Quantitation

Analyze → Quantitate identifies peaks, fits the curves, and calculates concentrations.

Schemes Quanto calculates

External standard

The target quant has no internal standard. The response is the peak area, or the peak height when Quantitate by height is on for the analyte. The curve is inverted to give concentration. With the default linear fit forced through the origin, concentration is response divided by the slope. Other fits invert their own equation. See Calibration curves.

Internal standard (ISTD)

The quant is linked to an ISTD quant. The curve is built from the ratio of target response to ISTD response. To read an unknown, Quanto divides the sample response by the ISTD response, inverts the curve, and multiplies by the ISTD concentration.

If an ISTD is assigned but its result is not ready, the concentration is left unset (shown as not calculated) rather than read from the target’s own curve.

ISTD analytes themselves are fitted as Average of response factors (mean of response divided by concentration). They are not given the Linear / Force / Equal default.

Surrogate

A surrogate is an analyte of type Surrogate. It is spiked, so it has a known dose. Recovery is 100 × calculated concentration / known dose. The same recovery window used for checks can flag it. See Checks.

Response factor

Average of response factors is a curve model, not a separate sample type. Concentration is response divided by the mean response factor (response / concentration at the standards). ISTD quants always use this model.

Reference curve

A quant can turn on Use reference curve and point at another quant. The concentration is read from that other quant’s curve, then multiplied by the curve multiplier (default 1). The multiplier is applied after the inverse and after ISTD denormalization. If the link or the bracket is missing, the concentration is not calculated.

Spike recovery

Spike recovery keeps the Cal group on Mode Calibration. The fortified vial is a Sample or QC with a Dose, in the same Cal group as the calibration samples. Conc comes from that curve. SpikeGroup pairs it with the unspiked Sample or QC vials (no dose) that share the name. RecPct is then 100 × (Conc − mean unspiked Conc) / on-column dose, and NConc subtracts the dose (including QC). With no SpikeGroup, RecPct stays 100 × Conc / on-column dose. See Spike recovery.

Standard addition

Standard addition is a Cal group mode, separate from spike recovery. In Cal groups, set Mode to Standard addition. Spiked aliquots are Sample with a Dose. Unspiked aliquots are Sample without a Dose. With at least two aliquots at different added doses, NConc is the intercept / slope of response (or response / ISTD response) against added on-column dose. That line is stored as a calibration bracket. Sample and Solvent RecPct is 100 × (Conc − NConc) / dose. See Standard addition.

The reserved dose name IS is the spike for ISTD and Surrogate analytes only. A target does not subtract the ISTD amount. On a normal Cal group, Calibration samples, and QC samples that are not in a SpikeGroup, do not subtract the dose toward native concentration; their dose is used for recovery percent. A QC with a dose in a SpikeGroup subtracts that dose. SpikeGroup is spike recovery only.

What is not a separate scheme

Quanto does not have a distinct “isotope dilution” mode beyond linking an ISTD. Bracket and partial calibration change which standards are on the curve. They do not change the arithmetic above. See Bracketing.

Example batches for external calibration, internal standard, spike recovery, and standard addition are in Example batches.

After the curve is inverted, dilution and the limit group’s final-concentration multiplier are applied to the reported final concentration. See Limit groups.

Which quant is reported

An analyte can have several quants. Two different choices are easy to mix up.

Which analyte applies is decided first, by acquisition key. Only analytes whose acquisition key matches the sample are processed. See Acquisition keys. There is no separate priority number on a quant.

Which quant on that analyte is the reported result for one peak is decided as follows. Deleted results and rejected results are ignored.

1. If you pinned a result by hand, and that pin is still live, that result stays the reported one.
2. If only one live result remains, that result is used.
3. Otherwise the live results are ordered by calibration range, smallest maximum first. When two ranges match, the quant key (QntKey) breaks the tie, ignoring case.
4. Results above the highest calibration response are set aside when at least one result is still on the curve. The comparison uses the raw response, not the ISTD ratio, against the highest enabled calibration response and against the fitted curve maximum.
5. Walking that list from the smallest range upward, Quanto picks the first quant whose calibration maximum still covers the sample ratio. That is the lowest range that still contains the sample.
6. If the sample sits above every range, the last quant in that ordered list is used (the widest range that was still eligible).

Qualifier pass or fail, the largest peak, and relative standard deviation are not part of this choice. Qualifiers affect identification and the sample-key report. See Peak identification and Sample keys.

Example

A pesticide has two quants, both on acquisition key 1:

• Quant key Low, calibrated from 0.1 to 10.
• Quant key High, calibrated from 5 to 200.

A sample on key 1 with a response inside the low range is reported on Low, because that range is tried first and it still covers the sample. A sample whose response is above the low range and inside the high range is reported on High. A sample above both ranges is reported on High and flagged too high. If you pin the High result yourself, that pin is kept even when the response would have fitted Low.

Clicking a peak when several quants share it pins the quant for that click. Clear pin lets the automatic rule run again.