they are not exposed. Used
for field sampling quality control to determine if media is contaminated once its left for
lab. Number of recommended field blanks is 2 per 10 samples with a max of 10 field
blanks.
Blind Spiked Samples - answerSamples spiked with a know quantity of contaminant.
Labeled in same manner as field samples. Used to verify lab is providing accurate
results. Be careful with this.
Calibration - answerLab instruments must be calibrated frequently with concentrations
of know samples. Field sampling pumps must be calibrated before and after sampling.
Primary Standard (sample pump) - answerdirect measurement of volume - pitot tube,
bubble meter, gilibrator, inclined manometer.
, Secondary Standard - answerCalibration device calibrated against primary standard
[rotameter] - used to check pump in the field
Limit of Detection - answerLowest concentration detected by the laboratory instrument.
Usually 3 times the instrument noise level [S/N>3]
Limit of Quantification - answerLowest concentration quantifiable in the lab. Usually 10
times the instrument noise level [S/N>10]
LOD<=LOQ
Minimum Airflow - answerThe minimum volume of air needed to ensure a measurable
sample. Must have some idea of actual airborne concentration. Can use a threshold
that you interested in detecting; example, 0.1 X TLV or 10% TLV
Minimum Airflow Continued - answerConcentration = mass/volume
Use LOD or LOQ for mass
Volume=m3
Concentration=mg/m3
Sampling Statistics - answerNIOSH Recommends the following sampling strategie to
ensure an employee in the upper 10% of exposure range is included in sample
Workers 1478....>50
Samples 1477......22
This strategy ensures that we are 95% confident that we are capturing the upper 10% of
exposure range.
Sampling Statistics - NIOSH Rule of Thumb - answer>= 6 samples required for valid
estimate of confidence interval around the mean
> 11 samples required to estimate variance
How many samples to take? - answerNIOSH exposure manual says if PEL or STEL
considered a ceiling value, then 3 non-random, worst-case exposure periods should be
sampled and if none exceeds either limit then one can be personally confident they are
not normally exceeded. However, this sampling cannot be considered statistically
significant because it was not random.
Lower Confidence Limit - answerOSHA uses to ensure there was an over exposure.
Based on analytical error. See page 2 of equation sheet.
Cumulative Error - answerSum of the squares of the errors. Errors will be given to you
in problem. See page 2 of equation sheet.
Aerosols - Gravimetric Analysis - answerPump and filter used to collect aerosol. Sample
filter weighed before and after sampling and the mass of aerosol is the difference in
weights.
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