IC lab 2

Calibration

1. all chromatogram and the log sheet are posted as pdf files in a folder on the website
2. download template & raw data from website, save file as XY_IC_EDA09.xlsx (XY being your initials)
   
3. orient yourself in the workbook
4. note everything you do in the 'comment' worksheet (first tab)
   
5. separate samples from standards; don't alter the raw data sheet, do manipulations on a seperate worksheet in the same workbook
   
6. determine concentrations of the standards and fill in the 'Standards' spreadsheet, using the dilution factors you calculated
   
7. plot peak area versus standard concentrations of each anion, using a scatter plot
   

• note: Excel is always interpreting the first highlighted column as the parameter plotted on the X-axis
• you can highlight multiple cells, rows, and columns by holding the 'Ctrl' button while clicking the cells
• place each chart as new sheet into your workbook
  

7. graphs should show a linear trend, concentrations should increase with peak area
8. note that we had problems with the first standards of the run, check chromatograms of all run standards, decide which measurements to use
   
9. use the Excel trendline function to make a line fit

• go to one of the chart
• then go to the Chart/Add Trendline menu
• select the linear trendline
• under options, click Display equation on chart
• the line and equation are displayed, but the equation has too few significant digits
• select the equation and go to menu Forward/selected data labels/Number and set the format to scientific with 2 decimals
  

10. write down (or copy/paste) the equations for each anion
    

Determination of sample concentrations

11. enter the sample data (all samples, including DI water) similarly to the standard in your spreadsheet,
    
12. fill out the top part of the "Samples summary" worksheet with detailed info on 'your' samples
    
13. use calibration equations derived above to determine the concentrations of your samples

• Y in the equation is the peak area, X the anion concentration
• watch out for dilutions of the samples: use the equations of the standard curves first to convert peakarea into concentration, then multiply by the dilution factor

14. For each of your samples sample, check if the peak areas fall within the range of the calibration curves and highlight all the ones that exceed them (look at on-line pdf files, compare peak areas to those of the samples)

• Note any other problems with the runs of your samples that are apparent in thechromatograms
  
• for the samples that were measured diluted and undiluted, take the measurements that fall in or the closest to the range covered by the peakareas of the standards
  
• this can mean that you take the Cl measurement from the diluted sample, and the Fl measurement from the undiluted sample

15. Put the concentrations of your samples into the sample summaries tab
16. Transfer the file (one Excel file per person) to the appropriate folder on the courseworks website by Tuesday, 1pm.
    

Putting it all together

• look at the data, also in comparison  with our previous measurements and see if anything surprises you or if you see any patterns.
• a few samples were measured  twice or more times, you'll need to decide on your best estimate of the concentration for each sample
• feel free to use data for any samples of the data set
  
• plot the data up in a way that makes the differences apparent
• think about the differences and try to explain them in the context of  the sources and sinks of major anions in water
  
• it might help to make predictions, or state hypotheses on what changes you expect to see, then  look at the data and see if they meet your expectations or not
• look at differences between locations or differences over time at the same location
• also compare your results with the NYC water monitoring report results
• take notes on your findings