IC lab 2

Calibration

• all chromatogram and the log sheet are posted  on courseworks
• save the data file you worked on in class as XY_IC_EDA10.xlsx (XY being your initials)
• orient yourself in the workbook
• note everything you do in the 'comment' worksheet (first tab)
• separate samples from standards; don't alter the raw data sheets, do manipulations on a seperate worksheet in the same workbook
• determine concentrations of the standards and fill in the 'Standards' spreadsheet, using the dilution factors you calculated from teh standard name
• 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, label them by  the name of teh particular anion
  

• graphs should show a linear trend, concentrations should increase with peak area
• 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 may have 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
  

• write down (or copy/paste) the equations for each anion
• enter the sample data (all samples, including DI water) similarly to the standard in your spreadsheet,
  
• fill out the top part of the "Samples summary" worksheet with detailed info of all samples
  
• 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
• 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 the chromatograms
  
• 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 sampl
• Put the concentrations of the samples relevant to your study into a new tab
• Transfer the file (one Excel file per person) to the appropriate folder on the courseworks website by Thursday, class time.

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