Instrumental Analysis ACS Final Prep Exam Questions With Correct Answers

Instrumental Analysis ACS Final Prep Exam Questions With Correct Answers what are the difference between calibration sensitivity and analytical sensitivity - answercalibration sensitivity is the slope of a calibration curve at the concentration of interest while analytical sensitivity is a response to the noise ratio how to calculate calibration sensitivity - answery=mx+b (m is the calibration sensitivity) graph concentration vs mean analytical signal how to find the analytical sensitivity - answerAs (concentation) = calibration sensitivity/SD [ ] how to find the coefficient of variation for the mean of each of the replicate sets - answerCV = SD/Average x 100 how to find the detection limit for method? - answer3.3*SD(blank)/calibration sensitivity voltage in a series - answerVt = Vc + Vb + Va Voltage in a parallel circuit - answer1/Veff = 1/Va + 1/Vb Capacitance in a series - answer1/Ceff = 1/Ca + 1/Cb capacitance equals - answerQ/V if a spectrum is the result of a single scan while another is the result of multiple scans, how man individual spectra were summed to increase S/N from 4.2 to 43? a) formula? b) answer - answera) (S/N)a = sqrt(n) (S/N)b b) 105 what type of noise can be reduced by decreasing the temperature of a measurement - answerthermal noise what type of noise can be reduced by decreasing the frequency used for the measurement - answerflicker noise what type of noise can be reduced by decreasing the bandwidth of the measurement - answerenvironmental noise What would be an appropriate source and detector to determine the emission lines for lithium from 200 to 780 nm? - answerflame and photo multiplier tube (PMT) you've been asked to measure the UV absorbance of a sample containing poly cyclic aromatic hydrocarbons, a byproduct of the incomplete combustion of organic matter. What would be an appropriate material for the sample container? - answerfused silica or quartz which of the following changes will result in a decreased effective bandwidth? a) increasing the number of blazes in the monochromatic grating b) switching from a short-pass filter to a long-pass filter c) increasing sample concentration d) decreasing the amount of stray light - answera what would be the distance between blazes for a grating where the first order diffraction line for 600 nm light is reflected at 10 degrees and the angle of incidence light is 45 degrees? a) formula b) answer - answera) n(wavelength) = distance*(sin(i)+sin(r)) b) 680 nm which of the following would be considered a discontinuous wavelength selector? a) quartz prism b) Czerny-Turner Grating (monochormator) c)interference filter d)glass prism - answerc which characteristics are desirable for a radiation transducer? a) high sensitivity to short wavelength light b) low S/N ratio c) consistent high output when not illuminated d) constant response over large wavelength range e) all of the above - answerd what is the appropriate process for atomization for AAS and AES? (3 steps) - answerdesolvation, vaporization, atomization the doppler effect is one reason for line broadening in atomic spectroscopy. What is the effect on a measured signal? - answermovement of excited atoms toward the detector causes a shortening in the wavelength of the emitted light it is better to select an excitation source for AAS with ____bandwidth - answersmaller what is the general layout for AES? - answersample --> source --> wavelength selector --> detector a)name the electrical signals that are considered analog? b) how is the information encoded in an analog signal? - answera) current, voltage, charge, and power b) an analog signal is a signal where the amplitude of the signal changes with time, so the information is encoded either through the amplitude or frequency of the signal (and the signal can be wavelength, magnetic field strength, T,etc) what is a figure of merit? - answerit is a numerical value characterizing the quantitative instrument performance and include precision, bias, sensitivity, detection limit, dynamic range and selectivity How long would it take to discharge a 0.015 microF capacitor to 1% of its full charge through a resistance of 10 mega Ohms? a) formula b) answer - answera) vc= Vc e^(-t/RC) b) t = 0.69 seconds select the type of ionization technique used in MS that would result in significant fragmentation a) MALDI b) electron impact c) high performance d) chemical ionization - answerc which is true for chemical ionization? a) considered a "hard ionization" technique b) analyte reacts with electron beam