The shipboard ion chromatograph (IC) is used to determine concentrations of major cations (Na+, K+, Mg2+, and Ca2+) and anions (Cl-, Br-, SO42-) in pore water. Each ion set is separated and detected in its own flow path. Sample is directed from the anions and cations sample loops into their respective chromatographic columns in which dissolved ions absorb to a stationary phase resin. A unique eluent flows through each column and competes with sample ions for adsorption sites. This causes a gradual separation of sample ions into discrete bands within the column—ordered by each ion’s strength of adsorption (influenced by ionic radius and ionic charge). The separated analyte bands are carried off by the eluent from the column into a conductivity detector, which integrates each analyte’s signal over a short time interval. Analyte concentrations in the samples are calculated based on calibration curves created prior to each sample sequence by analyzing a set of known standards and blanks.
In order to maintain a consistent retention time for each ion, the columns are housed in a temperature-controlled chamber and the eluent flowrate is kept constant. For reduced background conductivity and better detection of the analytes, the anions flowpath employs a chemical suppressor and a CO2 exchange membrane between the column and the detector. These suppressors remove sodium and bicarbonate (as CO2) from the eluent solution and convert anions to their more conductive acid counterparts.
The ion chromatograph is a fairly safe and straightforward instrument to use. The following are a succinct overview of several important safety precautions that are described in more detail within this user guide.
Figure 1: Metrohm 850 Professional Ion Chromatograph
Figure 2: Metrohm 850 Professional IC Autosampler
The following is an overview of the sequence of events which occur when a sample is analyzed. Consult IC Flow Path and Function.pptx for greater detail about the instrument flowpath.
The IC employs the MSM to lower the background conductivity of the anions eluent in order to gain detector sensitivity while measuring anions. The MSM is composed of an acidic cation exchange resin which exchanges hydronium ions for the sodium ions originating from the sodium bicarbonate of the anion eluent. The bicarbonate is converted to carbonic acid which has a much lower specific conductivity (and is mostly removed in the MCS). In addition, the anion salts are converted into their mineral acid counterparts, eg NaCl becomes HCl, NaBr becomes HBr, etc, which have much higher specific conductivities.
The anions baseline is typically at 1.4 µS/cm. It is normal for the baseline to jump up to between 5-7 µS/cm when the MSM switches cartridges. The baseline eventually stabilizes.
A Metrohm representative created the default method for data acquisition during the initial instrument installation. The Method consists of a time program, device setup and type of chromatogram evaluation. The time program is a series of instrument events that control sample and eluent uptake and flow through the system, it should never need to be adjusted by technicians or scientists. The Devices menu enables the user to assign hardware and hardware parameters. The menu is particularly useful to assign variable names and locations to the hardware (pumps, columns, detectors, etc) that the method uses for control and data calculations. Finally, the Evaluation menu contains the parameters necessary for analyzing chromatograms, constructing a calibration curve and compiling results. Use this menu to add additional calibration standards, check standards, or to specify additional analytes and their retention times.
Make sure all reservoirs are filled with the following reagents:
Dosino Reservoir | 18 mega-ohm DI water |
Suppressor Rinse Solution | 0.1% methanol in DI water (1 mL methanol to 1 L DI water) |
Suppressor Regenerant Solution | 0.05 M sulfuric acid solution (2.7 mL sulfuric acid to 1 L DI water) |
Anions Eluent | 3.2 mM sodium carbonate/1.0 mM sodium bicarbonate solution (purchase concentrated packs from Metrohm, called “A Supp 5 Eluent Snips”)
|
Cations Eluent | 1.7 mM nitric acid/1.7 mM PDCA (pyridine-2,6-dicarboxylic acid)
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Standards
The dilution scheme for the standards from IAPSO standard seawater is displayed in the following table. Use a fresh bottle of IAPSO every expedition. To reduce contamination of the IAPSO bottle, decant a few mLs of IAPSO into a secondary container and use this volume to prepare standards. Parafilm the IAPSO lid after use to reduce evaporation. Additional calibration standards may need to be prepared to constrain the instrument response for low analyte levels.
Prepare a standard curve, 10 mL per level, in IC vials:
Standard 1 | Standard 2 | Standard 3 | Standard 4 | Standard 5 | Standard 6 | Standard 7 DF1000 (From DF100) | Standard 8 DF2000 (From DF100) | Standard 9 DF10000 (From DF100) | |
IAPSO (µL) | 150 | 125 | 100 | 75 | 50 | 25 | 1000 | 500 | 100 |
DI water (µL) | 9850 | 9875 | 9900 | 9925 | 9950 | 9975 | 9000 | 9500 | 9900 |
To prepare "pourable" 100 ml standards, use the following recipe: (pipette IAPSO in a 100 ml volumetric flask and bring to volume with DI water)
Standard 1 | Standard 2 | Standard 3 | Standard 4 | Standard 5 | Standard 6 | Standard 7 DF1000 (From DF100) | Standard 8 DF2000 (From DF100) | Standard 9 DF10000 (From DF100) | |
IAPSO (mL) | 1.5 | 1.25 | 1 | 0.75 | 0.5 | 0.25 | 10 | 5 | 1 |
DI water (mL) | 98.5 | 98.75 | 99 | 99.25 | 99.50 | 99.75 | 90 | 95 | 99 |
To add/edit standards, select METHOD panel and Standards in the Evaluation window. Here you can also add/edit check standards information. Standard concentrations of 0 for particular analytes are not considered by the software when calculating the analyte calibration curve.
Constituent | Standard 1 150% | Standard 2 125% | Standard 3 100% | Standard 4 75% | Standard 5 50% | Standard 6 25% | Standard 7 10% | Standard 8 5% | Standard 9 1% |
Sodium (mM) | 721.0 | 600.9 | 480.7 | 360.5 | 240.3 | 120.2 | 48.07 | 24.03 | 4.807 |
Potassium (mM) | 15.69 | 13.08 | 10.46 | 7.847 | 5.231 | 2.616 | 1.046 | 0.5231 | 0.1046 |
Calcium (mM) | 15.81 | 13.18 | 10.54 | 7.906 | 5.271 | 2.635 | 1.054 | 0.5271 | 0.1054 |
Magnesium (mM) | 81.21 | 67.67 | 54.14 | 40.60 | 27.07 | 13.53 | 5.414 | 2.707 | 0.5414 |
Chloride (mM) | 839.3 | 699.4 | 559.5 | 419.6 | 279.8 | 139.9 | 55.95 | 27.98 | 5.595 |
Bromide (mM) | 1.295 | 1.079 | 0.8632 | 0.6474 | 0.4316 | 0.2158 | 0.08632 | 0.04316 | 0.008632 |
Sulfate (mM) | 43.41 | 36.18 | 28.94 | 21.71 | 14.47 | 7.235 | 2.894 | 1.447 | 0.2894 |
MagIC Net deals with calibration curves slightly different from other types of laboratory instrumentation. When a new batch of vials are run, the calibration from the previous run (which is the active calibration) is gradually overwritten by the individual calibration points of standards in the new batch. For example, after STD 1 is analyzed the calibration curve will consist of STD 1 and standards from the previous run (less the previous STD 1). After STD 2 is analyzed, the calibration curve consists of STD1, STD2 and the other levels of standards from the previous analysis. Eventually, all standards are analyzed and the active calibration consists only of calibration points from the current analysis. It is then samples may be analyzed. It is important to recognize that classifying an aliquot in the sample sequence as a “Standard” will cause the software to incorporate it into an updated calibration curve. This is desirable at times, but if the user analyzes a standard simply to check analytical accuracy or monitor instrument drift, then they should classify the aliquot as a “Check Standard” or a “Sample”. MagIC Net has the functionality to edit and apply calibration curves post run. Consult the section about reprocessing samples for instructions.
All samples are diluted 1:100 (100 µL sample made up to 10 mL with DI water).
However, this dilution scheme may need to be adjusted for pore waters with high salinity relative to IAPSO. The Hamilton dilutor is quicker and more precise than using the Eppendorf pipettors for adding the DI water. Use the Eppendorf pipettors for adding sample to each vial. Make sure to switch the pipette tips between each sample. Vortex mix the samples and standards before analysis.
Load a method to configure the IC’s operational parameters. The method loaded will be the method used by MagIC Net for the instrument equilibration. Other saved methods may be specified individually for each sample in the sample sequence.
The sample sequence consists of a Sample Table created in MagIC Net workplace. The Sample Table contains information on how a sample will be analyzed (Method), how the sample is identified (Ident and Info 1), its position in the AS (Position), how the sample is classified by MagicNet for calibrations (Sample Type), and dilution factors (Dilution) to be incorporated into the final calculation of concentrations.
Figure 1 : Sample/sequence table example
Method | 369 (expedition number) |
Ident | Text_ID of the sample. Standards are not yet entered into the LIMS so use something like DF100 or DF100 CHECK (for a check standard). The TextID must be entered here for MUT to upload the data to LIMS properly. |
Sample Type | Sample, Standard 1–9, Blank or Check Standard (check standard number refers to standard number) |
Position | Autosampler vial position |
Injections | 1 |
Volume | 10 µL |
Dilution | Select “1.” Dilution is supposed to be the dilution factor for manual or hand dilutions performed by the analyst prior to the sample being placed in the system; however, the standards are built around 1:100 being baseline, so we don’t want the software to calculate dilutions. Note: MagIC does not seem to identify updated dilution factors where it reports “Final Concentrations” when “reprocessing” samples after a run. In these cases, use the values reported as “Concentrations” |
Sample Amount | 1 |
Info 1 | Here you can enter a comment or Label ID for example. Use this field to enter a name that the user may interpret (in contrast to the TextID used in the Ident field). |
Value 1 | Dosino Dilution Factor, the dilution factor performed by the automated dilution system. For hand dilution, set this to “1.” |
The IC will analyze samples according to the order in the sample sequence, not necessarily the position in the autosampler rack. You can insert samples into the sequence on fly by right clicking on the sequence table and selecting “Insert New Line”. Enter the sample info and double-check that the Position corresponds to where to put the vial in the autosampler rack (at the end, for instance.)
To shut down the IC, navigate to the Equilibration tab and select the red Stop HW button. Eluent uptake will terminate. Disengage the tubing from the peristaltic pumps on the IC and on the autosampler. Leave the instrument on.
An overview of IC calibration techniques may be reviewed here: IC Calibration Principles.pptx. The calibration curve and sample chromatograms may be viewed by navigating to the Database panel and selecting a result of interest in the Determination Overview window. In the Curves 1 window are tabs for Anions and Cations. Select either, the window will populate with the sample Chromatogram. Click on the Calibration curve radio button. Select the element to evaluate from the pull-down menu to view its calibration curve and the calibration table (Figure 3). Several statistics and the curve equation are also displayed in this window.
Figure 3: Calibration curve display of a sample within the database tab.
The analysis results are also displayed under the Database tab within the windowpane entitled Results. Results are only shown if the software has identified a peak within the retention time window specified for the analyte. The analytes are distinguished by the type of ion (cation or anion) and then ordered by retention time. The result fields include the retention time, peak height, peak area, concentration (without accounting for dilution), and final concentrations (with accounting for dilution). Beneath the results table is a list of all the parameters and equations defined in software to reach the results displayed for the particular sample.
Information about the instrument configuration during the select sample acquisition may be found in the Information windowpane of the Database tab.
Occasionally sample chromatograms may need to be 'reprocessed' if the software's autointegration feature has misidentified an analyte peak or if a calibration curve needs to be adjusted and reapplied. Samples with low sulfate concentrations (below 1 mM) should be reprocessed using only the lowest standards (1 mM and lower) as the y-intercept of the normal calibration underestimates the y-intercept for the low standards. The instructions below are an overview of the reprocessing procedure. Consult the Metrohm documentation provided on this page for more detail about reprocessing samples.
Each change to reprocessed samples is saved into the Database archive. To undo a reprocess and restore a previous sample state, right click on the sample and select "Show History." A new menu will appear showing a list of each time the sample has been reprocessed. Select a previous sample state, right-click and select "Make Current." A duplicate of the previous sample will be generated into a new line and will become the current sample displayed in the Database. To return to the Database, right-click the the new sample and uncheck the "Show History" box.
Use MUT uploader to upload results to the LIMS.
In case 398_export_template is missing, create a new template in Tools > Templates > Export Templates
The following hints will aid in monitoring and troubleshooting instrument performance while analyzing a sample sequence.
Cations
Figures (x-x) are typical chromatograms collected when measuring an aliquot of IAPSO diluted 1:100 (DF100). The order cations elute the ion exchange column is governed by first by the strength of the ionic charge and second, by cation size, where smaller, highly charged analytes are the last to elute.
A general rule for changing an instrument component in the flowpath: Don't allow air to enter the flowpath! Bubbles in the lines ultimately end in pump, analytical column or detector and can lead to problems with each. When exchanging a component ensure the peristaltic pumps are pumping fluid. Remove the component, insert the new component, and allow the eluent to pump until the component fully fills and begins to spill from the component's OUT side. Then, with the eluent still flowing, connect the component OUT side to complete the flowpath. Doing so will lessen the chance of air accumulating in the tubing and instrument components. Wipe up any residual liquid mess.
In the case of changing the ultrafiltration membrane or autosampler peristaltic pump tubing, disconnect the sample line at the in-line filter located in between the autosampler and the IC. Run 1 sample of DI water. The AS probe will draw in the water and flush the air from the ultrafiltration membrane, new tubing and the in-line filter. After the last bubbles have exited the in-line filter, reconnect the in-line filter to complete the flowpath. Wipe up any residual liquid mess.
For maintenance, there are a couple of great guides, located in the Metrohm_backup\METROHM MANUALS folder on the desktop
Main Instrument Guide: IC Essentials Manual.pdf
IC Maintenance Guide: IC Maintenance and Troubleshooting Guide.pdf
Outlines maintenance schedules to follow
Autosampler Guide: Autosampler.pdf
Dosino guide: Dosino.pdf
Anion/cation pump maintenance: 850_pump_maintenance.pdf
Parts information to send in requisitions: Metrohm_parts_guide.pdf
More on the autosampler’s ultra-filtration: Metrohm_ultra_filtration.pdf
Software guide: Metrohm USA_MagIC Net User Guide.pdf
Calibration Techniques: IC Calibration Principles.pptx
Pumps: Once an expedition
Column: If the retention times are changing. The column should be one of the last things to change when troubleshooting. They are expensive!
Anions, Cations inline-filters: Every several runs
Guard Columns: Every several runs
H2O Scrubber: Check every run, replace if the beads start to fade from orange to transparent
CO2 Air Scrubber: Check every run, replace if the material within begins to clump.
MSM Peristaltic Pump tubing: Every Several Runs
Any tubing: On an as needed basis, if there is a lot of sample carryover.
Autosampler Probe: Check every run, replace as needed
Peristaltic Pump Tubing: Every several runs, or monthly
Ultrafiltration membrane: Inspect every run, replace if discolored.
Solutions
Cations Solution: Replace if the bottle has been sitting around for a week or so
Anions Solution: Make fresh every analysis.
Water: As needed
Methanol: As needed
Sulfuric: As needed
Bottle Air scrubbers: Soda lime turns from white to pink when then absorbent is near the point of exhaustion. The absorbent should be changed out when 2/3 of it has changed color.
Changing Inline Filters
Figure 4: Frits within the guard columns. The left hand frit has a buildup of iron oxides filtered from the sample to protect the anions column.
Figure 5: Example of a clean inline filter membrane (left) and dirty membrane (right).
Figure X: Example of H2O scrubbers used in-line with the MSM air inlet. From left to right: a regenerated scrubber ready to use, a scrubber removed from the instrument which must be regenerated, a new scrubber which must be regenerated before use.
Top depth CSF-A (m): position of observation expressed relative to the top of the hole.
Bottom depth CSF-A (m): position of observation expressed relative to the top of the hole.
Top depth CSF-B (m):
Bottom depth CSF-B (m):
sample description: observations recorded about the sample itself
test test_comment: observations about a measurement or the measurement process; some measurement observations may be under Result comments
result comments: observations about a measurement or the measurement process; some measurement observations may be under Test Comments
Consult Metrohm’s IC Troubleshooting guide for information concerning troubleshooting common IC problems. Below are additional issues the technicians have encountered over the years:
Check standards are coming out low:
MagIC Net misidentified an analyte: This usually happens when two peaks are within the same retention time window. Sulfate is the worst offender. Reprocess the sample by adjusting the time window to identify the correct analyte.
Most LIMS components are directly saved as a pair of components: a RESULT table name for the name of the parameter, and RESULT.entry for the text or numeric result. For the Ion Chromatograph, however, it was necessary to create a different structure. Two of the name fields in the RESULT table are analyte and concentration, and any given result is a marriage of these two fields (e.g., analyte = Sulfate and concentration = 28.657. These are organized on the RESULT table by use of the RESULT.replicate_count field, so a given analyte entry and concentration entry have the same replicate_count (e.g., /0, /1).
ANALYSIS | TABLE | NAME | ABOUT TEXT |
IC | SAMPLE | Exp | Exp: expedition number |
IC | SAMPLE | Site | Site: site number |
IC | SAMPLE | Hole | Hole: hole number |
IC | SAMPLE | Core | Core: core number |
IC | SAMPLE | Type | Type: type indicates the coring tool used to recover the core (typical types are F, H, R, X). |
IC | SAMPLE | Sect | Sect: section number |
IC | SAMPLE | A/W | A/W: archive (A) or working (W) section half. |
IC | SAMPLE | text_id | Text_ID: automatically generated database identifier for a sample, also carried on the printed labels. This identifier is guaranteed to be unique across all samples. |
IC | SAMPLE | sample_number | Sample Number: automatically generated database identifier for a sample. This is the primary key of the SAMPLE table. |
IC | SAMPLE | label_id | Label identifier: automatically generated, human readable name for a sample that is printed on labels. This name is not guaranteed unique across all samples. |
IC | SAMPLE | sample_name | Sample name: short name that may be specified for a sample. You can use an advanced filter to narrow your search by this parameter. |
IC | SAMPLE | x_sample_state | Sample state: Single-character identifier always set to "W" for samples; standards can vary. |
IC | SAMPLE | x_project | Project: similar in scope to the expedition number, the difference being that the project is the current cruise, whereas expedition could refer to material/results obtained on previous cruises |
IC | SAMPLE | x_capt_loc | Captured location: "captured location," this field is usually null and is unnecessary because any sample captured on the JR has a sample_number ending in 1, and GCR ending in 2 |
IC | SAMPLE | location | Location: location that sample was taken; this field is usually null and is unnecessary because any sample captured on the JR has a sample_number ending in 1, and GCR ending in 2 |
IC | SAMPLE | x_sampling_tool | Sampling tool: sampling tool used to take the sample (e.g., syringe, spatula) |
IC | SAMPLE | changed_by | Changed by: username of account used to make a change to a sample record |
IC | SAMPLE | changed_on | Changed on: date/time stamp for change made to a sample record |
IC | SAMPLE | sample_type | Sample type: type of sample from a predefined list (e.g., HOLE, CORE, LIQ) |
IC | SAMPLE | x_offset | Offset (m): top offset of sample from top of parent sample, expressed in meters. |
IC | SAMPLE | x_offset_cm | Offset (cm): top offset of sample from top of parent sample, expressed in centimeters. This is a calculated field (offset, converted to cm) |
IC | SAMPLE | x_bottom_offset_cm | Bottom offset (cm): bottom offset of sample from top of parent sample, expressed in centimeters. This is a calculated field (offset + length, converted to cm) |
IC | SAMPLE | x_diameter | Diameter (cm): diameter of sample, usually applied only to CORE, SECT, SHLF, and WRND samples; however this field is null on both Exp. 390 and 393, so it is no longer populated by Sample Master |
IC | SAMPLE | x_orig_len | Original length (m): field for the original length of a sample; not always (or reliably) populated |
IC | SAMPLE | x_length | Length (m): field for the length of a sample [as entered upon creation] |
IC | SAMPLE | x_length_cm | Length (cm): field for the length of a sample. This is a calculated field (length, converted to cm). |
IC | SAMPLE | status | Status: single-character code for the current status of a sample (e.g., active, canceled) |
IC | SAMPLE | old_status | Old status: single-character code for the previous status of a sample; used by the LIME program to restore a canceled sample |
IC | SAMPLE | original_sample | Original sample: field tying a sample below the CORE level to its parent HOLE sample |
IC | SAMPLE | parent_sample | Parent sample: the sample from which this sample was taken (e.g., for PWDR samples, this might be a SHLF or possibly another PWDR) |
IC | SAMPLE | standard | Standard: T/F field to differentiate between samples (standard=F) and QAQC standards (standard=T) |
IC | SAMPLE | login_by | Login by: username of account used to create the sample (can be the LIMS itself [e.g., SHLFs created when a SECT is created]) |
IC | SAMPLE | login_date | Login date: creation date of the sample |
IC | SAMPLE | legacy | Legacy flag: T/F indicator for when a sample is from a previous expedition and is locked/uneditable on this expedition |
IC | TEST | test changed_on | TEST changed on: date/time stamp for a change to a test record. |
IC | TEST | test status | TEST status: single-character code for the current status of a test (e.g., active, in process, canceled) |
IC | TEST | test old_status | TEST old status: single-character code for the previous status of a test; used by the LIME program to restore a canceled test |
IC | TEST | test test_number | TEST test number: automatically generated database identifier for a test record. This is the primary key of the TEST table. |
IC | TEST | test date_received | TEST date received: date/time stamp for the creation of the test record. |
IC | TEST | test instrument | TEST instrument [instrument group]: field that describes the instrument group (most often this applies to loggers with multiple sensors); often obscure (e.g., user_input) |
IC | TEST | test analysis | TEST analysis: analysis code associated with this test (foreign key to the ANALYSIS table) |
IC | TEST | test x_project | TEST project: similar in scope to the expedition number, the difference being that the project is the current cruise, whereas expedition could refer to material/results obtained on previous cruises |
IC | TEST | test sample_number | TEST sample number: the sample_number of the sample to which this test record is attached; a foreign key to the SAMPLE table |
IC | CALCULATED | Top depth CSF-A (m) | Top depth CSF-A (m): position of observation expressed relative to the top of the hole. |
IC | CALCULATED | Bottom depth CSF-A (m) | Bottom depth CSF-A (m): position of observation expressed relative to the top of the hole. |
IC | CALCULATED | Top depth CSF-B (m) | Top depth [other] (m): position of observation expressed relative to the top of the hole. The location is presented in a scale selected by the science party or the report user. |
IC | CALCULATED | Bottom depth CSF-B (m) | Bottom depth [other] (m): position of observation expressed relative to the top of the hole. The location is presented in a scale selected by the science party or the report user. |
IC | RESULT | analyte | RESULT analyte name: name of the analyte for this result (e.g., Calcium, Sulfate) |
IC | RESULT | concentration (mM) | RESULT concentration (mM): concentration of the analyte |
IC | RESULT | dat_asman_id | RESULT data ASMAN_ID: serial number of the ASMAN link for the data file (binary format) |
IC | RESULT | dat_filename | RESULT data filename: file name of the data file (binary format) |
IC | RESULT | ssup_asman_id | RESULT spreadsheet uploader ASMAN_ID: serial number of the ASMAN link for the spreadsheet uploader file |
IC | RESULT | ssup_filename | RESULT spreadsheet uploader filename: file name of the spreadsheet uploader file |
IC | SAMPLE | sample description | SAMPLE comment: contents of the SAMPLE.description field, usually shown on reports as "Sample comments" |
IC | TEST | test test_comment | TEST comment: contents of the TEST.comment field, usually shown on reports as "Test comments" |
IC | RESULT | result comments | RESULT comment: contents of a result parameter with name = "comment," usually shown on reports as "Result comments" |
IC User Guide: 29th September 2022