answers

watching

views

23 Nov 2019

The measurement of Li in brine is used by geochemists to help determine the origin of brine in oil fields. The analysis of replicate samples of a marine sediment sample gave the results shown below:

Sample Preparation [Li] Found in Original (Micrograms/g) Analytical Method

1. None 25.1 Standard Curve

2. Dilute to 1/10 with water 64.8 Standard Curve

3. Dilute to 1/10 with water 82.5 Standard Addition

a) suggest a reason for the increasing concentration of Li in samples 1 through 3

b) What value would you reccomend for the real concentration of Li in the sample and why?

c) Name an analytical method other than a calibration curve or standard addition that can be employed to obtain an accurate and precise measurement of Li in these marine sediment samples.

answers

watching

views

For unlimited access to Homework Help, a Homework+ subscription is required.

Join us on Discord

Chemistry Study Group

Join now

Related questions

HELP WITH PART D) E)

Question: STANDARD CURVE PREPARATION Always indicate the volume of water (or additional solution) to be add... STANDARD CURVE PREPARATION Always indicate the volume of water (or additional solution) to be added to complete any dilution.

a) A stock solution of 6mg/ml BSA is provided. Calculate the dilutions for the preparation of the following BSA standards (2.0ml volumes of each): 60, 170, 500, 1500, 3000ug/ml. Also include the dilution factor for each preparation. On a separate sheet of paper with a heading of Calculations, include one complete sample calculation of this dilution calculation.

b) To 0.5ml of your unknown samples (and dilutions of your samples) and to 0.5ml of the standards add 2.5ml of Biuret reagent. Calculate the final concentration of BSA after addition of the Biuret reagent. iv. neatly show one sample calculations.

c) Hypothetical absorbencies with respect to the concentrations in âaâ are: 0.16, 0.20, 0.28, 0.45 and 0.70. v. Use computer software such as excel to plot a standard curve using these absorbencies against the concentration of each BSA standard prior to the addition of Biuret reagent (use concentrations as given in step 11a directly) vi. Label the figure as Figure 1 and give it an appropriate descriptive title. The title should be above the figure. vii. Plot a second standard curve using the same absorbencies (0.16, 0.20, 0.28, 0.45 and 0.70) against the concentration of the BSA standard after the addition of the Biuret reagent (as calculated in step 11b) viii. Label this figure as Figure 2 and give it an appropriate descriptive title.

d) A sample prepared with 0.50ml of protein sample A and 2.5ml of Biuret reagent gave an absorbance of 0.51. Calculate the protein concentration of the original protein A sample, in ïg/ml, twice: once with each standard curve. ix. On the calculation sheet (see iii), neatly show all the calculations required to solve for the concentration of the protein sample. Remember to perform this calculation twice: once with each standard curve. Include a title to separate this calculation from others on the page.

e) A protein sample was prepared with 5.0 x 10-2 ml protein sample B, 0.45ml water and 2.5ml of Biuret reagent . It had an absorbance of 0.22 in the spectrophotometer. With this data, calculate the protein concentration of the original protein B sample, in ïg/ml, using either standard curve. x. On the calculation sheet (see iii), neatly show all the calculations required to solve for the concentration of the protein sample. Include a title to separate this calculation from others on the page. Refer to the Figure that was used to solve for the concentration.

The standard curve equations are:

y=0.0002x+0.1706

y=0.0011x+0.1706

Good Afternoon,

I am doing a laboratory report for the course entitled: Principles of Instrumental Analysis. It is a 4th year course and i have been tasked with the following analytical problem, "Determine the DEET composition in common bug sprays." In other words, I have to determine the concentration of DEET in a couple of bug sprays. The sprays and DEET are supplied. Secondly, I have to prepare a protocol for measuring the concentration of DEET in my samples and a GC:MS method for analysis of DEET. By the way, GC:MS is short for 'Gas chromatographyâmass spectrometry' and as you may know it is an analytical method that combines the features of gas-chromatography and mass spectrometry to identify different substances within a test sample. Basically, I need your help in giving me a layed-out protocol (such as we would see in a manual) of what I will do in the lab to answer the above analytical problem. You can think of it as a lab manual that you would write so that someone else could go in the lab and perform the experiment in your place.

It should have all of these components.

1. Brief (!) introduction of the problem (1 short paragraph)

2. Sampling â how much (be precise), in what form, how many, where, etc.

3. Sample preparation â list all reagents needed up front. Then list all steps and procedures you will use to prepare the samples for instrumental analysis. You should know what concentration ranges you are aiming for.

4. Standards preparation â list steps involved in preparing your standards used for calibration (if you need to do this).

5. Instrumental Analysis â list the procedure for running the instrument, including any blanks, standards. The sequence of runs (sample, standard, blank, etc) should be listed.

6. Data Analysis â how will you go from the raw data provided by the instrument to a value with a Â± deviation on it.

Please refer to the above question. Can you give me a detailed layout of how I will determine the concentration of DEET in my samples before doing the GC:MS analysis? You do not need to determine the composition or synthesize DEET. You need to determine the concentration of DEET, in a couple of bug sprays. The sprays and DEET are supplied.

I'm not quite understanding. Thank you for your clarification once again.

1. Samples of drinking water were analyzed for lead contamination. Analysis of the drinking water showed a lead concentration of 12.54 ppb. Analysis of a sample of the same drinking water spiked with 20.00 ppb lead gave a concentration of 29.63 ppb. Calculate the spike recovery. Is the method sufficiently accurate?

2. A chemical technician wants to verify the precision of an analytical procedure used to determine citric acid concentration in orange juice. She obtains 10.00 mL of a particular orange juice and dilutes it to 100.00 mL with water. She then analyzes five aliquots of the solution with the following results:

Aliquot 1 12.33 mg/mL

Aliquot 2 12.59 mg/mL

Aliquot 3 11.89 mg/mL

Aliquot 4 12.11 mg/mL

Aliquot 5 11.71 mg/mL

What can you say about the precision based on these results? Should the method be certified?

3. Your company is interested in using a new, faster method to determine copper concentration in aqueous solutions. Before implementing the new method you must check it out to see if it is sufficiently accurate and precise. You also want to know how well the new method compares to the old method. To test the new method you obtain a lake water SRM that is certified to contain 0.0283 Â± 0.0002 ppm copper and analyze it by both methods with the following results:

Copper concentration (ppm)
Old Method	New Method
0.0235	0.0233
0.0240	0.0231
0.0239	0.0233
0.0236	0.0232
0.0240	0.0231

What can you say about the new method? Is it as good as the old? Is it better? Do the two methods yield essentially the same results? Is it sufficiently accurate to warrant changing to the new method? Back up your responses with statistical calculations.

Weekly leaderboard

Home

Homework Help 3,900,000

Chemistry 830,000

Related textbook solutions

Basic Chemistry

Principles of Chemistry Molecular Approach

Principles of Chemistry Molecular Approach

Chemistry: Structure and Properties

Chemistry: A Molecular Approach

Chemistry: A Molecular Approach

Principles of Chemistry: A Molecular Approach

Chemistry: The Central Science

Related questions

Weekly leaderboard

Sample Preparation	[Li] Found in Original (Micrograms/g)	Analytical Method
1. None	25.1	Standard Curve
2. Dilute to 1/10 with water	64.8	Standard Curve
3. Dilute to 1/10 with water	82.5	Standard Addition