Can I use ASV to measure heavy metals in sea water?

Sea water or salinity will not affect the analysis because group 1 and group 2 elements do not respond to voltammetry. Thus, salt content, NA, K, Mg, and Ca do not interfere with voltammetry as it would with ICPOES, ICPMS, or AA methods. Therefore ASV can be used to measure metals in seawater.

Why do I have to use a prepared standard each time instead of a pre-prepared diluted standard (with electrolyte and distilled water), which is more representative of what I need to use in the field?

This is not a recommended practice because standards that are less than 1 ppm in concentration are not stable and can change concentration in storage. Also, if a standard is prepared with the electrolyte and DI water before use and is stored in the bottle, the components of the electrolyte will react with the Arsenic in the standard, and again will not be a stable concentration.

Deposit Time and Range Setting are variable depending on the concentration of metal to be determined. Can you define what these parameters do?

Deposit time refers to the length of time that the negative potential is applied to the working electrode in order to plate the metal in solution to the surface of the working electrode or film. Deposit time has an inverse relationship to concentration. That is, the lower the concentration the longer the deposit time required. Conversely, the higher the concentration the shorter the required deposit time.

Range Setting refers to the maximum current that will be measured when the metals leave the working electrode. The range setting can affect the voltammogram produced in VAS. A higher range setting is designed for larger peaks. If the peak for a metal reaches the top of the y-axis (µA) and becomes a flat line, basically cutting the top of the peak off, then a higher setting is required. For small peaks use a lower range setting. If the voltammogram in VAS y-axis is all less than 10 µA, a setting of 12.5 µA is sufficient and will provide the least amount of background noise. Running a sample or standard that is low in concentration (small peak) at a higher range setting will produce wavy or jagged lines along the peaks and baseline (more noise). Electrode conditions sample matrix can affect the overall background signal at times and may require a larger range setting to get the voltammogram to “fit” into the range setting (in VAS this appears as the voltammogram is nothing but a flat line).

All Cogent application notes supplied for the PDV6000plus have recommended deposit times and range settings for each application included.

On a scale of 10, what is the level of complexity of operation of Cogent instruments (1 = pH paper, 10 = atomic absorption)?

Rating= 3 to 4 on such scale of complexity of operation.

Are there any potential interferences with the use of this
Cogent instruments for measuring metals in groundwater?

Other metals or humic acid may interfere, if they are present at substantial concentrations. However, it is easy to treat the sample or work around these interferences if present.

What is the latest software version?

VAS 4.5.1 Build 567.

Using the PDV 6000plus unit as a stand alone instrument, can I add more elements/ more concentrations to the menu?

Yes, there are 10 programmable menus that can be stored internally on the Hand held unit. Each position can have 6 different calibration levels. These menus are accessible through the VAS software.

The use of the standalone unit must be tested for all standards and the sample matrix must be checked first using the VAS software for interferences. The standalone unit does a quality control check on the standard peak and performance must be verified that the electrode conditions are in good operating condition and that the peak windows are located in the correct position.

Using the PDV6000plus as a standalone instrument can I add more electrode conditioning steps?

Yes. There are 10 electrode conditioning menus in the standalone unit that can be modified through VAS for a specific application. If more than 1 step is required for any conditioning procedure, the menus can be programmed as Step 1 and Step 2 and use more than one menu to complete the conditioning procedure desired.

Can I turn off the “time out” feature on the PDV 6000plus handset?

Yes. Setting the “Automatically turn off after idle” setting in the INSTRUMENT / PROGRAM / PROPERTIES function in VAS to zero seconds will deactivate this function.

Is there a way to print data in VAS and still use the software while it is printing data?

The latest version of VAS allows the use of VAS while printing.

Does the PDV 6000plus have a Calibration Certificate?

There is a warranty certificate available that verifies the instrument performance on delivery. The PDV 6000 is not a “pre-calibrated” instrument. A standard is analyzed along with the unknown sample to quantify the value. There are 2 methods for instrument calibration: direct standard comparison (peak) with the sample (peak) or standard addition where known levels of standard are added to the sample generating a calibration curve in the sample matrix.

I am performing a calibration check with a standard, but when I calculate the results, it is 2 times the expected concentration?

When using VAS to calculate a result, the volumes of solution must be entered properly into the ‘Initiate Run’ box. These can be edited afterward if there has been an error. The most likely cause of a result 2 times greater or 2 times less than expected is a matter of entering the correct value in the sample volume and electrolyte volume boxes in the dialog box.

For example, I am doing a check with a standard to verify that my calibration is still within acceptable limits and I am expecting a 10 ppb result, but VAS returns 20 ppb. From my check of the parameters entered into VAS, I entered a sample volume of 10 ml and an electrolyte volume of 10 ml (a total analysis volume of 20 ml). The analysis provided VAS the answer to the amount in the sample but attributes the concentration only to that amount entered into sample volume (10 ml). The actual volume in the analysis cup is 20 ml, and thus the concentration of the “10 ml” sample is 20 ppb (a 2 times dilution of the sample), even though I know the concentration I put in the analysis cup was 10 ppb.

If I wanted to read the actual analysis concentration in the cell, I need to enter that all of the solution is the sample. In Sample volume I enter 20 ml, and in the Electrolyte Volume I enter a small number 0.001 ml (this number cannot be zero). Then when I calculate the result in VAS the result returned is attributed to the total volume in the analysis volume (20 ml). There is no longer a dilution factor applied to the sample result.

This dilution must be taken into account when running the PDV 6000 unit as a standalone instrument. If my handset reads 10 ppb, and I used 10 ml of sample with 10 ml of electrolyte, then the 10 ppb result is the concentration in the cell. The actual “Sample” result is 2 times the number on my handset.

Is the PDV 6000plus, Compatible to USB connections?

Yes, and there are many serial to USB converters commercially available, and can be used to attach the PDV 6000plus to a computer with only USB connections.

NOTE: It is important that the manufacturers’ drivers for the converter are installed properly and tested for any conflicts on the computer, particularly those using Windows Vista. There is a test communications feature in VAS to check the communication between the computer and the PDV 6000, and must be verified before field use.

All new PDV6000plus instrument are supplied with Serial to USB converters as standard.

Are there any case studies comparing the PDV 6000 to lab based techniques?

Yes, please refer to the Case Studies Section of the Cogent website.