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Convert Detector Signal to Concentration

Source: R/step_sec_concentration.R
step_sec_concentration.Rd

step_sec_concentration() creates a specification of a recipe step that converts detector signals to absolute concentration values using calibration factors and injection parameters.

Usage

step_sec_concentration(
  recipe,
  measures = NULL,
  detector = c("ri", "uv", "auto"),
  injection_volume = NULL,
  injection_mass = NULL,
  sample_concentration = NULL,
  flow_rate = 1,
  concentration_units = "mg/mL",
  normalize_to_mass = TRUE,
  role = NA,
  trained = FALSE,
  skip = FALSE,
  id = recipes::rand_id("sec_concentration")
)

Arguments

recipe

A recipe object.

measures

Character vector of detector column names to convert. If NULL, will convert all measure columns.

detector

Type of detector signal being converted:

  • "ri": Refractive index detector (assumes dn/dc normalized)

  • "uv": UV detector (assumes extinction coefficient normalized)

  • "auto": Attempt to detect from column names

injection_volume

Injection volume in uL. Required for absolute concentration calculation.

injection_mass

Injected mass in mg. Alternative to using sample_concentration and injection_volume.

sample_concentration

Sample concentration in mg/mL. Used with injection_volume to calculate injected mass.

flow_rate

Flow rate in mL/min for peak area calculations.

concentration_units

Output concentration units. Default is "mg/mL".

normalize_to_mass

Logical. If TRUE, normalize the chromatogram so that the total area equals the injected mass. Default is TRUE.

role

Role for generated columns.

trained

Logical indicating if the step has been trained.

skip

Logical. Should the step be skipped when baking?

id

Unique step identifier.

Value

An updated recipe with the new step added.

Details

This step converts detector response (after dn/dc or extinction coefficient normalization) to absolute concentration. The conversion uses the known injected mass to normalize the chromatogram area:

$$c(t) = \frac{S(t) \times m_{inj}}{\int S(t) \times F \times dt}$$

where:

  • S(t) is the normalized detector signal

  • m_inj is the injected mass

  • F is the flow rate

Workflow for concentration determination:

  1. Baseline correct the chromatogram

  2. Apply detector-specific normalization (dn/dc or extinction coefficient)

  3. Apply this step with known injection parameters

  4. Result: concentration at each elution point

See also

Other sec-detectors: step_sec_dad(), step_sec_dls(), step_sec_intrinsic_visc(), step_sec_lals(), step_sec_mals(), step_sec_rals(), step_sec_ri(), step_sec_uv(), step_sec_viscometer()

Examples

if (FALSE) { # \dontrun{
library(recipes)
library(measure)

# Convert RI signal to concentration
rec <- recipe(~., data = sec_triple_detect) |>
  step_measure_input_long(ri_signal, location = vars(elution_time), col_name = "ri") |>
  step_sec_baseline() |>
  step_sec_ri(dn_dc = 0.185) |>
  step_sec_concentration(
    detector = "ri",
    injection_volume = 100,        # uL
    sample_concentration = 2.0,    # mg/mL
    flow_rate = 1.0                # mL/min
  ) |>
  prep()
} # }